Water for animals AGL/MISC/4/85 - Disaster risk reduction

Water for animals AGL/MISC/4/85based on the workofPh. PALLASFAO ConsultantLand and Water Development DivisionFOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONSRome, 1986This electronic document has been scanned using optical character recognition (OCR)software and careful manual recorrection. Even if the quality of digitalisation is high, the FAOdeclines all responsibility for any discrepancies that may exist between the present documentand its original printed version.1

Table of ContentsForeword1. Introduction1.1 Rangelands and livestock1.2 Water is a necessity for livestock1.3 Man, livestock, water and rangeland are components of the same system1.4 Suggestions for use of the book2. Objectives of the manual3. Interrelations between the components of the system (man, water, livestock,rangeland)3.1 Man and water3.1.1 Creation or improvement of water supplies3.1.2 Water lifting devices and maintenance3.1.3 Cost of water3.1.4 Water and rangeland management3.2 Man and livestock3.3 Water and livestock3.3.1 Water quality3.3.2 Water requirement3.3.3 Location of the water supplies3.3.4 Watering facilities3.4 Livestock and rangeland3.4.1 Rainfall and rangeland resources3.4.2 Stocking rate and carrying capacity3.4.3 Overgrazing problems3.5 Concluding or summary statement4. Selection of the type of water supply and distribution4.1 Water source4.2 Distribution of water supplies5. Surface water resources development for rangeland5.1 Surface water utilization and development5.2 Excavated reservoirs2

5.2.1 Advantages and conditions of use5.2.2 Selection of sites5.2.3 Construction5.2.4 Stock watering and protection of the pond5.2.5 Maintenance5.2.6 Case study and cost5.3 Impounded reservoirs5.3.1 Main characteristics5.3.2 Selection of sites5.4. Rainwater harvesting techniques5.4.1 Preliminary considerations5.4.2 Methods for improving catchment runoff efficiency5.4.3 Building water storage tanks5.4.4 Case study and cost5.5 Concluding statement6. Groundwater resources development for rangelands6.1 Occurrence of groundwater6.1.1 Continuous and discontinuous aquifers6.2 Groundwater exploration techniques6.2.1 General approach6.2.2 Purpose of preliminary survey6.2.3 Preliminary hydrogeological survey - methodology6.2.4 Additional investigations required for continuous aquifers6.2.5 Additional investigations required for discontinuous aquifers6.3 Groundwater development techniques6.3.1 Selection of the type of well and pump6.3.2 Dug wells6.3.3 Drilled wells6.3.4 Well cistern associated with a drilled well6.3.5 Springs6.4 Water lifting devices6.4.1 Main requirements6.4.2 Different types of water lifting6.4.3 Man or animal powered water lifting devices6.4.4 Motor driven pumps6.4.5 Wind powered pumps6.4.6 Solar pumps3

6.5 Groundwater monitoring6.5.1 Need for groundwater monitoring6.5.2 Rainfall observations6.5.3 Water level fluctuations6.5.4 Water abstraction6.6 Case study and cost6.6.1 Well construction6.6.2 Water lifting6.7 Conclusion on groundwater developmentReferencesForewordThis book is intended to outline water, plant, man and animal relationships for thoseconcerned with obtaining water for animals. It has been found that simply obtaining a watersupply for animals often makes a difficult situation worse. This book is planned to includeenough about water, for example, to help the animal or pasture expert at least go in the rightdirection. On the other hand, limited but important animal and pasture aspects are includedfor the expert in water and clearly are not comprehensive. This book attempts to cover thesituation in the Sahelian zone of Africa and regions which are similar.4

1. Introduction1.1 Rangelands and livestock1.2 Water is a necessity for livestock1.3 Man, livestock, water and rangeland are components of the same system1.4 Suggestions for use of the book1.1 Rangelands and livestockVarious definitions of rangeland exist but it is commonly described as an area of shruband/or grass receiving less than about 750 mm of annual rainfall. Within this definitionrangeland may vary from mild sub-arid wooded savanna to desert.In terms of land use, rangelands constitute the greatest land area in the world. This naturalresource is used primarily for extensive livestock production mostly through nomadic andtranshumance systems well represented in the Sahelian and Sub-Sahelian zones of Africaand in the equivalent areas of the Near East.1.2 Water is a necessity for livestockHowever palatable and plentiful the forage or range may be, the livestock using it must haveall the water they need, or they will not thrive. Water at regular intervals, as well as amplesupply of forage, is essential if livestock are to be turned off in a marketable conditions.Water is the major component of the animal organism (65 to 70 percent of its weight).Deprivation of water quickly results in loss of appetite, and death occurs at the end of a fewdays (3 to 5 days for zebus, 6 to 10 days for sheep, and 15 days or more for camels) whenthe animal has lost between 25 and 30 percent of its weight.Inadequate stock water development in range areas not only contributes to an unstablelivestock industry and serious livestock losses, but prevents profitable utilization of badlyneeded grazing areas and encourage destructive overgrazing in the vicinity of existing watersupplies. The prime objective in developing a rangeland water supply may therefore besummarized as the provision of adequate clean water to enable an even utilization of theforage available without affecting the fragile equilibrium of the rangeland ecosystem.1.3 Man, livestock, water and rangeland are components of thesame systemProviding adequate water for livestock on range is not merely a question of developingenough wells and springs and ponds to supply water needed by livestock. A properdistribution of stock water in relation to the available forage is equally important.The problems associated with the rational utilization of grazing land and water resourcesinvolve ecological situations within a region, and in one or several countries, so that theidentification and definition of the actions to be taken seem to be extremely complex.However the various elements (biological, ecological, sociological, economical, animal, etc.)5

to be taken into consideration are all mutually inclusive and interconnected. For example, thedistribution of the watering points cannot be fixed independently of the characteristics of therangeland and of the herds; the type of water lifting devices to be installed on the wellscannot be decided without taking into account the maintenance capacity and the wishes ofthe future users.Man, water, livestock and rangeland have therefore to be considered as elements of thesame system, interacting one on each other in such a way that their interrelations must beused as a background for planning any livestock development project in arid and semi-aridcountries.1.4 Suggestions for use of the bookChapters 3 and 4 are intended for the water expert who wishes to begin to know aboutanimal water requirements and the importance of rangelands. Chapter 5 is intended for thosenot already familiar with surface water development while chapter 6 is for those unfamiliarwith groundwater.2. Objectives of the manualIt is not always possible to obtain at the right time the professional studies and expertise thatmight be desired to plan all of the components of livestock project. It is not unusual that thewater specialist has to plan the water resources development component of a livestockproject independently of the livestock and rangeland experts. It happens also that a livestockexpert has to plan a stock raising project without the help of a water specialist. In both casesthe experts must know the basic elements of the field for which they are not specialists.More generally, anyone who is preparing a livestock development project needs to know allthe water related aspects involved in the stock raising activities as well as all the constraintsconnected with the livestock watering which will affect the water resources developmentaspects of the project.This manual was therefore prepared to help the water specialist in understanding thelivestock watering problems and the livestock and rangeland specialists in understanding thewater resources development and management problems. It is not intended to replacetechnical literature or professional advice when available at the right time, but to serve as ahelpful substitute when those sources of information are unobtainable or as a guide to topicson which further information is needed.This manual essentially deals with the problems related to the improvement of the traditionalmigratory systems of animal production through a more adequate water supply to livestockover the rangelands. Very little will then be discussed about the livestock production systemslike enclosed farms and ranches, in which the management of animals, range, water and allrelated resources are, or should be, fully integrated and well coordinated. Very little will bediscussed about the watering problems of livestock in the areas where agriculture is theprevailing activity.6

3. Interrelations between the components of the system(man, water, livestock, rangeland)3.1 Man and water3.2 Man and livestock3.3 Water and livestock3.4 Livestock and rangeland3.5 Concluding or summary statement3.1 Man and water3.1.1 Creation or improvement of water supplies3.1.2 Water lifting devices and maintenance3.1.3 Cost of water3.1.4 Water and rangeland management3.1.1 Creation or improvement of water suppliesNatural water supplies (small ponds during the rainy season, permanent lakes or riversduring the dry season) are the main source of water for livestock belonging to the extensivemigratory animal production system. However, as a consequence of the growing number oflivestock, artificial watering facilities have been created either for enabling livestock to grazelarger areas and make full use of the forage resources of the rangelands or for wateringlivestock along the transhumance routes.The different techniques of water development will be examined in chapters 5-6.3.1.2 Water lifting devices and maintenanceWhile the main function of the pumps and water lifting devices, which is to produce water,and especially groundwater, to make it available to livestock, they should also suit the habitsand preference of the human users as well as their capacity to maintain mechanical devicesand water structures. Some common devices are discussed in Chapter 6.3.1.3 Cost of waterIn an agricultural environment, water users are usually sensitive to the cost of water even indeveloping countries. The small farmer in Tunisia or the vegetable producer in an oasis ofMauritania are perfectly aware of what their well and their pump cost and how many litres offuel they need to irrigate their garden every month. But in a rangeland environment of adeveloping country, cost of water is an abstract concept, since it is usually not related to a7

price stockbreeders have to pay to water their animals. Most of the investment and operatingcosts are borne by the national budget.On the other hand cost of water is commonly used as an indicator to judge the economicalfeasibility of water development. Physical parameters (depth to water, type of rock to be dugor drilled) affect the cost of water. Costs are closely related to local conditions and to theproper financial and technical management of the project. It is often misleading to drawgeneral conclusions on correlations between cost of water and hydrogeological orhydrological situations. This is the reason why this aspect of the water development is notdiscussed in this manual. In normal practice this analysis should be carried out for eachcase, especially when alternatives (surface water or groundwater, dug or drilled wells) areavailable.3.1.4 Water and rangeland managementUntil recently it was considered that good management of a system including rangeland andwater supply could only be attained through a single agency or authority, which would takecare of the maintenance and repair of the water supply and pumps as well as of theconservation of the rangeland.The disappointing results obtained so far by many of these organizations have led livestockdevelopment planners to use informal groups of livestock owners, pastoral associations orcooperatives as a channel for some of the development activities including partial financingof wells, maintenance and repair of pumps, and conservation of rangeland (fire protectionessentially). The direct involvement of the population concerned is expected to improve theefficiency of the livestock development projects and in the meantime to lighten the financialweight of large projects on the national budgets. This trend observed during the last fewyears to assign more responsibility to the pastoral communities in managing their wells,pumps and rangelands, is unfortunately too recent to allow positive results to be observed.Additional creative efforts in this field are still needed. For example, why not to assign thetask of monitoring ground-water (water level fluctuations, water use) to stockowners' groupsor cooperatives?3.2 Man and livestockThe relationship between livestock and the human population is important and hasconsiderable bearing upon the use of the rangelands and the type of distribution of thewatering facilities.There is a range of situations from the truly nomadic herdsmen who move with the animalstogether with their families and possessions, to the sedentary situation where thestockbreeder and his family has a permanent home, usually associated with a village.However, in order to stay within the general purpose of this manual, only the pure pastoraland semi-sedentary systems which include important movements of the herds will beconsidered.a. Purely pastoral systemThe purely pastoral system concerns the extensive migratory animal production system inuse within the Near East, Sahel, Sudan and Sub-Saharian zones of Africa. The traditionalpastoral communities own and manage the great animal resources in these regions. In thissituation the herds constantly move in search of grazing areas and water. During andimmediately after the rainy season, livestock move northwards (in Sahel area) in order to8

exploit the meagre grazing resources of the Sub-Saharian areas. When the dry season iswell set up, herds move southwards in order to eventually stay for the rest of the dry seasonin the vicinity of the permanent water supply points. The permanent dry season water supplymay come from the large river systems (Niger, Senegal, Chart, Logone) or permanent lakes(de Guiers in Senegal, Rkiz in Mauritania, Lake Chad). Permanent ponds are common inwetter regions while occasionally deep wells, either artesian or equipped with pumpingfacilities, may be used.It is clear that the planning of the water supply layout must take into consideration theseasonal movements of the livestock as well as the possible competition between farmersand stockbreeders for the utilization of the watering facilities during the period in which theherds have to enter the agricultural areas.b. Semi-sedentary systemIn the areas where the average annual rainfall exceeds 350-400 mm, stockbreedersprogressively settle and become agro-pastoralists. Their way of life based on the interactionbetween stockbreeding and agriculture includes four different periods:i. as soon as the first rains take place - usually in June in the Sahel area), the herds movetowards the high lands (plateaux) which are not used for agriculture. One herd is usuallyconducted by only one shepherd who may be either a stock owner or a wage earner. Thisperiod is commonly called "petite (small) transhumance" in the French literature;ii. immediately after harvesting - mid-September in Sahel area - part of the herds come backto the villages to eat the residues of the crops during approximately one month;iii. when the crop residues are exhausted the livestock is taken back to the grazing areaswhich may be as far as 30 to 40 km away from the village. This period is commonly called"grande (great) transhumance" in the French literature, usually lasts until December-Januarywhen most of the natural ponds dry up;iv. during the 4-5 months preceding the rainy season, the livestock uses the grazing areaslocated close to the villages and is watered from the village wells.3.3 Water and livestock3.3.1 Water quality3.3.2 Water requirement3.3.3 Location of the water supplies3.3.4 Watering facilities3.3.1 Water qualitya. Salinity tolerance in livestock varietiesLivestock needs fresh drinking water for normal health and high production. The total saltcontent of water is the most important characteristic in determining the suitability of water for9

stock and it is also the easiest water quality data to obtain even in the field. Other qualitycharacteristics are usually of secondary importance.Excessive intake of saline water may cause sickness and death. Adult sheep appear to befairly tolerant, and indeed are often given free access to salt licks, obviously in circumstanceswhere they do not ear enough to cause ill effects. Cattle are less tolerant than sheep butmore tolerant than pigs and poultry.The standards at present considered to be safe upper limits of total salts in water for stock inWestern Australia are indicated in Table 1.Table 1: UPPER LIMITS OF TOTAL SALT CONTENT OF WATER FOR LIVESTOCKLivestock Total dissolved solids (in g/l)Poultry 2.8Pigs 4.3Horses 6.4Cattle (dairy) 7.1Cattle (beef) 10.0Adult dry sheep 12.8While most animals can therefore tolerant fairly high levels of total salts, the amount ofmagnesium in the water may be critical. The following concentrations of magnesium in waterare considered to be safe upper limits for stock on dry feed. Higher levels can be toleratedwhen pastures are green and succulent:Lactating cows and horses 0.25 g/lDry cattle and weaner sheep 0.40 g/lAdult sheep0.50 g/lAnother useful guide to animal water supply is shown in Table 2. This table is primarilyintended for human drinking water, since people often drink the same water as animals.b. Effect of excessive water or feed salt content on livestockThe amount of salt in the feed or water which will produce symptoms of salt poisoning in thevarious domestic animals are Indicated in Table 3.10

Table 2: WATER QUALITY STANDARDS FOR ARID REGIONSSuitability for permanent supplygood fair moderate poorColour colourless colourlessTurbidity clear clearOdour odourless hardly perceptible slight slightTaste at 20°C none perceptible pronounced unpleasantTotal dissolved solids (mg/l) 0-500 500-1000 1000-2000 2000-4000EC S/cm) 0-800 800-1600 1600-3200 3200-6400Na (mg/l) 0-115 115-230 230-460 460-920Mg (mg/l) 0-30 30-60 60-120 60-1200-5 5-10 10-20 20-40Cl (mg/l) 0-180 180-360 360-710 710-1420SO 4 (mg/l) 0-150 150-290 290-580 580-1150Source: Schoeller (1977)Table 3: TOTAL QUANTITY OF SALT PRODUCING SYMPTOMS OF SALT POISONINGLivestock Total amount of salt per day (in g/l)Poultry 4 - 8Pigs 100 - 200Cattle 1800 - 3600Sheep 100 - 200The main symptoms in sheep and cattle are excessive thirst, abdominal pain, loss ofappetite, diarrhoea and increased urination.c. Deterioration of water qualityThe water quality can deteriorate over the years (mainly groundwater) and even from seasonto season, and it is wise to check suspect water before letting stock have access to thesupply.During the warmest months, high evaporation increases the concentration of salt in the waterstanding in troughs or in ponds for a long time and it may be advantageous to place thewater troughs in the shade to limit the water temperature.d. Bacteriological water qualityWhere possible animals should be given water which is bacteriologically clean as well aschemically satisfactory.11

