GROUNDWATER AND SURFACE WATER INTERACTIONS IN STREAMS OF THE PALOUSE BASIN, NORTHWESTERN IDAHO AND SOUTHEASTERN WASHINGTON

Water levels in the aquifers of the Palouse Basin have been dropping since the 1950s. In the 1960s, attempts were made to restore water levels in the upper aquifer, so withdrawals were shifted to the lower aquifer. As a result, water levels in the upper aquifer have stabilized, but water levels in the lower aquifer are dropping at a rate of one to two feet per year. Recharge to the lower aquifer appears to be very small or nonexistent. If recharge to the upper aquifer were better understood, steps could be taken to sustain groundwater levels in both the upper and lower aquifers. Stream flow throughout the Palouse Basin could be infiltrating and eventually recharging the upper aquifer. This study measures the gain or loss of water in two creeks in the Palouse Basin using the salt-dilution method, piezometers and seepage meters. The piezometers and seepage meters show inconclusive results. The salt-dilution method appears to be the most effective method, showing a 78 to 83 percent loss along one of the streams. This loss coincides with the surficial geology interface between loess-covered and uncovered colluvium and residuum. Topographic maps also show that streams change from perennial to intermittent at this interface. This interface could be significant throughout the basin.