Ref erences - ROOT of content

~ Refin its present form is one of the thin materials, may in the future also methis requirement. It remains to be seen if these synthetic materials will blavailable at competitive prices. Current research will determine the potentuse of thin materials like acrylic fibre mats and various makes of polypro:pylene fibre mats.erencesIBUSSER, J.W. and H. KODDE. 1977. Resultaten van een landelijk onderzoeknaar de inspoeling van zand in drainbuizen. Cultuurtechnisch Tijdschr.16, 6:266-273.I CAVELAARS, J.C. 1966. Hydrological aspects of the application of plasticdrain pipes and filter materials. Transact.Symp.Hydrol.and Techn.Problems of Land Drainage, Prague 7th-12th Oct.1966.DUNN, I.S. 1959. Tractive resistance of cohesive channels. ASCE Proc.Journal of Soil Mechanics and Foundation Div. 85, No.SM3, June 1959.HOFSTEE, J. and H.J.FIEN. 1971. Analysemethoden voor grond, gewas, wateren bodemvocht. Rijksdienst voor de IJsselmeerpolders, Kampen.JONKERS, H.J. and G. MIEDEMA. 1975. Resultaten van het onderzoek naar deintreeweerstand van drains op.proefvelden. Meded.C.D.114.KOMO. 1976. Ontwerp NEN 7047 en 7048.MEIJER, H.J. and J.A.C.KNOPS. 1977. Veldonderzoek naar de bestendigheidvan cocosvezels als afdek- of ‘omhullingsmateriaal voor drainbuizen.Cultyurtechnisch Tijdschr. 16, 6:261-265.NIEUWENHUIS, G.J.A. 1976. De invloed van perforatie en filter op de intre6weerstanden van drainbuizen. 1nt.Nota ICW 921.OGINK, H.J.M. 1975. Investigations on the hydraulic characteristics ofsynthetic fabrics. Publ. Delft Hydraulics Laboratory 146.OLBERTZ, F.N. 1965. Taschenbuch der Wasserwirtschaft. Wasser u.Boden,Hamb~SCHOLTEN, J. 1974. Tien jaar onderzoek van drainagematerialen in OostelijkFlevoland. RIJP, Flevobericht 96.SEGEREN, W.A. and F.C.ZUIDEM. 1969. Ontwikkelingen in de drainagetechniek. Cultuur.Verh. Min.van Landbouw, Den Haag.SHERARD, J.L. 1953. Influence on soil properties and construction methodson the perforinance of homogeneous earth dams. Techn.Memo USDI, 64.5.SOMEREN, C:L.van 1965. The use of plastic drainage pipes in The Netherlands.Meded.C.D. 62.450

[Paper 2.16Ab s tract'The most familiar drain clogging problem has been the highly visible Fe'sludge called ochre which is caused primarily by the bacterial precipitacionof Fe2. Studies with chemically precipitated iron have usually been conductedin laboratories using waters devoid of the complexing agents present in drainoutflow. Iron complexing with such agents as tannins and humic acids oftenremain in solution in canals and ponds and there seems to be little informationon the role of complexing agents in relation to ochre formation. Ironp recip ita t ing bacteria of the gener a Lepto thrix, Ga Z lione 7, Za, Sp haeroti Zus,Namaniel la, Toxothrix, Pseudomonas and Enterobacter have been grown in monitoredbacterial growth chambers resembling drain lines. Ochre developedonly when the bacteria were present. Tannic acid, citric acid, lactic acid,and sulfonated ligning stimulated ochre formation when injected at 1ppm andsuch compounds are known to be present in groundwater in trace amounts.The clogging characteristics of chemically oxidized iron was separated frombiologically precipitated iron by injecting biocides and Fe2 into bacterialgrowth chambers. A continuous injection of 0.5 ppm free residual chlorineoxidized Fe2 in the flowing water and killed bacteria with no subsequentochre formation. The Fe3 precipitated by NaOCl did not stick to glass slides,beakers, polyethylene or PVC tubing.Complexing agents may contribute to clogging. Suspended colloidal organicmatter can stick to glass slides and bacterial growth chambers and willappear red when stained with carbolfuchsin. Organic matter sorbs and apparentlyoxidizes iron so that the resultant deposit is a thin, translucenttan. The deposit is usually thinner than gelatinous ochre. Certain complexationproducts such as citric acid and iron will stick to glass slides, polyethyleneand PVC in bacterial growth chambers. Additional studies areneeded to establish the extent to which humic acid, tannins, lignins andother naturally occurring complexing agents with Fe can form particles capableof sticking in the zone abutting the drain envelope.ad dit ion al methods are needed for estimating ochre potential before installingdrain lines. While Fe2 flowing into drains is essential for ochre formation,there are other factors such as pH, soil type and temperature that shouldbe considered. There is still no reliable way for predicting the severity oflochre formation since the biotic factors at any given location can only beassumed and not evaluated in advance of drainage operations.45 1

Paper 2.17IRON CLOGGING: DIAGNOSIS AND THERAPYH. Kunt ze,Niedersächsisches Landesamt fiir Bodenforschung,AuBeninstitut fiir Moorforschung und angewandte Bodenkunde,'Bremen, Federal Republic of GermanySummaryKnowing the causes of chemical and biological iron clogging and the siteswhere this may be expected are important for counter-measures. Both can bedetermined by an+?rohydrographic analysis of the site and field or laboratorytests on Fe content and pH in water and soil (Tables 3 and 4). Withia 20 years research program it was found that: Allochthonic clogging (alienorigin of iron) is a continuous problem. Counter-measures therefore showonly short-term effects. Continuous maintenance (mechanical and chemicalcleaning) remains necessary; Autochthonic clogging (indigenous origin ofiron) is only a temporary problem. It depends on soil ripening with time ofdrainage (3 to 4 years). The iron oxidation within the soil can be enhancedby subsoiling and liming. If iron clogging problems are expected, filtersshould not be used, except special Antoc-filters, and with submerged drainoutlets. Plastic pipes develop adhesion forces for iron hydroxides. Drainslopes (>0.4%) are necessary to overcome these adhesion forces by tractiveforces in partially filled drain pipes. The inlet openings should be as laras possible (>I .2 mm).1. Introduction .Drainage is one of the most important methods of soil reclamation and improvement.For these purposes high investments are necessary. High investmentsare only justified if a long-term efficiency is guaranteed. This dependson research of wet sites, design of drainage systems, materials ofpipes and filters, installation methods and maintenance of water levels inthe main water courses.Within the last twenty years much progress has been made in pre-drainage investigationS.of soils and in developments of new materials and installation452.

techniques. Marginal sites, which had been excluded from drainage in formertimes, can now be reclaimed. Their drainage.systems, however, need moremaintenance.Silting causes a widespread damage in drain systems. According to Henning(1966) three forms of disturbances of drainage discharge exist: silting (66%),ochering (30%), other reasons (rooting, subsidence, pipe-defects)(4%). ForIpeat soils and mineral soils we get a different picture, namely:soil type si 1 t ing ocher ing othersIpeat soils 43 56 1 %mineral soils 79 15 6 %IIn most cases silting and ochering are found together. It then becomes verydifficult to restore the discharge function of a drain, because ochre and'mineral particles can form a cement-like substance.The aims of this study were:to determine the causes of ochering and the sites where it may beexpected ,to find methods of preventing ochering and ,to conduct experiments with equipment for cleaning iron-clogged andsilted drain pipes.Ichemical ochre formation+py self-oxidation and isoelectric precipitation,ofthe dissolved Fe , because of changes in the pH-value (>pH 7.6)and the redox potential E (>300 m V),hbiochemical ochre formation by numerous autotrophous and heterotrophousiron-organisms.

In most cases the two processes occur simultaneously or in succession. Thecomposition, consistency and adhesion of the ochre at boundary layers dependon the dominating type of ochre formation.The water-dissolved iron pH < 4 originates from the weathering of rocks or++from soil-forming processes (Tab.2). Generally the Fe content increaseswith the clay content. It decreases with increasing pH and Eh values of thsoil suspension. Iron clogging may be permanent - allochthonic (of alienorigin) or temporary - autochthonic (indigenous), the latter for exampleoccurring in marshy moor, moor gley, or clay moor. Allochthonic iron clog-++ging may even occur in clayless soils, if Fe is conveyed by groundwaterfrom an extensive iron-rich catchment area. It is found particularly at' valley margins in the presence of pressure or alien inflowing water. Autocthonic ochre habitats cause iron clogging only temporarily after drainage;its extent depends on the iron content of the soil and the intensity ofaeration. Allochthonic iron clogging in drains is a permanent process,even if the iron content in the groundwater is low.An orohydrographic analysis of the site, on the basis of geological-pedologicalmaps, facilitates the forecast of the type of ochre formation. Certain site characteristics, such as colour of the surface water and of thesoil profile, indicate the likelihood of ochre formation (Table 3). Thisfirst guess may be supported by analysis of water and soil samples for++their total Fe, Fe and pH-values. The degree to which iron clogging islikely to occur can be determined by interpretation of our numerous comparativetests (Tables 4 and 5).3. Degree of iron cloggingIn recent years colorimetric field or laboratory tests were standardized tdetermine the iron content in water or soil. If one's aim is to protectdrains from ochre, such tests can indicate the degree and type of ochreformation in each individual case, one must then decide whether:454a pipe drain is not feasible because it will soon clog (allochthonico.chre, >1 ppm Fe in water, pH

4. Counter-measuresThere are three possible counter-measures:a) Ochre formation should take place in the soil before the water entersthe drain. Generally, this should be the aim if the ochre formation isautochthonic-transitory.The Society for Rural Water Resources Engineering (Kuratorium fÜr Wasserund Kulturbauwesen KWK) supported 20 years of research programmes to testvarious ways of preventing, reducing and removing ochre deposition in drainpipes. The various problems, and their possible solutions obtained fromdifferent pilot surveys, are summarized as follows.4.1 Ochre formation before the waterenters the drain1 4.1.1 SubsoilingSubsoil loosening (repeatedly) promotes oxidation and precipitation of theiron in the soil, provided soil texture and moisture content (< plasticlimit) are suitable. Subsoiling will only increase aeration if coarsepores ( >IO pm) are created and maintained. Mole drainage may also contri-bute to such aeration effects. After immature, reduced soils with autoch-thonic ochre hazards are browned sufficiently, pipe drains can be placedin the pre-aerated soil.++However, to prevent a remobilization of Fe , any subsequent iron-reduction455

++The intensity of Feoxidation in the soil depends not only on the availi-bility of oxygen, but also on the pH-value. The liming requirements of thesoil increases with the clay content and decreases with the humus content(Table 6). Often line applications for ochre precipitation in the soil arehigher than those needed for optimum fertility. A four-fold lime applica-tion in addition to drainage, for example, was necessary to precipitate730 t Fe/ha in an alluvial meadow soil (Table 7). Recently oxidized (i.e.non-chrystalline) iron in the soil is liable to reduction if the pH-valueand soil aeration decrease in the course of land use. Therefore, a relati-vely high Ca-level must be maintained in the soil by successive liming andit must be controlled by regular tests. Ca-losses via drainage may reach UTto 0.8 t/ha in humid climates, whereas the withdrawal by crops is relativelsmall.Liming of the whole field is often very expensive. Therefore, at anothertrial, liming was concentrated on the drain ditch or its immediate neigh-bourhood. The lime quantity (0.5 - 2.0 kg/m drain ditch) was thus reducedto 10% of the area application. This lime distribution forces most of theiron precipitation to occur near the drain, thus deteriorating the physicalcharacteristics of the soil in this important reach. The permeability oflimed drain ditches decreases substantially with increasing iron depositior(Table 8).4.1.3 Filter materialsCoarse filter material in the refilled drain excavation (gravel, slag, orvoluminous, coarse-pored filter jackets) creates an additional aerationspace around the drain in periods when the groundwater level is below draindepth. Predominant ochre precipitation in the filter provides a clean drainbut it may clog the effective filter pores (Table 9).I 4.1.4. Vyredox-MethodA final evaluation of the Vyredox-method is not yet possible because ‘testinis still in progress. This technology was developed for water supply plants456

Oxygen-rich water is pressed via feeding wells into the groundwater aroundwell galleries to promote iron oxidation in the soil. The inflowing externalwater disposes of most of its iron content in such iron zones by adsorption.Because of its high cost, this method is feasible only for localized,Fe-rich groundwater sources or for protection of important outletditches.4.2 Precipitation of ochre in the ditchThe possibilities of promoting iron oxidation in the soil are restrictedto certain sites (suitable for liming or subsoiling) and to the autochthonicochre type. Therefore, the counter-measure 2 (iron clogging in theditch) must be attempted in most cases.I4.2.1 Drain slopeA s t e e p (artificial) d r a i n s 1 o p e is often considered apossible solution. The iron content of the drain water increases with thedistance of flow and the chance for aeration towards the drain outlet, ir-respective of the slope. The critical limit for the tractive force may beassumed only above 0.4% slope, in partially filled clay pipes of 50 mm 4,which corresponds with the findings of other authors. As a matter of fact,iron clogging and sand deposition often go hand in hand. Soil particles>60 pm are increasingly detained with higher iron content in the drainsludge, while these may be washed out from iron free sediments (Fig.1).4.2.2 Plastic pipesThe higher adhesion of ochre to plastic material must be considered even insmooth pipes. The adhesion to plastic surfaces exceeds that to clay pipes byup to 30% (Table IO).One of the reasons for this is the reaction to neces-sary production agents (stabilisators, emulgators). Thus a reduction of ochreadhesion by modified plastic material appears to be limited. This additionaladhesion can be overcome only above 10 - 20% slope, depending on size anddegree of partial fill of the pipes. Such high slopes are not available fordrains (Table 11).457

Ge w. %00< 60pmiy =O35 .3.L~ r10.560LO20O. a. ... . a.1O .5 10 15 20 % FeGew. %100 1..--20 -Oy = - 3.2 x r 08.9O 5 10 15 20 % FeFig. 1.Content of iron and particles < 60 pmdrain sludge.and > 60 ym in the4.2 .:3 Inlet openingsThe inlet openings into drains are particularly liable to iron clogging.Their size, form, and distribution must be carefully considered. On the onehand, they should be as large as possible to avoid hanging menisci between.opening and surrounding soil particles. On the other hand, wide slots intexture-labile soil require jacket filters, which themselves are liable toiron clogging. If there is an ochre hazard the minimum opening width shouldbe 1.2 mm.4.2.4 Submerged drain outletsSubmerged drain outlets will prevent aeration of the drainage water, particularlyin permanently water-filled drain systems. Special drain outlets,which back up water into drain pipes by syphon devic,es were, tested. Thismethod is possi,ble in very deep drains or section-wise in less deep, smallsystems. The method is restricted to very permeable soils because backing u€458