3.3.2 Water requirementa. Factors affecting the water requirementsThe water requirement of livestock is the total quantity of water required by animals for theirmetabolic processes as well as for the heat regulation of their body. They vary according to anumber of factors such as the food intake, quality of the food, and air and water temperature.b. Food intakeThe demand for food varies according to the type and class of animal and the particularfunctions occurring such as during pregnancy, in lactation or whilst being fattened. Moreoverthe food requirement may be affected by the quantity of energy consumed by animals,mostly to reach the water supply from the grazing areas. The values of dry matter intakeindicated in Table 4 correspond to a minimum requirement level for maintenance of animalson rangeland.c. Quality of the foodNatural pastures are usually thought to be dry, but in many instances individual plants, orpart of plants, remain green for long periods after rain has ceased and this moisture is ofbenefit in reducing the dependence of animals on water supplies. During the growth period(wet season), grass may contain as much as 80 percent water. The moisture contentprogressively decreases until the straw contains only 10 to 15 percent water. The green podsof Prosopis may supply an important part of water requirement of animals even under desertconditions.Vegetation in arid areas may, unfortunately, have a high content of salt. The waterconsumption of sheep grazing on saltbush is two to three times greater than that of sheep ongrasslands, and the importance of salt free water is greater.d. Air temperatureThe water requirement related to dry matter intake increases with air temperature. Table 4shows the effect or air temperature on water requirement.Table 4 WATER REQUIREMENT AND AIR TEMPERATUREAir temperature (in °C)Water requirement (in l/kg of dry matter consumed)-17 to +10 3.510 to 15 3.615 to 21 4.121 to 27 4.7more than 27 5.5In the case of pregnant cows the quantities are multiplied by 1.5 and for lactating cows they areincreased by 0.87 l per kg of milk produced.Source: Agricultural Research Council (1965)12

e. Voluntary water intakeThe voluntary water intake is the quantity of water which has actually to be supplied toanimals and corresponds to that part of the water requirement which cannot be provided bythe moisture content of the forage. This is the parameter to be taken into account whenplanning a water supply system for livestock.Table 5 summarizes the effect of the various factors governing the water requirement andgives an estimate of the voluntary water intake corresponding to the three main seasons inthe Sahel.The voluntary water intake has been calculated from the water requirement by assuming awater supply from the plants corresponding to:i. 70 to 75 percent of moisture content of the plants during the wet seasonii. 20 percent of moisture content of the plants during the dry and cold seasoniii. 10 percent of moisture content of the plants during the dry and hot season.Table 5: ESTIMATED WATER REQUIREMENT AND VOLUNTARY WATER INTAKE OFLIVESTOCK UNDER SAHELIAN CONDITIONSAnimalTropical Mean DailydryLivestockUnits (TLU)liveweightin kgmatterintake inkgWET SEASON Airtemp 27°Ctotalwaterreq. inl/dayvolun.waterintake inl/dayDRY COLDSEASON Air tempfrom 15-21totalwaterreq. inl/dayvolun.waterintake inl/dayDRY HOTSEASON Air temp27°Ctotalwaterreq. inl/dayvolun.waterintake inl/dayCamels 1.6 410 9 50 15 37 35 50 50Cattle 0.7 180 5 27 10 20 19 27 27Sheep 0.1 25 1 5 2 4 4 5 5Goats 0.1 25 1 5 2 4 4 5 5Donkeys 0.4 105 3 16 5 12 11 16 16Note: One Tropical Livestock Unit (TLU) is equivalent to an animal of 250 kg liveweight onmaintenance. It corresponds to the "Unité Bétail Tropical (UBT)" of the French literature. Inthe Sahelian countries, 1 TLU is approximately equivalent to 1.4 cattle or to 10 sheep orgoats.3.3.3 Location of the water suppliesThe spacing of water supplies across the land is partly dependent on drinking frequency, butalso affected by the walking ability of the animals, a requirement for uniform utilization of theforage resources and the maximim daily discharge of the water supply.In terms of vegetation utilization, productivity is reduced by wider spacing because the areasclose to water become overgrazed and those further from the water are undergrazed. InAustralia, areas of 17 000 ha (circle of 7.35 km radius) for cattle and 4 000 ha (circle of 3.5km radius) for sheep may be grazed from one water source, although shorter distanceswould seem desirable for maximum production and uniform use of vegetation.13

In Sahelian countries, it is usually considered that cattle can walk 6 to 10 km from the grazingarea to water and sheep and goats can walk 3 to 5 km from the grazing area to water.These figures have however to be considered as rough optimal averages since livestock caneasily walk twice as far in case of necessity.Drinking frequency is another debated question among the stockbreeding specialists. It isusually thought that a daily water intake for cattle is necessary during the hot season whilesheep and goats may be watered every second day only and camels can afford to staywithout drinking for 4 to 5 days.However recent observations made in Niger have proved that water intake every second daymay be profitable for cattle too when the distance from the grazing area to water exceeds 5-6km. Observations were made on two similar herds (Serres 1980) using grazing areas located10 km away from the water supply. For the herd which was watered daily, an important partof the day was spent for the walking activity. Grazing has to take place partly during the nightand very little was remaining for rest and ruminating. Table 6 shows the main results of theobservations. For the herd which was watered every second day, the daily grazing time wasincreased as well as the time for ruminating, therefore facilitating the digestion of the straw.Moreover the animals which spent less energy for walking were less tired and could walkfaster as shown on Table 6.Table 6: RESULTS OF OBSERVATIONS MADE IN NIGER ON TWO SIMILAR HERDS ONEWATERED EVERY SECOND DAY AND THE OTHER ONE EVERY DAYActivity WATER INTAKE EVERY SECOND DAY DAILY WATER INTAKETime spentfirst dayTime spentsecond dayDailyaveragePercent of totaltimeTimespentPercent of totaltimeGrazing 6h 40 9h 7h 50 33% 6h 30 27%Walking 7h 2h 4h 30 19% 8h 30 37%Ruminating 4h 50 5h 40 5h 15 22% 3h 30 15%Rest 5h 20 7h 20 6h 20 26% 5h 20 22%Watering 0h 10 0 0h 05 negligible 0h 10 1%TOTAL 24h 00 24h 00 24h 00 100% 24h 00 100%Source: Serres (1980)3.3.4 Watering facilitiesa. Design and organizationThe design and organization of a watering facility for permanent use must usually be differentfrom that for temporary or seasonal use. The drying up of a pond or reservoir can be used tocontrol grazing, while permanent boreholes may ensure overgrazing in a considerable areaaround the borehole. Control methods near boreholes must be based on locally availablethorn shrubs which are used to make paths to the borehole. Permanent installations mayprovide a basis for one or a few families to settle if the borehole produces enough water forgardening as well as stock. Considerable efforts are needed to resolve the problems relatedto design of the watering facility and for the organization to operate and maintain it, since itmust be an integral part of the animal production system.14

. Watering troughsIn order to allow livestock to drink easily and in order to avoid crowding around the wateringplace, the use of watering troughs properly build and set up is advisable even if the watersource is an impounding surface reservoir or a simple dug well.ShapeCircular and rectangular troughs are commonly used for cattle. Circular troughs provide thegreatest storage capacity per unit of material used, while rectangular troughs give thegreatest drinking space in proportion to their capacity. V or U shaped troughs are commonlyused for sheep.MaterialIf properly constructed, reinforced concrete troughs are usually the most satisfactory forpermanent use because of their durability.Wooden troughs constructed from 5 cm thick material, well braced and preferably paintedwith non-toxic paint are satisfactory if they are not exposed to frequent drying out.Reinforced galvanized metal troughs are durable, lightweight and usually of moderate cost.InstallationSubstantial masonry foundations are preferable for most troughs, for they provide support,anchorage and alignment. All stock troughs should be anchored sufficiently to preventlivestock from moving them or tipping them over.Drinking spaceIn order to avoid crowding, sufficient drinking space should be provided at troughs to waterwithout undue delay the full number of livestock that come to drink at any one time. About 0.7to 1.0 m of drinking space should be provided for each cow and only 0.3 to 0.4 m to eachsheep or goat. When the water source is a dug well from which water is drawn by hand orwith animals, the number and distribution of the troughs around the well should be in relationto the maximum expected discharge of the well. Modern dug wells in pastoral area areusually equipped with six circular troughs one metre diameter made of concrete anddistributed around the well.HeightCattle troughs range from 0.5 to 0.7 m in height, the lower height being preferable for calvesand other young livestock.Ordinarily, sheep troughs should not be more than 0.3m high.WidthTroughs with a top width of 0.7 m or more can be used from both sides if properly located.Wide troughs should be provided with suitable guardrails to prevent livestock from steppingor being crowded into the trough.15

c. Storage tankAdequate storage facilities are particularly needed when discharge is smaller or greater thanthe requirement during watering times. The usual conditions of low discharge requiringstorage will be wells equipped with pumps operated by windmills, and low yielding springsand free flowing wells. When wells are operated by motor driven pumps and the discharge ismuch higher than the daily average water demand for watering livestock, storage is neededto avoid wasting of water.The capacity required for the storage tank will depend largely on the flow available from thewater supply, the number of livestock and the dependability of the pumping unit; wherewindmill power is used for pumping, it is desirable to provide sufficient storage for about oneweek because calm periods may prevent windmill operation for several days at a time.If storage requirements are relatively small, combination storage and drinking tanks areusually the most satisfactory and cheapest.If greater storage is required, wooden, steel or concrete tanks are commonly used.For very large storage capacity, an excavated earth reservoir may be the cheapest solution.3.4 Livestock and rangeland3.4.1 Rainfall and rangeland resources3.4.2 Stocking rate and carrying capacity3.4.3 Overgrazing problems3.4.1 Rainfall and rangeland resourcesThe forage production from the rangelands will be examined here only in those aspectswhich affect the water supply design (distribution and quantity) aiming at an even utilizationof the forage available.The biomass annually produced by the rangelands depends mainly on the absoluteavailability of the growth limiting factors and is therefore strongly influenced by both thequantity of precipitation and the quality of the soils. In the Sahel countries, for the same valueof annual rainfall, the actual response of the rangelands in terms of forage production showsa great variability according to the quality of the soil and the availability of nitrogen andphosphorus. There is evidence that soils with higher rainfall tend to be lower in nitrogen andphosphorus. While weight of forage is higher in wetter conditions the nutrient value of theforage may actually be lower. It is therefore impossible to give a simple and generalrelationship between rainfall and forage production. However various authors have givententative representations of the variations of the dry matter production of rangelands as afunction of rainfall.Figure 1 shows an estimation of relationship between mean annual rainfall and dry matterproduction in Somalia. The wide range of precipitation taken into account for representing thevariations of productivity Indicates the great uncertainty prevailing in this field.16

For the preparation of the 2nd phase of a Livestock Development Project in Mali, J.J. Boudet,rangeland specialist consultant for FAO, developed an exhaustive picture of the variations ofthe dry matter production of rangelands in relation to annual rainfall and its variability.Figures 2 and 3 graphically summarize the data included in FAO's report.While Figures I through 3 can provide a rough estimate of rangeland productivity, it ispreferable Co have actual assessments by pasture specialists for the particular area ofconcern. Such specialists may use actual testing of pasture but often are forced to assess byeye using their experience.Productivity of grazing lands can be improved by controlled grazing, sowing to increasegroundcover, introduction of legumes to increase fertility, control of brush, waterconservation, reduction of wind erosion, removal of weeds and application of fertilizers.However, many of these methods are too expensive for some extensive grazing areas.3.4.2 Stocking rate and carrying capacityCarrying capacity is commonly expressed as number of animal units per hectare whenspeaking of intensive ranching or dairy operations, but when referring to extensive nomadicgrazing carrying capacity is usually hectares per animal unit. The carrying or grazing capacityof a rangeland is defined in the following paragraphs as the amount of grazing land whichshould be made available to a Tropical Livestock Unit so that it can be maintained withoutdeterioration of the natural resources of the area over the long term. Other definitions includethe necessity of efficient production (milk or meat) but it is believed that under arid and semiaridarea conditions, the main purpose of grazing over a large part of the year is themaintenance of the livestock.Stocking rate is defined as the amount of grazing land actually available to a TropicalLivestock Unit. The correct stocking rate should always be less than the carrying capacity.17

Fig. 1: Relationship between mean annual rainfall and rangeland productivity in Somalia (Hunting Services, 1976)Fig.2:Relationshipbetweendrymatterproductionandannualrainfall inSahelenvironment(Dataderivedfrom Table 3 Annex 5 of Livestock Development Project, 2nd phase, Mali, Cooperative Programme FAO/World Bank)18

Fig. 3: Relationship between carrying capacity and annual rainfall in Sahel conditions(Data derived from Table 3 Annex 5 of Livestock Development Project, 2nd phase,Mali, Cooperative Programme FAO/World Bank)19

Fig. 4: Rainfall probability under Sahelian conditions (Data derived from Cocheme andFranquin 1967)The carrying capacity or ability of an area to feed stock is primarily a function of the drymatter production of the considered rangeland. It is therefore related to rainfall as well as tothe soil quality.Figure 3 shows the relationship between carrying capacity and annual rainfall for Mali. Foreach value of rainfall the carrying capacity may vary from a maximum corresponding to badquality soil and low nutrient content to a minimum corresponding to ideal soil conditions. Itshould be noted that the lower the annual rainfall, the wider the range between the maximumand the minimum carrying capacity. This is normal since the dry matter production ofrangelands tends towards zero for small values of rainfall and bad soil conditions.In assessing the carrying capacity of rangelands from data on dry matter production, severalfactors are taken into account including the slow deterioration of forage quality over the dryseason (decrease of protein content) and the increasing risk of forage destruction as timegoes on.The purpose of these remarks is to emphasize the uncertainty which prevails on the actualdetermination of the carrying capacity of rangelands and the difficulty of giving a simplerelationship between the most commonly available data - the rainfall - and the grazingcapacity of an area.Attention should also be drawn to the variability of rainfall over a given area from year toyear. The simple knowledge of the average annual rainfall is not sufficient to predict therange of variations of the carrying capacity of an area. Figure 4 shows the probableoccurrences of rainfall under Sahelian conditions.20

As an example, an area receiving an average annual rainfall of 300 mm may receive only200 mm in one year out of five and as much as 400 mm in one year out of five. This alsomeans, according to Figure 3, that an area with 300 mm average rainfall may have NOcarrying capacity at all one year in ten on all the medium Co bad quality soils.A much simpler table (Table 7) presents grazing capacity with the generally acceptedassumption that 50 percent of the forage production is utilized.Table 7: GRAZING CAPACITYMean annual rainfall mm DM production t/km 2 Grazing capacity ha/TSU1000 150 5750 100 10500 50 15250 25 303.4.3 Overgrazing problemsIn a Sahelian rangeland, the seeds produced by the grasses (graminaceae) reach theirmaturity and fall onto the soil at the end of the rainy season. The seeds are then buried bythe trampling of the livestock and thus protected during the dry season. They can germinate8-9 months later when the rain comes back again. The conservation of the rangelanddepends therefore directly on the seeding process and more precisely on the quantity ofseed produced which requires a normal development of the plants.When the vegetative cycle is disturbed by overgrazing, the plants react by accelerating theirrhythm of development which affects the quality of the seeding process. Repeating thisphenomenon during several consecutive years may lead to the disappearance of certainspecies, to the benefit of other species usually less palatable for livestock and sometimes noteaten at all by the animals. This modification of the vegetation may therefore result in animportant decrease of the grazing capacity of the rangeland as a consequence ofovergrazing during the vegetative period of the grass.When stocking rate is excessive during the dry season, the vegetation may also temporarilydisappear but this will generally not affect the germinating capacity of the seed buried intothe soil and the range should resume after the next rainy season approximately at the samelevel as before for the same amount of rainfall.3.5 Concluding or summary statementThe provision of water for animals under extensive grazing or nomadic systems is oneelement of the man, animal, environment situation. The relations are basically simple but arefraught with variations, exceptions, special conditions which make generalizationsunsatisfactory. This means that each area or region needs to be studied in an integratedmanner so that physical additions, such as watering points, will have a positive rather thannegative effect on the people concerned and on the region. The brief outline of this chapter,however, at least provides a starting point for those who are faced with estimating waterrequirements.Chapter 4 attempts to show how the information in this chapter or from other sources may befurther used for selection of type of water supply.21

4. Selection of the type of water supply and distribution4.1 Water source4.2 Distribution of water supplies4.1 Water sourceThe first question a planner may ask when dealing with livestock watering problems onrangeland areas is whether surface or groundwater will be used. In many circumstancesthere is no choice since only one source of water can physically or economically bedeveloped. But assuming that both ground and surface water can be considered, Table 8may guide the planner in tentatively selecting the most convenient source of water on whichto concentrate the investigation efforts.Water harvesting techniques, although they are briefly described in this manual, are notmentioned in Table 8 since they can be considered only if neither surface nor groundwatercan offer a solution.Table 8: TENTATIVE SELECTION OF THE MOST SUITABLE WATER SOURCEPresence ofshallow aquiferSHALLOWCONTINUOUSAQUIFERNO SHALLOWCONTINUOUSAQUIFERPeriod of useof watersupplyPermanentrangeland(throughout thedry season)temporaryrangeland (2-3months afterthe rainyseason)Topography Rainfallflat tomoderateslopesmoderate tosteep slopesflat slopes200-300mm300-600mmMorphology SoilcharacteristicsNo suitable sites forsurface watermobilization- Marked valleys- Narrow sections +wide imperviouspossible pond sitesSuggested watersource toinvestigateGROUNDWATER(dug wells)GROUNDWATERGROUNDWATERGROUNDWATERSURFACE WATER(impoundedreservoirs)GROUNDWATERmoderate slopes Sandy soils GROUNDWATERsteep slopesClayey and sandysoilsrocky soilsSURFACE WATER(excavatedreservoirs)SURFACE WATER(impoundedreservoirs)SURFACE WATER(impoundedreservoirs)22

4.2 Distribution of water suppliesIt is clear that one of the criteria for location of the water supplies will be the availability ofwater but it is also a good practice to set up a preliminary layout of the water supply systemin order to ensure an even utilisation of the forage resources, and plan the additionalinvestigations necessary for siting the water supplies.The layout will simply consist of fixing the average distance that should occur from a watersupply to another in order to allow all the livestock that can be fed 5 years out of 10 from agiven rangeland, to be suitable watered. The following procedure is suggested to determinethe distribution of the water supplies over the considered rangeland.a. First check if a 20 km interval between water supplies is feasibleThe distance of 20 km corresponds to twice the average walking capacity of cattle undersemi-arid conditions. Over an area of 30 000 ha (circle of 20 km diameter), the number ofTropical Livestock Units (TLU) which should be watered from each supply is equal to 30 000divided by the carrying capacity (C cap in ha/TLU) corresponding to the average rainfall year.Assuming maximum daily water intake of 40 l/TLU, the maximum daily requirement (V maxday ,in m 3 /day) to be met by each water supply will beV maxday , should then be compared to the amount of water expected, Q exp in m 3 /day, that eachwater supply can deliver in 12-16 hours daily operation. If V maxday is less than Q exp , then take20 km as an average distance from one water supply to another.b. If the maximum daily water production Q max of one supply is not sufficient to meet Therequirements of the livestock which an be fed by a 30 000 ha rangeland area (circle of 20 kmdiameter), then determine the optimum interval between water sources according to thefollowing procedure:Using the same symbols as before, the maximum number of TLU which can be watered fromeach supply will be:The rangeland area (in ha) necessary to feed N TLU will be N TLU x C cap and eventually themaximum interval D max between water supplies will be approximately:inExample:Determine the optimum distance between water supplies on a rangeland with a carryingcapacity of 10 ha/TLU and assuming that average daily water production from each supplycannot exceed 20 m3/day.23

