Effects on ground-water levels in the Missouri River alluvial aquifer caused by changes in Missouri River stage, Fremont and Monona Counties, Iowa

Abstract

An analysis of available hydrologic data was conducted to evaluate the effects on groundwater levels in the Missouri River alluvial aquifer caused by changes in Missouri River stage at selected sites in Fremont and Monona Counties in western Iowa. Daily mean groundwater levels and river stage measured during November 1995-September 1996, simulated daily mean river stage for November 1995-December 1996 derived from simulated daily mean discharge for eight alternative water-management plans for the Missouri River, and simulated daily mean groundwater levels for November 1995-December 1996 for selected water-management plans were used in the study. The measured data represent hydrologic conditions for the Current (1998) Water-Control Plan of the U.S. Army Corps of Engineers. Groundwater levels in the alluvial aquifer vary in response to river stage, precipitation, proximity to drainage ditches, evapotranspiration, and pumpage. In Fremont County, measured groundwater levels generally were lower than river stage during the spring, summer, and fall months. In Monona County, measured groundwater levels generally were higher than river stage. Water levels in wells at distances greater than about 8,000 feet from the river in Fremont County and about 6,500 feet in Monona County likely were more affected by precipitation Abstract 1 itation, discharge from evapotranspiration, aquifer properties, and land-surface altitude.