DRAINAGE OF CLAY OVERLYING ARTESIAN AQUIFER .1. HYDROLOGIC ASSESSMENT

The performance of subsurface drains in a clay soil overlying an artesian aquifer is evaluated at a site in Imperial Valley, California. Field studies are undertaken to examine water and salt movement through the soil profile and the response of subsurface drains under surface irrigation. Water penetrated to all depths soon after the passing of the irrigation advance front. Peak drain flow occurred shortly after irrigation had stopped. Soil and drain-water salinity remain nearly constant throughout the year, and have changed little over the past several decades. The drains intercept only a small percentage of deep percolation water and do not contribute significantly to the overall drainage of the field.