Analysis of Flow through Sturgeon Lake and Backwater Channels of Mississippi River Pool No. 3 Near Red Wing, Minnesota

Abstract

Flow rates through Sturgeon Lake and backwater channels of the Mississippi River in the vicinity of the Prairie Island Nuclear power Generating Plant are determined as a function of total river flow and of wind direction and wind velocity, particularly for low flow conditions. The analysis is made in order to determine; (a) how much of the Sturgeon Lake flow is drawn into the cooling water intake of the plant, and (b) by how much plant effluent cooling water or blow down water is diluted by sturgeon Lake effluent before entering the Mississippi River. A channel network analysis including effects of wind stress on the water surface in addition to bed shear stress and local (minor) energy losses was made to provide the required information. Forty-three channel and channel segments were used to describe the entire system. The Sturgeon Lake/North Lake system was studied before the complete analysis was made. In the absence of wind, flow through Sturgeon Lake amounted to about 22 percent of total river flow. At low plant withdrawal rates and at zero wind, the flow through the backwater channel in front of the plant outlet (channel 42) was about 10 percent of total river flow. Winds from 5 to 30 mph had a very noticeable effect on flows through Sturgeon Lake, particularly when total river flows were less than 10,000 cfs. The analysis was made without consideration of stratification effects near the plant intake and outlet.