FV 62 : BohernKMnO4- CONT. IN DRAIN WATER FIG. 2OoUWa>-U O283.I, L I AL $ 1 , , I I1L.m 1.5. 1.6. "' 20.11. 112. 1.1.lF74 1.2. 1.3. 1.4.Fig.2. COD of the runoff iron drains with Antoc and duo-fiZter(Scheffer and Kuntze, 1975).Sand-ochre deposits are best removed by high pressure flushing. Individualdrain pipes and open collector ditches are most suited for this method, aswell as for all other functional controls. The expense of high pressureflushing depends on the degree of iron clogging, and on slope and diameterof the drain pipe, but less on the type of pipe (Table 16). Regular flushintevery 2 - 3 years will maintain an ochre-endangered drain in good conditionThe intervals between flushes should be shorter in the beginning.4.3.2 Chemical methodsVery persistent aged ochre needs a radical cure with acids and reductionagents. In such cases the necessary acid-ochre proportion must be determine(first, to avoid inflow of excess acid into the open ditches (Table 17). Thebest method is: to dam the acid in the drain for several hours, repump theacid ochre suspension into tank-wagons, and repeat the process with freshacid. A subsequent mechanical water flushing is generally required inaddit ion.460

II' 5. Final remarksThe last example demonstrates that a successful protection against ochre1 requires a combination of different measures. The efficiency of the methodsmentioned depends on a timely recognition of ochre type, the degree ofclogging, and its aereal extent.' Ochre-endangered sites always need drainage. Generally they have a good soilpermeability and drainage is possible. However, it depends on the potentialto avoid iron clogging by counter-measures with lasting effects whetherdrainage of such sites is feasible.Ref erences46 1

TABLE I . Composition of iron ochre from drain pipes(n = 21).Fe203A1203MnOCa0Mg 0-_. so;co2Org. matterCINPH3:O - 65.9 '0.2 - 39.3o - 12.90.06 - 12.80.13 - 1.55o - 7.54O - 9.0425.5 - 53.5I I - 303.6 - 7.1*in % of dry matter without solid fractionIL. Petersen, 1966)TABLE 2. Iron content of rocks, .sediments,'soils and clay minerals.Mineral Fez03 Fe0Magma t i t eGraniteSyeniteDioriteGabbroBasaltSddimentsupper Bunter (clay) .lower Bunter (sand)lower :!uschelkalk (limestone)loesswind blown sandSoils (acc. clay content)Clay mineralsKaoliniteSmec ti teIlliteVermiculiteChlorite1.6 I .n2.7 3.33.2 4.43.2 6.0'5.4 6.44.43.6 o. IO. 71.8o. 2. 0.40.1 - 5O - 302 - 53 - 12o - 15Iron containing minerals in soilsSideritePyrrholinPyriteVivianiteGoethite, LimoniteLepidokroki teHaemat i teMaghemiteMagnetite .Jarosite, cat clayacc. Scheffer and Schachtschabel, 1976

Table 3.Characteristics of sites for estimating iron ochre damage'Danger ofironcloggingColourSurface of Bottom Soilwatervery low free clear colourless free of ochre equal, diffusse ironcolour without 0x1-dation and reductionhor i zon slow sporadic some ochre flakes thin layer of sporadic iron stainsoilyochre flakesmedium wide spread many ochre flakes Ked-brown coloured iron stainsoilysedimentheavy coherent light brown-red distinct ochre iron concretionsoily COlOUK sediment. Ivery heavy . coherent brown-red colour heavy layer of bog iron-oreoily muddy ochre sludge distinct oxidation .& reduction horizonsKuntze and Eggekman, 1968TABLE 4. Iron ochre damaging for tile drains depending on Fe++-contentand pH of the groundwater'ph >7Fe++-content (mg/])pH>7Degree of damagingc0.5 6.0 >9.0 very highKuntze and Eggekman, 1968TABLE 5.Delimination of the soils by the danger of iron ochring from the Fe++-content andpH of the groundwater.Soil (n=)GroundwaterFe++ (mg/l) P"~~~high bog (8) 0.5 (0.3 - 0.7) 4.5 (3.5 - 5.5) noneDanger ofiron clogginglow moor (18) 5.4 (0.2 - 33.5) 6.0 (4.7 - 7.4) low - mediumtransition moor (15) 8.7 (1.8 - 19.3) 4.8 (3.6 - 6.1) medium.- highpeaty soil (31) 8.7 (0.3 - 43.3) 6.2 (4.3 - 7.0) low - highclay pan moor (20) 13.8 (2.1 - 58.5) 6.3 (4.3 - 7.7) high - very high' Kuntze, 1966463

TABLE 6.pH levels of soils needed to prevent deposition of ochre in drains% 2 p ' soil** 4(h) 4-8( 60(H)o - 5 S 5.5 5.0 4.5 4.5 4.0 4.05 - 12 1s 6.0 5.5 5.0 4.5 4.0 4.012 - 17 SL 6.5 6.0 5.5 5.0 4.5 4.017 - 25 L 7.0* 6.5 6.4 5.5 4.5 4.0> 25 L, LT, T 7.0* 7.0 6.0 ' i.5 4.5 4.0* favourable, if additional free CaCO well distributed in the soil, is present forstabilization of soil structure** S = sand sL = sandy loam LT = loamy clayL = loam T = clay LS = loamy sandTABLE 7. kg/ha Fe-total precipitated in the soil (0-140 cm) with differentdrainage and liming*Undrained Drained + Ca0 Drained + Cal Drained + Ca2 Drained + Ca4209 377 354 187 460 590 467 564 730 047 kglha.compared with undrained+I44 810 +I06 403 +I13 337 +375 860 kg/hacompared with unlimedbut drained* Kuntze, 1967TABLE 8. Physical and chemical qualities of soils in the drain trench (1966).cm undersoil surfacePermeability (cmlday)Total pore spaces (vol.%)a b C a b C35 - 4060 - 65 '100 - 10535 - 4060 - 65100 - 10535 - 4060 - 65100 - 10535 - 4060 - 65100 - 10529.9 1.520.1 8.6 10.911.6vol.% macropores (>50p)11.2 3.98.4 6.6 9.63. I%Fe - total3.20 8.073.89 3.11 2.483.79% Ca00.14 0.420.14 0.33 1.5547.5 42.547.6 55.2 46.549.4vol.% macropores (50-lop)4.1 2.52.5 1.7 3.23.7++mg Fe /IO0 g soil18 629 7 4138% CaCO30.891.08at al unlimedbl. refilled soil mixed with lime 125 kg/m3 - 19561cl refilled soil mixed with lime (100 kg/m3 - 1956)4 64

~~~TABLE 9. Permeability of drain filter materials 4-12 yearsafter installation *Filter materialinchlhoursawdust, coarse 15.41fine sand 8.92humic crumb soil, fine sand5. I4sawdust, decomposed 0.40slag with supporting Fe(OH), O. 25sawdust with Fes 0.03humic crumb soil, fine sand with Fes 0.03glass fibre envelope with Fe(OH)30.02*Ford et al., 1968Table IO. Adhesion (g/cm2) of different suspensions at surfaces of materials (brick = 100) *Material Water Artificial ochre Bentonite Bentonitelochre Natural ochrebrick O. 31 5+0.003( 100) O. 423+0.002( 100) O. 405?0.002(100) 0.401 k0.004 (100) O. 369?0.003( 100)ultramid 0.395?0.004(!26) 0.442'0.002(104) 0.429~0.004(106) 0.437t0.002(109) 0.436?0.003(118)PE-hard 0.395?0.004(126) 0.482~0.002(114) 0.475~0.002(117) 0.478+0.004(119) 0.434+0.003(117)PVC-hard 0.370~0.006(117) 0.513?0.003(121) . O.48lkO.OOl(ll9) 0.475+0.002(118) 0.444?0.002(120)PVC-firmed 0.405?0.003(129) 0.529t0.003(125) 0.503?0.003(124) 0.50040.001(125) 0.453?0.002(123)Polystyrol O. 390'0.005(124) 0.556?0.002(l3l) 0.51 7?0.003(128) 0.528?0.002(132) 0.493+0.002( 134)* Kuntze, 1968. TABLE I I . Tractive force of water (g/cm2) within drain pipes of different diameters dependingon slope and degree of filling*Fillingof pipe% slope of pipe0.2 O. 5 I 2 5 IO 20diameter NW 50 m0.1 d 0.0006 0.0015 0.0030 0.'006 0.015 0.030 0.060.2 d 0.0012 0.0030 0.0060 0.012 0.030 0.060 0.120.4 d 0.0021 0.0054 0.0107 0.021 O. 054 0.107 0.211.0 d 0.0025 0.0063 0.0125 0.025 0.063 0.125 0.25diameter NW 100 m0.1 d 0.0012 0.0030 0.006 o. o1 2 O. 030 0.06 '0.120.2 d 0.0024 0.0060 I 0.012 O. 024 0.060 '0.12 0.240.4 d 0.0043 0.0107 0.021 0.043 O. 107 0.21 0.431.0 d 0.0050 0.0125 0.025 0.050 O. 125 0.25 0.50diameter NW I60 m0.1 d 0.002 0.005 0.010 o. o2 0.05 0.10 0.200.2 d 0.004 0.010 o. O20 0.04 o. IO 0.20 0.400.4 d 0.007 0.017 0.034 0.07 O. I7 0.34 0.681.0 d 0.008 0.020 0.040 0.08 0.20 0.40 0.80* Kuntze and Eggelman, 1973465

~TABLE 12.Iron ochre in aerated and unaerated pipes*Place of sampling in Branch drain with Bran$h drain withthe drain pipe free outlet back water outletupper third2.752.12middle third2.230.57lower third I .O6 0.87* Kuntze, 1968TABLE 13.Degree of ochring of drains with free outletand backwater*Place of sampling Branch drain with Branch drain within the drain free outlet backwater outlet 'g lm vol. % glm vol. xupper third 177.3 7.2 177.7 7.4middle third 183.7 7.7 136.2 5.7lower third 68.2 2.9 336.5 14.0average 176.7 7.4 233.4 9.7* Kuntze, 1968TABLE 14. Content of phenols and %O4 of extracts of filter nbterialswith tannin (in g of dry matter)*Mate r ia 1 Phenols mnOU 'high moor peat,slightly decomposedmgwood wool1.02 mgrye straw0.37 mgspruce sawdust0.05 mgoak sawdust1.86 mgMimosa' 51.3 mgTr illo' 53.9 mg59.3 mg73.5 mg95.3 mg49.8 mg110.6 mg1990.0 mg2746.0 mgI* Kuntze and Scheffer, 1974'Wood of the acacia &curreus or A. molissima' Fruit of-the Quercus valonea' 466

TABLE 15:Average silting and ochring degree depending onfilter material*Filter Date ' Dry matter HCI-Fe tinsoluble(glm) kim) (gh)Duo 1x174 67.7 1.9 13.8An tOC 1x174 16.1 1.0 2.5Duo XI76 29.7 4.8 6.0Antoc XI76 31.9 7.8 5.0-* Ochre trial Eokkerm, installed 1972TABLE 16.Demand of time and water consumption (1150 m) with high pressure cleaning of ochreddrain pipesDiameter Type of Slope Degree'ofpipeochring(ca) (a) (b) (a) (b) (a) (a) (b) (gh) (a) (b)I4 3' 93 clay 2'54" 118 0.25 2'42" 107

Group 300Installation methods

~CONTENTS3.013.023.033.04, 3.053.063.073.083.093.103.113.12Technical improvements desired inSwedish agriculture (J.Lundegren)Methods of land drainage in Denmark(V.P. Johansen)General information on subsurfacedrainage in The Netherlands(T.E.J.van Zeijts)Developments in land drainage(W. H. Naarding)Trenchless drainage experiments inDenmark (S.E.Olesen)Comparisons between trenchless andtrenching sub-drainage (R.Eggelsman)Trench versus trenchless-drainagetechniques (W. H .Naarding)Soil disturbance with deep workingfield implements in field drainagesituations (G. Spoor)Trenchless drainage (R.C.Reeve)Drain laying quality survey(Ph.Cros, H.Lechaux and J.Wolsack)A method to predict changes in hydraulicconductivity caused by the trenchless andtraditional drain pipe laying technique(D. Boels)Application of operational research duringthe execution of drainage systems(A.Hagting and F.C.Zuidema)47 147748 151252753654356 157 1590598599470

Paper 3.01TECHNICAL IMPROVEMENTS DESIRED IN SWEDISHLAND DRAINAGEJ. Lundegren,Lantbruksnümden, Skara, Sueden' 'SummaryToday's drainage techniques and desired improvements are discussed.1. IntroductionSwedish agriculture contains about 3 O00 O00 hectares. of cultivated land, distributed amongst about 100 O00 holdings. From an investigation by "The 'National Central Bureau of Statistics" in 1974 we know that 1 018 500 ha aresystematically drained while 1 950 500 ha are not. The investigation alsosays that 300 O00 ha was drained already before 1930 and that 618 500 harequire drainage today (for the first time or anew). We estimate that about1 300 O00 ha can produce successfully without or with sporadical drains..45% area with 'permepblesoils & sporadical drains35% systematidally drainedareaarea drained before 193020% àrea requiringdrainage todayFig. 1.Distribution of Swedens 3 million ha cuZtivated Zand.(Boundary Zines are naturally not sharp.)471i

Yearly 15 O00 - 19 O00 ha are drained in Sweden. We consider that thisis inadequate and we often discuss the need of some kind of stimulus tothese kinds of long lasting investments.Projecting is not compulsory but almost every hectare is still projectedby one of the 24 County Boards of Agriculture. Projecting fee is about150 Skrfha* which means 3-4% of the total land drainage cost. The averagesize of such a plan is nowadays 12,5 ha embracing about 6 700 m mains andlaterals.Drainage costs have developed during the last years almost exactly asthe general inflation in Sweden, which means that land drainage is stillas profitable as before. Of course there is a great cost difference betweendrainage performed with direct-laying special-machines (chain- or weeldiggersand the more expensive method with excavator and manual pipelaying. Averagecosts are now about 5 O00 Skrfha for performance and material, includinglaterals and main pipes up to about 200 mm diameter. (We often use mainpipes bigger than 200 mm but in cost statistics we call those pipes culvertsand not land drains.) ,INDEXtGeneral consumption price index-_- Parmers product price index_______ Land drainage cost index472Fig.2.Drainage costs in Sweden develop almost exactly the same wayas the general inflation.*lo0 Skr = 21,2 USD = 48,8 NLG = 45,5 DEM = 11,l GBP

Pipe material for land drainage was previously tiles from several provincialbrickyards, but today corrugated PVC-pipes dominate clearly. This change hashad a strong influence on the drainage technique and on saving of labour.Three years ago we got a Swedish (and Scandinavian) standard for manufacturingand testing PVC- and PEH-pipes. Swedish standard 3063, 3064.20 O0015 O0010 O001ANNUAL LAND DRAINAGEIN SWEDEN (in ha)1 ............................................ ...................................7..........................................5 ............................O00 -1:::::: ...............................................................................................................................1970 1971 1972 1973 1974 1975 1976Fig.3. During €he last five years Swedish land draining has changedpipe material from tiles to corrugated PVC.2. Today's drainage techniqueLand drainage in Sweden is always performed by special contractors. They areorganized in small companies with one or a few machines each and two or threeworkmen on each machine.About 80% of the land drainage can be done with special machines of differentwheel- or chain types. The remaining 20i of the soils are so stony that wehave to use common excavators and manual pipe laying. There is still no trenchlessmachine in use, except for cable works.Most laterals have 50 m inner diameter and they are layed down 80-100 cm473

deep; 120-140 cm in organic soils. Lateral spacings vary from 12 to 20 m inmoraines and mineral sediments, and from 15 to 40 m in organic and muddysoils. Lateral spacing is determined mainly depending on soil permeabilityand trafficability demands.Nowadays no drainage machine is manufactured in Sweden. From Finland we importa digging-wheel-machine UKKO-MARA built on a Ford 7000/5000 frame. Onthe same frame this factory also builds a chain-digging-machine, MARA 655.From England we import the Dutch designed BARTH K 140 and K 150, both chaindigging machines with caterpillar frames. Recently one K 170 was delivered toSW-Sweden, thus indicating the contractors interest in increasing his capacityand running reliability. From England also comes a HOWARD MKV, and aSwedish designed DRAINER, both chain diggers; and from Norway a diggingwheel-machine,RAADAHL, built on a Muir-Hill-frame.DIGGING TIME (in Po) OF THE TOTAL MACHINE WORKING TIMEIN THE FIELDloo $?80 fDIGGING SPEEC60 %40 %20 %ILength of Zateral drains .10 25 50 1 O0 200 $00 mFig.4. Digging time in percentage of the totaZ machine-workingtime in the fieZd depends on digging speed (2.5-5.0-7.5-10. O m/min)and on average Length of Zateral drains (20-25-50-100-125-200-300 m).FieZd study from county Skaraborg in SW Sweden.474

