Management at 27 low-head dams affects water surface elevations for a 1050km stretch of the Upper Mississippi River (UMR) between St Louis, Missouri and Minneapolis, Minnesota. A systemic overview is given of current operating plans at dams on the UMR and historical data are analysed to determine how well the operating plans are being met. Water level elevations at all 27 dams are regulated as a function of discharge, although plans are specific for each dam. The management objective is to maintain a target water level at specific locations (control point) in each impoundment over specific ranges of discharge. The target water level and control point may change as discharge changes in each impoundment. In some of the impoundments water regulation causes drawdowns below the elevation for which the dams were planned, and at other dams no drawdown occurs. During the navigation seasons of 1980 to 1990, water levels were within their target window for an average of 72·5% of the time for 25 dams analysed. Difficulties in meeting targets are caused by winds, local rainfall events, ice dams and rapidly fluctuating discharges from tributaries with upstream reservoirs used for peaking hydropower.