V maxday = 1200/10 = 120m 3 /daySince V maxday is more than the maximum daily discharge of an average water supply, thedistance will be less than 20 km and comes:D max = 0.6 20 x 10 = 8 kmThis example is for cattle and would be modified accordingly for other animals.5. Surface water resources development for rangeland5.1 Surface water utilization and development5.2 Excavated reservoirs5.3 Impounded reservoirs5.4. Rainwater harvesting techniques5.5 Concluding statement5.1 Surface water utilization and developmentSurface water is usually the main source of water for purely pastoral livestock in semi-aridregions. During the rainy season, precipitation over limited catchment basins runs off andconcentrates in natural ponds where the soils are sufficiently impervious to prevent leaking.Most of these ponds dry out a few weeks after the end of the rainy season, due to thecombined effect of evaporation and seepage. During the dry season, a great part of thelivestock moves towards permanent surface water such as large rivers or permanent lakes orponds. This method of utilization of surface water only requires leading the herds to waterand is always preferred to groundwater by stockbreeders. However, sedimentation andlocation often make the rational use of surface water difficult and the improvement of thenatural storage conditions desirable. Sanding up of ponds decreases their storage capacityuntil it becomes negligible so that the actual number of usable poinds is smaller every year.This phenomenon is aggravated by overgrazing and resulting desertification which makesthe upper soil layers more sensitive to the wind and water erosion. The remoteness anduneven distribution of the permanent lakes and rivers during the dry season results in theovergrazing of the pasture lands surrounding the water supplied. Moreover the agriculturalarea increases to the detriment of the rangelands which become smaller while the livestockpopulation tends to grow every year.The main purposes of surface water development will be to increase the storage capacity ofnatural ponds to extend their period of utilization, and to create new surface water reservoirsin order to better the rangeland resources.However, permanent water supplies will rarely be desirable because of the following factors:a. In arid and semi-arid regions, runoff coefficients vary in the opposite direction with the sizeof the basin; the bigger the catchment basin, the lower the runoff coefficient. Therefore thequantities of water which can be collected by intercepting the runoff are usually small.24

. Evaporation is high and may exceed 2 m/year which corresponds to the maximum depthof most of the ponds even after deepening.c. Seepage also contributes Co loss of water in the surface reservoirs and the techniques oflining (with plastic or rubber sheets) are too costly in developing countries.d. If significant permanent water supplies can be established they will probably be used foragriculture which is a much more profitable activity than extensive stockbreeding.e. Permanent surface reservoirs in a hot climate are often subject to health hazards whileparasitic diseases are much less common around non-perennial ponds.Some general guidelines for excavated and impounded reservoir location design andconstruction follow for those who are not civil engineers. Ref. 14, 19, 21 and 63 arerecommended for those wishing more detail. It is clear that larger excavated and impoundedreservoirs are "water harvesting" devices broadly speaking, but the term is generally used forsmaller storages where the tributary runoff area is treated to increase runoff. The basicmethods to choose a drainage area and a storage volume are the same.There is essentially a continuum in gradation between large reservoirs and cisterns. Thesubdivision of reservoirs which follows is arbitrary but the reader will observe that there arereservoirs which are excavated in one part to form an embankment, depending ontopographic conditions. The arbitrary division is only for convenience. Small reservoirs areknown by other names in many areas, particularly in Asia where they are usually calledtanks.5.2 Excavated reservoirs5.2.1 Advantages and conditions of use5.2.2 Selection of sites5.2.3 Construction5.2.4 Stock watering and protection of the pond5.2.5 Maintenance5.2.6 Case study and cost5.2.1 Advantages and conditions of useAn excavated reservoir is one of the simplest to construct and the only type of earth reservoirthat can be constructed economically in relatively flat terrain. The fact that the capacity ofthese reservoirs is obtained by excavation limits their practical size, and they are best suitedto locations where a comparatively small reservoir is sufficient, a small amount of runoff isexpected, and impervious soils prevail.Since they expose a minimum amount of surface area in proportion to their volume, they areadvantageous in areas where evaporation losses are high and water scarce. Under suchconditions, livestock can utilize a greater part of the available water. The ease with whichthey can be constructed, their compactness, their safety from flood-flow damage, theirflexibility of location and their low maintenance requirements make their use popular in most25

of the semi-arid areas where extensive stockbreeding is the main activity. Improved naturalponds are also included in the same category of surface water storage system.Excavated reservoirs are preferably located in the topographically low area of small closeddrainage basins or in upland watersheds where the drainage divide is low and thetopography is gentle. In some areas ancient sand dunes, now fixed by vegetation, form idealclosed areas.In some regions excavated reservoirs reach the groundwater table and may become more orless permanent.5.2.2 Selection of sitesThe location of stock watering reservoirs or ponds within a rangeland area is essentiallydetermined by the nature of the soils and the hydrological conditions.a. Nature of the soilsAn adequate depth of impervious soil which can be easily excavated is essential forexcavated reservoirs. If there is any doubt as to the nature of the soil, numerous test augerholes should be bored over the proposed reservoir area to determine the suitability of the soiland particularly the permeability of the sub-soil strata. Sites with porous soils or withunderlying strata of sand, gravel, fissured limestone and other porous materials should notbe selected unless such strata are not of sufficient magnitude to cause trouble. Actually theeasiest way for identifying possible sites for an excavated reservoir with the best probabilityof success is to select an area where water naturally accumulates or has accumulated andwhere clayey deposits cover a large area. In any case the thickness of the clayey layer hasto be checked by test holes before deciding on the suitability of the site for excavating areservoir or deepening a natural pond. However, it is possible to select a site even in case ofinsufficient clay thickness provided that during the construction work, the clay is carefully putaside and then spread again and compacted over the bottom of the reservoir afterexcavation.If hard rock is found costs of excavation will increase greatly.Where there is no opportunity for studying the characteristics of the soil with adequateapparatus, some indication of the permeability of the soil can be obtained by filling test holeswith water or by forming suitable containers from samples of soil and filling them with water.The holes or containers may be filled several times or puddled if necessary to representconditions at the reservoir site. Observation of seepage will indicate what may be expectedfrom the planned reservoir.The fact that a reservoir may lose considerable water Immediately after excavation does notnecessarily mean that it will be unsatisfactory: frequently new reservoirs do not retain watersatisfactorily until they become sealed. This may require several months or even a year ormore, depending on the soil type and on the quantity of fine material transported by therunoff water.b. Hydrological conditionsBefore undertaking the excavation work, it is necessary to estimate the probability of fillingthe reservoir by the expected water supply (usually runoff water). The hydrologicalinvestigations which can yield reliable information are usually lengthy and expensive so that,26

if such studies are envisaged, it should be checked that their cost does not exceed a fractionof the total construction cost. This is likely to happen only in the case of large reservoirswhich may justify preliminary hydrological studies. In most cases the preliminaryinvestigations will be limited to an enquiry with the local inhabitants and, in the case ofalready existing ponds, to a careful survey of the trails of mud which give evidence of thewater extension during the wet season.Where possible the drainage area should be chosen to minimize sediment runoff into thepond and the drainage area should be relatively small.5.2.3 Constructiona. ShapeAlthough excavated ponds can be built to almost any shape desired, a rectangle iscommonly used in relatively flat terrain. The rectangular shape is popular because it is simpleto build and can be adapted to all kinds of excavating equipment.The side slopes should be as flat as possible for easy access of the livestock unless thepond is planned to be fenced and equipped with external watering troughs. In that case aslope ranging from 2/1 to 3/1 may be acceptable. If one or two sides are of firmer materialtheir slopes could be steeper.b. Building the pondThe reservoir area should first be cleared of vegetation. The next step is to mark the outsidelimits of the proposed excavation with stakes indicating the depth of cut from the ground tothe pond bottom.In semi-arid areas where water is unlikely to accumulate in the excavation during the workperiod, any kind of available equipment can be used. Normal tractors equipped with abulldozer blade or simple bulldozers are generally used. But if the waste material has to betransported far away from the excavation, additional equipment (power shovel and trucks)may be needed. For small reservoirs located in areas where manpower is not a constraint,hand operation can be envisaged at least for the digging work, while the transport of thewaste material may be assigned to animals like mules or donkeys.If the thickness of the impervious upper layer is insufficient when compared to the planneddepth of the pond, the topsoil should be temporarily stockpiled for later use as sealing layerover the bottom of the pond. In that case, the clayey material should be properly compactedafter it has been spread and moistened.5.2.4 Stock watering and protection of the pondComplete fencing of the reservoir is usually recommended to avoid damaging by tramplingand water pollution by livestock. When the pond is fenced a watering system has to beinstalled outside the fenced area and may consist of several troughs set up around a well fedthrough a water supply pipe that runs below the bank of the pond. The water inlet inside thereservoir should be protected against clogging by a strainer made of a piece of screen. Thepipe itself may be of small diameter, 2 inches for example, arid made of steel or plastic.Figure 5 shows a typical water piping and trough system for stock watering from a fencedpond (from Techniques Rurales en Afrique - BCEOM/IEMVT, 1973).27

Although fencing ponds for stock watering is highly recommended in all handbooks dealingwith extensive stockbreeding, it should be mentioned that the advantages usually derivedfrom fencing ponds in developing countries are often more than offset by the increasing costand maintenance requirement and by the fact that fewer animals can water at one time.Moreover, it is extremely difficult in hot climates to prevent livestock (and sometimes herders)from destroying fences which they consider as an unjustified obstacle to reach water whenthey are thirsty.5.2.5 MaintenanceA pond, no matter how well planned and built, must be maintained in order to preserve itsstorage capacity as well as a proper functioning of the watering facilities, if any, throughoutits expected life. When fenced, a pond needs a permanent maintenance in order to ensurethe integrity of the fence during the whole period of presence of water in the reservoir, butthis constraint is so costly that watching and maintenance are not sufficient and the fencesdisappear a few weeks after the pond has come into operation. This experience usuallyresults in the planner giving up the fencing of ponds.In the case of non-fenced ponds, the main objective of maintenance is to remove the wind orwater transported material which accumulates and decreases the storage capacity of thepond. This operation is necessary every 4 to 5 years.5.2.6 Case study and costAn example is given for excavated reservoirs (natural pond improvement) in Mali, within the6th Region. The main characteristic of that region is the presence of a large area inundatedby the Niger river covering 38 000 km 2 This particular area called "Delta Interieur du Niger"plays an important role in the livestock management of the 6th Region since it containsimportant vegetal resources (essentially an aquatic grass known as "bourgou") which isexploited from November to May - i.e. during the dry season - by as many as 1.6 millionbovidae representing 25 percent of the total livestock in Mali. Immediately after the beginningof the rainy season most of the cattle transhumes to the Northwest, North and Northeast inorder to exploit from June to October, the natural ponds and rainfed fodder resources of theSahelian rangelands. When moving from the Delta to the Sahel or from the Sahel to theDelta, the herds always take fixed itineraries, well visible on aerial photographs and even onsatellite imagery since these axes of transhumance may be 200-300 metres wide. Alongthese routes, the livestock need watering and a programme of a first phase of pondimprovement including 20 sites located west of the Delta was established in 1975 andimplemented in 1978-79.An enquiry carried out in 1979 on 7 ponds out of the 20 which were dug indicated that in oneseason about 638 000 cattle and 187 000 sheep and goats have watered during a total of569 days corresponding to an average of 1120 cattle and 328 sheep and goats per day andper pond during 81 days.In 1978-79, the cost of deepening the 20 existing ponds by a private contractor was MalianFrancs (FM) 206 166 344. The preliminary studies and the supervision of the work werecarried out by the Malian Administration (Service du Genie Rural) and cost FM 22 700 000.The total cost of the 20 ponds, each one of 2500 m 3 average useful capacity, amountedtherefore to FM 228 866 344 in 1979 - i.e. approximately US$ 380 000 or US$ 19 000 perpond.28

Figure 5: Watering facilities outside the reservoir area29

A new programme of pond improvement was established in 1983 including 45 sites locatedWest and East of the Niger Internal Delta. The average capacity of the ponds is expected tobe 5000 m 3 /pond - i.e. twice as much as for the ponds deepened in 1979. Table 9 shows asummary of the estimates costs for the preliminary surveys, the excavation work itself andthe supervision. The total amount as estimated in the Preparation Report for the 2nd PhaseProject (FAO 1983) corresponds to approximately 972 million FM - i.e. US$ 1.6 million orUS$ 36 000 per pond. The average cost per pond is therefore twice as much as in 1979, butthe average cost per cubic metre capacity is approximately the same.Table 9: COST ESTIMATE FOR DEEPENING 45 PONDS IN MALI (FAO 1983)UnitWestDeltaQuantity of workEastDeltaGourma sudSeno-MangoTotalNumber of ponds Unit 13 15 17 45Averagecapacity/pondDescription of WorkClearing ofbrushwoodRemoving stumpsand rootM3 5080 5250 5750M2 4 332 14 900 0 19232Unit price inMalian FRTotal costin 1000 FM38 731Unit 0 40 206 246 6 400 1 574Digging M3 66 026 78 690 97 600 242316Digging hard soil(add)M3 0 0 45 000 45000Spreading material M3 3 306 3 400 4 630 113362 150 520 9793 000 135 0004 400 49 878Banking up M3 0 9 500 0 9 500 2 650 25 175Removing rocks M3 0 100 0 100 30 000 3 000Compacting M3 24 426 9 500 4 630 38556TransportingmaterialM3/100M 2 656 82 000 0 84656104 4 010156 13 206Moving track km 217 529 154 900 70 400 63 360Equip site out oftrackkm 43 54 32 129 96 400 12 436to site diffi ground km 10 18 0 28 162 600 4 553Pumping water M3 5 776 9 000 0 14776Mob/demob tooperat area970 14 333Unit 13 15 17 45 150 000 67 500Sub total in 1000 FM 915 735Supervision (4% cost of work) 36 629Preliminary surveys (lump sum) 19 520TOTAL in 1000 Malian Francs 971 885Equivalent in US dollars 1 619 808Average cost per pond in US dollars 36 00030

This example shows the main items to be considered for preparing a cost estimate forexcavating surface water reservoirs. The unit prices of course will differ.5.3 Impounded reservoirs5.3.1 Main characteristics5.3.2 Selection of sites5.3.1 Main characteristicsAn impounded reservoir, also called embankment pond, is made by building an embankmentor earth fill across a narrow valley so that, while excavated reservoirs usually consist ofimproving an existing situation (natural ponds), the impounded reservoirs create a completelynew surface water storage structure.Excavated reservoirs are preferably located at the lower end of small and closed watershedswhich may be part of longer catchment basins cut in several isolated sub-basins by naturalweirs usually made of ancient fixed dunes. On the contrary, the impounded reservoirs areintended to intercept runoff from open watersheds. This important difference has thefollowing consequences for the impounded reservoirs. The volume of runoff water is oftenbigger than the capacity of the reservoir itself so that it is usually necessary to provide aspillway to bypass surface runoff after the pond is filled. The implementation of impoundedreservoirs requires a more accurate estimate of the surface runoff than for excavatedreservoirs since both the embankment and the spillway have to be designed accordingly.In semi-arid areas the reservoirs built for watering livestock are necessarily of small capacityfor the following reasons:a. if natural conditions make it possible to build a large artificial reservoir, its water is certainlygoing to be used for agriculture rather than for extensive stockbreeding;b. if for any reason agriculture is not feasible, an easy access to water for a great number ofanimals is not to be recommended because of the risk of overgrazing the nearby rangelands.Therefore the impounded reservoirs for watering livestock in semi-arid countries will usuallyhave a small to moderate capacity (from a few thousands to a few tens of thousands cubicmetres) and consequently be usable only part of the average year (from a rainfall point ofview). They rarely can be the only source of water supply for livestock on permanentrangelands. Limiting the size of ponds is one way of providing some degree of managementof the grazing resources.5.3.2 Selection of sitesSelecting a suitable site for the impounded reservoirs is important and preliminary surveysare needed before final design and construction. However, this manual is not intended to bean exhaustive handbook for dam construction and the purpose of the indications givenhereafter is just to draw the attention to some important points which have eventually to bestudied by a specialist.31

a. Morphological characteristicsA good site is where a dam can be built across a narrow section of a valley, the side slopesare steep and the slope of the valley floor permits a large area to be flooded. Sites wherewater may expand over large areas under shallow depth should be avoided since they wouldexpose a large surface of shallow water to high evaporation.b. Adequacy of the drainage areaThe contributing drainage area should be large enough to fill the reservoir at least 8 yearsout of 10. However the drainage area should not be so large than expensive overflowstructures (spillways) are needed to bypass excess runoff during storms. Where rainfall is nottoo variable the drainage area can often be chosen to have a minimum cost overflow.However, in many semi-arid areas this is not the case and irregular, high intensity storms ofshort duration may cause extensive damage if proper spillways are not constructed.The amount of runoff that can be expected from a given watershed depends on so manyinterrelated factors that no set rule can be given for its determination. The physicalcharacteristics that directly affect the yield of water are relief, soil infiltration, evaporation rate,plant cover and surface storage.c. Nature of soils in the ponded areaSuitability of a pond site depends on the ability of the soils in the reservoir area to hold water.The soil should contain a layer of material that is impervious and thick enough to preventexcessive seepage. However, the presence of a surface layer of sand or other permeablematerial does not necessarily mean that the proposed sites should be abandoned; thesepervious layers may just be an alluvial deposit covering an impervious bedrock.In most cases detailed investigations including auger holes and laboratory tests should becarried out.d. Foundation conditionsParticular attention should be paid to the nature of the soils at the proposed dam location inorder to ascertain that the foundation would ensure stable support for the structure, andprovide the necessary resistance to the passage of water.Good foundation materials, those that provide both stability and imperviousness, are amixture of coarse and fine textured soils like gravel-sand-clay or sand-silt-clay mixtures.When the soil beneath the dam location is able to ensure the stability but not theimperviousness, a cut-off core of impervious material must be installed under the dam.e. Fill materialThe availability of suitable material for building a dam is a determining factor in selecting apond site. Enough suitable material should be located close to the site so that placementcosts are not excessive.Materials selected must have enough strength for the dam to remain stable and be tightenough when properly compacted, to prevent excessive or harmful percolation of waterthrough the dam.32