In one year Swedish contractors buy all together 8-10 new machines, mainlyFinnish MARA and Dutch BARTH. These moderate size machines have shown to berather suitable for Swedish conditions where digging depth normally is varyingbetween 0.80 and 1.25 m, and where the drainage projects are not biggerthan a few thousand metres each. Normally the machine must be transported onthe roads between different projects once or twice a week.For topographical reasons the average length of lateral drains is limitedto about 100 m in Swedish land drainage. Therefore, the machines must movequite often from one position to the next. Danish and Swedish field investigationsshow that the length of laterals has more economical importance thehigher digging capacity the machine has. A high-capacity machine is moreexpensive and must therefore be used more effectively.3. Technical improvementsIt is very expensive today to develop a new drainage machiie and thereforedesign and performance must be adapted more to an international market ratherthan to needs and desires in different countries. Following desires arementioned at first hand with reference to aims and conditions in Swedish landdrainage.The draining season is always limited by our winter climate. The contractorsare urgent to start in early spring (March-April) and continuetill late autumn (November-December). The limited soil trafficabilityin spring and autumn leads to a desire that ground pressure of thedr ina e machine must be limited and preferably not bigger than 30 kPa/Icm .gMany machines already realize that demand while there are still improvementsto do on supplying machines such as gravel hoppers, etc. Ourlimited digging season also brings about a desire that the running reliabilityof the machine should be high enough to permit hard work withlittle demand of repairings.The machine driver is expected to perform a careful output of work 8-10hours per day. It is therefore necessary to offer him good working surroundingsand from this point of view many desires can be drawn up.Permanent vibrations can be irritating and even dangerous to one’shealth. Cold (or hot) weather can be very trying if the machine doesnot havema protecting cab. Many machines only have manual depth regulation.It is in that case to be wished that the sighting line can beset up in a comfortable position and not backwards as to be found onsome machines.475

To get maximum capacity from the projected pipe dimension and to getmaximum length of the drains in hilly fields it is necessary to followthe projected depth and gradient very carefully, with a fast-diggingmachine that claims some kind of automatic depth control. Many differentsystems have been tested. Experience has shown that the rotatinglaser beam gives very good digging results with high security. Thissystem is therefore superior to but also much more expensive than othersystems. However, with a well-working laser system it is proved thata three-man contractor team can be reduced to a two-man team withoutcapacity losses if you use chain- or wheel diggers with direct-layingof corrugated PVC- or PEH-pipes. On the other hand, if you already havea two-man team you can increase the digging capacity by about 25% or300 m per day when using automatic laser-plane control. Thus an expensiveequipment can still be profitable, and also give a better result.In Swedish soils it is very urgent to arrange a permeable backfillaround the pipe. Normally gravel or coarse sawdust to a level of 2-10 cmabove the pipe is used for that purpose. It is a desire, therefore, thatthe digging chain or wheel leaves a clean bottom of the ditch,also whenthe field is ploughed or harrowed. We have noticed that many importedmachines for that purpose must be completed and reconstructed with soilploughsor similar equipment. It is a desire that this problem should bepayed more attention to, already in design and manufacturing.4. Trenchless drainingTrenchless draining is not yet tested in Sweden. A few contractors haveshown some interest in buying such machines, but after discussions and in-vestigations of the prospects they have declined.We must remember that trenchless machines are very expensive and that theaverage size of our drainage projects is not bigger than about 5,000 m each.We also think that it can be difficult to supply the machine continuously wit3those quantities of filter material (over 1 m per 100 m) we need. Finally,in certain regions re-draining already constitutes up to 50% of all drainingprojects. In re-draining it is often necessary to connect old drains with thenew system and you can do that only when you know where the old drains are.We think that it might be difficult to observe those old drains with thetrenchless technique, as well as to observe all different types of cablesthere are in an agriculture province.We are, in spite of all desires mentioned here, still tempted to say that weare rather satisfied with the drainage technique we use today. We think thatin the single case drainage results (effect, and length of life) today aremore depending on the contractor team and the working conditions, than onthe drainage machines.476

Paper 3.02.METHODS OF LAND DRAINAGE IN DENMARKV.P. JohansA .Danish Land Development Service,HjuZtorvet, Denmark.SummaryThe methods of land drainage, covering materials, and soil mechanics arediscussed briefly below.IntroductionThe methods of land drainage in Denmark are not very advanced in the technicalrespect. During the last 10 years the trenching has been done mainly bymeans of different kinds of back-acting excavators. The subsequent installationof pipes and application of covering materials is done by hand. About90 per cent-of the drainage is carried out in this way (Table I ) .Approximately 4 per cent of the total drainage i5,OOO halyear), i.e. 200 ha,has been done by means of continuous excavating drainage machines with trenchingchain during the last 2-3 years. Application of covering materials directlyon the pipes is possible immediately after placing of the pipes in theditch. This type of drainage machine performs a good quality of work withtile pipes-and with plastic pipes as well, and should be an alternative inthe future land drainage in Denmark. However, because of a very fluctuatingrate of drainage, the contractors are not very happy to'invest in such machinerywithout alternative utilization possibilities.Another problem is the size of the different fields - many of the drainedfields were only 1-3 ha, which is not sufficient to cover the cost of transportationof the machinery.477

TABLE 1.' DRAINAGE METHODS IN DENMARK(rounded figures)YEAR19791971197219731974117519761977AREAHA5001)6000500040034500600955034590d9496958486879386?YNGLFL.HAIN-TRENCHER64774 '34ITRENCHLESSPCT IIThe method of trenchless pipe drainage has been applied for 4-10 per cent ofthe total drainage during the last 5 years, mainly by use of unwrapped, corrugatedplastic pipes. The result differs from place to place, but in largerfields with uncomplicated soils it seems to be a useful alternative becauseof the low costs.Covering materialsParticularly in the western part of Denmark the soil conditions are very difficultin view of pipe drainage (post-glacial soil.) and a very careful coveringof the main part of the pipes is absolutely necessary.Sawdust from conife.rous trees is commonly used as covering

!IATER I ALFILTERINGQUALITYINCREASE INPERMEABILITYCOVERING MATERIALS:TOP SOILSAW DUST +SPHAGNUM +SAND-GRAVEL +II++++IPREWRAPPED MATERIALS:S P HAG NUMCOCONUT FIBRESTRA~ANTOCFIBERTEX '++iISphagnum, coconut fibre, and antoc are used onlyto a very small extent in practiceTo some extent gravel is used as cover material, but compared with sawdustit is quite heavy, and the manual application into the trench is quite expensive.The cost of both materials is almost the same.To prevent fine particles to enter into the drain from below, a tissue called"Fibertex", is often applied as a filter underneath the pipes, with forexample sawdust covering the pipes. By this combination a very effective anddurable filter is obtained, and the method is useful for drainage work byexcavators with manual pipe installation and for the chain-trench machines aswell, but not for trenchless drainage.In certain areas there is a very heavy precipitation of iron compounds, ochre,in and around the drain pipes. This sometimes causes complete clogging of thepipes. In such areas always 8 or 10 cm pipes are used in the lateral drains.Besides tile pipes, plastic pipes with large perforations 2-3 mm are used.479

Soil mechanicsBy using back-acting excavators and to some extent chain-trench machines,the replacement of loose soil material increases the permeability of thesoil around the pipe.The method of trenchless drainage may cause some compaction of the soilaround the drain. Experiments in Denmark have shown a lower drainage effectcompared to the excavating method, especially when the drainage is carriedout under wet soil conditions in loamy soil. However, the difference ineffect seems to decrease after a few years..4 80

I1 Paper 3.031 GENERAL INFORMATION ON SUBSURFACE DRAINAGEIN THE NETHERLANDST.E.J. van ZeijtsI Government Service for Land and Water Use,1Utrecht, The NetherZands,ISummaryA review is given on geographic conditions, the present state of drainageand the various projects in which drainage plays a role.1. IntroductionThis paper aims at providing some general information on subsurface drainagein the Netherlands for participants of the Drainage Workshop from abroad. Itis also intended to supply some background information for the discussionnotes of the Dutch participants, in which specific aspects of subsurfacedrainageresearch will be considered.The term subsurface-drainage means the lowering of groundwater level by meansof horizontal, closed drainage systems. Other methods of drainage - for example(deep) draining by wells or drainage by ditches - will hardly be mentioned.Drainage of excess water to the sea by watercourses, streams, riversand canals will not be considered, nor will water supply by means of infiltration.On the whole, the subject is approached with agricultural applications inmind. Applications in horticulture - for example in greenhouses - w ill notbe considered.48 1

2. Conditions.' 2.1ClimateThe Netherlands lie in the temperate climate zone (51 to 53,5 ON) and havean oceanic climate. The daily air temperature averages are lowest in January(+1,7 OC) and highest in July (+17,0 OC).The annual averages for the total amounts of precipitation and evaporation -measured on an area of open water - are 765 m and 691 mm,respectively. Theprecipitation is rather evenly distributed throughout the year, while evaporationreaches a peak in the summer. The graph of Fig.1, which is drawn onthe basis of a normal annual average, shows that in the period from April toAugust there is excess evaporation (203 m in total) and in the period fromSeptember to March excess precipitation (277 mm in total).Fig.1. Trend of the average amount of precipitation andevaporation per month (De Bilt 1931-1960, KIVMI).2.2 Topography2The area of The Netherlands is. about 41 O00 km (4 100 O00 ha) of which 61nper cent, or about 25 O00 km' (2 500 O00 ha), is farmland. Of the total area4 82

about 27 per cent - protected by dikes and dunes - is below the averagesea level; 71 per cent lies between O and 50 m above sea level, while only2 per cent is higher than that. The lowest point, 7 m below sea level, isin the west of the country, and the highest point is 321 m above sea levelin the extreme south.Because the country is so low the groundwater level is usually found at alimited depth below ground level. Table 1 shows this.TABLE I .Percentages of the agricultural area in the differentwater-table classesWaterlevel in m below surfaceWater-table %classes mean highest mean lowestI< 0,20< 0,501I1< 0,250,50 - 0,80I II10,25 - 0,400,50 - 0,801I11< 0,400,80 - 1,2014I110,30 - 0,500,80 - 1,205IV0,40 - 0,800,80 - 1,205V< 0,40> 1,2018V0,30 - 0,50> 1,209VI0,40 - 0,80> 1,2026VI1> 0,80> 1,608VI1> 1,20> 2,oo2From this table it appears that the depth of the groundwater in the winteron 90% of the farmland is less than 1 meter. As a consequence of too highgroundwater levels there is more than 10% yield’reduction in at least 40%of the grassland area and 20% of the arable area.483

,ITABLE 2.Average area of topographical plots‘Iassified < 1,0 ha 1,O-1,5 ha 1,5-2,5 ha 2,5-4,0 ha > 4,O haplot area*Percentage 8 28 40 13 I I* Plots are averaged per municïpalityThis table shows that on the whole the plot size in the Netherlands is rathsmall; 76 per cent of the farmland is situated in municipalities with an avrage plot size of less than 2,5 ha. As the plot size in arable areas shouldbe at least 7,5 ha and in grassland areas at least 3 ha, the existing plotsize is unsatisfactory for good agricultural exploitation.In view of the small plots and the number of ditches surrounding them, therare obviously a great many ditches in The Netherlands (Photo 1). The waterlevels in these ditches vary depending on the season and the level controlin the areas concerned. Table 3 gives an impression of the water levelsthat often occur. The data in this Table are estimates and are not basedon an accurate survey.TABLE 3.Depth of ditch-water levels in m below ground levelAreas in summer in winterclay soils 0,75 - 1,50 1,OO - 1,50low-land peat soils 0,25 - 1,OO 0,25 - 1,OOsandy soils 0,50 - 1,25* 0,50 - 1,25* Ditches and watercourses situated in sandy areas often contain nowater in the smer, because the grounhater level has dropped belowthe bottom of the ditch with no possibility of a water supply.2 -3: SoilsThe soils in the Netherlands are rather varied as can be seen from theralized soil map of the Netherlands on Fig. 2. Not all the features onmap are important for subsurface-drainage. The main ones can be summarin the following four groups:gene.thiszed484

I1. the marine loamy soils, in the north and south-west;2. the loamy and clayey fluviatile soils, in the centre;3.the low-land peat soils,: in the west and north-west of theIJssel Lake;4. the sandy soils in the east and south.Before describing these 4 groups-in more detail let us make the followingcomments.The materials, in the top layer of mineral soils, have almost alwaysbeen transported by wind, water or glaciers. Soil weathered from solitrock is only found in the south-east of the country. The material depositedby wind can be found in the Holocene coastal and inland dunesand in the Pleistocene sand and loess; the material deposited by wateis either of Holocene marine origin or of Holocene fluviatile origin;the material of glacial origin is either glacial till or boulder claymainly found in the north of the country.,Nearly all the soils are'easily workable; in other words, there is noserious mechanical resistance when'digging the trenches. This is justas true for trenchless subsurface-drainage. One exception'is the heav:river-clay soil (the clayey part of the fluviatile area) when it is e:tremely dry.I 'It has already been mentioned that many of the cultivated soils are t cwet. All cultivated soils are, to a certain extent, supplied with adrainage system. This means that for many months of the year the areahas sufficient bearing capacity for the mechanical installation of thedrainage pipes. However arable areas in particular are not drained duringthe growing season. The danger exists, therefore, that the subsurface-drainagesystem is constructed at a time when the groundwaterlevels are too high, which can seriously affect the quality of thesubsurface-drainage.4 86

1. Marine soilsThe clay content of these soils varies from 8 tot 40 per cent. The soil isoften stratified and the clay content decreases with depth. Sea-clay soilsare naturally calcareous but the older soils are usually only slightly calcareousin the top soil.The permeability factor (K) of these soils is usually between 0,05 and 0,50m/d. Greater permeability occurs, for example, in the Lake Yssel Polders(0,50 to 5,O m/d), while there are lower permeabilities in the heavy non-calcareousclay soils. Most of the sea-clay soils are used for arable farming.2. Fluviatile soilsThese soils are usually calcareous and of loamy texture; the deeper subsoilsare coarse in texture, as far as they are situated on the natural banks ofthe rivers. These soils are about 1 m higher than the general level of thefloodplain. Because of this relative elevation and permeability of the subsoil,these soils need hardly any subsurface-drainage.ISoils situated in the backswamps are about 0.5 m below the general level ofthe floodplain. These' soils are always non-calcareous and clayey, both inthe topsoil and in the subsoil. The subsoils are cracked locally and thenhave a high permeability ( 1 tot 5 m/d). If their permeability is low, theyhave an open drainage system of furrows; the other soils can be subsurfacedrained.The first-mentioned fluviatile soils are used as arable land, orchards andgrassland; the other soils are used as grassland and locally some willowcoppice.3. The Zpw-land peat soilsThe peat varies greatly depending on its origin. The Holocene peat lies on aPleistocene sand layer and varies in thickness from < 1 m (especially in thenorth) to > 10 m (especially in the west). The peat layer is often coveredby a-thin clay layer, which largely determines the suitability of the soil.The permeability factor of the peat ranges from 0,05 to 2,50 m/d. Thesesoils are used almost exclusively as grassland.487

