Expanding water supplies via expensive water projects is no longer feasible due to a variety of factors, including a lack of productive new sites for dams, political opposition to increased expenditures, and environmental opposition to adverse ecological impacts. Consequently, many western states are busy designing water conservation policies to utilize existing supplies more effectively. This module investigates agricultural water conservation within the context of a farmer diverting water from a river to irrigate crops. Crops generally do not consume all of the water diverted into irrigation. Return flow may occur directly from the field, or in the form of groundwater that flows into a river or is pumped from a well.
Irretrievable losses occur through evaporation or a variety of other means.
Highly efficient irrigation systems apply water more uniformly over fields in a more timely manner, thereby enabling crops to increase their consumptive water use from smaller irrigation diversions. The million dollar question for agricultural water conservation policy is whether the 5.5 units of reduced irrigation diversion due to an increase in irrigation efficiency in Exercise 1 constitutes conserved water increasing instream flows. Western states are divided over the answer. The answers to these questions depend on the hydrology of the river from which irrigation water is diverted. This module analyzes the relationship between increased on-farm irrigation efficiency and water conservation for two opposite hydrologic cases.