Optimal Conjunctive Use of Surface and Groundwater with Recharge and Return Flows: Dynamic and Spatial Patterns *

This paper derives the efficiency price patterns for a comprehensive spatial and dynamic model of conjunctive water use incorporating conveyance losses, canal return flows, and groundwater recharge. The first-best shadow price of surface water is composed of a charge for water that flows into the farm and differential credits for water that flows to other uses. The shadow prices can be used as the basis of water pricing schemes or for exchange rates to facilitate water trading. We show that farmers near the headworks use irrigation water in the optimal program, and only farmers more distant from the headworks extract groundwater. We also illustrate the possibility of reswitching in the sequence of resource use. It may be efficient for some farms to switch from one source to another and then switch back again, e.g. groundwater to surface water to groundwater.