Irrigation Efficiency Improvements: A Water Scarcity Solution or a Possible Mechanism of Injury?

Increasing irrigation efficiency has been cited as a potential solution to water scarcity problems. Many rivers in the Western United States depend on irrigation return flows as a source of water supply.  Return flows are important for satisfying downstream water rights and delivering water for interstate compacts.  Improvements to irrigation systems, such as sprinklers and drip systems that replace flood and furrow irrigation, have the potential to affect water supply in the river resulting in a change to the stream conditions existing when the water rights were appropriated; such improvements can cause injury to those vested rights.  Applying water with a more efficient system results in less water lost to surface runoff, evaporation and seepage.  Though the water user may divert the same quantity of water, the amount of water consumed increases. 

A 2011 United States Supreme Court decision addressed this issue in the context of the Yellowstone River Compact.  (Montana v. Wyoming, No. 137, Orig.).  This compact includes a provision protecting rights existing at the time of ratification.  The Court ruled that irrigation methods in place at the time of the compact could be improved within the state’s compact rights, regardless of any reduction to flows caused by such changes.

In another 2011 development, the State of Colorado took two measures in the Arkansas River Basin pertaining to irrigation systems improvements.  First, Colorado promulgated Compact Rules Governing Improvements to Surface Water Irrigation System and, second, entered into an agreement with the State of Kansas to change the Hydrologic-Institutional Model, the tool used to measure compact compliance, in order to recognize improved efficiencies of systems supplied with ground water.  Both measures were designed to ensure that return flows used in Kansas at the time of the compact would not be consumed by improved water irrigation practices in Colorado.