The best material for an earthfill dam contains particles ranging from small gravel to finesand and clay in the desired proportions. The material should contain about 20 percent byweight of clay particles. Though satisfactory earthfills can be built from soils that vary fromthe ideal, the greater the variance, the more precautions needed.As for the foundations, if the material selected for the earthfill is pervious, a core of claymaterial has to be placed in the centre of the fill.f. Spillway requirementsThe function of a spillway is to pass excess storm runoff around the dam so that water in thepond does not rise high enough to damage the dam by overtopping.Emergency spillways for small dams in semi-arid countries should have the minimumcapacity to discharge the peak flow expected from a storm of a frequency of 1 year in 10 anda duration of 24 hours. As a very rough estimate it is possible to use the following formula(derived from Figure 15 of Agricultural Handbook No. 590, USDA) correspondingapproximately to the most usual situation in semi-arid countries. For a small drainage area(from a few hectares to a few square kilometres) with moderate slope over the drainage areaand with moderately permeable soils,D = 1.84 x A 0.675in which D is the peak discharge in litres per second per millimetre of maximum daily rainfallwith a frequency of 1 year in 10 and A is the drainage area in hectares.In mild climates, the protection of the spillways against erosion is obtained by installingherbaceous vegetation on the bottom of the spillway. This solution cannot apply in semi-aridclimates where the spillways are usually of two different types. One type is the naturalspillway, a secondary drainage which runs parallel to the main valley and needs only minoradjustments to bypass the excess storm water (see Figure 6a). The other is the linedspillway where no natural saddle is found. An artificial spillway has to be excavated besidethe dam and then lined with stones, concrete or asphalt (see Figure 6b). The lined spillway ismore expensive than the first one.The ideal solution might consist of selecting a site or oversizing the dam in such a way that aspillway would not be required. But, because of the great variability of rainfall andconsequently of runoff, such a solution is rarely feasible in the more arid areas. Either thecatchment basin has to be very small and for most years the reservoir would remain emptyor the benefit gained by eliminating the spillway would be more than offset by the increasedcost of the dam.g. Design of the damThe detailed design of a dam, even if it is small, cannot be treated here in the framework ofthis manual. The main points which have to be taken into consideration are:i. a water supply pipe through the dam is needed for the stock water troughs;ii. cutoffs through the foundation and the dam itself may be needed in order to ensuretightness;iii. the top of the dam should be wide enough to ensure the stability;iv. side slopes upstream and downstream should be low enough to prevent collapse.33

5.4. Rainwater harvesting techniques5.4.1 Preliminary considerations5.4.2 Methods for improving catchment runoff efficiency5.4.3 Building water storage tanks5.4.4 Case study and cost5.4.1 Preliminary considerationsWater harvesting consists of collecting and storing water from an area that has been treatedto increase precipitation runoff.A water harvesting system is composed of a catchment or water collecting area, a waterstorage structure, and various other components such as piping, evaporation control andfencing.Assuming that 65 percent of the precipitation water can effectively be harvested, the quantityof water (V) which can be collected and used, after deduction of losses, from a catchmentarea (A) with an average annual raingall (P) can be estimated by the following formula:If the annual water requirement for one adult cattle is assumed to be approximately 15 m 3 ,including the losses around the watering troughs, the corresponding catchment area A canbe estimated by the proceeding formula rewritten as follows:For example, in an area receiving an average annual rainfall of 200 mm, the catchmentnecessary to collect enough water 1 year out of 2 for one adult cattle would be 115 m 2 . If thesame water supply has to be reliable 8 years out of 10, the value of rainfall taken intoaccount in the formula should be 100 mm instead of 200 (see Figure 4 Rainfall probability) sothat the catchment area required would become 230 m 2 .34

FIGURE 6: DIFFERENT TYPES OF SPILLWAYNatural spillwayLined spillway35

In general the use of water harvesting techniques in semi-arid areas of developing countriesis limited because of the cost involved for treating large catchment areas and for buildingwater storage facilities. Where hard rocks are exposed, collection of rainwater in cisterns hasbeen used for centuries in North Africa in the 100-150 mm rain zone. In these areas the rockis hard at the surface but softer below so that cisterns are easy to excavate.5.4.2 Methods for improving catchment runoff efficiencyThe methods used to increase runoff include vegetation management, land alteration,chemical treatment and soil cover.These methods are widely used in Australia and in United States. Vegetation managementis, for obvious reasons, not applicable in semi-arid countries, while treating soil surfaces toprevent infiltration is too costly for developing countries. However, areas of bare rock requireminimum treatment, mostly to channel the water to a cistern.a. Land alterationCollecting banks and contour drainsLand alteration is often the simplest and least expensive method of water harvesting when itinvolves nothing more than building walls or ditches to collect runoff from existing ormanmade catchments such as rock outcrops or roads.The purpose of the dykes is to increase the catchment area corresponding to the plantedstorage.36

A similar method consists of digging drains almost parallel to the natural topographicalcontours with the purpose of draining water from a bigger catchment area. Figure 7 illustratesthis method.FIGURE 7: CONTOUR DRAINSRoaded catchmentsIn the roaded catchment (Fig. 8) the soil is compacted by heavy rollers to make it moreimpervious. Each road is 8 to 10 metres wide and is separated from the next one by a Veedrain running parallel to the roads and collecting the water to the main drain o directly to thetank. When properly shaped from suitable materials the best roaded catchments can bealmost as effective as bitumen surface. The efficiency of roaded catchment is due partly tothe camber (degree of slope from crest to trough) and partly to the water shedding ability ofits surface: the steeper the camber and the more impermeable the surface, the more readilywill the catchment shed water. Usually it is not possible to achieve a camber steeper than 1to 4 and it is undesirable to have it less than 1 to 8. Although this method is claimed to bevery cheap (Carder 1970), it does not seem to be applicable in semi-arid areas of mostdeveloping countries. Difficulties include:i. soils should be such (sand and clay) that they become impervious by. compaction andallow ater to be conveyed through unlined drains;37

ii. fencing of the whole catchment is necessary;iii. permanent maintenance of the catchment is necessary to preserve the efficiency of thesystem.FIGURE 8: ROADED CATCHMENTSb. Chemical treatmentThe paraffin-wax treatment is being used at selected installations in the hotter regions ofArizona for providing livestock with drinking water. This treatment consists of applying a lowmeltingpount paraffin-wax, usually sprayed onto a prepared catchment surface in a moltenform. The wax when heated by the sun penetrates the soil to a depth of 1 to 2 cm, coatingeach sol] particle with a thin wax film and creating an efficient water repellent surface.Although paraffin-wax treatment has proved to be relatively low in cost in the United Statesand remarkably efficient when properly applied on well prepared catchments, the wax doesnot provide significant soil stabilization and needs a careful permanent maintenance.Moreover the whole catchment should be fenced in order to avoid trampling by livestock.This method therefore is also not applicable in most developing countries.c. Soil coverBefore installing a catchment soil cover, the soil surface should be cleared, smoothed andcompacted. Dykes around the perimeter of the apron are usually necessary to collect waterand direct it to the storage. Several types of soil cover are in use mostly in Australia and the38

United States. Although these techniques are not easy to extrapolate to developing countriesbecause of the high level of maintenance required, a short description is given hereafter offour methods. Details on the material and installation procedures can be found in theHandbook of Water Harvesting (Frasier and Myers 1983).Asphalt-fabric membranesThis is a field-fabricated membrane of an inert fabric saturated in-place on the preparedcatchment surface with a water-based asphalt emulsion. The water in the asphalt emulsionpartially softens the fabric, allowing the membrane to conform to the irregularities of thecatchment surface. The asphalt emulsion soaks through the fabric Co bond a layer of soil tothe underside of the membrane, which provides additional weight to the vovering. During thecuring process, the asphalt hardens, forming a semi-rigid membrane with high tear strength.The asphalt cements the fabric threads and seals the pore spaces.Properly installed and maintained, asphalt fabric membranes are highly resistant tomechanical damage and deterioration by weathering processes. The asphalt hardens slowlyand, within 6 to 12 months, the membrane becomes semi-rigid and cattle can walk on Itssurface without causing damage. This may not apply in the case of very hot climates wherethe asphalt may soften.The material with a proper maintenance has a projected life in excess of 20 years, but newasphalt emulsion coats for the entire catchment (1 to 1.5 litres/m 2 ) are usually required at 3-to 5-year intervals.The initial cost of material in 1981, including the seal coat asphalt was approximately US$1.75 to 2.00 per m 2 in the United States. It is clear that costs of material and installation mightbe much higher in developing countries (perhaps multiplied by a factor of 3 to 4).A disadvantage of this method is that the runoff water from the asphatic surface is oftendiscoloured by asphalt oxidation by-products in low rainfall areas with high solar radiation.Gravel covered sheetingsThe treatment consists of a waterproof membrane such as polyethylene or roofing tar paperon the prepared catchment surface and covered with a shallow layer of uniform-sized gravel.In some installations an asphalt emulsion tack coat is used to bond the membrane to the soiland/or the gravel to the membrane. The purpose of the gravel is to protect the membranefrom sunlight weathering processes and to provide some resistance to minor mechanicaldamage.When properly installed and maintained, the gravel covered membrane treatment is ratherresistant to weathering deterioration and has a projected life of 15 to 20 years.The main disadvantage of this treatment is due to its extreme susceptibility to mechanicaldamages so that fencing of the whole catchment is necessary, but even with this precaution,a continuous maintenance is required to repair holes and punctures from rodents ormechanical sources.39

Reported 1981 costs of the material in USA are as follows:steel rimUS$ 15 to 25/m 3 capacitylinerUS$ 4 to 8/m 3 capacitypoured concrete bottom US$ 5 to 20/m 2 of bottom area.Extrapolations to remote areas of developing countries should take into consideration thecosts of transport and installation that may multiply the original figures by a factor of 2 to 3.Maintenance requirements for this type of tank are low.b. Plastered concrete tanksThe plastered concrete storage tank consists of a thin (8 to 10 cm thick) vertical circular wallof reinforced concrete with a dense plaster coating on the inside and outside surfaces. Thebottom of the tank is of poured concrete. Maximum tank dimensions are 2 m high and 10 mdiameter (150 m 3 capacity). These storages have been used in semi-buried as well asaboveground installations.Properly constructed and Installed on a well prepared site, plastered concrete tanks are verydurable and require limited maintenance.Reported 1981 on-site costs of plastered concrete tanks in the USA range from US$ 5 to10/m 3 of tank capacity but the same remarks apply as for steel rim tanks in the case of costextrapolation to developing countries.c. CisternsCisterns are covered storage tanks. They have been in use for many centuries all around theMediterranean sea. In Egypt, Libya and Tunisia they were typically excavated as describedbelow. However, in Roman times they were constructed both below and above ground wherecap rock did not exist and were made of concrete, stone and brick with either archedconcrete or wooden beam roof.The typical North African cisterns of older design consist of a vertical shaft section excavatedfrom ground level through the top soil and through the hard cap (if any). The most suitablesoils for traditional cistern construction are made of clayey silt or soft marls. This material isexcavated and removed to form the storage volume. Storage shapes are irregular dependingon the subsurface material and can be round, square, rectangular or in the form of narrowgalleries. Cisterns are 6 to 7 metres deep and storage volumes reputedly vary from 30 to 500m 3 . The cisterns are generally lined with a cement mortar to improve the impermeability andstability of the soil. Water is removed by bucket and rope through the vertical shaft.Experience has shown that about 400 sheep can be watered during the 2 to 3 months thatpasture is available near each cistern.Cisterns of more modern design are constructed of reinforced concrete of regular shape andincorporate such geatures as silt trap, inlet chamber, trash rack. access hatch and ladder,outlet pipe and watering trough. Typical storage volumes are 300-500 m 3 . Some examples ofcisterns currently being built in Libya will be examined in the next paragraph (5.4.4 Casestudies and cost).Old Islamic open reservoirs known as birkahs are found in many regions of Saudi Arabia withremnants of wing walls to divert water. Most of these were for village water supply along41

trade routes. Modern birkahs and renovated ancient birkahs are still in common use. Thewater gathering principles were similar to the north African cisterns, that is channels or dykesor walls were used to gather water by gravity for the reservoir.5.4.4 Case study and costThe inland and coastal lands which comprise the Central Wadi Zone and the Gulf of Sirteareas generally have an extremely low and unreliable rainfall. Average annual rainfall variesfrom a maximum of some 200 mm near the coast to 50 mm at the southern extremity of theproject area.Poor rainfall characteristics, combined with unsuitable soil and topography make theserangeland areas generally only suitable for livestock grazing for 2 to 3 months a year. Since1977 the Libyan Government realized the importance of this grazing source and sponsoredthe implementation of a rangeland development programme. Project activities commenced in1978 with the major objective to continue to assist and strengthen the efforts of theGovernment to improve the pastures of the central rangelands and develop the livestockindustries in the area. Water supply to the livestock immediately appeared to be an importantproblem to be solved. Oligo-Miocene aquifer occurs along the coast of Sirte and consists oflimestone and dolomitic limestone alternating with marls but water is usually saline (morethan 6 g/l) except in recharge areas in the wadi beds. Water harvesting became therefore theonly possible solution for stock watering. In the study carried out in 1982 within the CentralWadi Zone, Australian Consultants (Ashley L. Prout and Antony Middleton) recommendedthat water points be provided every 3-4 km and be of sufficient size to supply water to theaverage flock (220 equivalent adult sheep) and the stockbreeder families - i.e. 500-600m 3 /year.To increase the size of the existing catchments feeding the planned storage facilities, lowconcrete or stone walls were constructed as wings extending from the entry of the tank to adistance of 50-60 m on both sides.The cisterns built in the framework of the project are of 2 types. The large 1000 m3 capacityreinforced concrete types are built under contract to the project. The small 200 m 3 capacitytypes are being built by local farmers who are subsidized by the Secretariat of Agriculture onthe basis of US$ 10 200 per cistern of 200 m 3 minimum capacity.The actual cost of these cisterns (Prout, and Middleton 1982) is estimated at US$ 85/m 3 ofstorage for the small cisterns (200 m 3 capacity) and US$ 204/m 3 of storage for the largecisterns (1000 m 3 capacity).5.5 Concluding statementThere is a wide range of surface water possibilities for stock water supply. Where conditionsare ideal one or more methods may be considered. However, many of the techniques usedin more developed countries may be too costly for the less developed countries. Care istherefore needed when planning to use surface water. The most likely locations for extendingdrinking water are where natural ponding already occurs. Care in reservoir sizing is alsoneeded to avoid overgrazing of the fodder resources.42

6. Groundwater resources development for rangelands6.1 Occurrence of groundwater6.2 Groundwater exploration techniques6.3 Groundwater development techniques6.4 Water lifting devices6.5 Groundwater monitoring6.6 Case study and cost6.7 Conclusion on groundwater development6.1 Occurrence of groundwater6.1.1 Continuous and discontinuous aquifersGroundwater originates for all practical purposes from infiltration of rainfall below the rootzone, either directly on the soil or in ponds, lakes and river beds. The rocks of the earth maybe classified most simply as sedimentary, intrusive and metamorphic. The sedimentaryformations are of particular interest for groundwater and include unconsolidated andconsolidated sediments. A special kind of sedimentary rock is limestone which is relativelyeasily soluble and therefore often has extensive systems of openings in which groundwatermay move and be stored.Hydrogeologists further classify rocks as to their ability to yield water to wells. Thus anaquifer is a rock which is permeable enough to supply water to wells, while an aquicludetends to be very poorly permeable.The groundwater is found in the pore spaces between the solid rock or solid rock particles. Inunconsolidated and poorly consolidated sediments the pore spaces are simply the openingsbetween the grains. Weather rock is in this respect similar to sediments.Some rocks have essentially no such pore spaces, but instead may be fractured or dissolvedfor several reasons. Examples of rocks with "fracture" permeability are hard solid rocks in afault zone, basalt flows fractured during the cooling process and limestone fractured andfurther dissolved by groundwater. Ancient metamorphic rocks tend to consist of finecrystalline materials which weather easily to clay near the surface and which often do notcontain open fractures. Coarse granite, however, has the useful property of fracturing within90 m or so of the earth's surface and these fractures can carry groundwater. The greatinternal crystal pressures when the crystal was formed at great depth. Removal of theoverlying rock eventually results in load release fractures.6.1.1 Continuous and discontinuous aquifersIn the French literature on groundwater in Africa aquifers are often called continuous ordiscontinuous. in reality there is a general gradition from one to the other and absolutesealing of an aquifer from other areas is relatively rare. from the point of view of low43

discharge wells usually needed for animal water supply, however, the concept may beuseful.a. Continuous aquifers are those aquifers in which all points are connected hydraulicallythrough a porous medium (sand, gravel, clayey sand, sandstone, calcarenite etc.).b. Discontinuous aquifers are those aquifers in which hydraulic connections arediscontinuous and no correlation is possible from one well to another. groundwateroccurrence is exclusively related to weathering or fracturing of the rocks and the matrix of therock is almost completely impervious. this type of aquifer usually occurs in crystalline rocks(igneous or metamorphic) like granite, basalt, gneiss, crystalline schists etc., or insedimentary rocks such as quartzitic sandstones, crystalline dolomites and occasionally hardand massive dolomitic limestones.In many tropical regions the depth of weathering of the rock is considerable. On the positiveside some rocks weather to reasonably permeable material. Unfortunately the weatheringusually makes it difficult to determine what underlies the weathered zone.6.2 Groundwater exploration techniques6.2.1 General approach6.2.2 Purpose of preliminary survey6.2.3 Preliminary hydrogeological survey - methodology6.2.4 Additional investigations required for continuous aquifers6.2.5 Additional investigations required for discontinuous aquifers6.2.1 General approachThe operations to be carried out for a groundwater development project may be subdividedinto:- a preliminary survey at a regional scale- a detailed survey to select the best well locations.6.2.2 Purpose of preliminary surveyThe main objective of a preliminary survey is to minimize the cost of groundwaterdevelopment. Planning a preliminary groundwater survey includes minimizing the total costof study and implementation of the groundwater development project. It is essential to keepthis concept in mind in order to avoid oversizing the study in relation to the expected finalgroundwater development. The importance of the exploration phase of the project should notbe neglected, particularly in areas of discontinuous aquifers where little information isavailable.The results to be expected from a preliminary survey are summarized below:a. Identification of aquifers and estimation of their characteristics:44

