THE SUSTAINABILITY OF IRRIGATED AGRICULTURE IN THE LOWERCOLORADO RIVER REGION

摘要

There are some 160,000 acres of irrigated agriculture in the region of the Lower ColoradoRiver from below Imperial Dam to the Mexican border. Included in this region are sevenirrigation districts, 6 in Arizona and 1 in California, and these districts presently operateon a run-of-the-river basis, diverting waters from the Colorado River and returning flowsto the river through agricultural drains and groundwater flows.Demand for water is increasing in the region due to urbanization, particularly the rapidlygrowing City of Yuma but also the cities of San Luis, Somerton and Wellton, Arizona.Mexico also diverts large volumes of surface water and increasingly relies ongroundwater pumping to meet it water needs. The region presently has areas ofgroundwater excess, where drainage wells and open drains are needed to relieve highgroundwater tables, and areas of declining groundwater tables, especially near the borderareas with Mexico and potentially along the lower Gila River. Treaty requirementsnegotiated with Mexico regulate salinity of return flows to the river, resulting in muchwater being bypassed to the Santa Clara slough in Mexico and potentially being desaltedon a large scale basis by the Yuma Desalting Plant in the future.Sustainability of irrigated agriculture over the long term for this region will depend onmany factors, including (1) the overuse of groundwater supplies, especially along thelower Gila River and along the Mexican border area; (2) the reduction in surface watersupplies due to water conservation; (3) reduction in groundwater recharge as flood eventson the Colorado and Gila Rivers become even more infrequent with continuedconstruction of upstream flood control storage; and (4) general impacts on agriculture andwater rights from conversion of agricultural lands to urban uses.