4. Sandy soilsThe sandy soils mainly consist of fine sand (diameter of the sand grains IO!to 210 pm). The percentage of silt (2 to 50 pm) is predominantly lower than20 per cent and the percentage of organic matter in the plough layer usual11varies from 3 to 7 per cent. The permeability factor of these soils usuallyranges from 0,05 to 2,50 m/d and decreases as the silt content increases.In the north of the country, glacial till is often found at a shallow depththis poorly permeable, medium-textured material determines drain space. Saddy soils are suitable for both arable land and grassland, but are mainlyused as grassland.2.4 Land useThe Netherlands, with a population density of more than 400 inhabitants per,square kilometre, is one of the most densely populated countries in the worlThe demand for land, for various purposes, is therefore great. Apart from tineed for agricultural land, a great deal is also needed for town planning,road building, establishment of industry, nature conservation, open country-sides and outdoor recreation.This great demand has led to high land prices and to the necessity of makingthe available land area as suitable as possible for the purposes concerned.The Government plays an important role here both in town and country planniras well as in land development.The shortage of agricultural land has led to an intensive use of the soil.Table 4 gives some data to illustrate this.TABLE 4.Some data on the intensive use of soilDescriptionDataPrice of average good free-. hold farmlandFarm animalsf 2,50 to f 5,OO2 to 3 per haAverage yielda) potatoes 40 ton per hab) sugarbeets 55 ton per haper m2488

In order to make this possible, optimum planning of the farmland is essen-tial. Together with other land development schemes, such as plot enlargemeithe introduction or renewal of subsurface drainage is also important.3. Present state of affairs3.1 Drainage requirementsFor many years The Netherlands were drained by ditches. Since the middle o.the last century, subsurface-drainage has gradually become more important.The poor control of the water levels in the ditches and watercourses, intowhich the subsurface drains flowed, was a particularly serious problem. Thrimprovement in this level control and the installation of subsurface drainagemust be coordinated. The extent of subsurface-drainage in agriculturalland, according to the situation in 1977, is shown roughly on the map reproducedon Fig.3. This map shows that most of the drainage is found in thcsea-clay soits-of-the north and south-west of The Netherlands. The remainirmore widely dispersed, intensively drained areas are situated in reclaimedlakes and land consolidation schemes already completed. An accurate prognosisof the area requiring drainage is difficult. It depends on the folloting factors:a) the costs/benefit ratio for the intallation or renewal of subsurfacedrainage;b) the degree to which the installation of subsurface-drainage beconpossible through other measures, such as *lowering the waterlevels in the ditches and enlarging the plots by filling inthe ditches.'Roughly estimated, subsurface-drainage must be introduced or replaced in ar2other 5 O00 km (500 O00 ha). If the annual area of subsurface-drainage ofabout 25 O00 ha remains unaltered, then, on the basis of this prognosis, SLsurface-drainage must continue to be-installed for another 20 years. Fig.4gives a general impression of the situations where drainage pipes still ha\to be introduced or renewed'.490

When both maps are compared it can be seen that the most intensive subsurfatdrainage in the future will have to be laid in those ar,eas where there is aready a great deal of subsurface-drainage. Replacement of existing subsurfaldrainage is essential. The introduction of new subsurface-drainage must beexpected particularly in the north and west of the country. These are mainl:the upland reclaimed peat areas (Veenkoloniën) and the low-land peat soilswith or without a clay cover (O. 1 to > 1 m). The installation of new subsurface-drainagein the river-clay areas and in sandy soils is expected toa lesser extent.It is essential to note that both maps are based on average data for largeareas. This results in strong deviations in detail. The large areas where,according to the prognosis, less than IO per cent of the area requires subsurface-drainage,must not be ignored when determining the total area forsubsurface-drainage.3.2 System and criteriaIn The Netherlands, the singular system is used almost exclusively. The lattrals, the lengths of which are usually 150 to 250 my flow by means of outleiinto ditches or watercourses. The depth at which the drains are laid varyfrom 1,OOm to 1,30 my while the slope is usually 1:lOOO.' The design criteria for agricultural subsurface-drainage which have alwaysbeen handled by the Government Service for Land and Water Use are formulatecas follows. With continuous drainage of 7 mm/d, the difference in height be-tween the groundwater level and the ground level may not be less than:a) for arable land 0,50 mb) for grassland 0,30 mThe norm used for the Lake IJssel Polders is a height difference of 0,30 mwith a drainage of 10 mm per day. The distances between the drains, deter-mined on the basis of the criteria vary in general:. *492for' sea-clay soilsfor river-clay soilsfor low-land peat soilsfor sandy soilsfrom IO to 20 mfrom O to 20 mfrom O to 30 m .from 5 to 30 m

~ Cover3.3 MaterialsThe pipesj'A summary of the various pipes used in The 'Netherlands since 1958 is givenin Fig.5. Until about 1960 only clay tiles were used. The specifications forthese pipes are described in NEN 440. The usual internal diameter was 50 mm.Between 1960 and 1970, slotted smooth PVC pipes were used, usually with externaldiameters of 40 mm and 50 mm (NEN 7010). The most important advantageof this pipe, compared with the clay tile,was that the transport and installationcosts were much lower. In about 1968, corrugated perforated PVC drainagepipes appeared. This material took over practically the whole marketwithin five years. The reasons being that:corrugated pipes performed equally well as clay tilesthe material was cheap, labour saving and allowed a greaterdriving speed for mechanized draining.and envelope materialsCover and envelope materials are usually applied for two reasons:to stimulate the flow of groundwater to the pipeto prevent infiltration of residual soil particlesinto the pipes.Loose organic materials, mainly peat-fibre and to-a lesser extent heather andstraw were used in the past. After a transitional period, during which stripsof organic materials were used, the complete enveloping of the pipes is nowpractised almost exclusively.Table 5 gives the average use of cover and envelope materials in land con-solidations from 1973 to 1977. The use of material outside the land conso-lidations is comparable.! 493

TABLE 5.Application of drain cover and envelope materialsin land consolidations from 1973 to 1977Cover and envelope materialsPercentage of the lengthpeat-f ibre . 9flax 3coconut-f ibre 73f ibreglassIOother

3.4 MachinesSubsurface-drainage in The Netherlands was, until about 1955, installed exclusivelyby hand. Since then and within only a few years, machines havecompletely taken over and many technical improvements have since been madeto these specific draining machines, greatly improving their productivity.This development is illustrate'd in Table 6.TABLE 6.Developments in draining machinesFeatures 1955 1977engine power per machine ca 35 kW ca 150 kW(ca 45 hp)(ca 200 hp)number of laboures permachine ca I I 3 or 4capacity per week per machine5 to 71 km 15 tot 25 kmWith these developments the technical possibilities of draining machinesavailable in The Netherlands greatly depends on the year they were built(Photo 4 and 5). A few features of the modern trenchers are:a) complete traction on tracks (hydrostatically driven);b) engine power 125 to 175 kW (170 to 235 hp);c)d)e).f)excavator chain (usually semi-vertical, mechanically driven);working depth of excavator chain for Dutch conditionsto about 1,80 m;hydrostatic adjustment of the excavation depth;depth regulation by means of a rotating laser beam.Only a few drains have been laid by trenchless machines (Photo 6) becausestudies have shown that such drains - with the exception of those in sandysoils - are not as effective as those laid by trenchers. These remarks do noapply to the Willner trenchless machine which is a favourable exception(Photo 7). A rough estimate shows that about 75 trenchers are used by about40 specialized Dutch drainage-firms.496

3.5 costsAn estimate of the costs of subsurface-drainage is given in Tables 7 and 8.Table 7; Costs of subsurface-drainage in f per m in 1977Ma ter ia1Work ca 10% of Totalpipes envelope cost 3 and 41 2 3 4 5 6 =.4 + 5diameter none 0,70 0,60 O, 15 I ,4560 mmcoconutfibre1,15. 0,60 o, 20 1,95peat-fibre I ,40 0,60 o, 20 2,20glassfibre 0,90 0,60 O, 15 1,65diameter none I ,25 O, 60 o, 20 2,0580 mmcoconutfibreI ,95 .0,60 O, 25 2,80peat-fibre 2,45 0,60 0,30 3,35glassfibre I ,50 0,60 o, 20 2,30Included in the costs are:delivery of the material;execution of the work without any help fr'om the client;overheads such as the contractor's costs for administrative andexecutive personnel, profit and risks; these costs are calculatedas a percentage of the costs of materials and labour.Not included are the costs for:fittings such as outlets (ca f 0,05/m drain);costs of drawing-up the plan and supervision costs(varying from O to 20 per cent);value-added tax (usually 18 per cent, sometimespartially 4 per cent).Table 8 gives an approximation of costs for the much-used.60 mm corrugatedPVC pipes.497

~~TABLE 8. Costs of .subsurface-drainage in f per ha in 1977,with a drain diameter of 60 mmEnvelope Costs per Distance between drains in mmaterialmIO 20 30length of drains in ”perha900 450 3001 2 3 4 5none 1,85 1 665 835 555coconut-fibre 2,45 2 205 I 105 735turf-fibre 2,75 2 475 I 240 825glassfibre 2,lO I 890 945 630The costs in Table 8 are based on the prices given in Table 7, increased byf 0,05 per m’ for fittings, by 10% for the costs of drawing-up the plansand for supervision and by ,an average of’ 12% for value-added tax.4. Agricultural applications4.1 .FarmingMost of the subsurface-drainage workeither owners or users of agricultural land. The scale of operations isusually small; most of the orders are for 3 to. 10 ha. The agreement procedurbetween the client and the drainage contractor is straightforward and usual1follows this pattern:the drainage contractor estimates the costs;in The Netherlands is commissioned bywhen the contractor and the ‘client have reached an agreement,it is confirmed in writing;after the work has been completed the agreed amount is paid.A variation on this procedure and one which occurs rather often, is when anengineering bureau, specializing in land development plays an intermediaryrole. Since 1975 ,a Government policy has existed to help with the costs ofprivate land development; this also includes subsurface-drainage. The498,

Government subsidies amount to 30 per cent of the costs and are granted bythe Government Service for Land and Water Use.4.2 Land developmentLand development in The Netherlands means either developing or improvingrural areas for new or existing land uses. At present there are several formsof land development either in preparation or actually in operation. The mostimportant operational form is that of land consolidation. The aims of landconsolidations vary from area to area, but are mainly the following:to increase the accessibility of rural areas by building or improvingcountr? roads;to improve water management by introducing or improving watercourses,weirs, pumping plants, etc.;to improve parcelling by re-allocating plots and shiftingfarm buildings ;to protect and restore the countryside by planting and conservingtrees and shrubs;nature conservation by, for example, transferring land ownershipto the Government or to a nature conservation society;to provide facilities for outdoor recreation..A land consolidation project is prepared by representatives of the area concernedin conjunction with the Government Service for Land and Water Use.The owners and tenants decide on a land consolidation scheme by vote.The work for a land development scheme is done by contractors and. the projec:is directed by land development engineering bureaus; the Government Servicefor Land and Water Use has the general supervision and pays the costs.The average costs of a land consolidation scheme are about f 5 O00 to f 6 O01per 'ha. About two-thirds of these costs are covered by the Government. Therest is temporarily financed by the Government but must be paid back by theowners,within 26 years after the transaction.499

Together with these improvements in water management and parcellation, superfluousditches can be filled up and other ditches and watercourses areei'ther enlarged or introduced. Subsurface drainage is also often introducedat the same time. A specific problem, however, is that the subsurface-drainageworks and land division works can hamper each other. It is then inevitablethat the old drainage system is eliminated by filling in the ditches,before the new subsurface-drainage is installed. In the intervening period,however, there is no drainage system at all and with heavy rain seriousdamage and delay could occur.This risk is kept to a minimum by:, a) working as much as possible in summer;b) giving all the responsibility to one contractor, thusensuring the smooth running of the work.One disadvantage is that a great deal of compensation must be given to thefarmers if they are not able to use their land during the growing season.4.3 Land .reclamationSeveral polders are being formed in Cake IJssel which, after draining, areparcelled by the IJsselmeerpolders Development Authority. In this land di-vision the following points regarding groundwater control are considered.1. The number of,ditches is kept to a minimum.2. The subsurface-drainage system is singuiar.'In the last few years, this has led to plots with a length of about 1300 mand a width of about 500 m; the length of the subsurface-drains being about250 m. One special aspect of draining in the Lake IJssel Polders is thatthe soils mature after they have been drained. In the course of maturingthe drained soil cracks by shrinkage above the groundwater level. Becausethese cracks are permanent, they improve permeability. This permeabilitylargely depends on the 'texture of the soil. The plan for subsurface,drainage500