- geological setting,- hydraulic continuity,- groundwater quantity and quality assessment and expected water demand,- depth to water from the ground,- physical characteristics of the formation to be penetrated to reach water.b. Identify appropriate development methods:- performance of dug or drilled wells,- well depth, diameter, and where wells are open Co aquifer,- construction methods,- technical specifications,- use of local or imported techniques,- costs.c. Selection of pumps or water lifting devices.d. Assessment of the risks of failure.A preliminary survey may identify the groundwater conditions and, taking these and otherconditions into account, a reasonable basis for choice of groundwater development may beobtained. Identifying groundwater conditions includes determining the location and physicalproperties of the aquifer, estimating the quantity and quality, and determining depth to thewater table from the surface. The groundwater conditions will determine what kinds of wellsmay be constructed. Depending on these possibilities and on the local resources andeconomics, costs are compared and a choice may be made. Finally typical technicalspecifications for the wells and pumps may be prepared.6.2.3 Preliminary hydrogeological survey - methodologya. Review existing geological and hydrogeological informationIn most countries geological and hydrogeological maps of a scale ranging from 1/200 000 to1/1 000 000 exist or are in the process of preparation and can provide essential informationon aquifers, their extension, their boundaries and their lithology, and on the depth to waterlevel. This information is usually sufficient to determine whether or not the aquifers arecontinuous within the area considered for the livestock water supply project. In addition to theclassical geological and hydrogeological maps, satellite images may provide complementaryinformation on geological formations and structures. Aerial photographs may also beavailable and geophysical sueveys have been made for many regions.b. Water well inventoryInformation from an inventory of water wells is the basis for a more accurate identification ofthe aquifer(s) which will then be tapped in the framework of the future groundwaterdevelopment project. From the data collected on the existing dug and drilled wells it will bepossible to establish the hydraulic continuity of the aquifer and to map the depth to water, thedistribution of the good wells (the discharge of which exceeds a minimum value admissiblefor the considered purpose) and water quality. In the case of discontinuous aquifers, the datacollected should also include dry wells (dug or drilled) in order to establish a correlationbetween as many parameters as possible. Well discharge is usually correlated with:45

i. the nature of the water bearing formation;ii. the formation fracture characteristics, if any (from air photo interpretation);iii. the distance to important tectonic structures (from satellite imagery and air photointerpretation); andiv. the depth of penetration of the wells into the aquifer.In many countries this information has already been collected by the Service responsible forthe Water Resources Inventory in which case the additional field investigations required willbe limited to updating the inventory or checking questionable information.6.2.4 Additional investigations required for continuous aquifersa. PurposeFor continuous aquifers there is usually no need for additional investigation sinceextrapolations can be made from the data collected in the existing wells to predict the resultsof new wells. With regard to regional groundwater resources and the possibility of overexploitationof the aquifer in relation to the expected use of water for the livestock, the risk isusually small in the case of continuous aquifers since the water demand is extremely smallwhen compared to potential aquifer recharge. For example a rangeland area receiving 300mm annual rainfall and located in a zone where a continuous aquifer can be exploited mayhave the following characteristics:i. a carrying capacity of 10 ha/TLU;ii. for 1 km 2 there might be 10 TLU corresponding to a potential water demand, includinglosses at the watering places, of approximately 100 m 3 /year;iii. over the same area, the average amount of precipitation will be 300 000 m 3 /year and maybe as low as 150 000 m 3 one year in ten;iv. in the case of low rainfall, the water demand for livestock represently only 0.07 percent ofprecipitation;v. the recharge of the aquifer is very likely to be higher than 0.07 percent of precipitation.In the case of continuous aquifers, a preliminary survey of the area, which is often limited tothe study of the existing information (geological and hydrogeological maps and wellinventory), is usually sufficient to prepare the water supply project. The location of eachwatering place will then be based essentially on non-hydrogeological criteria (good grazingarea, spacing between wells to avoid overgrazing, proximity of a village or of a transhumanceroute). However, additional investigations may be necessary in areas lacking wells and nearthe boundary of the sedimentary basin or in the vicinity of an area of unacceptable waterquality.b. Investigations in the vicinity of basin boundariesThe problem usually consists of determining the extent of the aquifer or the extent of thesaline water intrusion into the aquifer in order to locate future production wells successfullyand avoid deterioration of the water quality with time.46

Electrical soundings distributed along profiles perpendicular to the limit of the basin andcalibrated on reconnaissance boreholes or test wells are usually sufficient to solve this kindof problem.c. Investigations in areas lacking wellsThis problem may arise in subsaharian areas where the surface geology indicates the likelyoccurrence of aquifers but no data are available to prepare the ground-water developmentproject.There is no precise method for solving this problem since investigations will essentiallydepend upon the geological subsurface structure. The investigation programme maytherefore vary from one single reconnaissance borehole for the entire area where geologicalstructure is flat and gently dipping, to a sophistocated survey involving geophysics andseveral reconnaissance boreholes where the geological structure is complex.Planning additional investigations in areas lacking wells should be handled by a competentgroundwater specialist.6.2.5 Additional investigations required for discontinuous aquifersa. Remote sensing methodsSatellite imageryThe digital nature of the satellite image allows computer manipulations of the image toconform any desired map projection and to enhance or extract specific levels of information.It is therefore advisable, when a high definition of the ground elements is required, to useenhanced imagery especially processed to identify and locate accurately:i. hydrographic networks which may indicate the thickness and characteristics of theweathered zone as well as subsurface tectonic structure,ii. vegetation which may give information on shallow groundwater occurrence, andiii. lineaments connected with geological structure.Aerial photographsAerial photographs are of great help for siting new wells in discontinuous aquifers. They areprobably the most efficient and cheapest tool to identify the small tectonic structures whichmay result in fracture of the bedrock and ground-water occurrence. Moreover the use of airphotosdoes not require particular skill: the fractured zones of the bedrock are usually clearlyvisible, sometimes indicated by vegetation alignment (because of the presence of waterunderground) and occasionally marked by sills or dykes of different rock types.b. GeophysicsGeophysics may be necessary in three main categories of situation:i. when more recent deposits, usually continental, cover the bedrock and are thick enough tohide its structure,47

ii. when weathered or fractured zones are poorly identified by remote sensing, andiii. when groundwater occurs within the weathered zone of bedrock and productivity of wellsdepends upon the thickness of the weathered zone.Four geophysical techniques can be used for the detailed investigations of discontinuousaquifers:i. the weathering of fractured bedrock zones results in the development of clay pockets whichhave a much lower electrical resistivity than the surrounding bedrock. This geologicalstructure due to the preferential effect of the weathering on the tectonized axes can easily belocated by electrical resistivity profiles method;ii. the increase of total porosity of the granite, gneiss or sandstones in connection with theweathering process, may result in the development of an aquifer thick enough to alter theelectrical resistivity of the formation according to Archie law:Rf/Rw = P -mbeing:Rf - the resistivity of the formationRw - the resistivity of the waterP - the porosity of the formationm - the cementation factor ranging from 1.5 Co 2 according to the nature of the rock.When P increases the resistivity of the formation decreases and may offer sufficient contrastwith the resistivity of the underlying bedrock to be identified by electrical sounding;iii. the speed of longitudinal waves is notably reduced in correspondence to the fracturedzones of the hard rocks. The presence and location of a fractured zone can be determinedby the seismic refraction method;iv. fractured zones of bedrock are often intruded by basic rocks like dolerites which have amagnetic susceptibility significantly different from that of the bedrock. This may create amagnetic anomaly which can be identified and located by electromagnetic methods. Thesemethods although little used in hydrogeology may be helpful to indirectly locate the fracturedzones of the basement, provided that the weathered zone or the sedimentary overburden arethin.While almost anybody can apply remote sensing techniques after a few days training,geophysical methods require high technical skill. Many developing countries have createdtheir own geophysical services which are able to apply electrical methods (resistivity profilesand electrical soundings) at a much lower cost that the expatriate specialized companies.48

Figures 9: Groundwater occurrence in granite and gneiss weathered and fractured zones49

Figure 11: Groundwater occurrence in two typical crystalline schists cross sections51

Note: For describing the recommended methods for selecting the best locations of well sites,capital letters indicate the leading method which may even be sufficient in most cases.Figures 9, 10 and 11 illustrate cases of groundwater occurrence in discontinuous aquifersunder different situations and show some hypothetical wells. Below each figure therecommended methods for locating well sites are also indicated.c. Reconnaissance boreholesIn almost all situations, reconnaissance boreholes are necessary before establishing theproduction wells in discontinuous aquifers. The objectives of reconnaissance boreholes areto determine the groundwater occurrence and the depth to water which affects the choice ofboth the production wells and the pump or water lifting device, and to determine the hydrauliccharacteristics of the aquifer in order to predict its yield and behaviour.Three drilling methods commonly used are cable tool, rotary and down-the-hole-hammer.A brief description of these drilling methods is given in section 6.3.3 (Drilled wells).d. Groundwater resources in discontinuous aquifersWhile the water demand for livestock is usually extremely small when compared to thepotential yield of a continuous aquifer (see paragraph 6.2.4a), the problem deserves morecareful attention in the case of a discontinuous aquifer. The amount of water in storage,which is limited to the fractures and fissures of the bedrock or to small pockets of weatheredformation, may not be sufficient to supply water to wells for the duration of the dry seasonand may be very sensitive to the interannual rainfall variations with the result that wells dryout during drought period. This of course depends on rainfall since in wetter areas theweathered zone usually contains considerable water. In dry regions, the annual recharge ofthe aquifer may occur only over its actual extent usually limited to the fractured zones a fewmetres wide. Where the zone corresponds to the bottom of a valley which concentrates therainfall it can be recharged from a wider catchment basin.Unfortunately there are no completely reliable methods for evaluating the groundwaterresources of discontinuous aquifers since investigations are usually carried out with theobjective of looking for the most productive zones without attention to the vertical andhorizontal extension of the aquifer which actually governs its storage capacity.However the production tests (aquifer tests) performed on reconnaissance boreholes maygive clues to the response of the aquifer to water abstraction and may guide the waterplanner in predicting the long term behaviour of the aquifer.52

6.3 Groundwater development techniques6.3.1 Selection of the type of well and pump6.3.2 Dug wells6.3.3 Drilled wells6.3.4 Well cistern associated with a drilled well6.3.5 Springs6.3.1 Selection of the type of well and pumpThe first factors to be considered for selecting the type of well and pump are the expecteddepth to water and depth of the well. When both depths are less than 10 m the most suitablesolution in pastoral areas consists of digging wells from which water will simply be extractedby hand or animal powered lifting devices. At the other extreme, when both depths aregreater than 70-80 m the only solution consists of drilling wells which will be equipped withmotor driven pumps.In between these two extremes all solutions are possible and other criteria have to beconsidered to decide whether to dig or to drill the wells and which pumps to install on thewells. Table 8 proposes a classification based on two additional criteria:i. the maintenance capacity of the country which will determine whether mechanical solutionscan be proposed;ii. the hardness of the formations to be penetrated to reach the aquifer which determines thedifficulty of drilling wells.It is clear that the solutions proposed in Table 10 should only be considered for preliminaryselection of the most suitable well and pump according to technical criteria, but otherparameters may be introduced which will modify the choice. Among the various factors whichaffect the final selection, the following should be considered:i. the preference of the users - as an example, in the 6th region of Mali, certain ethnic groups(Touaregs) clearly expressed their preference for dug wells while in the same area (west ofthe internal Delta of Niger River), the Fulanis were ready to use, maintain and even buycomplete pumping equipment with diesel engines to be installed on reconnaissanceboreholes recently drilled by the Malian administration;ii. the economic considerations - one contractor drilled well in very hard rock (quartzite,granite) costs three to four times less than a contractor dug well in the same formation and itmay be cheaper to set up a pump and engine maintenance service than to dig a number ofwells.In general, drilling boreholes into hard rock requires heavy and sophisticated equipment andtherefore costs are nearly the same regardless of availability and cost of labour. Largerdiameter dug wells, when carried out with heavy equipment, tend to be more costly becauseof the larger number of people and the longer time involved. When the water table isrelatively shallow, however, wells are dug by local people when the formation is soft. Even in53

the harder rock use of hand methods to break out blocks of rock can be relativelyinexpensive provided the labour is provided by the farmer.Table 8: SELECTION OF THE TYPES OF WELL AND PUMP OR WATER LIFTING DEVICEDepthtowaterlevellessthan 10mfrom 0to 70-80mmorethan 70-80 mDepth towaterbearingformationless than 10mfrom 10 to 70-80 mmore than 70-80 mmore than 70-80 mHardness offormations to bepenetrated toreach the aquifersoft to hardMaintenancecapacity of thecountrynot applicableRecommendedwellRecommendedwater liftingmethodsoft to medium poor dug wells hand/animalpowered waterlifting devicegood drilled wells wind/solar/motorpumphard poor dug wells animal pow. wat.liftinggood drilled wells motor driven pumpssoft to medium poor well cisternassociatedanimal poweredhard poor with drilled well lifting devicegood drilled wells motor driven pumpssoft to hard good drilled wells motor driven pumps6.3.2 Dug wellsIn this method the hole is constructed by digging to the desired diameter and depth with handor power Cool (air hammer, explosive...). The dug out materials are 42 removed by liftingthem from the hole in some type of container. The hole is shored, lined or cased as the depthis increased. For shallow depth and when casing is used, a common practice is to addcasing (metallic or cement shaft) at the surface, allowing it to sink of its own weight as thehole is excavated below the bottom of the casin.One of the limitations of the traditional well digging is the difficulty of penetrating far enoughinto the aquifer to ensure an adequate depth of water in the well at all times in the future. Thedifficulty is made worse by the fact that the water table fluctuates seasonally and may evendrop considerably at the end of a long dry period.A system known as "telescoping" has been devised for modern wells to minimize thisdrawback. This consists of constructing the production section of the well (that located belowthe water level) separately from the upper part. When the well reaches the water, thediameter is reduced and a concrete perforated shaft is used to line the part of the well whichis under water at the time of the construction. The material is excavated within the smallertube to allow it to sink under its own weight and new shafts are added on top until a sufficientdepth of water is reached. If by chance the water level drops down at the end of a dry period,water production can be resumed simply by digging deeper and adding new concreteperforated shafts.54

Fig. 12: Dug well55

In the case of very hard formations, lining the well may not be necessary over the wholesection as indicated on Figure 12. Weathered rock is generally fairly easy to excavate and forvery large wells stairs may be formed during excavation. Excavation of solid rock below theweathered zone requires the use of wedges, bars and hammers to break out blocks. Thiscan usually be done by hand to two to five metres below the weathered rock. Sometimes thesolid rock appears to be unfractured but careful inspection will show minute cracks wherewedges may be driven. Use of explosives in hard rock is of course possible, but the objectiveis the opposite of rock quarrying where large unfractured blocks are desired. Instead theblocks should be broken and the remaining walls fractured as much as possible.6.3.3 Drilled wellsWater well drilling is a difficult technique requiring a long experience, which cannot be gainedby reading a few lines of a textbook. This paragraph is simply intended to provide the rangeand animal experts with the basic information needed to understand the major componentsof a drilling programme.a. Drilling methodsThe cable tool of percussion method of drilling is based upon the principle of applyingsufficient energy to pulverize the soil or rock by percussion. The energy applied is varied bycontrolling the length of the stroke and the weight of the drill stem and bit. The bit isconnected to a cable and, by means of a rocker arm on the drill rig, it is raised and releasedto exert its energy on the bottom of the hole.In cable tool drilling there are basically three major operations: first drilling of the hole bycrushing the rock or clay or other material by the impact of the drill bit; second, removing thecuttings with a bailer as cuttings accumulate in the hole; and third, driving or forcing the wellcasing down into the hole as the drilling proceeds.Cable tool is the simplest drilling method which is designed primarily for medium hard rockand cobbly or bouldery materials. However the method can apply in many cases, the majorconstraint being the extreme slowness of the operation. On the other hand this method doesnot require large investment in purchase of rig and tools nor does it need lengthy training foroperating the machine. Small private enterprises should be encouraged to use cable toolscapable of drilling at low cost.Conventional mud-rotary drilling is accomplished by rotating a drill pipe and bit by means of apower drive. The drill bit cuts and breaks up the rock material as it penetrates the formation.Drilling fluid, usually made of mixed water and special clay (bentonite), is pumped throughthe rotating drill pipes and holes in the bit. The fluid swirls into the bottom of the hole, pickingup the drill cuttings, then flows upward in the well bore, carrying the cuttings to the surface.The cuttings settle out of the mud in puts before the mud is recirculated.In the rotary drilling method the well casing is usually not introduced into the hole until drillingoperations are completed, the walls of the hole being supported by the weight of the drillingfluid.The mud-rotary method is effective for drilling most rocks. Drilling is rapid in all except thehardest rocks. Difficulty may be encountered in penetrating loose, hard boulders. The rotarymethod is best suited for deep wells (deeper than 200 m), for wells aimied at developing56

artesian aquifers (aquifers under pressure) and for reconnaissance wells except in hardestrocks.The air-rotary and down-the-hole-hammer methods are usually associated in the drilling ofthe same well since air-rotary is applied in the soft and slightly consolidated part of theborehole (usually the upper part, corresponding to the weathered formation) whereas thedown-the-hole-hammer method is used in the hardest formation (usually corresponding tothe basement). Air-rotary is similar to mud-rotary in principle, the main difference consistingof substituting mud with air and consequently mud pump with air compressor. Down-thehole-hammerdrilling consists of using air to drive a percussion hammer set at the lower endof the drilling string. Therefore air has two purposes: to drive the hammer and to carry thecuttings to the surface. Air consumption varies with the bit diameter and air pressure. In orderto ensure the proper upward transportation of the cuttings it is usually considered that thevertical air velocity should be equal to 15 m/s minimum. Foam is sometimes added to the airin order to help carry up the cuttings and to limit the erosion of the wall of the borehole by theair flow.The main advantage of the down-the-hole-hammer method is rapidity of drilling in very hardformations: a penetration rate of 15-20 metres per hour is not exceptional. On the other handthe diameter of the hole is limited by the air velocity required to carry up the cuttings: most ofthe rigs commonly used can drill with a maximum diameter of 8½" which needs an airdischarge of 27 m 3 /minute with 3½" diameter drill pipes.The reverse circulation method is used for drilling very large diameter boreholes inunconsolidated formations to obtain highly productive wells for irrigation purposes. Thismethod does not suit the usual requirements of groundwater development in rangelandareas (limited discharge of the wells in order to avoid overgrazing around the water supply).b. Casing selectionDiameterThe minimum diameter of the casing should primarily be selected in relation to the expectedor requested discharge of the well. Larger diameter may be necessary because of particulardrilling conditions requiring the installation of a casing in the upper part of the well (risk ofcollapsing or artesian pressure in the aquifer), but in most cases of wells drilled in rangelandareas, casing diameters ranging from 6" to 8" are sufficient to set pumps of a capacityvarying from 0 to 50 m 3 /h (see Tables 11, 12, 13 and 14).Table 11: SIZE AND WEIGHT OF API CASINGS USED FOR SHALLOW TO MEDIUMDEEP WATER WELLSOuter diameter Wall thickness Inner diameter Weightinch mm inch nun inch aim kg/m6 5/8 168.3 0.24 6.22 6.13 155.86 25.37 177.8 0.27 6.91 6.45 163.98 29.79 5/8 244.5 0.28 7.14 9.06 230.22 43.657

