Lake Water Level Management as a Tool for the Control of the Littoral Zone: An Optimization Approach
Tsiros, Ioannis X.
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The reduction of the littoral zone is used as a lake restoration technique that results in nutrient control and water quality improvement (Yount and Crossman, 1970; Burton et al, 1979;). In contrast, in other cases the littoral zone operates as a protective and pollutant filtering zone and its maintenance is desired (Toth, 1972; Water Resources Management Program Workshop, 1986); in some cases also its protection as a freshwater wetland is desired. A number of studies and observations indicate that, in both cases, the fluctuations of the lake water level can be used as a management tool for controlling the littoral zone's existence and extent. ( Jorgensen, 1983; Clausen and Johnson, 1990). The reduction or protection of the littoral zone requires totally different lake water level management during the year. The water balance of the lake and a number of constraints reflecting the specific characteristics of the system, the several water uses and the requirements for the protection or reduction of the littoral zone pose an optimal control problem. Based on the above concepts, an optimization approach has been developed for management of the water levels in lakes and reservoirs where the littoral zone plays an important role. Inputs to the model consist of hydrological data for the watershed and the lake or the reservoir and data on water demand. The model can also be linked with an appropriate watershed model for direct input of hydrologic data. The objective function and the constraints formulations are based on the management purposes and on historical data concerning the status of the vegetation zone versus different water elevations. Model outputs are the amount of the water that must be released and the monthly averaged lake elevations during the year. The optimization model uses a dynamic programming algorithm. Detailed descriptions of the approach, sensitivity and testing of the algorithm for hypothetical cases are given in (Tsiros, 1987). The theoretical background of the approach is based on the results of a comprehensive field monitoring program presented and discussed extensively in (J0rgensen, 1983). This paper describes the model's formulation, its major assumptions, and its application in a real case problem where impacts to the littoral zone have occurred because of a water development project. The applicability of the approach to regional reservoir planning and management, the limitations and further extensions of the approach are also discussed in the context of applying the proposed approach for management guidelines and recommendations concerning lake management with regard to lakeside vegetation zone control.