Developing an Optimal Water Intake Rule Curve for the Chitgar Lake

Water bodies are in danger of anthropogenic eutrophication, i.e. fast growing of algae and the subsequent problems. High amount of nutrients existing in water column is the driving force for eutrophication and phosphorus is the key limiting nutrient in freshwater resources. Chitgar Lake is an artificial lake with recreational purposes in Tehran. It is predicted that the lake may face some quality problems, especially eutrophication, due to high phosphorus concentration. There is a wide variety of management tools to reduce the phosphorus concentration in lakes. One of the easiest practices in artificial lakes and reservoirs is the hydrological manipulation, i.e. setting operational rules for water outtake from the lake or water intake to the lake (in case artificial water transfer system to the lake exists). In this paper, a general phosphorus mass balance model for lakes, LakeMab, is adapted to the Chitgar Artificial Lake. The adapted model is then calibrated and validated using two years data of total phosphorus (TP) concentrations in the lake. Using NSGA-II, the water intake rule curve is optimized for minimizing the average intensity of violation of TP concentration standard in the lake during high algal growth period of the year. The results show that optimized rule curve will reduce the TP compared to current rule curve, but not lower than the desirable amount of 40 mgP/m3.