Estimates of evapotranspiration are determined for each of four areas delineated by dams along the river, which allows areal variations in temperature to be considered in calculating water-use rates. The accounting surface can be used to identify wells that yield water that will be replaced by water from the river and provides a uniform criterion of identification, based on hydrologic principles, for all users who pump water from wells. The accounting surface was generated for the reach that begins at the east end of Lake Mead and ends at Laguna Dam by using profiles of the Colorado River and annual high water-surface elevations of reservoirs, lakes, marshes, and drainage ditches. The accounting surface represents the water table of the river aquifer that would exist if the only source of water to the aquifer were the river. Wells with a static water level above the accounting surface are presumed to yield water that will be replaced by precipitation and inflow from tributary valleys.
Water pumped from wells on the flood plain is presumed to be river water.
A well inventory is needed to locate wells, provide current information for each well, and provide precise position and elevation information necessary to identify wells that yield water that will be replaced by river water. All new sites and those previously inventoried must be located precisely to ensure that the correct well can be revisited for future data collection and to ensure that well ownership is properly identified.