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Agricultural drainage water management in arid and semi-arid areas 29On the basis of computer simulations, Varela-Ortega et al. (1998) analysed the responses offarmers in Spain to increasing water prices. Results showed that in modern irrigation districts,where irrigation efficiency is already quite high, no changes in water demand would occurunless the prices became restrictively high and farmers needed to change to rainfed farming. Incontrast, in areas with the older irrigation systems, farmers would have ample scope for improvingtheir water use efficiency.An alternative to volumetric pricing is tiered water pricing. In this system, farmers pay alower volumetric price for a reasonably necessary amount of water to grow a certain crop. Ahigher volumetric price is charged for additional amounts of water. Such a system is explicitlydesigned to reduce the amounts of water that generate most of the drainage water. The reasonablynecessary amount should include the minimal leaching requirement in order to maintain afavourable salt balance in the rootzone unless sufficient rainfall occurs in the area. A mainproblem would be to define the ‘reasonable necessary amount of water’. In Broadview WaterDistrict, California, the United States of America, tiering levels differ only between crops andnot between soils, because farmers consider the latter approach to be inequitable. Tiering levelswere established at 90 percent of the average depths applied in the years before the systemwas implemented. This system of tiered water pricing led to a decrease in water applied to fiveof the seven main crops. More importantly, the drained volume in 20 of the 25 subsurfacesystems in the water district decreased by 23 percent and the salt load declined by 25 percent(Wichelns, 1991).Volumetric pricing policies are typically only applicable in on-demand systems. Other systemsdeliver fixed amounts of water to farms, and they fall outside the responsibility of the individualfarmers. In such systems, more gains could be obtained by matching supply and demand moreclosely to each other in a technical/operational way.Subsidies on practicesA changeover to water saving or pollution prevention measures might not always be the objectiveof individual farmers nor might it always be to their advantage. In the case of Iran, it wascalculated that the investments in sprinkler irrigation are of the same order of magnitude as thevalue of the water that can be saved, if this is used to irrigate a larger area or high-value crops(Perry, 2001). However, if the water saved is diverted to irrigate land in other areas, upstreamfarmers will be investing while benefits accrue to other areas. Another example is the case offarmers located in the higher areas with free drainage in the Panoche Fan. Farmers in theseareas contribute much to the pollution, but there is no direct incentive for them to invest in watersaving or pollution prevention measures. In both cases, subsidies might stimulate farmers toinvest in water saving technologies or pollution prevention measures.Charging/subsidizing outputsA final instrument proposed by Weersink and Livernois (1996) is a charge on the crops. In thecase of nitrogen leaching, the charge focuses on crops that need large amounts of nitrogen, andthus have a higher risk of causing pollution. In irrigated agriculture, one could think of policiesthat discourage growing crops with large water requirements (such as alfalfa) by charging thecrops or by promoting deep-rooting crops or less-water-demanding crops through subsidies. Acommon example is where farmers pay a price per area depending on the crops grown.
30Framework for selecting, evaluating and assessing the impact of drainage water managementCombined measuresA single economic or policy instrument will probably not resolve water pollution problemsoriginating from irrigated agriculture. Combinations of policies can help to enforce their effect.Especially in situations where farmers are inequitably charged, a combination of measures mighthelp to charge farmers more equitably. For example, emissions from an irrigation district couldbe measured and fines applied where limits are surpassed. These fines could then be distributedamongst the farmers, applying a ranking based on how farmers have used their inputs or whatmeasures they implement. The most inefficient users should then pay comparatively more thanthe most efficient ones.SELECTION AND EVALUATION OF DRAINAGE WATER MANAGEMENT OPTIONSNormally, more than one drainage water management option will need to be considered andimplemented to attain the desired objectives. In this case, interactions and trade-offs occur.Because of the complexity of the processes and interactions, computer models are best suitedto selecting an optimal combination of drainage measures. As was explained in Chapter 2, theselection of a set of drainage water management measures requires more considerations thansolely technical feasibility. Figure 11 shows a flowchart for selecting a set of drainage watermanagement measures (AHCC, 2000).Step 1 is to gather technical, environmental, social, economic and institutional informationabout the site and the available drainage water management options. Step 2 is to evaluate thedesirability of the options from a technical and environmental perspective. Typically, this stepFIGURE 11Flowchart of process for selecting an optimal set of drainage water management optionsStartStartStep 1: Gather technical,Step 1: Gather technical,environmental, social,environmental, social,economic and institutionaleconomic, and institutionalinformation, and determineinformation and thethe drainage waterdrainage watermanagement options.management options.Step 2: EvaluateStep 2: Evaluatedesirability of the optionsdesirability of the optionsfor the site from afor the site from atechnical andtechnical andenvironmental perspective.environmental perspective.Step 3: Rank the optionsStep 3: Rank the optionsfor the site based on theirfor the site based on theirtechnical andtechnical andenvironmental suitability.environmental suitability.Step 4: Evaluate theStep 4: Evaluate theeconomic feasibility andeconomic feasibility andefficiency of the site’sefficiency of the site’soptions and re-rank optionsoptions and re-rank optionsif required.if required.Step 5: Evaluate the social,Step 5: Evaluate the social,organization andorganisation andinstitutional issues, ifinstitutional issues, ifnecessary, re-rank again.necessary, re-rank oncemore.Step 6: Integrate theStep 6: Integrate thetechnical, environmental,technical, environmental,social, economic, andsocial, economic, andinstitutional information,institutional information,culminating in aculminating in arecommended plan.recommended plan.Source: based on AHCC, 2000.Step 7: Write a reportStep 7: Write a reportdescribing recommendeddescribing recommendedoptions and the order inoptions and the order inwhich they should bewhich they should beimplemented.implemented.EndEnd
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