is drawn-up in accordance with a standardization of the soil profile andusing results obtained from experimental plots with varying drain distancesand drainage materials.5. Non-agricultural applicationsNon-agricultural-applications will be discussed only briefly. This will bedone in such a way that the more interested reader can find some guidefor closer orientation.5.1 Outdoor recreationWhen planning those areas that are going to be used for outdoor recreationin one form or other, the lowering of the groundwater level is often justas important as in agricultural areas.Design standards used in the application of subsurface-drainage are givenin Table 9.TABLE 9.Drainage criteria for outdoor recreation sitesPurposeAmount of waterwhich has to becontinuallydrained(mm/d)Permissible minimumdrainage depth (heightdifference betweenground level and groundwaterlevel)(m)Playing-f ields 15 0,5Lawns for ballgames 15 0,5Camping sites IO 0,sPleasure parks 7 0,3 to 0,4and playgroundsBesides, measures must be taken to prevent water stagnation on the field orin the top layer. There are no general standards for this in The Netherlands.As the use becomes more intensive, more measures will.be adopted.*'50 1

Humus-deficient and silt-deficient sand in thicknesses of 0,05 to 0,20 m isdeposited over the toplayer to store the water temporarily during and directlyafter heavy rain.Where the permeability of the subsoil is poor and cannot be improved thesandy top layer is brought into contact with the subsurface-drainage by fillingthe drainage trenches with easily permeable material (usually coarsesand). This ensures that water, which could stagnate on the poorly permeablesubsoil, can flow to the drainage trench via the top layer (Photo 8).In general there are no important differences in material and work comparedto agricultural applications of subsurface-drainage.5.2 Construction of roadsSubsurface-drainage is applied under three different circumstances in roadbuilding. These are: lowering the groundwater level; preventing perchedgroundwater tables; draining surface water.a) Lowering the groundwater levelSand is usually used for improving the subsoil and for raising the road-bed.In order to obtain a subsoil with a satisfactory bearing capacity, thegroundwater level must be sufficiently deep beneath the hardsurface. Forvery intensively used roads this is at least 0,80 m. Ditches or subsurfacedrainsare used here.b) Preventing perched groundwater tablesbThe most frequently occurring form is the stagnation of water on the bottomof the sand-bed. By installing, along the road, one or more subsurface dsainsinto this sand-bed, these perched groundwater tables can be prevented quiteeasily (Fig.6).502

The drainage of surface water is not discussed because subsurface drainagefor this reason is only applied in The Netherlands in exceptional cases.i5.3 Town planningNew urban and industrial areas are'often built in places with groundwaterlevels that are too high and with soils that have insufficient bearing capacity.From 1950 to 1970, such sites were usually made more suitable by applying2 to 5 m sand. This sand is usually taken from the subsoil elsewhere andto the site.through pipelines by sand pump dredgers. Because this methodwas very expensive, another solution was needed. This was found by loweringthe groundwater level by subsurface drainage. Raising with sand is nowadaysonly necessary to achieve a subsoil with a high enough bearing capacity, inorderato make construction work possible. The required thickness of the layercan now be reduced to about 1 m. A serious problem here is however that constructionwork'; for example pile-driving for foundations and sewage work,disturbs the subsurface drainage. Additional subsurface drainage installedafter completion of the work is expensive.The IJsselmeerpolders Development Authority has developed a solution thathas recently been used in the area being prepared for the construction503

of the new town of Almere in the Lake Yssel Polders. It consists of an interlockingdrainage system. After the first drainage system has been laidat a depth of 2 to 2,5 m below the future ground level, a second system,perpendicular to the first, is laid about 0,2 m higher. Because a layer ofwell permeable material (lavaliet) is put about the pipes in both systems,they are linked to each other at the points of intersection. The fact thatsome disturbances occur with this system is accepted, but with the intersectingnetwork, drainage is almost always possible (Fig.7).o 60 5 4mmrrn *?- IFig. 7. Interlocking drainage system in AZmere.Deep drainage should be mentioned as an exceptional form of-subsurface drainage.This technique, in which the drains can be accurately' laid at a depthof 4 to 4,5 m, uses chain trenchers fitted with a shaft behind the excavatorchain. By means of this shaft the flexible pipe can be directed to the bot-'tom of the trench. This technique is used for example in draining the sandraisedsites.Another application is the temporary lowering of groundwater levels, especiallywhen laying underground pipelines for the transport of liquids andgasses. Subsurface drainage, which will be linked up with a pumping installation;is first placed'below the level of the pipelines. Since accuracy inlaying is less important here, depths of 5 to 7 m can be reached.504

Ii,Vertical drainage is used in the west of The Netherlands for urban developmentschemes and construction of roads, when situated on strongly compressiblesubsoils such as an clay-peat layers. This method of drainage speedsup the settling process and therefore ensures that settling after buildingremains limited.If a strongly compressible subsoil is overloaded, for example with a sandlayer for a building ground, then settling will occur. Settling means thatthe volume of pores must decrease. If the pores are saturated with water,it hampers the volume-decrease of the pores. It is only if the water canflow away that settling occurs. Because the pores are very small (permeabilityis low) and the relative distance that the water in the pores must coveris great, drainage and settling will be very slow.This flow can be improved by connecting the water in the layer verticallywith the surface and with the easily permeable sandy subsoil. By using adrill-jet, these connections can be achieved by drilling a hole in the layerand then filling it with easily permeable sand. These sand-drains, with adiameter of 0,2 to 0,3 m are laid 2,5 to 3,5 m apart in a pattern of equilateraltriangles.For a few years, synthetic materials have also been used for this verticaldrainage in The Netherlands. A strip of synthetic material is placed in thelayer and the water forces its way into the strip and flows up or down thelength of the strip.6. Institutions involved in the researchThe following sections summarize the most important institutions involvedin drainage research and their activities.Ministry of Agriculture and Fisheriesa) The Government Service for Land and Water Use in Utrecht is involvedin subsurface drainage, through its connection with the preparationand supervision of land development projects. Its work on subsurfacedrainage is mainly in planning and judging plans made by others. Scientificresearch is also supported by field trials.505

The Institute for Land and Water Management Research in Wageningen,which is closely associated with the Government Service for Land andWater Use, studies, land development, water management, water qualityand soil improvement.The International Institute for Land Reclamation and Improvement inWageningen is active in scientific research, education and researchprojects for developing countries. Subsurface drainage is one of thesubjects dealt with.The mutual interests in subsurface drainage of the institutions mentioned,are discussed'in the Drainage Contact Group.d) The Agricultural University of Wageningen. Drainage is part of thecurriculum and research programme of the Department of Land and WaterManagement:.Ministry of Transport and Public WorksThe IJsselmeerpolders Development Authority in Lelystad is responsible forthe preparation and planning of the Lake IJssel Polders and a few other newareas.This body is active in scientific research and in the planning and executionof projects including subsurface drainage. The Authority has experience bothin agricultural and urban drainage.Trade and Industrya) For general research into subsurface drainage, the major engineeringbureaus dealing with land development are the following:Grontmij in De BiltHeidemij in ArnhemTheir main work is preparation of projects and research necessaryfor the execution of the projects and supervision of the work doneby contractors.All these institutions maintain informal contact in the Drainage StudyGroup.506

Trade and Industry are active in research and development of drainmachines and drainage materials. This research is usually done byprivate industry.The KOMO Institute in Rijswijk is an establishment for research, standardizationand inspection of materials and constructions. This Instituteis involved with the following activities concerning subsurfacedrainage.I. Deciding the specifications for drainage materials. This is donein consultation with trade and industry and various Government services.These specifications are published in the form of Dutch Standards papers(NEN) by the Dutch Standardization Institute. They are included afterinternational consultation on specifications.11. The granting of a quality guarantee mark to factories, whoseproduction processes are continuous tested by the KOMO Institute.111. The inspection of materials.Ref erences.Information and Documentation Centre for the geography of The Netherlands.1974. A compact geography of The Netherlands. Utrecht (German, French,English).GEODERMA. 1970. Soil survey research in The Netherlands. Vol. 4, No. 3,September, Special Issue (English).NMRDING, W.H. 1977. Developments in land drainage. Reprint of "CultuurtechnischTijdschrift" (April/May Issue). Government Service for Land andWater Use, Utrecht (English).NAARDING, W.H. 1977. A review on international experience with trenchlessversus trenching drainage. Mededeling Nr. 121, Cultuurtechnische DienstUtrecht (English).KNOPS, J.A.C. and F.C. ZUIDEMA. 1977. Guidelines for the selection of envelopematerials for subsurface drains. Reprint of "CultuurtechnischTijdschrift" (April/May Issue) (English).GLOPPER, R.J.de and W.A. SEGEREN. 1971. The Lake IJssel Reclamation project.Endeavour V01.30, No.110, May.VAN DER KANT, N.F. and S. SPANJER. 1977. Operational aspects of subsurface ,drainage in the Lake IJssel Polders in The Netherlands. IJsselmeerpoldersDevelopment Authority.DE BAKKER, H. 1978. Major soils and soil regions in The Netherlands. Junk-The Hague/Pudoc, Wageningen.507

Paper 3.04DEVELOPMENTS IN LAND DRAINAGEW.H. NaardingGovernment Service for Land andWater Use, Utrecht,The Netherlands .SummaryThe change from clay to smooth plastic and then to corrugated P.V.C. pipesgreatly reduced the labour required and the cost of transport on the site,and advanced mechanization, technical developments in cover and envelopematerials also did much to further mechanization and rationalize drainage.As a result of these factors, drainage has been mechanized to such a degreethat it requires a minimum labour force.Developments in the field of automatic depth regulation systems have alsocontributed to this process.Because of the increased mechanization and rationalization of agriculture,the need for drainage has risen sharply, but drainage maintenance in someplaces is far from satisfactory; it is most essential that instructionshould be provided with regard to maintenance.1. IntroductionIn the course of water control board, land consolidation and reclamationworks, land drainage has been - and is being - improved in large areas ofThe Netherlands. As a result of improved land drainage, land consolidationand reclamation, large areas of agricultural land are being drained. Sincen1967 about 20,000 hectares (200 kmL) per year have been provided with aland drainage system. In 1975 interest was aroused in the private sectorby the possibility of grants for private civil engineering projects. Thelaying of pipes, like other civil engineering activities, has been trans-formed in the past 20 years from a manual to a fully mechanized operation.The range of materials has undergone a similarly swift transformation. Be-512

fore 1956 practically all pipes were made of vitrified clay. In that yearthe first tests were carried out with plastic pipes.The replacement since 1961 of loose peat fibre by new cover and envelope materialshas also brought about vast changes. This ready acceptance of newpossibilities obviously means that practical application often outstrips research.This, however, may easily produce disappointing results, and indeedhas done so in some cases. Laboratory research must concentrate in thefuture on making a sound pre-selection of those materials that are suitablefor practical use. When drainage networks were installed in areas that usedto be drained piecemeal by ditches and drainage ditches, sufficient attentionwas not always paid to providing instruction about drainage maintenanceConsequently the functioning of the drains in these areas sometimes gaverise to dissatisfaction.2. Drainage pipesUp to 1956, as we have said, practically all the pipes used were collarlessand collared clay pipes and, these were in short supply, concrete pipes. Incollaboration with the Heidemaatschappij, field research was carried out inthat year with smooth plastic pipes. Of this development Van Someren wrote(Med. No.4 CD, 1959):"It looks as though smooth plastic pipes of the specificationsand perforation now in use do not, to say the least, functionLess well than the clay pipes. Their drainage qualities are notthe only important factor, however. As regards installationcosts, too, the smooth plastic pipe opens up new prospects forthe near future, because it increases the possibility of furthermechanization and thus a saving of labour costs. This particularaspect will gain progressively in importance, so that clay pipes,which have had a monopoly for about a hundred years, will soonfind it very difficult to compete with plastic pipes".In 1959 the first smooth plastic pipes were put into practical use; in 1962they were already used for 20% of the area drained that year, and for 33%between 1963 and 1965. The subsequent development is shown in Table 1, whichgives the pipe materials used in land consolidation projects.513

TABLE I .Length of drainage in land consolidation projectsYear corrugated ,smoothplasticplasticPipe materialclaytotalkm % km % km z km z1966 1474 52 1354 48 2828 100967 1515 52968 1843 60969 208 - 5 2192 56970 4 22 I 1 1728 42971 1649 43 1041 27972 , I550 37 679 16973 2879 93 - -400 48 2915 100252 40 3095 100502 39 3902 100594 47 4044 IO0157 30 3847 100939 47 4168 100216 7 3095 1001974 2111 I O0 - - - - 2111 100I975 3648 , 100 - - - .-3648 100.After about 1967, when drain covering strips were developed and put to practical use, it was no longer possible to check whether the joints of smoothplastic pipes had come adrift. The firm of Wavin therefore produced a pipe,with a fitting at the ends which made the joints secure. This proved satisfactoryprovided the machine was manned by a reliable pipe layer.,In 1963 a completely new type of pipe started to be manufactured: corrugatePVC pipe. It had the same compressive strength as the smooth plastic pipes,but because of the corrugat;on took much less raw material. Another importantadvantage was - and still is - its great flexibility, which enabled itto be delivered and used in rolls of a manageable diameter and considerablelength. This also had a beneficial effect on the amount of labour required.The first field tests with these pipes were carried out round about 1964. I11969 the production of corrugated pipes got well under way, and they wereused for 5% of land consolidation drains. By 1971 this proportion had risento 43%, and at present practically no other pipes are used. The transitionfrom clay to smooth plastic and subsequently to corrugated PVC pipes hasconsiderably reduced transport and labour costs, besides promoting mechanization.

