Modeling Artificial Recharge in Coachella Valley, California:
Historical Data, Model Approach, and Simulation Results
by Gerald T. O'Neill,
Eric M. LaBolle, and Graham E. Fogg
regional groundwater flow model of Coachella Valley, California, developed for
testing the effects of various management alternatives on the groundwater resources,
was used to simulate historical artificial recharge events in the upper part
of the basin. Development of groundwater resources in the basin has steadily
increased since the early 1900's. From 1936-73, water levels had declined nearly
100 ft in the Palm Springs area. Since 1973, significant artificial recharge
has occurred from spreading basins located a few miles west of Palm Springs.
The artificial recharge, combined with a few years of above average rainfall,
reversed the declining trend in water levels in 1979, and by 1996, water levels
in the Palm Springs area had increased over 80 ft to their early 1950's levels.
The spreading basins overlie a thick gravel and sand alluvial aquifer. Infiltration
through the vadose zone was not explicitly modeled, but recharge rates were
sufficiently high (>1 ft/d) that effects on measured water levels were typically
observed within a year. The regional flow model was calibrated to hydrologic
conditions in the basin from 1936-96. The historical period was divided into
fifty-one, mostly one-year, stress periods. Calibration focused primarily on
estimation of the significant water budget terms, i.e., recharge and pumpage.
Natural and artificial recharge rates were estimated along the Whitewater River
stream channel and at the spreading basins. Parameter calibration was moderate
and geologically based. The full 60 years of hydrologic record, including effects
of major precipitation events and drought, pumping, agricultural drainage, and
artificial recharge, was reproduced with unusual accuracy by the model. Results
provide insights into the interplay between these major hydrologic phenomenon
on a basin scale and highlight the impacts of the artificial recharge.