Water Quantity Quality Demand of Eutrophication Urban Lake under Different Hydrologic Year

摘要

As eutrophication is seriously in Liu Hai lake in Beijing city, ecological water demand including water quantity and quality is needed to alleviate that situations. The ecological water demand of urban lake is calculated by two stages. The demand of water quantity is firstly calculated by assure the water quality satisfying the water use. Then that of water quality was achieved after water quantity data input into the well-mixed mass balance water quality model of lake. The minimum water quantity demand of it is 907.1x10~4 m~3/a and that of optimal water demand is 1615.1x10~4 m~3. The concentration of TN and TP under condition of minimum lake flow is no less than 0.669 mg/L and 0.033 mg/L. The reduce rate of TN and TP pollutant discharge is 37.3% and 76.2% under the P=50% hydrologic year, 26.6% and 73.5% under the P=75% hydrologic year, 16.4% and 68.2% under hydrologic year P=95%. The concentrations of TN and TP under condition of optimal lake flow are no less than 0.887mg/l and 0.044mg/l. The rate of TN and TP discharge are 16.9% and 68.5% under P=50% hydrologic year, 2.6% and 64.9% under P=75% hydrologic year, 0% and 57.8% under P=95% hydrologic year. The calculation results of eco-environmental water demand can provide reasonable rules of water distribution for management departments. The further research of water allocation optimal models integrated water use benefit and water discharge treatment cost was suggested in the paper.