SEDIMENT DISTRIBUTION AND QUALITY IN A SMALL WISCONSIN RESERVOIR

Abstract

ABSTRACT Eau Galle Lake is a small Corps of Engineers impoundment on the Eau Galle River in west central Wisconsin. A sediment survey was conducted to document reservoir sediment characteristics in relation to reservoir morphometry, hydrodynamics, and water quality. Sediment conditions at Eau Galle Lake tend to be lakelike, rather than exhibiting a more typically reservoir-like dependence on hydrodynamics. Sediment distribution patterns in the reservoir are primarily influenced by basin morphometry, which has resulted in sediment deposition and quality being depth related. A deep central basin, circular shape, and multiple inflows have contributed to the existence of two distinct sedimentary zones. The transport zone, which is characterized as a high-energy environment, exists in the shallow, littoral areas of the reservoir. Turbulent processes dominate the transport zone, thereby, discouraging the permanent deposition of fine particulates. As a result, transport zone sediments have a relatively large median particle size and low moisture content. The deep central basin of the reservoir is characterized as an accumulation zone of low energy. Sediments in this less turbulent area are characterized by a smaller median particle size and high moisture content. Sediment chemical characteristics of nutrients, metals, and organic matter are higher in the accumulation zone. Therefore, the deep sediments may be more influential to water quality through exchanges at the sediment/water interface.