3. Cover and envelope materialsWhen drains'are laid, a highly permeable material is often put on or aroundthe pipes. Its function is discussed in another paper (2.15) entitled "Guidelines'forthe selection of envelope materials for subsurface drainage".In former times the cover material most commonly used was peat fibre. Thejob of delivering it, transporting it along the drain trenches and puttingit on the pipes was time-consuming and labour-intensive. When smooth plasticpipes were introduced, the job of transporting them on the site was simplifiedbecause they were lighter and more of them could be transported pertrip. Investigations were consequently started to find out if economies couldalso be made in the transportation and laying of cover material, which wouldhelp to rationalize drainage even more.At first glass fibre was thought to be suitable for the purpose: the pipescould either be delivered prewrapped, or it could be wrapped round them onthe drainage machine. At that time clay pipes were already wrapped in glassfibre, one strip being placed underneath and one on top. Field tests soonshowed, however, that glass fibre had certain drawbacks in fine sandy soils.In these soils it was vital that the permeation surface should be increasedand this could only be done by using a thick layer of cover of envelope material.A means therefore had to be found of producing voluminous materialsin strip form, in order to achieve the same efficiency on the site. The firmof Ripken and the Griendtsveen Turfstrooisel Maatschappij took the initiativein manufacturing peat fibre strip. To enable this to be used on the drainagemachine, the firm of Van der Ende of Tiel designed a reel which could holdfour rolls of peat fibre.Another completely different voluminous material that was applied in looseform was flax fibre, a waste product from flax industry. From 1962 onwards,bales of this material were marketed by Horman of 's:Gravendeel. It was usedmainly in the sea clay region of North Brabant. By 1968 the product had beensufficiently developed to be delivered also in strip form.In 1972 coconut fibre strip was introduced. It very soon became widely used,and by 1975 coconut fibre strip and pipes prewrapped in it had practically515

captured the market. This can be seen from Table 2, which gives the lengthof drains laid in land consolidation projects and the cover and envelopematerials used in percentages of the total length.TABLE 2. Length of drains laid in land consolidation projects and the coverand envelope materials used in percentages of the total lengthPipe materialCovered and corrugated smoothclayenvelope plastic plasticma ter ia1 covered wrapped covered wrapped covered% % . % % %69 72 75 69 72 '75 69 72 75 69 72 75 69 72 75loose peat fibre - 5 - - _ 2 1 2 - 15 19 -peat-fibre strip 3 8 - - - 8 2 1 - - - - - 7 - -flax fibre strip - 12

granules deposited loose in experimental fields have given very good resultsin the past, and the industry has been continually urged to deliver pipesprewrapped in this material so that they can be laid mechanically. Polypropylenefibre was developed after it was discovered in North Holland that coconutfibre sometimes rots quickly. The structure of polypropylene fibre isvery similar to that of coconut fibre, and it is manufactured in differentthicknesses so that the ideal mixture can be composed for use in each particularsoil. It is true to say that, owing to the technological developmentsof recent years, cover and envelope materials have also done a great deal tomechanize and rationalize drainage work.4. Mechanization of pipe-layingUntil 1954 laying of drains in The Netherlands was carried out entirely byhand. In that year the first “Buckeye” trenching machine was imported fromthe United States, and within a few years pipe-laying became largely mecha-nized.As early as 1958 there were 80 pipe-laying machines operating in The Nether-lands. The following figures for land’consolidation work on Schouwen illu-s trate the change:19541955 20% of pipe-laying was mechanized1956 75% was mechanized1957drainage pipes were laid entirely by handpractically all pipe-laying,was mechanized exceptfor some difficult sites1958 less than 10% was done by handThe first machines were equipped with wheel excavators, but it was not longbefore chain excavators began to be produced in The Netherlands. The chainexcavator was originally built onto a wheel tractor; later the rear wheelswere replaced by caterpillar tracks. Later still, machines were built witha complete track undercarriage. In the course of the years many technical improvementshave been made, horsepower has been considerably stepped up andthe depth of digging increased.517

The first tests with a trenchless machine was carried out in 1968. With thisystem the aperture needed for inserting the pipe is not made with a wheelor chain excavator, but with a plough body. Through the rear of the plougha corrugated PVC pipe is deposited on the floor of the mole passage. Thismethod has already been used for. some time abroad. Further information abouthe development of trenchless drainage may be found in the article entitled"Trenching and trenchless drainage" (Paper 3.07).In the past few years various automatic depth regulation systems have alsobeen developed which makes it unnecessary to fix the depth of each drainlength beforehand. The reliability of these systems has not yet been sufficientlytested; this is a field of investigation for the future. Indeed, anautomatic depth recorder must first be developed which can be combined withthe automatic depth regulation system already in use.5. Drainage maintenanceAs we said in the introduction, insufficient attention is sometimes paid todrainage maintenance in areas where drainage is new and has been laid in thcourse of land consolidation. This leads to complaints about and dissatisfation with the way in which the drainage network functions. In areas wheredrains are laid it is therefore essential to provide instruction about maintenance, and interest contractors in buying maintenance machines. In Drenthfor instance, in collaboration with the National Council for Agricultural Dvelopment and the Government Service for Land and Water Use, regular demonstrationsare given of ditch and drainage maintenance machines. The localland consolidation committee also carries out one maintenance, at the sametime checking that the work has been,properly executed. As many local contractorsas possible are invited to come and watch this maintenance, most owhom immediately purchase the necessary equipment. Flushing equipment withpressure of 15-20 atm. has also been acquired by farmers, cooperatives andfarming communities for their own use. It is essential not only to flushthrough the drains but also to maintain open dicthes and the drain outletsinto the dicthes, Failure to. do so causes a blockage or reduces-the draindischarge. This is especially the case .where the groundwater contains iron.In these regions the end pipes have to be cleaned regularly several times ayear. This takes little time and is usually most effective.518

Ref erencesBRINKHORST, W. & S. SPANJER. 1967168. De waterhuishouding van OostelijkFlevoland. Cult.Tijdschr. 7:55-64.HEESEN, H.J. 1962163. Eindbuiselement voor drainage "type Kleverskerke".Cult.Tijdschr. 2:194-197.JONKERS, H.J. & G. MIEDEMA. 1975. Resultaten van het onderzoek naar de intreeweerstandvan drains op proefvelden. Med. Cult. Dienst 114.KODDE, H. 1971172. ContrSle en onderhoud van drainage. Cult.Tijdschr. 11186- 195.KOENWT, J.A.J. & A. VAN RIJEN. 1970/71. Overpeinzingen bij de drainsleuf.Cult .Tijdschr. 10:29-34.NAARDING, W.H. 1968169. Ontwikkelingen in de drainagetechniek I en II. Cult.Tijdschr. 8:135-138; 298-303.SOMEREN, C.L. VAN. 1959. De ontwikkeling van de techniek van machinale drainage.Med. Cult. Dienst 4.SOMEREN, C.L. VAN. 1961. Kort overzicht van de huidige stand van de drainagetechniek.Med. Cult. Dienst 29.SOMEREN, C.L. VAN. 1963. De toepassing van plastieken draineerbuizen.Med. Cult. Dienst 46.SOMEREN, C.L. VAN. 1965. The use of plastic drainage pipes in The NetherlandsMed. Cult. Dienst 62.ZEIJTS, T.E.J. VAN. 1968169. Nieuwe ontwikkeling in de drainagetechniek.Cult. Tijdschr. 8:85-90.ZUIDEMA, F.C. 1967168. Een nieuw nomogram voor de bepaling van de diametervoor drainreeksen. Cult. Tijdschr. 7:156-165.JAARVERSLAG. 1969. Afd. Grondverzet en Mechanisatie. Cult. Dienst.Med. Cult.Dienst 82.5.1 9

TRENCHLESS DRAINAGE EXPERIMENTS IN DENMARKS. Elsnab OlesenDanish Land Development Service,Hjultorvet, Denmark.SummaryAfter the appearance of corrugated plastic drain pipes the interest in trenchlessdrainage has increased, mainly because of greater working capacity.of 'the machinery and consequently smaller constructions costs. In 1972 the ResearchDepartment of Hedeselskabet (Danish Land Development Service) initiatedexperiments with trenchless drainage and investigations of practicaldrainage projects .In four experiments trenchless drainage has been compared with trench drainageThe experiments were carried out on sandy loam and loam soils at differentmoisture contents. Two types of machines for trenchless drainage with,differentshape of the plough body and different depth control system were used.IntroductionTrenchless drainage carried out as mole drainage has been utilized almost aslong as drainage by closed drain systems has been known. The method is basedupon a torpedo shaped sword being drawn through the soil by which a soil"mole" is made that functions as a drain during some time. At the beginningthe sword was built upon a horse-drawn plough. Today the drawing power isusually a crawler tractor.The moles have got a limited durability, and .in practice the method is usedonly in some peat soils or in clay soil with more than 40 per cent clay. Forsoils with little hydraulic conductivity the mole drainage is often carriedout at narrow intervals across and above drain pipes with a highly permeablebackfill, for instance gravel (Hallgren & Johansson, 1948). This method isonly of little interest under Danish soil conditions, but has been utilizedto some extent in other countries, for instance in England.527

Many methods have been tried to stabilize the moles. Ede (1957) mentions depositingof cement during mole drainage, and Busch (1958) describes utilizationof plastic tapes which are formed as a pipe in the mole.Utilization of trenchless drainage methods was not very important until theappearance of corrugated plastic drain pipes in the early sixties.Various types and sizes of trenchless drain machines have been developed.The types which are of interest for Danish soil conditions are built ascrawler tractors of 100-300 HP with a pipe laying device formed as a torpedoor as a plough or a combination (see Lundegren, 1974). Mainly corrugatedplastic pipes are used, but some machine types are able to lay tilepipes. The biggest machines can work at a depth of 1.8 m with a maximumpipe diameter of 15 cm inclusive of pre-wrapped filter materials. The outputof work may be very great, about 600-700 m of pipes can be laid per hourin a more or less stone-free soil. It is double as much as the output bychain trench machines. However, as an average over a longer period the outoutfor both machines is much smaller.By increasing speed the demand for a quick and exact depth control systemsecuring the pipes being laid with an even slope is increasing. One candistinguish between the following systems:1. Manual control of the hydraulic system by sighting to targetrods, placed traditionally by levelling of height piles.2.Manual radio control of the hydraulic system from sights adjustedfor suitable slope of each pipe and a sighting pointat the machine.3. Automatic telecontrol by a halogen light adjusted for suitableslope for each pipe and a receive and control unit at the machine.4. Automatic telecontrol by laser adjusted for suitable slopeof a drainage section and a height adjustable receive andcontrol unit at the machine.The systems have got different working and functional advantages and disadvantages:.With manual systems it takes some time to observe and correct deviationsfrom the projected depth. After hitting stones the machine can bestopped immediately, the obstacle be removed, and then the machine continuesat the same sight line. If the stones only cause a small raising of the

sword, and if the projected slope is big, one may continue with ess or noslope at: all, until the original sight line is reached, by which back slopecan be avoided. In such a case an automatic depth control might cause backslope, because the sword continues immediately after the stone in the originaldepth.As to the manual systems, it is considerably easier to mount telescopes thana system of target rods. System 4 utilizing a plane of laser rays demands avery careful mounting. In order to utilize the laser equipment rationally,the ground must be relatively level, i.e. the difference in height must beonly a couple of metres in the area in question.The three first mentioned depth control systems have been examined by Vossand Zimmerman (1974a, 1974b). They found great deviations between actualand projected drain depths and slopes, especially at the beginning of thepipes. From their results one might expect some back slopes to appear whenmanual depth control is applied to projected slopes less than approximately0.2 per cent. In a stone-free soil and by using automatic depth control, itshould be possible to obtain a minimum slope of 0.05 per cent without anystretch with back slope.Materials and methodsIn December 1972 Hedeselskabet (Danish Land Development Service) made 3 experimentsin order to compare trenchless drainage to chain trenching drainage.In September 1973 another experiment with trenchless drainage versustrenching by back-acting excavators was made. In all the experiments corrugatedPVC-pipes with and without prewrapped filter materials were used.Nr. @kse, Brovst: The land is a post glacial marine deposit, and the soilis sandy loam with a clay content of about 16 per cent (Table I). The flatground had a high groundwater table and was used as pasture. The projecteddrain depth was 1.2 m, the slope 0.2 per cent, the drain length 100 m, andthe distance between-drains 18 m. The trenchless drainage machine was a"Drainomat" with manual depth control after target rods. The chain trencherwas a Holland-drain make.529

