Stream Depletion by Wells in the South Platte Basin‐colorado1

Abstract

The agricultural production from the Lower South Platte Basin in Colorado represents a significant portion of the state economy. Until the early 1950's the production had developed almost exclusively by use of river water. Drought conditions combined with improved well technology resulted in an inordinate amount of well development in the valley during the period 1952‐56. These wells were used for supplemental supply in many cases, but the application of sprinkler irrigation brought many acres of here‐to‐fore dry land into irrigated production. As a result of the vast amounts of groundwater withdrawal by the newly developed wells, senior surface appropriators found a decreasing amount of water available for use in the streams. The legislature, observing the doctrine of prior appropriation, ruled that all surface and ground water in a tributary would be treated and administered as one resource. This, of course, spelled doom for the well‐oriented segment of the economy. Analysis of a segment of the river on an inflow‐outflow basis was made with careful determination of all inflow‐outflow in the study reach to include correlations required to determine ungaged side‐channel in‐flow and unmetered irrigation wells. Results indicate that wells have intercepted normal return flows to the river resulting in a decreased amount of surface water during the irrigation season. Stream depletion appears to equal the expected consumptive use of well water which ranged between 40% to 50% of the groundwater extraction.