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Management of Farm Irrigation Systems


American Society of Agricultural Engineers

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Conjunctive water management involves coordinating the use of groundwater and surface water in time and in space. The water sources might or might not be in hydraulic connection with each other. In this chapter, conjunctive water use involves the combined use of surface and groundwater to supply crop water needs.

Two simplified examples of conjunctive use follow. Farmer Allen uses river water to irrigate his crops. In dry years, with below average stream flow, his surface water supply is severely limited by late summer. To augment this surface water supply, he pumps groundwater. In wet years, when the surface water supply is sufficient, he uses no groundwater for irrigation. Farmer Brown relies almost entirely on groundwater to irrigate his crops. In an effort to preserve the groundwater resources for sustained use, he uses surface water stared in on farm ponds when it is available. Both are conjunctive using ground and surface water. Unless there is a complicating regional effort to preserve groundwater, Farmer Brown's situation might be analyzed through standard economic approaches (Harper et al., 1989). Regional problems will not be addressed here. Farmer Allen's problem, determining when and how much groundwater or river water to use, can be addressed via an approach presented in this chapter. There are many other conjunctive use water management situations not addressed.