Study On Water Quality Process Of Guanting Reservoir Based On Different Operation Modes

Guanting reservoir（GTR）is an important urban water resource in Beijing and its surrounding areas,and its water quality is of great strategic significance.Based on relevant study of Guanting Reservoir,the hydrodynamic water quality model of Guanting Reservoir was established by mathematical means,the self-purification and migration law of water quality parameters such as nitrogen and phosphorus in the reservoir was simulated,their changes with time and space was described,and the scheme of restoring the water quality of GTR was further considered through the method of joint operation of water quality and quantity combined with the current ecological flow of Guanting basin.the reasearch of this paper is hoped to provide reference for the scientific operation management and water quality improvement of GTR.The main conclusions are as follows:（1）The average concentrations of DO,NH₃-N,COD_Mn and BOD₅ in GTR from 2010to 2017 were 9.77,0.45,4.76 and 2.54 mg·L^-1,respectively;the long-time average concentrations of TP and TN were 0.15 and 3.44 mg·L^-1,respectively.（2）The three-dimensional hydrodynamic water quality model of GTR was established,and the verification results showed that the fitting degree of water level is high,the relative errors of WT and DO are 10.33%～24.72%and 11.01%～22.32%respectively.The relative errors of NH₃-N and COD are within 30%,while the relative errors of TN and TP are 23.70%～29.45%and 13.98%～29.16%respectively.（3）The simulation results show that water velocity in GTR area is relatively small,and the distribution of flow field in each reservoir area is significantly different in wet,normal and dry seasons.The surface water temperature is between 0～25℃,with an average of 13℃;the bottom water temperature remains within 10℃in every period;the DO concentration in the surface water tends to be saturated(DO>10 mg·L^-1),while the bottom water is in anoxic or anaerobic state for a long time(DO<2 mg·L^-1).（4）The results showed that TN concentration in different seasons was sorted as winter>summer>autumn>spring,but there was a small peak in the bottom water in summer,and the concentration in the surface water was higher than that in the bottom water in winter.TP concentration was higher in summer,lower in autumn,lowest in spring and winter,and TP concentration fluctuation in vertical direction is relatively lower.The high concentration of Chl-a was mainly discovered in surface water in summer and autumn,and much lower Chl-a concentration appears in spring and winter.（5）In the process of water diversion and ecological discharge,Chl-a concentration decreased by 3.62～7.22 ug/L,but separate process of water diversion or ecological discharge had little effect on Chl-a concentration.TP concentration was low in the late stage of ecological discharge,but increased significantly in the early stage of water diversion from the Yellow River.TN concentration is less likely to change considering ecological discharge scenario alone,but increases by 122.19%on average when considering water diversion from the Yellow River.Considering the water diversion from the Yellow River and ecological discharge scenario synchronously,TN concentration increases firstly and then decreases.In engineering practice,diversion from the Yellow River to increase GTR storage capacity,and reduce the concentration of nitrogen and phosphorus is practicable,ecological discharge to inhibit the growth of algae should be considered at the same time.The research methods and results give postive impetus for scientific understanding and quantitative solution of water diversion from outer basin,hold a good application prospect in water quality evolvement process of GTR regulated by reservoir ecological operation and reservoirs under similar conditions,and provide reference for scientific management of reservoir water environment.