Table 12: SIZE AND WEIGHT OF WIRE-WOUND SCREENS USED FOR WATER WELLSNominal Outer diameter over socket Inner diameter Weightinch mm inch mm kg/m5 4 3/4 120.6 4 101.1 106 5 5/8 142.8 4 7/8 123.8 128 7 1/2 190.5 6 5/8 168.3 16Table 13: PVC CASING AND SCREENS CHARACTERISTICS - STANDARD WALLTHICKNESS FOR WELLS UP TO 100 m DEPTHNominal diameter Outside diameter over socket Wall thickness Inside diameter Weightinch mm inch mm inch mm inch mm kg/m5 125 5.79 147 0.26 6.5 4.99 127 4.16 150 6.85 174 0.30 7.5 5.90 150 5.57 175 7.99 203 0.33 8.5 7.02 178 7.48 200 9.41 239 0.39 10.0 8.08 205 10.0Table 14: SIZE AND CAPACITIES OF DEEP WELL PUMPSNominaldiameterVERTICAL TURBINE PUMPSOutsidebowldiameterDischargerangeMinimumdiameter oftubewellNominaldiameterSUBMERSIBLE PUMPSOutsidebowldiameterDischargerangeMinimumdiameter oftubewellinch inch mm m 3 /h inch mm inch inch mm m 3 /h inch mm4 3 3/4 95 4-13 4 3/8 111 4 3 3/4 95 4-18 4 3/8 1116 5 1/2 140 10-45 6 1/8 155 6 5 3/8 137 12-84 6 152MaterialCasing maintains the hole through loose, caving or flowing materials and seals outcontaminated or undesirable waters. It must be strong enough to resist earth pressure and,depending upon method of placement, may have to withstand considerable shock andcompressive stress. Casing should also be sufficiently resistant to corrosion to last 25 to 50years.Until recently drilled wells were cased with steel or wrought iron pipe casings using welded orthreaded and coupled joints.For the last 10-15 years, plastic (PVC) pipes have proved to be very convenient because oftheir lightweight and their high resistance against corrosion. PVC pipes can be used for wellsto 300 m depth, however the standard wall thickness allows a maximum setting depth ofapproximately 100 m. For deeper wells specially manufactured thicker pipes should be used.Table 13 shows an example of PVC pipe characteristics for shallow wells similar to thosewhich are drilled in alluvial aquifers or in the basement.58

c. ScreensThe most important part of any well is that area where the water flows from the aquifer intothe well. The proper construction and development of this section of the well is essential forthe efficient production of the optimum amount of groundwater.Consolidated rock aquifers may often be completed as open hole, that is, no perforatedcasing or screen is required. In unconsolidated sand and gravel aquifer and more generallyin all water bearing formations likely to cave or collapse when water flows, a screen orperforated casing is necessary to allow the water from the aquifer to enter the well and tostabilize the aquifer material.Screens are manufactured according to several designs and from a variety of corrosionresistant material.Tables 12 and 13 show the main characteristics of two types of screens commonly used inwater wells - wire-wound screens and PVC screens.If the water bearing formation is unconsolidated and fine (sand), it is usually necessary toinstall properly sized gravel behind the screens in order to prevent the finest elements fromentering the well. If the aquifer formation is such that it may collapse or cave, gravel packmay also be needed to stabilize the wall of the well. The grain size distribution of the gravelpack is selected in relation to the slot opening of the screens and the grain size distribution ofthe aquifer. formation.d. Well developmentWell development is the process of removing clay, silt, fine sand, drilling mud and otherdetererious material from the vicinity of the well screen and from behind the gravel pack. Thisoperation increases the permeability of the material surrounding the screen, thus increasingthe well efficiency.The most commonly used methods for well development are as follows:- surging- backwashing- jetting- air lifting- overpumping- acidizing- use of dispersing agents (polyphosphates).These different procedures are described in detail in the specialized literature on water welldrilling.e. Pumping testThe pumping test is an important operation to be carried out after completion of the well andhas two main purposes. The first is to determine the characteristics of the well in order toselect the proper pumping equipment, and the second to determine the characteristics of theaquifer in order to estimate the effect of the planned programme of water development on theaquifer.59

The procedures of the test are slightly different according to the purpose to be reached.When the wells are drilled in the framework of a large programme of water development,short duration tests aiming at the selection of the suitable pumping equipment are usuallysufficient for most of the wells. More sophisticated tests are performed only on a few wellsselected by the hydrogeologist.6.3.4 Well cistern associated with a drilled wellThis technique consists of using a large diameter lined well to extract, with traditional drawingmethods, water coming from a nearby drilled well connected with the large diameter well.Although the corresponding investment is high (cost of a dug well + cost of a drilled well), thewell cistern has proved to be convenient for water production in areas where mechanicalwater lifting devices cannot be installed because of their maintenance requirements.The well cistern/drilled well technique is suitable when the following conditions are met:a. either when the aquifer is confined and cannot be exploited by dug wells because it is toodeep (more than 80 m) or because water is under pressure;b. or when the water bearing formation consists of hard rocks in which water flows throughfissures and from which bigger discharge can be obtained by drilled wells tapping a deeperaquifer section than dug wells.Figure 13 shows a typical drilled well and a well cistern.60

Fig. 13: Well cistern associated with a drilled well61

It is also common practice to pore the drilled well inside the dug well, but it is difficult to keepthe dirt and debris in the dug well from entering the borehole and reducing its efficiency.6.3.5 SpringsSprings with a significant flow of water - say over 20 m 3 /h have usually been developed longago and are currently used for either irrigated agriculture or human needs, but smaller flowsare often overlooked as potential sources of water for livestock consumption, mostly in aridand semi-arid countries where a small water flow immediately evaporates if not properlycollected and conveyed. A spring discharge of less than 0.5 m 3 /h does not usually show anyflow. Water disappears by evaporation and evapotranspiration in the middle of the vegetationwhich naturally develops around the spring. Properly collected and distributed the samewater could meet the requirements of 300 to 400 cattle.a. Small spring sitesSmall springs usually occur as outflows of catchment basins of limited extension and withpoor hydraulic characteristics in mountainous areas. Examples may be found in Mauritania(small springs flowing out of very compact Cambro-Ordovician quartzitic sandstones allaround the Plateau of Tagant which received 200 mm average annual rainfall) and in Niger(small springs of the Air mountains).b. Discharge measurementsA simple and accurate way to determine flow volume of small water supplies is the 90°"V"notch. A "V" notch suitable for determing flows up to 10 m 3 /h can easily be made from apiece of flat metal measuring 40 x 25 cm from which a triangular notch with a right angle hasbeen cut out. The graduations Co be written on the side of the notch opening are shown onFigure 14a. The positions of the graduation referred to the bottom of the notch are as follows:Graduation (dischargem 3 /h)Vertical distance in mm from the bottom of the notch to thegraduation0.5 191 342 433 52.54 595 6510 85The "V" notch is placed in a channel through which all the water from the spring is forced toflow. On the spring side a small level pool of water, at least one metre long should be formedas shown on Figure 14b. After positioning the "V" notch and making sure Chat all the water isflowing through it, flow readings are made. For design purposes, flow measurements shouldpreferably be made at the end of the dry season or when the spring discharge is lowest.c. Selection of the diameter of the delivery pipeOnce the location of the water troughs has been fixed, two parameters should bedetermined; one is the distance (preferably measured horizontally) from the spring to the62

water outlet, and the other is the vertical difference or head between the spring and theoutlet.Figure 15 can be used to select the smallest pipe diameter to carry the desired discharge asshown in the following example:spring discharge = 0.5 m 3 /hdistance spring-outlet = 30 melevation difference between the spring and the outlet = 3 mthe hydraulic gradient is the elevation difference divided by the distance or 3/30 =0.1 (thisgradient is equivalent to 10 m of drop per 100 m of pipe)Figure 15 shows that the pipe diameter necessary to convey 0.5 m 3 /h under 10 m drop per100 m of pipe is between 3/4 inch (19 mm) and 1 inch (25 mm). Therefore a one inch pipewould be selected, since the 3/4 inch pipe is too small.d. Spring developmentThe most important point to remember is "DO NOT increase the water level of the spring".The normal water level of the undisturbed spring should be marked and no attempt should bemade to increase or lift this level for any reason. If the water level is increased, the extrapressure may cause the spring to flow out through another outlet which may be far awayfrom the present one.The Figures 14c, d, e show the steps to be followed for the development of small springs,using only local material. After the position of the undisturbed water level has been marked,the spring should be excavated to approximately one metre below the old water level and adrain constructed in order to channel the water outside the spring area. The drain can thenbe used to install the delivery pipe. The pit dug at the spring location should be large enoughto allow for the installation of a collection chamber made from concrete pipe 30 to 50 cmdiameter and 1 m long, and filling of the space around the collection chamber with stones, sothat water can flow into the chamber.63

Figure 14a: SPRING DISCHARGE MEASUREMENT WITH A 90° "V" NOTCHFigure 14b:90° "V" NOTCH GRADUATION64

Figure 14c: THE UNDISTURBED SPRINGFigure 14d: PREPARATION WORK FOR SPRING DEVELOPMENTFigure 14e: COLLECTION CHAMBER USING A CONCRETE PIPE65

Figure 14f: COLLECTION CHAMBER AND OVERFLOW ENTIRELY MADE OF STONE66

Fig. 15: PIPE FLOW CHARTS67

An overflow is needed to divert the excess flow from the spring. A seepage seal should coverthe spring and extend so that surface seepage does not enter the spring. The chambershould have a tight cover so that sunlight cannot enter through the opening and allow algaeto develop.Should the concrete pipe not be available locally, a chamber can also be constructed withonly stones and clay as shown on Figure 14f.6.4 Water lifting devices6.4.1 Main requirements6.4.2 Different types of water lifting6.4.3 Man or animal powered water lifting devices6.4.4 Motor driven pumps6.4.5 Wind powered pumps6.4.6 Solar pumps6.4.1 Main requirementsThe ideal water lifting device for groundwater production in rangeland areas of developingcountries should be capable of delivering a minimum of 20-30 m 3 /day - the amount necessaryto meet the daily requirements of 500-700 cattle, be able to be operated by only one personif necessary, and should require little or no maintenance.In fact there are no devices which can meet all these conditions and the solutions proposedcan only take into consideration one or two of the above conditions and be as close aspossible to the third one. For example, hand water lifting does not require any maintenance,can be carried out by one person but can deliver 20 m 3 /day only under very restrictiveconditions - i.e. water level depth not exceeding 10 m and 5 to 6 people drawing at the sametime. Another example may be the animal powered water lifting which can meet thedischarge requirements (5 to 6 animals working at the same time can easily draw 20-30m 3 /day even if the water level is very deep) and does not require any maintenance, butcannot be operated by a single person.It is clear also that the water lifting method should suit the type of well (dug or drilled) alreadyexisting or planned.6.4.2 Different types of water liftingMany types of water lifting devices are in use in various parts of the world for irrigation,domestic supply or livestock watering. Those which may be envisaged in rangeland areascan be classified as follows:a. man or animal powered water lifting devices traditional devices for dug wells hand or foot pumps for drilled wells68

. motor driven pumps diesel engine and vertical turbine pump generator and submersible pumpc. wind powered pumpsd. solar pumpsThe possible uses of each type of water lifting method in association with suitable water workare suggested in Table 10 in relation to various hydrogeological criteria and maintenancecapacity of the country. More detailed information is given hereafter.6.4.3 Man or animal powered water lifting devicesa. Traditional water drawingIn pastoral areas a skin or rubber bucket is hung on a rope and operated either manually orwith the help of an animal (usually bullock or camel). Traditional water lifting is suited to largediameter dug wells where 5 to 6 people or animals can draw water at the same time providedthat the well supplies enough water. Well cisterns associated with a nearby drilled well arebuilt with the intention of being exploited by traditional water drawing, mainly by animalpowered water lifting. The graphs in Figure 16 show the range of maximum dischargeattainable by 5 to 6 people or animals in relation to the depth of the water level. In the case ofhand water drawing, the discharge decreases rapidly with the depth of water but whenanimals are used the discharge is not very sensitive to the increase of water depth. This isdue to the fact that the duration of each elementary operation in a complete drawing cycle isnot equally affected by the variation of the water depth as indicated in Table 15.69

Fig. 16: Hand and animal powered water lifting - Discharge range from one wellTable 15: OPERATING TIMES OF ANIMAL POWERED WATER DRAWING FROM A WELLOperationsDepth to water40 m 70 mGetting up and down a 40 1 bucket 1' to 1' 30" 2' 30" to 3' 30"Surface operations (emptying the bucket) 2' to 3' 2' to 3'Filling the bucket 1' 1'Total 4' to 5' 30" 5' 30" to 7' 30"The operating times measured in several locations in Niger and Mali show that increasing thedepth to water affects the time necessary to get the bucket up and down which representsonly 26 percent (40 m depth) to 45 percent (70 m depth) of the complete cycle.It is therefore rather easy to attain a daily water production of 20-30 m 3 of water from a singlewell, whatever is the depth to the water level, provided that the hydraulic characteristics ofthe well are such that it can effectively supply that amount of water, and that 5 to 6 animalsare used at the same time.70

The only difficulty with animal powered water drawing is that it requires two people, one foremptying the bucket and one for guiding the animal. This particular condition may not becompatible with pastoral customs of certain ethnic groups. During the transhumance period,the Fulani shephers, for example, are used to being alone with their herds.Hand drawing for watering livestock is used when the water level is very shallow, and insedentary areas where the density of the wells is sufficient to reduce the number of animalsto be watered from each well.b. Hand and foot pumpsThe graphs of Figure 16 clearly show the important progress represented by hand or footpumps when compared with the simple drawing of water, since one or two people operatinga hand or foot pump can produce as much water as 5 to 6 people or 3 to 4 animals drawingwater with a bucket. The graphs of Figure 16 have been obtained by plotting the theoreticalperformances of the pumps as indicated by the manufacturers, and corresponding to newpumps operated by one or two men in excellent physical condition.The power delivered by the average man is estimated at 0.08 hp which corresponds to awater discharge of:- 2.16 m 3 /h if the water level is at 10 m- 0.72 m 3 /h if the water level is at 30 m- 0.43 m 3 /h if the water level is at 50 m- 0.27 m 3 /h if the water level is at 80 mwhen assuming a mechanical efficiency of the pump of 1/1.Actually, because of the decreasing efficiency of the pumps with their state of wear(especially the tightness rings) and with the depth of water, and because of the unequalpower of the pump operators, the discharge of a hand pump over several hours operationrarely exceeds 0.7-0.8 m 3 /h even for shallow water level.Moreover, there are few hand pumps capable of working at depths exceeding 50-60 m.In arid and semi-arid rangelands environment of developing countries, the hand or footpumps present several disadvantages since they cannot deliver more than 8-10 m 3 /daywhich is not sufficient for a normal water supply in rangeland area. If the utilization of handpumps is nevertheless envisaged, the density of wells should be considerably increased inorder to supply the required quantity of water to the livestock. In addition, pumps requireregular maintenance in order to keep their efficiency at an acceptable level. Themaintenance operations may require truck mounted lifting equipment when the pumps areinstalled at depths exceeding 20-30 m: the weight of a piston pump with 30 m transmissionrods may indeed reach 200-250 kg for those operated through a lever and 450-500 kg forthose operated through a wheel and a handle. Proper maintenance is a prerequisite forreliable hand pump based water supplies.However, in spite of these major disadvantages, hand pumps are certainly a technicalsolution to be considered in very hard rocks which make the digging of large diameter wellstime consuming while drilling by down-the-hole-hammer method requires only a few days tocomplete a 100 m borehole. Hand pumps are also appropriate in poorly permeable aquiferswhich cannot be developed by dug wells widely scattered over a large area but would bebetter exploited by a denser network of drilled wells. Hand pumps are preferred to motor71