TABLESoil texture of the subsoil at the four experimentalfieldsParticle size 0-0.002 0.002-0.02 0.02-0.2 0.2-2.0 mNr. gkse 16 20 . 63 1Vi umgar d ' 18 10 39 330strup 14 13 50 23Frederiksdal 21 21 37 21Vimgard, UZfborg: The land is sloping, and the soil is a sandy moraine loamwith a clay content of about 18 per cent. The experiment was laid out in arainy period, and the autumn ploughed soil had a high moisture content tobelow drain depth. The projected drain depth was 1.2 .my the slope.0.5 percent, the drain length 100 m, and the distance 18 m. The drainage machineswere the same as at Nr. flkse. In order to obtain the projected drain depth,the trenchless drainage machine had 'to be drawn by an extra crawler tractor.@stmp, Homslet: The land is undulating, and the soil is a moraine loamwith a clay content of about 14 per cent. The experiment was laid out whenthe moisture content was near field capacity. The projected drain depth was1.2 m, the slope 1-2 per cent, the drain length 100 m, and the distance 18 m.The drainage machines were the same as at Nr. 0kse. To steer the trenchlessdrainage machine transverse to the natural slope and to obtain the projecteddrain depth, the machine had to be drawn by a four-wheel driven tractor.FrederiksdaZ, Nakskuou: The land is flat, and the loamy moraine soil has a clacontent of about 21 per cent. At the time of drainage the soil was dried upby the previous crop. The trenchless drainage machine was a "Cornelius" withradio control of the drain depth. Trenching was done by a back-actor. Inorder to obtain the projected drain depth of 1.1 m, the trenchless drainagemachine first had to grub to half drain depth, and then do the final run andlaying of the pipes. The projected slope was 0.4 per cent, the pipe length100 m, and the distance 12-16 m.530

The drainage efficiency of each drain was estimated on the basis of simultaneousmeasurements of drain discharge and groundwater levels at a distanceof 0.75 m from the pipe centre. In most cases there is a rectilinear relationbetween the head of water at a certain distance from the pipe and thedischarge (Luthin ì3 Worstell, 1959). For a homogeneous soil this slope canbe used to compare the drainage efficiency of the different drain pipes inthe experiment.In the experiments different pipe diameters and envelope materials wereused, but in this article only results related to the drainage machines willbe discussed.Results and discussionOn the sloping and newly ploughed areas at Viumgard and gstrup the trenchlessdrainage was not satisfactory in spite of the extra drawing power. It1 was found that the trenchless pipes were laid 5-10 cm lower than projected,and that stretches with back slope occurred in most of the drains. On theflat pastures at Nr. 0kse the depth control was satisfactory except whenpassing furrows and similar irregularities. There were no difficulties asregards the depth control of the chain trench machine in the 3 experiments.As the control method was the same for the 2 machines and both staffs wereexperienced, the bad results of the trenchless drainage may be due to afaster laying speed. The measurements at drains with back slopes are excludedfrom the evaluation of efficiencies.The experiment at Frederiksdal with manual radio control of the trenchlessdrainage machine had an entirely satisfactory drain depth and slope.Corrugated plastic drain pipes with and without envelope materials could beused without any difficulties by the tested machine types.In Table 2 the average figures of the water level and discharge measurementsmade are shown together with the calculated efficiencies for pipes laid bytrench and trenchless machines. The highest values indicate the best drainageeffect. The discharge figures are based on intermittent measurements duringrunoff periods and do not give information on the total yearly discharge.53 1

Table 2. The a-verage efficiency of drain pip.es. Trench versus trenchless drainage.number of drainstrenching trenchlessnumber of measurementstrenching trenchlessdischarge, l/s.hatrenching trenchlesswater level, head in mtrenching trenchlessefficiency l1s.ha.muenchlng trenchlessNr. Bkse1972173193317L1974175197517610101010101010102040u O20204040200.440.500.270.260.21o .190.280.335.510.190.160.110.610.270.230.186.92.61.82.40.31.71.21.819761771977178991010362740300.420.280.500.36O .160.130.200.192.62.22.51.9Viunaaard:' 1972/731973/74,1971, 175. 1975/7619'7 6 177666666666624424236182342423618O .230.490.510.250.370.20o. 37o. 390.250.330.29o .470.490.310.370.370.510.540.420.470.81.01.00.81.00.50.70.70.60.71977/786666660.330.320.340.391.00.8olstrup:1973174191417519761771977178333333336216166216160.220.380.140.280.150.270.090.20O .400.390.280.32O. 310.32O .140.240.51.00.5o .90.5O .80.60.8Frederiksdal :1973/7419741756666111316160.260.370.340.410.250.270.310.371.01.41.11.1

The table shows that at Nr. gkse the drainage efficiency was relativelylow as regards the trenchless method in the first year after drainage. Apparently,an increase of the efficiency has happened for both methods, whichmay be due to a gradual improvement of the soil structure. Further theresults indicate that the difference between the efficiency of the two drainagemethods is being reduced as time goes by. The efficiency of the trenchlessmethod is about 80 per cent of chain trenching in the last.part of theperiod. The same relation of efficiencies was found in the experiments atViumgard. At gstrup the results indicate that the efficiency of the trenchlessdrainage is almost as good as the efficiency of chain trenching. AtFrederiksdal the efficiency is the same for both drainage methods.The experiments show that if the trenchless drainage is made when-the soilis dried up to drain depth - i.e. normally in the period of June to October -a drain effect just as good as by trench drainage can be obtained at a moraineloam soil. If the trenchless drainage method is used when the soil iswet to drain depth, a lower drain effect must be expected. The reason isthat the soil loosening effect of the sword at a given type of soil and agiven depth primarily depends upon the water contents of the soil. Under dryconditions the soil is partly lifted, cracks are formed, and after layingthe pipe some loose earth falls into the "grub track". With a high moisturecontent in the soil the sword will press the soil sideways and compact it,and after laying the pipe, the furrow will close again. This will decreasethe hydraulic conductivity of the soil. However, the experiments indicatethat the soil.structure and thus the conductivity will improve later'on.ConclusionsThe present knowledge of the applicability of trenchless drainage under Danishsoil conditions can be summarized as follows:The trenchless drainage system is most suited for relatively flat areas. Forundulating areas drainage transverse to the natural slope may give difficultiesin machine steering. Irregularly undulating areas together with limiteddrain depth may restrict the use of rational drainage schemes.533

A disadvantage of the trenchless method is that damage to existing drainagesystems will not be observed immediately, but may result in wet spots, lateron. At this time searching and repair can be difficult and expensive.The experimental results have shown that trenchless drainage carried out ona loamy soil at low moisture content results in a satisfactory drain effect.Under wet soil conditions the resulting drain effect was smaller than by normal trenching. The best time for drainage will be in the period of June toOctober.On loamy sand trenchless machines are less sensitive to stones than trenchin]machines.On sandy soil it can be assumed that the trenchless method results in satisfactorydrain effect irrespective of the soi moisture content at the timeof drainage.The trenchless method does not exclude usingintrusion of silt and sand.pre-wrapped -pipes to preventPractical experience has shown that on heavy badly structured, clay soil thttrenchless method results in an unsatisfactory drain effect.On mineral soil with low moisture content the power required to pull thesword through the soil often impedes a drain depth to more than 100 cm withoutprevious loosening of the soil to about two-thirds of the actual draindepth. The additional soil loosening is always advisable as it might increasethe drain effect.On flat areas and by using levelling sight and manual depth control a minimumslope of 0.2 per cent can be achieved satisfactorily. Passing furrows,etc. at a normal speed may cause unacceptable depth control.l,As the trenchless machines can cover about 6 hectares a day, and moving tothe next area is time-consuming, the method is best suited for areas abovethis size.Compared with traditional trenching, control with the trenchless drainageis both difficult and time-consuming. The pipes can, however, be located bya special probe rod immediately after laying.534

Ref erencesBUSCH, C.D. 1958. Low cost subsurface drainage. Agricultural Engineering‘39: 92-93, 97 and 103.EDE, A.M. 1957. Continuously formed concrete tube for drainage. AgriculturalEngineering 38: 864-966.HALLGXEN, G. och D. JOHANSSON.-1948. Om tubelering. GrundfÖrbattring 2:193-207.LUhDEGREN, J. 1974. Vasteuropeiska draneringsmaskiner. GrundfÖrbattring 2:165-170.LUTHIN, J.N. and R.V. WORSTELL. 1959. The falling water table in tile drainage.111: Factors effecting the rate of fall. Trans. of ASAE V01.2,No. 1.OLESEN, S.E. and S. Aa. ANDERSEN. 1977. Forsdg med gravefri draening. HedeselskabetsTidsskrift 98: 41-48.VOSS, B. and F. ZIMMERMAN. 1974 a. Zugkraftbedarf und Verlegegeschwindigkeitgrabenlos arbeitender Dranmaschinen. Wasser und Boden 26: 98-102.VOSSS B. and F..ZIMMER.MAN. 1974 b. Untersuchungen Über die Festigkeitsanderungenim Boden sowie die Verlegengenauigkeit von Rohren beim Einsatzgrabenlos arbeitender Dränmaschinen. Wasser und Boden 26: 102-105.535

Paper, 3.06COMPARISONS BETWEEN TRENCHLESS AND TRENCHING SUBDRAINAGER. EggeIsmanInstitute for Peat Research and AppZied SoiZ Science,Bremen, Germany.SummaryFirst pedological and hydrological field researches have shown, that in amarsh soil (heavy silty clay) with groundwater influence the trenchless SUdrainage method has somewhat better effects than the trenching subdrainagemachine with cutter chain, especially if they work under wet conditions.IntroductionI -Subdrainage is still today an important way of soil m,,,:ration in CentralEurope. Since 1955 an area of 60,000 to 70,000 ha have been drained yearlyin the Federal Republic of Germany, total more than 1.4 mill. ha (Eggelsma1978).For about five years more and more trenchless subdrainage machines are woring in our country, in North-western Germany nearly 70 machines. This machtype needs only 2 to 3 men for the fully mechanized drainage work in the f(marking-off, levelling, laying corrugated plastic pipe).ProblemThe German drainage contractors prefer the trenchless machines, because thmethod is very economical. From the view of soil science we recommend thetrenchless method for peat, marsh and loam soils, because these soil types536 -

our lowland areas are mostly wet and soft nearof groundwater and humid climate).y the whole year (influenceIn these wet soils the trenching subdrainage machine destroys the soil structurewith its cutter chain. Wet disturbed soils, refilled into the draintkench, prevent or hinder the water streaming to the drain pipe (Fig. I ) . Inthat case we find a high entrance' resistance of groundwater at the drain(Cavelaars, 1967; Eggelsman, 1969)./------Fig.1. Scheme of the groundwater level at drain trenchafter refilling with wet silty clay soil.The trenchless subdrainage machine breaks up the soil (Fig.2). This mach neis careful with the soil structure, if the plough has the right form andangle. If the soil is dry enough, it even meliorates the soil structure(Eggelsman, 1973).But in fact'there are no exact researches upon the influence of the trenchlesssubdrainage machines on the soil structure and the drainage effect.537

Both machine types worked in. 1972 under substantial same.conditions. Thedrainage fields have a heavy silty clay, type: Brack-Marsch (see Table I).TABLE I.Dates of soil analysis from 90-120 cm depthAnal y s isDimensionPlottrenchlessSubdrainagetrenchingfine sand > 60 um 3 2coarse silt . 60 - 20 um % 41 34of drymedium + fine silt 20 - 2 vm23 32matterclay < 2 um content 33 ' 32~~ ~~~. organic matterCaC03pH-value (nKC1)% 2.5 2.5% . 0.05 0.43- 4.6 5.2The soil has a hydraulic conductivity of 15 cm/d (=upper layer) and 30 cm/d(layer under drain).Before drainage both fields were used as grassland, after subdrainage thefarmers used them as arable land, mostly with cereals and rape.The single subdrainages have a depth of 1.3 m (at the outlet) to 0.9 m atthe end. The (artificial) drain slope is 0.25%. The drain distance is IO m.The corrugated plastic pipe (PVC) have coco-filters (full-wrapped filterpipes).Field research methodIn the winter 1977/78 we measured in both drainage fields:-depth of groundwater under surface between the drain pipes,- potential height of groundwater at drain pipe,- drain water runoff,539

- soil moisture and consistence through estimation by finger touch(MÜller et al., 1970),- soil infiltration rate above drain, measured at a depth of 50 cmunder surface,- soil pressure resistance in the former drain trench resp. direct uponor near the drain pipe,--soil shear resistance direct upon or near the drain pipe,soil condition of the surface layer.All pedohydrological field methods are described by Eggelsman (1977).ResultsThe soil moisture and soil consistence in the former drain trench resp. di-rect above the trenchless.drain, estimated in the soil layer of 40-80 cm un-der surface are as in Table 2.TABLE 2.Estimation of soil moisture and consistencePlot of Soil Soilsubdrainage moisture consistencepF-valuet renchless moist stiff to 3.0 - 2.5plastictrenching wet soft 2.2 - 1.4The drain water runoff from both kinds of subdrainage fields was nearly thesame .In both kinds of subdrains we could see the beginning of iron ochre cloggingat the drain outlets.The other results of the pedohydrological field measurements are summarizedin Table 3:540

TABLE 3.Results of the pedohydrological field measurementsKind of measurement Dimension Plot oftrenchlessSubdrainagetrenchingGroundwater depth in thecentre between drain pipescm 63 76Potential height of groundwaterat the drain pipecm14 26Rate of soil infiltration cm/d 65 600(medium) (very high)Soil pressure resistance2kg/cm 4-6 1-2(medium) (very slow)Soil shear resistance kg/cmO. 5 o. 2 - o. 1(medium) (slow to veryslow)2Soil condition of thesurface layersatisfactorymoderateDiscussionOur first researches in one soil type - certainly in a difficult and sensitivemarsh soil - show that the pedohydrological situation at the trenchlesssubdrainage field may be somewhat better than at the trenching subdrainagefield. Also the soil conditions seem to be somewhat more favourable at thetrenchless subdrainage field than at the trenching subdrainage field (Tab.3).The contrasts between infiltration rates and soil pressure resistances arecaused by the different soil moisture resp. consistence (Tab.2).ConclusionOur first test has shown that in silty clay marsh soil the trenchless subdrainageseems to be somewhat better. But more researches are necessary, onthe one hand pedohydrological researches over a longer time, on the otherhand especially more researches in other soil types.54 1I

