An evaluation of bank storage at Painted Rock Reservoir, Maricopa County, Arizona

Abstract

Painted Rock Dam is a flood-control structure on the lower Gila River, Arizona, managed by the U.S. Corps of Engineers. Water budgets conducted by that agency showed large imbalances between reservoir outflow and storage changes, suspected to be due to bank storage return. This study was an attempt to quantify these imbalances by a waterbudget analysis of the flood periods. Bank storage was found to be a significant flow component, particularly from the 1966 and 1979 floods. Reservoir operations as well as the maximum reservoir stage controlled both the total volume and the rate of bank storage return. Reservoir operations were responsible for the low bank storage returns from the 1973 flood despite its large size. The 1967 and 1978 water-budget analyses may have been affected by significant measurement errors. It was not possible to assess the error for all components. The largest source of error is probably in the measurement of discharge past the dam. In addition, sediment accumulation in the lower reservoir area appears to have affected the stage—volume relationship at lower reservoir stages.