driven pumps because of the small well discharge which would not justify the cost of motordriven pumps.But again, this solution - drilled wells and hand pumps - whichever technical justification isput forward, may be acceptable ONLY IF proper maintenance of the pumping equipment isguaranteed.6.4.4 Motor driven pumpsa. When should motor driven pumps be considered?Motor driven pumps installed in a drilled well are the only technical solution for producinggroundwater in areas where both water level and water bearing formation are deeper than70-80 m. If the water level comes closer to ground surface other solutions than motor drivenpumps are technically feasible and have schematically been presented in Table 10. Themotor driven pump solutions should always be considered in the case of high qualityrangeland extending over an area offering substantial groundwater potential. Indeed with theassumptions of a daily water requirement of 40 l/TLU during the hot season, waterproduction by animal powered drawing of 30 m 3 /day from one well (either dug well or wellcistern associated with a drilled well), and 10 km walking capacity for livestock from thegrazing area to water supply, corresponding to a total area of approximately 30 000 ha whichmight be grazed from one water source, then one well can water 750 TLU. This means thatthe animal powered well is convenient only if the carrying capacity of the consideredrangeland is less than 40 ha/TLU.In the case of rangeland offering better carrying capacity - say 20 ha/TLU - the solution forwatering all the livestock which could graze over that rangeland would consist either of 2 dugwells with animal powered drawing or 1 drilled well equipped with motor driven pump.Perhaps this example is not really feasible since most probably 2 drilled wells with theirpumping equipment would also be necessary for security reasons (in the case of engine orpump failure, water has still to be made available for livestock). But let us imagine the case ofan excellent range-land with a 5 ha/TLU carrying capacity so that 6000 TLU would have tobe watered. The solution would be EITHER 1 (or better 2 for security reasons) drilled wellswith motor driven pumps OR 8 dug wells.b. Selecting the discharge of the pumpThe maximum quantity of water to be pumped every day V maxday usually depends upon thecarrying capacity of the rangeland. Assuming a walking capacity of the livestock of 10 kmand a drinking requirement of 40 1/TLU, V maxday in m 3 /day would roughly be equal to 1200divided by the carrying capacity in ha/TLU.During the pumping test carried out on the well after its completion the exploitable dischargeof the well Q exp would be determined. If Q exp is such that the daily maximum waterrequirement - V maxday - can be pumped in less than 12-16 hours, then the discharge - Q pump ofthe pump to be installed can be fixed in such a way that the maximum daily pumping time willrange from 5-6 to 12-16 hours. If Q exp is not sufficient to pump V maxday m 3 in less than 12-16hours, then drilling an additional well has to be considered.The internal diameter of the casing limits the size of the pump bowl which may be aconstraint to selecting the pump discharge, but for wells to be used in a rangelandenvironment, the maximum discharge required rarely exceeds 25 m 3 /h and a 6 inch (150mm) diameter casing is sufficient in most cases to accommodate a suitable pump. Howeverit is recommended whenever possible to select the casing diameter of the well before drilling72

starts according to the expected required discharge, i.e. for discharge ranging from 5 to 15m 3 /h plan 6 inch casing minimum and for discharge ranging from 15 to 40 m 3 /h use preferably7 to 8 inch casing minimum.c. Vertical turbine pump with diesel engine or electrical submersible pump with powergenerator?Both solutions have advantages and inconveniences:i. installation and removal of submersible pumps are easier since only the pump and thecolumn has to be set down or removed while vertical turbine pumps also require a shaft andbearings and are more delicate to install;ii. if a submersible pump is to be used the well may be located outside the shelter of thepower generator. This may be considered as an advantage since any repair on the well or onthe pump is made easier;iii. electrical submersible pumps require sophisticated systems of automatic control andsecurity which need periodical visits by a good electrician for maintenance and repair;iv. the electric pumping unit, which consists of a pump, an electric motor, a generator and adiesel engine, is more expensive and more energy consuming than a mechanical pumpingunit consisting of only a pump and an engine.It therefore seems that in spite of inconveniences connected with a more delicate installation,vertical turbine pumps are preferred for the equipment of wells located in remote areaslacking electrical maintenance facilities.d. Determining the main characteristics of the pumps and enginesEfficiency of the pumping unitsThe two systems in use for equipment of pumping stations are schematically issultrated inFigure 17 which also indicates the average efficiency of each component and the overallefficiency of each system.73

Fig. 17 Efficiency of turbine pump and diesel engine compared to that of submersiblepump and power generatorVertical turbine pumpThe only parameters to be provided for ordering the pump are:a. the well casing inside diameter which will determine the maximum size of the pump bowl;b. the requested discharge;c. the total vertical water lift.The total vertical lift is the sum of the following elements:- depth to water level below ground under static conditions,- maximum seasonal or interannual water level fluctuation,- drawdown corresponding to the expected discharge (from pumping test results),- elevation of the storage tank above ground in order to allow water to flow out to thewatering troughs when needed.On the basis of these data, the manufacturer will calculate the total dynamic headcorresponding to the sum of the total vertical water lift and the friction losses at the givendischarge and or different pump and column characteristics. The total dynamic head willdetermine the number of pump stages required.Diesel engine for vertical turbine pumpAlthough the characteristics of the motor will be determined by the manufacturer as afunction of the expected discharge, the total dynamic head and the pump efficiency, it maybe useful for the water project planner to estimate the required power of the engine, first to74

check the offer of the manufacturer, and then to calculate the expected energy consumptionnecessary to determine the operating cost of the pumping station.Defining:P mot as the power delivered by the engine in HP,Q pump the discharge of the pump in m 3 /h,H lift the total vertical water lift in m from pumping level in the well to point of delivery in thetank. Assuming the friction losses equal 15 percent of h lift , the total dynamic head wouldcorrespond to 1.15 x h lift .Defining: Te ff as the efficiency of the pump and the diesel engine (0.48 according to Figure17)A simple formula to estimate the nominal power of the engine would therefore be as follows:Submersible pump and power generatorThe same data as for the vertical turbine pumps are required to order the submersiblepumps. These are well casing inside diameter, discharge and vertical water lift.The manufacturer will usually take care of calculating the power required to run the motor ofthe pump and the characteristics of the generator as well as the power of the engine whichwill drive the generator. However it may be useful for the water project planner to estimatethe characteristics of the various components of the system in order to check the offers ofdifferent manufacturers and also to calculate the likely energy consumption of the pumpingstation.The power required to run the electrical motor of the pump is estimated as follows:P mot : the electrica1 power absorbed by the motor of the pump in kWQ pump : the discharge of the pump in m/hH lift : the total vertical water lift in m from pumping level in the well to point of delivery in thetank; assuming the friction losses equal 15 percent of H lift , the total dynamic head wouldcorrespond to 1.15 x H lift ,T eff : the efficiency of the turbinesM eff : the efficiency of the electrical motor75

or simply, if assuming T eff = 0.8 and M eff - 0.9 (see Figure 17),However, starting an electrical motor requires additional power which may be estimated as15 percent of the power calculated by the proceeding formula. Eventually the power P motgen ofthe engine associated with the generator will be:P motgen inwhereG eff - is the efficiency of the generatorD eff is the efficiency of the diesel engineor simply, if assuming G eff = 0.9 and D eff = 0.6,P motgen inP motgen inHence, by comparing the power required for a given discharge and head by the system -vertical turbine pump + diesel engine with that required by the system -submersible pump +electrical motor + generator + diesel engine it clearly appears that the latter will consumemore energy for the same output.6.4.5 Wind powered pumpsa. Wind energyWith the help of windmills, wind energy can be converted into mechanical or electrical power.The power which can theoretically be supplied may be estimated by the following formula:P th = K x A x V 3where:P th is the power in kWA is the area swept by the rotor in m 2V is the wind velocity in m/s76

K is a coefficient depending on the density of the air and the characteristics of the rotor; for arough estimation of P th , K may be made equal to 0.00064Since the power relation with the windspeed is cubic, it is very important to obtain reliablewindspeed data in the project area for a sound evaluation of the technical and economicalanalysis of the windmill water lifting project.b. Wind analysisTo evaluate the possibilities of windmill for supplying water to livestock in rangeland areas,an analysis has to be made of the wind. This study should cover the following items:i. Average annual windspeedWind speeds should be measured 10 m above ground surface in order to reflect the actualwind characteristics to be used by the mill. The wind velocity in secondary meteorologicalstations is usually measured at much lower heights, and corrections can be made with thefollowing empirical formula:where:V 10 = average wind velocity at 10 m above ground (m/s)V h = average wind velocity at height h (m/s)h = height of windspeed measuring device (m)a = surface roughness coefficient ranging from 0.2 and 0.25 in open areas on landThe technical feasibility of a windmill project can be roughly evaluated from the averageannual windspeed as indicated in Table 16.Table 16: TECHNICAL FEASIBILITY OF A WINDMILL PROJECT IN RELATION TO THEAVERAGE ANNUAL (OR SEASONAL) WINDSPEEDAverage annual or seasonalwindspeed (m/s)less than 2.5 m/sTechnical feasibility of a windmill projectgenerally not feasible2.5 to 4 m/s technically possible but may be doubtful from an economicview pointmore than 4 m/sii. Average monthly windspeedsgenerally feasibleFor water project planning connected with rangeland development it is important to knowwhether windspeed will be sufficient and that, consequently, water will be available duringthe months of presence of the animals on the considered rangeland area. To evaluate thisfactor, the average windspeeds are plotted on graphs.iii. Daily wind patternIn general, windspeeds are not constant throughout the 24 h of a day. Often there is littlewind at night, wehreas strong winds may blow in the afternoon. In any case the windspeed77

distribution over the day will most probably not correspond to the likely distribution of thewater demand for watering livestock. It is therefore necessary to associate a storage tank toany wind powered pumping system.iv. Windless periodsIf windmills are being considered for supplying water to livestock in rangeland areas,windless periods are one of the most important items of the wind analysis. If the probability ofhaving one lull period of more than 2 consecutive days during the dry and hot seasonexceeds 20 percent -a 2 day lull period will probably occur during the hot season 2 years outof 10 - then the water project has to be seriously reexamined. Storage tanks may possiblyhelp to overcome the difficulty of the lull periods but the cost of one water supply may rapidlybecome excessive.c. Windmill pump performanceThe maximum extraction efficiency of the theoretical wind power cannot exceed 59.3percent. Actually the efficiency of the conversion of wind energy into mechanical energyranges from 15 to 40 percent according to the type of windmill. If the pump efficiency is alsotaken into consideration, then the overall efficiency of a. windmill-pump will be ranging from10 to 30 percent only.P usable = (0.1 to 0.3) x K x A x V 3The total power output of a specific windmill-pump combination can therefore be predictedfrom the windspeed frequency distribution over the different period of the rear (months forexample) corresponding to the rangeland occupation plan. However another two parametersshould also be taken into account to determine the expected performance of the system: thecut-in and cut-out windspeed. The cut-in windspeed or starting windspeed is the minimumwindspeed required for the mill to start running, depending on load and starting torque. Thecut-out windspeed or maximum windspeed is the speed above which the windmill isdesigned to be governed out of the wind for safety reasons. Usually the cut-in speed isaround 3 m/s while the cut-out speed is around 8-10 m/s. It is obvious that only thewindspeed frequency distribution figures between these 2 limits should be used for theperformance calculations.Actually the windmill performance is difficult to assess accurately under real field conditions.Moreover the figures presented in manufacturers manuals are often difficult to adjust to localconditions and sometimes are rather optimistic. However, when the windmill and the pumpare well designed and well keyed to one another, there should not be much differencebetween the performances of the various makes, and these should all correlate with figuresderived directly from theoretical formulas.Table 17 (Van Vilsteren 1981) gives an indication of average windmill-piston pumpperformance for the most common combinations available on the market.78

Table 17: GENERAL WINDMILL-PISTON PUMP PERFORMANCE FIGURES FORDIFFERENT ROTOR DIAMETERS AND DIFFERENT ELEVATION HEAD (Cut-in windspeed3 m/s; V design 3 m/s; Cut-out 10 m/s)DISCHARGE IN m 3 /hTotal elevation head m 5 10 15 20Rotor diameter m 3.5 5.0 7.0 3.5 5.0 7.0 3.5 5.0 7.0 3.5 5.0 7.0WI 3-4 3.2 6.5 13.0 1.6 3.2 6.5 1.1 2.2 4.4 0.8 1.6 3.2N 4-5 4.2 8.5 17.0 2.1 4.2 8.5 1.4 2.8 5.6 1.0 2.1 4.2D 5-6 6.5 13.0 26.0 3.5 6.5 13.0 2.2 4.4 8.8 1.7 3.5 6.5S 6-7 8.5 17.0 34.0 4.2 8.5 17.0 2.8 5.6 11.2 2.1 4.2 8.5P 7-8 10.7 21.5 43.0 5.4 10.7 21.5 3.6 7.2 14.4 2.7 5.4 10.7E 8-9 13.0 26.0 52.0 6.5 13.0 26.0 4.3 8.6 15.2 3.2 6.5 13.0E 9-10 16.5 31.0 62.0 7.7 15.5 31.0 5.2 10.3 21.0 3.8 7.8 16.5D (m/s)Table 17 shows the practical limit of pumping depth when windmills are expected to supplywater to livestock in rangeland areas. If elevation of the storage tank and friction losses alltogether are taken equal to 5 m and if a discharge of 5 m 3 /h is considered as the minimumrequired, it appears from Table 17 that with 5 m rotor diameter the maximum pumping depthwill be in the order of 15 m (20 m total head), while with 7 m rotor diameter, the maximumpumping depth may possibly reach 35-40m. The practical limit of piston pumps, however, is25-30m. For greater depth the rods used for transmission of the vertical movement to thepiston may be subject to frequent breaks.d. Maintenance requirementsLike any mechanical device, windmill-pump equipment requires maintenance (lubricating,change of piston leather of the pump, checking of the cut-off device). In remote areas ofdeveloping countries the maintenance requirements of windmills even if limited are animportant constraint.In the Eastern part of Mali (south of Gao) 38 windmills were installed in 1956-60 in rangelandareas and also close to villages. From 1959 to 1962 the windmills were periodically visited bymechanics belonging to a contractor in charge of the maintenance and worked perfectlyduring all that period of time. Later on, the lack of spare parts and the difficulty of ensuring acontinuous maintenance resulted in a rapid decline of the efficiency of the windmills whichbroke down one after another.6.4.6 Solar pumpsThe use of solar energy in developing countries is now seen as a serious and worthwhileendeavour. Various governmental and international agencies as well as commercial firms areinvolved in research and development, including water lifting of the various methods forharnessing solar energy; the most promising is the photovoltaic system, which directlyconverts solar energy into electricity. Up to now the main limiting factor to the utilization ofsolar energy was the excessive investment required but it cannot be excluded that atechnological breakthrough similar to that of microprocessors in electronics may be achievedand that thereby solar powered devices may become highly competitive in water lifting at79

least for irrigation. When water is to be used for watering livestock in remote areas, anadditional constraint is the maintenance requirement of such sophisticated devices.6.5 Groundwater monitoring6.5.1 Need for groundwater monitoring6.5.2 Rainfall observations6.5.3 Water level fluctuations6.5.4 Water abstraction6.5.1 Need for groundwater monitoringIn principle a groundwater project designer should always be in a position to predict the longterm behaviour of the aquifer in relation to the planned programme of water abstraction andto the possible climatic fluctuations which may affect the recharge of the aquifer. Water wellsshould be designed in such a way that in no case the water level would drop down out of thereach of the designed water lifting devices. This means for example that dug wells should bedeep enough to always contain sufficient water for the users to draw it. This means also, inthe case of the drilled wells, usually much deeper than the water level, to design the pumpingequipment in such a way that no risk would occur for the pumps to run dry and either to bedamaged or to let thousands of animals without water.The problem of water resources has already been discussed in paragraph 6.2.4 for thecontinuous aquifers and 6.2.5 for the discontinuous aquifers. While the water resources of acontinuous aquifer are relatively easy to estimate and in most cases they are, by an order ofmagnitude, bigger than the water demand for extensive stockbreeding, the problem maybecome serious in the case of discontinuous aquifers. Because hydraulic extrapolations arehazardous in discontinuous aquifers, the classical methods of groundwater resourcesevaluation do not apply and therefore the water project should be designed on a step by stepbasis in such a way that each new step of water development would be designed andimplemented on the basis of a careful analysis of the effect of the previous step on theaquifer. This is possible only by planning, together with the water development operations ofthe project, a careful monitoring of the rainfall over the area concerned, the water levelfluctuations in selected wells (possibly all if they are far away from each other) and thequantity of water withdrawn every year from the wells.Although less important in the case of continuous aquifers, it is worthwhile, also in that case,to follow the fluctuations of the precipitations and of the water level in selected wells in orderto be able to notice any abnormal drop which may affect the utilization of the wells.6.5.2 Rainfall observationsIn a rangeland area, a rainfall observation network is usually planned in order to correlateprecipitation and dry matter production and thus to predict the carrying capacity of the areaduring the next dry season. The same rainfall observations can be used for groundwaterrecharge monitoring.80

6.5.3 Water level fluctuationsIn an area where wells are scattered and where no hydraulic connections exist from one wellto another but statistical correlation's, water level observations should be made on almostany well, at least during the starting phase of the project. The observations should be madetwice a year, one of them being made during a period of non-utilization of the wells (usuallythe end of the rainy season).When water level has to be measured during the period of intensive water drawing, themeasurements should possibly be made early in the morning and the situation of the well(whether or not in production) should be noted together with the water level.In the case of continuous aquifers, the drilling of a few piezometer holes should beconsidered if the corresponding marginal increase of the total project cost is reasonable (sayless than 5 percent of the total cost of the water project). Well protected piezometers are thebest way for observing the fluctuations of the water level without being disturbed by the localdepression due to water abstraction from the well itself.6.5.4 Water abstractionThis is the most difficult parameter to be determined but at least in the case of discontinuousaquifers it is important to estimate the quantity of water withdrawn from the wells.If by direct counting (for vaccination) or by statistical sounding, the number of animals whicheither transit or stay in the considered area is known, the estimation of the water abstractionis quite easy.If no information is available from the Animal Husbandry or Veterinary Service a tentativeestimation of the number of animals watered by the wells should be made once every threeor four years, by counting the animals watered during a full day by randomly selected wells(one over ten). The well inventory should have been completed befrehand so that to know atleast the number of wells supplying water in the area and to make extrapolation of soundingresults possible.6.6 Case study and cost6.6.1 Well construction6.6.2 Water liftingBefore going through a few examples and their costs, it is worth mentioning that allconstruction works related to groundwater development carried out in rangeland areas, andall water lifting equipment are much more expensive than when the future water users aresedentary people living in villages. The two main reasons for the higher prices are distanceand maintenance difficulties. When the well sites are far away from the capital and from themain roads, they are often not accessible with normal vehicles. The water users are often notthe same from one day to another so that any involvement of the population in theconstruction works as well as in the maintenance of equipment is difficult.81

