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Agricultural drainage water management in arid and semi-arid areas 21Chapter 3Framework for selecting, evaluating andassessing the impact of drainage watermanagement measuresDEFINITION OF DRAINAGE WATER MANAGEMENT AND TASKS INVOLVEDIn the context of this publication, drainage water management refers to the management andcontrol over the quantity and quality of the drainage water generated in an agricultural drainagebasin in arid and semi-arid areas and its final safe disposal. This is achieved through irrigationwater conservation measures and the reuse, disposal and treatment of drainage water. Managingdrainage water at the field, irrigation-scheme and river-basin levels entails a number of activitiesincluding:• regulating water table levels in the drainage system to ensure the maintenance of favourablesoil moisture conditions for optimal crop growth and salinity control;• developing irrigation and drainage water management strategies to ensure that disposalregulations and water quality standards are met and dealing with issues, problems and conflictsthat might occur;• setting distribution priorities and criteria for reuse in water scarce areas; and• establishing cost sharing imposed on stakeholders for the use of poor quality water andrequired treatment to meet the water quality standards for drain discharge.DRIVING FORCES BEHIND DRAINAGE WATER MANAGEMENTThe main reasons for developing a drainage water management strategy are: (i) prevention ofeconomic and agricultural losses from waterlogging, salinization and water quality degradation;(ii) concern for quality degradation of shared water resources; and (iii) the need to conservewater for different water users under conditions of actual or projected water scarcity. In addition,the need to comply with drainage water policies and regulations can provide a strong incentivefor improved drainage water management.Many countries and states, e.g. Australia, India, Egypt and California, the United States ofAmerica, have a drainage water disposal policy and drainage effluent disposal regulations. InCalifornia, the United States of America, and in Australia, the drainage policy guidelines consistof difficult but achievable targets with an active enforcement of regulations. India and Egypthave policy guidelines of a general nature but have not reached the maturity of Californian andAustralian laws. Law enforcement often fails in these countries, mainly as a result of administrativeshortcomings and unrealistic quality guidelines for their conditions and resources. In thesecountries and in countries where clear laws and regulations are absent, the prevention of economicand agricultural losses and the conservation of water for other beneficial uses will normally bethe main driving factors behind the development of a drainage water management strategy.
22Framework for selecting, evaluating and assessing the impact of drainage water managementPHYSICAL DRAINAGE WATER MANAGEMENT OPTIONSFigure 9 identifies the physical drainage water management options that are available to planners,decision-makers and engineers and how they relate to one another. The measures have beengrouped into four categories: water conservation, drainage water reuse, drainage water treatmentand drainage water disposal measures.Conservation measuresA major goal of conservation measures is to reduce the volume of drainage effluent generatedand the mass discharge of salts and other constituents of concern while at the same time savingFIGURE 9Physical drainage water management options and how they relate to one anotherDriving force· Prevent economic and agricultural losses as aresult of waterlogging,, salinization and waterquality degradation.· Direct water conservation for other users of thesame water source in water scarce areas.· Comply with drainage water quality regulationsthat aim to:1. Maintain water quality standards of surfacewater bodies for other downstream users, i.e.agriculture, municipalities, industries, environmentand recreation.2. Reduce the drainage flow for areas with limiteddisposal options.ConservationSource reductionChange incropping patternShallowgroundwater tableGroundwatermanagementLand retirementChange incropping patternReuse inconventionalagricultureIntegrated FarmDrainage ManagementSystemsRe-use forreclamation ofsalt-affected soilsReuse in wetlandhabitatsReuseDirect useBlending“Conjunctive” useCyclicuseSalt harvest&utilizationIntraseasonInterseasonTreatmentPhysical treatment Chemical treatment Biological treatmentDisposalRiver discharge Evaporation Outfall drainSalt harvest&utilizationInjection in deepaquifers
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This publication provides planners,
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