But it.seems that in silty and clay gley soils our opinion is confirmed,that,the trenchless subdrainage may,be better than the trenching subdrainagesystem, especially when the machine works in wet soil conditions.The Ge-n subdrainage Standard DIN 1185 (1973) demands that subdrainageworks must be carried out only in soils which are dry enough, but that demandis not,always attainable in marsh and gley soils in our humid climate(Renger et al., 1975).Ref erencesCAVELAARS, J.C. 1967. Problems of water entry into plastic and other drainpipes. Agr. Eng. Symp. Silsoe/Bedford UK. Paper No.5 E 45.DIN 1 185. 1973. Dranung-Regelung des Bodenwasserhaushaltes durch Rohrdränung ,rohrlose Dranung und Unterbodenmelioration.Beuth-Vertrieb GmbH Berlin.EGGELSMAN, R. 1969. Akute Dranprobleme. Wasser und Boden, 21: p.1-8, Hamburg.EGGELSMAN, R. 1973. Dränanleitung. 304 p. 133 figs. 14 nomographs, 57tab:'(in German with English and French subtitles). Edition Paul Parey,Hamburg.English Edition: Instruction Subsurface Drainage. ICID, GermanNational Committee, Ed. Paul Parey, Hamburg, 1978.EGGELSMAN, R. 1977. Pedological-hydrological field methods and their .value ofprediction for water management, soil cultivation, and land scape maintenancein lowland areas. Geolog. Jb. F Vo1.4, p. 51-78, Hannover; (Germanwith English subtitles and summary).EGGELSMAN, R. 1978. Die Bedeutung der Dranung in der Bundesrepublik Deutschland.Wasser und Boden, 30: p. 78-79, Hamburg.NAARDING, W.H. 1976. A summary from the report: A review on the internationalexperience with trenchless drainage machines., Ed. Min. of Agriculture,Gov. Service for Land and Water Use, Assen.MULLER,-W., RENGER, N. & BENNECKE, P. 1970. Bodenphysikalische Kennwerte wichtiger BÖden, Erfassungsmethodik und Darstellung. Beih. Geol. Jb. BodenkündlicheBeitrage, 99:2, p. 13-70, Hannover.RENGER, M., STREBEL, O. & GIESEL, W. 1975. Beurteilung bodenkundlicher, kulturtechnischerund hydrologischer Fragen mit Hilfe von klimatischer

Paper-3.07ITRENCHING AND TRENCHLESS DRAINAGEW.H. NaardingGovernment Service forLand and water Use, Utrecht,The NetherlandsISummaryDraining is often done in The Netherlands using trenching machines: that isto say, a trench of the right depth is dug with a chain or wheel excavatorand the drain pipe is laid on the floor of the trench. With trenchless drainagea tunnel is made at the depth at which the drain pipe is to be laid, andthe drainage pipe is placed in the ground through an opening at the rear ofthe plough body.In recent,years trenchless drainage has been practised in different degreesin Europe. We therefore decided to investigate what use various Europeancountries make of trenchless drainage machines, what experiences they havehad with them and what research results are available on the efficient functioningof drains that have been installed without trenches. On the basisof the thus obtained data a brief survey will be given on:Developments in drainage techniques, the mòst important facts about trenchingmachines and trenchless machines; the use of trenchless drainage incertain European countries, construction costs of single drainage-system inThe Netherlands with trenching machines- and trenchless machines, drainageeffect of systems constructed by trenching o; trenchless techniques.Finally of both drainage techniques, advantages and disadvantages are summarized.IntroductionIn former times drain pipes were laid in The Netherlands by digging a trenchby hand and laying the drainagepipes - also manually - on the bottom of,the trench. After a sort of horse-drawn scraper, called Pratt's Ditch Digger,had been used, the discovery was made in America round about 1890 that atrench could be dug by means of a wheel. The first machine was called543

In 1954 a "Buckeye" machine was introduced in The Netherlands that could dja trench to the full required depth, the depth being regulated by means ofthe sole. The pipes still had to be laid manually. The disadvantage of thedigging-wheel machine was, that it had a comparatively small laying capacitWhen chain excavators were developed, laying capacity was increased.In the past 20 years the laying of drains has thus been transformed from acompletely manual to a more or less fully mechanized operation. The changeover from clay pipes via smooth plastic drainage pipes to corrugated plastjpipes has largely contributed to the increased laying capacity of drainagemachines. Besides, the laying capacity has also been significantly enlargecin recent years by increasing the tractive power of the machines, resultingin higher digging and driving speeds.An entirely different development in East Germany is the system produced bqmole drainage. The most important disadvantage of mole drainage is the factthat the tunnels are liable to cave in, particularly in less stable soilsand when there has been water in them for some time. It was believed thatthis danger could be eliminated by introducing a pipe into the earth withoLdigging a trench. A mole body, fixed to a vertical knife, was first used tcmake a tunnel in the ground by pushing the earth aside. 'The disadvantage ofthis method was that the earth around the pipe was extremely compacted.In the course of the years various manufacturers brought out their own modetheir aim being to reduce the pulling force as much as possible in order toobtain a good laying speed. It was supposed that this could be done by usina not too wide ripperleg with a sharp front. The leg was positioned at anangle of 90' to the horizontal (that is, the bottom of the trench).From experience with subsoilers we know that this shape demands a ratherhigh tractive power because the horizontal forces are great. Consequently,the earth is pushed aside and therefore not lifted sufficiently. This maycause the soil to be deformed.Having discovered this, manufacturers tried to find a system whereby thehorizontal forces would be reduced and the vertical forces increased. To544

-achieve this, the front of the ripperleg was made more concave, and a flatplate, wider than the rest of the ripperleg and the trench box, was made toextend over the whole length. The whole was positioned at a certain angleto the horizontal.The advantage is that the earth can be lifted more efficiently down to acertain depth. Generally speaking, the extent to which the earth is lifteddepends on the width of the ripperleg and its position to the horizontal.According to Mr. Gordon Spoor of the National College of Agricultural Engineeringin Silsoe, Great Britain, a ripper body with a width of 10-15 cmOpositioned at an angle of about 45 can still lift the earth down to about1.50 m below the surface; a ripper body with a width of 20 cm can do so downto about 1.50 m.If these depths are exceeded, the earth below this levelwill be compacted because the ground will choose the way of least resistance.Spoor calls the point at which the,earth ceases to be lifted and starts toslide along the ripper body "the critical depth".The "Willner" is based on another system. It consists of a'V-shaped ploughbody carried by a crawler tractor. The pipe is inserted in the ground throughan opening in the plough body. As the "WilIner" moves along, the plough bodylifts the earth by about 20 cm, the pipe is laid and the earth falls backand covers it. The depth of the body is regulated hydraulically.The "Willner" is an improvement on the other plough bodies we have described,in that the horizontal forces are comparatively weak and the vertical forcesstronger. This means, however, that it cuts less deep though the ground issufficiently lifted.With the results from these different shapes in mind, the Georg August Uni-versität of GÖttingen, West Germany, developed the Y-shape,which combinesthe V-shaped part with the narrow bottom part in such a way as toenableit to reach a greater depth than the "Willner". According to the designers,it achieves an ideal balance of forces, combining minimum horizontal forceswith maximum vertical forces. The machine is being used in the West German"Meliorationverband Norden" (Land Improvement Plan "Norden").Trenchless drainage techniques were developed because it was believed that545

.trenchless machines with their higher speed and lower maintenance costs,could do the work more cheaply than trenching machines. Designers were es-pecially intent on achieving a higher laying speed.Some general charaeteristics of the machinesTrenching machinesI. Over the years the power of trenching.machines has been considerablyincreased..About ten years ago most machines were.sti.11 fitted with- motorsof 100-150 hp; now, partly under the influence of the trenchless techniques,more powerful motors of up to 200 hp are used. These of course have a greaterlaying capacity, thus reducing the capacity differences with trenchlessmachines.2. Machines fitted with caterpillar tracks and able to achieve a depth of1.80 m vary in weight from 9.5 to 15.5 tons. The ground pressure ranges fron0.24 to 0.29 kg/cm2 (0.24 x 9.81 N/I-4 2x IO m and 0.29 X 9.81 N/1 X-4 2IO mrespectively).3. Most machines have a maximum working depth of 1.80 m. Those built forlaying main drains, horizontal dewatering systems and deep drains in urbanareas can generally reach a maximum depth of 3.00 m.4. Laying capacity depends on the depth and length of the drain, the soilstructure, soil and site factors and the power of the machine.Good organization is also essential for achieving maximum capacities; de-lays caused by poor organization have a direct effect on performance.Trenchless machinesI. Machines vary widely in horse power: viz. between 140 and 320 hp. Gene-rally speaking, the power increases according to the depth to be reached.546

The power of the machine also depends, of course, on the shape of the ploughbody.According to Trafford, the increase in-horse power required is represented3approximately by the formula (P = XD ). P being power, D depth and X a constantdepending on the shape of the plough body.Trafford considers trenchless drainage justifiable to a depth of 80-100 cm;greater depths require more horse power and also involve greater risks. Somemachines are therefore fitted with a winch to compensate for any lack ofhorse power. A number of unsophisticated machines are also towed by a winchon a tractor.2. Machines can be divided roughly into two classes: the first ranges from13 to 23 tons and has a ground pressure of between 0.24 and 0.29 kg/cm2 andthe other rangers from 27 to 41 tons and has a ground pressure of between2'0.46 and 0.72 kg/cm . Soil factors (i.e. the permissible ground pressure2per cm ) are of great importance when choosing which weight to use.' 3. The maximum depth which can be reached is between 1.20 and 2.20 m. Thiscan only,be achieved undèr ideal conditions: i.e. a more or less dry topsoiland a moist subsoil. The topsoil must be dry enough for the tracks to geta grip in order to exert the necessary pulling force.4. The laying capacity on certain factors, some of which we mentioned inconnection with trenching machines: the depth and length of the drains, thesoil structure, soil and site factors, the topography, the shape of theplough and the weight and power of the machine. These factors determine themaximum laying capacity, together with the conditions mentioned under 3: amore or less dry topsoil and a moist subsoil, and a not excessive depth. Ifthe topsoil is wet, capacity will be swiftly reduced and will hardly exceed -or may be less than - that of the trenching machines.547

5. Trenchless machines can be used most profitably on sites of over 10hectares because the loading and transportation of these heavy machines ismore time consuming, requires heavier low loaders and therefore, higher, costs.A trenching machine and trenchlessmachine combinedIt is not always possible or advisable to use trenchless machines. On wettopsoil, for instance, their capacity is severely reduced, and when layingvery deep drains they require excessive pulling force or exceed the criticaldepth. To overcome these difficulties, a drainage machine made by the firmof Steenbergen in Klaaswaal has been adapted in such a way that it can befitted with both a digging chain, as well as with a ripper body.If this combination model is purchased, the motor unit will have to be builtas a tractive tool. The additional digging chain and ripper body units canbe changed fairly easily. The construction of this machine s such that itcan be used in a greater number of situations.Application of trenchless drainage insome European countriesNotwithstanding the fact that trenchless techniques were introduced morethan ten years ago, one could describe their development as slow and hesitant,as against the development in West Germany where particularly in thenorthern alluvial soil over 50% is constructed in trenchless systems.In France 15% were laid by trenchless machines in 1974 and 30% in 1975.In England and Wales it was IO%, in Austria 5% and in The Netherlands alsoI - 5%.548

Cost of laying under drainage with trenching machinesand trenchless machinesoThe cost of drainage machines per meter depends on the purchase price of themachines, depreciation, interest, insurance, fuel consumption, lubricants,replacement chains, knives and other wearing parts, depreciation of tracksand other repair costs.From the calculations it has appeared that the machine costs per meter, atthe same combinations of hourly and yearly capacities, are IO-20% lowerwhen trenchless machines are used. This advantage is mainly gained by thefact 'that trenchless machines have less wearing parts than trenchers. Fortrenchless machines repairs are confined to regular welding of the point ofthe ripper leg.Because of the fact that in case of trenchless drainage, the machine is adrawer instead of a carrier, the track wheels and drive shafts have more tostand.Trenchless machines consume on average 10-15% less fuel than trenching machines.Under favourable laying conditions they also have a greater hourlycapacity, which means that they cost less per meter. The total cost of drainageper meter is made up of the cost of the machine, the materials and thetractor, wages, overhead supervision costs and taxes. Calculations haveshown that trenching machines with a yearly capacity of 500 km and hourlycapacities of 200 and 400 m, using corrugated pipes instead of clay ones,could save 0.56 and 0.25 guilders per meter respectively, i.e. 17% and 9%on the total costs.When'the costs of a trenching machine was compared with that of a trenchlessmachine of the she hourly capacity, using PVC corrugated pipes, the trenchlessmachine was found to save 0.31 and 0.16 guilders, or 11% and 8% respectivelyon the total costs.The greater saving was therefore made by changing from clay pipes to corru-gated PVC pipes. The differences become more pronounced of course, if one-549