6.6.1 Well constructiona. Dug wellsThe unit cost per metre for digging and lining large diameter wells depends on the depth ofthe wells, the hardness of the formation, the difficulty of access and the distance from thecapital. It is therefore difficult to give one single price for well digging even within one country.Moreover, in discontinuous aquifers, it is always necessary to drill a reconnaissanceborehole to ascertain the presence of water before digging a well, and the cost of the drillingshould obviously be added to the construction cost of the dug well. However, in the followingexamples dealing with groundwater development programmes in discontinuous aquifers, thecost of the reconnaissance boreholes will not be considered.In Mauritania (Burgeap 1982b), the average prices in 1980 are as indicated in Table 18.Table 18: AVERAGE 1980 COSTS OF 1 m OF DUG WELL, 1.8 m DIAMETER EXECUTEDBY THE MAURITANIAN ADMINISTRATION (DIRECTION DE L'HYDRAULIQUE) (Exchangerate: US$ 1 = 50 UM)Area Trarza Afrar Tagant Assaba-HodhNature of the rock soft hard hardMaximum depth 40 m 30 m 30 mDistance from Nouakchott 200-300 km 600-800 km 700-1000 kmAverage UM 28 000 34 000 40 000cost/m US$ 560 680 800Actually, according to the new policy of the Administration, 35 percent of the cost of dugwells are provided for in nature (unskilled manpower, material, fuel) by the local collectivities.In Niger, a special authority (OFEDES) is responsible for the construction of the wells. In1982 the prices charges by OFEDES for digging wells in Maradi-Zinder area (600-800 kmfrom Niamey) were as indicated in Table 19.Thus a well, 30 m deep, crossing 20 m of soft formation, 5 m of hard rock and penetrating 5m into the aquifer, would cost in equivalent US dollars:Moving equipment 865 865Digging and lining 25 x 202 5 050Supplement for hard rock 5 x 383 1 915Concrete shafts 5 x 107 535Ring shoe 78 7882

Table 19: UNIT PRICES FOR WATER WELL DIGGING BY OFEDES IN MARADI-ZINDERAREA (NIGER) IN 1982 (Exchange rate: US$ 1 = 285 CFA Francs)Description of work Unit Unit priceFCFA US$Moving equipment and preparation of well site Unit 246 504 865Digging and lining in soft terrain0 to 30 m m 57 480 20230 to 50 m m 63 240 22250 to 70 m m 72 726 25570 to 90 m m 87 276 306Price increase for hard rock m 109 200 383Supply and installation of concrete screenedshaft and gravel pack m 30 600 107Supply and installation of the ring shoe Unit 22 200 78Digging below water level (max 10 m) m 72 600 255Curb and surface anchorage Unit 148 200 520Supply and installation of surface super structure (block-holder) Unit 450 000 1 579Supply and installation of water troughs for livestock Unit 21 000 74Pumping test Unit 81 000 284Digging below water level 5 x 255 1 275Curb 520 520Water troughs (5)0 5 x 74 370Pumping test 284 284Total in US$ 10 892Average cost per metre in US$ 363In Mali, data have been collected on cost of dug wells executed either by foreign contractorsor by the local administration (Opération Puits).In 1979, 11 wells totalling 637 m were dug by the Administration in the area calledSenomango located in the 6th Region. The formations which had to be crossed areextremely hard (crystalline dolomite) and explosives had to be used. The LivestockDevelopment Project in Mopti Region (ODEM) bore all related expenses which amounted to:373.4 million Malian Francs (FM) for equipment293.0 million FM as operating cost.Even if only 3/5 of the expenses for equipment are taken into consideration the 11 wellscosted 517 million FM (approximately US$ 860 000) - i.e. 8000 000 FM/metre in 1979(approximately US$ 1350/m) without taking into account the cost of the reconnaissanceboreholes which were drilled on each well site before digging the wells.In 1983 a second phase of the Livestock Development Project in Mopti Region (ODEM) wasprepared by a FAO team (Investment Centre) and was later on financed by the World Bank.In front of the excessive costs of well digging, other alternatives were examined. The mostattractive one included a major involvement of the future users grouped in pastoralassociations in the construction work as well as in its financing, and the participation of local83

traditional well diggers properly assisted by one expatriate foreman. A similar approach issuccessfully being experienced by Non Governmental Agencies working in nearby areas(Bandiagara Plateau, North Tombouctou) where actual costs of well digging have beenbrought down to 250 000-350 000 Malian Francs per metre (US$ 350-500/m). The figureeventually adopted in the economic appraisal of ODEM Phase II for the cost of well diggingdown to 70-90 m in very hard rock was FM 500,000/m (US$ 715/m).In Upper Volta, 1982 costs for hand dug wells are reported to stand at a much lower levelthan in the 6th region of Mali - i.e. US$ 171/m. This important difference in cost is probablydue to the fact that the rocks are softer (weathered granite in most cases), the depths areusually smaller (20-40 m) and local well diggers can easily work without air compressor andexplosives, and most of the wells are dug for villages which actively participate in theconstruction work.b. Drilled wellsIn the case of discontinuous aquifers, reconnaissance boreholes are always necessary toascertain the presence of water before realizing the production works which are much moreexpensive and must be undertaken only after being sure of water occurrence. When theresults of the reconnaissance borehole are satisfactory, it is usually converted either into aproduction well, where the cost increase is mostly related to the casing and screen supplyand installation, or into a dug well, the cost of which is a completely new item to be added tothe cost of the reconnaissance borehole.However, it happens very frequently that one reconnaissance borehole is not enough toidentify the best location for water production and another borehole has to be drilled.Being:r: the rate of success in percent - i.e. the number of productive wells over 100 drillings,DC + : the cost of a productive well - i.e. capable of delivering a minimum discharge of 1 m 3 /h,completed with casing and screens (if necessary), developed and pump tested,DC - : the cost of a dry reconnaissance borehole,PDC: the actual cost of one production well including the cost of the unsuccessful boreholeswhich were necessary to identify the best location,ThenThe formula clearly shows how sensitive the actual cost of a production well is to the rate ofsuccess, which should be called probability of success when planning a water developmentproject - i.e. before implementing the project. It is therefore extremely important when dealingwith the economical aspects of a water project in an area of discontinuous aquifer to collectthe data necessary to establish the probability of success of the wells to be drilled.In Mali, an Important programme of drilled wells in the Western part of the country wasfinanced by the Saoudi Development Fund and the Fonds d'Aide et de Coopération (France)and was carried out from 1980 to 1982. More than 200 wells were drilled, mostly in thebasement formation (discontinuous aquifer) with the down-the-hole-hammer drillingtechnique. Drilling costs were accurately collected and analysed by BURGEAP (BURGEAP84

1982a). The cost of unsuccessful boreholes averaged Malian Francs 51,500 per m - i.e.approximately US$ 103/m. The actual cost of production wells including the cost ofunsuccessful boreholes is summarized in Table 20.Table 20: COST OF PRODUCTION DRILLED WELLS IN THE BASEMENT IN RELATIONTO THE NATURE OF THE GEOLOGICAL FORMATION - WESTERN PART OF MALI(BURGEAP 1982a)Nature offormationCoefficient ofsuccess (%)Average depth ofproductive well inmAverage cost of oneproduction well inUS$Average cost of onemetre of productionwell in US$Granite 24.5 38 24 360 641Schist 39 37 16 020 433KayessandstoneNarasandstone55 46 15 540 33733 40 16 720 418Claystone 25 58 36 800 634Tillite 55 47 15 940 339Pelite(Kayes)42 35 14 500 414Pelite (Nara) 47 47 15 060 320Dolerite 36 30 14 260 475Notes:- A well is considered as productive if it can deliver a minimum discharge of 1 m 3 /h under astable drawdown.- The cost figures were originally given in Malian Francs and have been converted to US$ byusing a constant exchange rate (US$ 1 = 500 Malian Francs) for comparison purposes withother countries.In Upper Volta a programme of 260 drilled wells was financed by the European Fund ofDevelopment. The cost of a production well, 50 m deep, drilled in basement hard rock from20 m to total depth, amounted to CFA Francs 2,700 000 (end of 1981), including the cost ofnegative boreholes (35 percent rate of success). Assuming a rate of exchange of 210 CFAfor US$ 1 in 1981, the unit cost of a production well was 257 US$/metre. In Mauritania aprogramme of 19 drilled wells for a total of 870 m was carried out in 1979 in Afollé region, at600 km away from Nouakchott. The drilling of hard to very hard formation made it necessaryto use the down-the-hole-hammer technique. The unit cost of a production well averaged 427US$/m.In continuous aquifers it is usually not necessary to drill a reconnaissance borehole beforeundertaking a production well (either drilled or dug); the probability of success of any well ishigh enough to take the risk of drilling or digging the production well directly. But in spite ofthe better probability of success, the unit cost of production well is usually higher than in thecase of wells drilled in hard basement rocks, essentially for two reasons:i. the wells are drilled by rotary method which requires a much heavier equipment as well asa sufficient water supply for preparing the mud. Since the well sites for watering livestock areusually located in remote areas of difficult access, the cost of transporting the drillingequipment and all necessary items (fuel, water, spare parts, etc.) becomes an important itemin the budget of the well construction;85

ii. the programmes of well drilling in rangeland areas are usually limited to the areas wherethe aquifer is deep and out of reach of hand dug wells. As a consequence of this limitation,the drilling programmes in continuous aquifers, usually include a small number of wellsamong which the high mobilization cost has to be shared.In Mali, a programme of 10 wells 150 m deep and located 300 km away from Bamakowaswas carried out in 1979-80. The wells were drilled in a clayer and sandy continentalformation and their cost (1980) averaged 668 US$/m.c. Well cistern associated with drilled wellThe cost of a well cistern is simply the sum of the cost of the production drilled well and thecost of the dug well. As the production well and the well cistern will not be equally deep it ismeaningless to indicate a cost per metre.In Mali the figures adopted by a FAO team (Organisation des Nations Unies pourl'Alimentation et l'Agriculture 1983) in the preparation of the second phase of a LivestockDevelopment Project in Mopti Region (ODEM) are summarized in Table 21.Table 21: ESTIMATED COST OF A WELL CISTERN ASSOCIATED WITH A DRILLEDWELL IN 1983 IN MALI (Exchange rate US$ 1 = 700 Malian Francs)DescriptionCost in Malian Francs in US$a. Drilled well (120 m deep) Successful production well 17 500 000 25 00070% cost negative borehole 9 000 000 12 857b. Well cistern (65 m deep) Digging, lining and connecting 32 500 000 46 428Sub total 59 000 000 84 285Contingencies (10%) 5 900 000 8 428TOTAL 64 900 000 92 713It should be noted however that the very high cost estimated in Table 21 may not berepresentative of an average situation since the well cistern is supposed to be dug inextremely hard basement rock.6.6.2 Water liftinga. Hand pumpsThe most recent review of the existing hand and foot pumps is dated 1978 (BURGEAP 1978)and the prices - ex factory - collected in this study should be multiplied by a factor rangingfrom 1.5 to 2 to approximately correspond to the present prices. The pumps reviewed byBURGEAP were all designed for a piston setting depth of 30 m for comparison purposes.The main results of the study are given in Table 22.86

Table 22: AVERAGE 1978 EX FACTORY PRICES OF HAND AND FOOT PUMPSType of pump (all pumps designed for 30 m pump settingdepth)Average 1978 ex factory price inUS$Piston pump hand operated through a level 680Piston pump hand operated through wheel and handle 1800 to 2800Piston pump foot operated with hydraulic transmission 800b. Motor driven pumpsMotor driven pumps are usually imported and their actual cost including supply, transport,insurance, taxes and installation may be much higher than the price FOB claimed by themanufacturer. The following examples illustrate the price increase resulting from the variousmanipulations of the pumping equipment from the factory to the well site.In Mauritania the African Fund of Development financed the equipment of pumping stationsin pastoral areas. The wells had been previously drilled in the framework of a programmefinanced by the European Fund of Development. The pumps and engines were purchased in1979 and installed on the wells in 1979-80. Detailed information is available on the cost ofsupply and installation of the equipment which consists of either vertical turbine pumps anddiesel engines, or submersible pumps with generators.A total of 25 pumping stations were equipped. A good correlation was established betweenthe cost of pumps, engines or generators and the product pump discharge in m 3 /h by verticallift in m. For comparison purposes the costs including supply and installation have beenconverted into US$ with an exchange rate of 46 UM for US$1 (approximately exchange ratein 1979).The following symbols are used in the formulas:Q = pump discharhe in m 3 /hH = vertical lift in metresFor the vertical turbine pumps the costs including the installation are related to the product Hx Q according to the following formulas:Cost of pump in US$ = 0.85 x H x Q + 14 900Cost of an engine in US$ = 0.75 x H x Q + 3790Cost of a shelter in US$ = 13 200 (for one well)Cost of the superstructure (tank, troughs) in US$ = 20 670 (for one well)For the submersible pumps the following relations were established.Cost of a pump in US$ = 1.3 x H x Q + 16 900Cost of a generator in US$ = 2.3 x H x Q + 7340Cost of a shelter in US$ = 13 200Cost of the superstructure (tank, troughs) in US$ = 20 670However it should be mentioned that in the particular case of the above equipment installedin Mauritania, the motors and the generators were oversized by a factor 2 to 3 and this maypartly explain the excessive price of all this material when referred to the physical pumpingconditions.87

In Mali two wells were equipped in the framework of a Livestock Development Project inMopti Region in order to experiment motor driven pumps for watering livestock in rangelandenvironment. Available figures expressed in Malian Francs do not include transport andinstallation and have been converted into US$ for comparison purposes on the basis of theaverage 1979-80 exchange rate (US$ 1 = 432 MF). A vertical turbine pump with a dieselengine capable of delivering 10 m 3 /h under 26 m head costs the equivalent of US$ 4900 in1978. The same equipment with transport and installation would have cost US$ 19 100according to the formulas established in Mauritania. A submersible pump (10 m 3 /h for avertical head of 50m) with a power generator driven by a diesel engine costs the equivalentof US$ 9880 in 1978-79. The same equipment with transport and installation would have costUS$ 26,040 according to the formulas established in Mauritania.The main purpose of these examples was to draw the attention of water project planners tothe huge difference which may occur between the prices FOB of pumping equipment and theactual cost of the same equipment after all expenses (transport, insurance, taxes,installation) have been paid.c. Wind powered pumpsFOB prices of windmills may also be very misleading since the actual cost of the equipmenton the well site including tank construction, transport and installation may be much higherthan the price claimed by the manufacturer. The following examples should therefore beconsidered with care if prices have to be extrapolated to real situations in remote areas ofdeveloping countries.An Italian manufacturer offers windmills at 1984 prices indicated in Table 23 (prices in ItalianLire have been converted into US$ on the basis of the average 1984 exchange rate of US$ 1= 1650 Italian Lire):Table 23: PRICES (1984) FOB OF WINDMILLS PRODUCED IN ITALY (Tower height = 12metres; pumping capacity is estimated for a vertical pumping lift of 15 m and an overallefficiency of the system (windmill, pump and transmission) of 15%)Rotor diameterin mPower in kW for an averagewindspeed of 6 m/sPumping capacity inm 3 /hPrice FOB in US$(1984)3.1 0.6 2 2 2005 1.5 5 4 9309 5.0 18 10 900In Mali a windmill was purchased in 1977-78 in the framework of the already mentionedLivestock Development Project in Mopti Region. The windmill and pump cost the equivalentof US$ 7050; the installation alone costs the equivalent of US$ 3500.d. Solar pumpsTechnology is now clearly oriented towards photovoltaic/electrodynamic rather thanthermodynamic transformation of the solar energy into mechanical energy. Therefore onlycosts of photovoltaic systems are examined here.Consultants (Sir William Halcrow & Partners) working for the World Bank and funded by theUN Development Programme tested 12 pump/motor systems and 6 types of solar panels in1982-83. Among the various systems tested, one category (20 m3/day output through 20 mdesign static head) may correspond to a livestock watering situation. Costs and results of the88

tests are thoroughly analysed in their reports as well as in a short note of World Water (WorldWater 1983); they are summarized in Table 24.There is room for improvement of efficiency of the photovoltaic system (pump and motor)which will tend to decrease the cost related to unit solar energy taken as 5 kWh/m 2 /day bythe UNDP/World Bank Consultants. The cost of solar cells is expected to decrease in thefuture mainly as an effect of volume increase in production. The prices indicated in Table 24are FOB and in the case of installation of solar pumping unit in a remote area of Africa forexample the transportation and installation cost together with taxes and miscellaneousexpenses may possibly double the original supplier price.Table 24: COSTS AND RESULTS OF SOLAR PUMPS TESTED AT SIR WILLIAMHALCROW 7 PARTNERS TESTING FACILITYSupplier(country)Grundfos(Denmark)Wm Lamb(USA)Sofretes(France)Trisolar Corp(USA)Complete system tender priceFOB (US$ (1982)Volume delivered in m 3 for 5 kWh/m 2 /day atdesign static headclaimedobserved13 360 20 3314 470 15 1621 050 20 2325 500 23 196.7 Conclusion on groundwater developmentUnless an important effort is made by developing countries to improve their maintenancecapacity of mechanical and electrical devices, the traditional water drawing (possibly withanimals) from large diameter wells (associated or not with drilled wells) is still and will likelyremain for several years the most reliable way for supplying water to livestock in remoterangeland areas.Cost of dug wells is usually high whichever approach has been chosen for their construction,either by contractors or by state organization. However, involvement o£ the users in welldigging has proved to be an efficient way for lowering the cost of groundwater developmentin the case of village water supply. When the water users are constantly moving from onewell to another, it is clearly difficult to get them involved in the construction works and wellmaintenance. Nevertheless in many African countries, stockbreeders tend now to organizethemselves through associations or cooperatives which may be financially involved ingroundwater development works. Properly guided, traditional well diggers may alsocontribute efficiently to lower the cost of well or well cistern construction.89

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