Study On Impact Of Water Diversion And Drainage On Water Quality Of Liangxi River

There have been many researches on the water quality control of urban mesh water systems nowadays,but there are still few studies on the effects of water diversion and drainage on water quality improvement.The effect of water diversion and drainage on water quality improvement has gradually been paid more attention.Based on the Liangxi River mesh water system,this thesis constructed the generalization of the network water system according to the hydrodynamic path and water flow control conditions of the Liangxi River area.According to the generalized map and boundary conditions,the hydrodynamic and water quality model of the Liangxi River network water system was built.Due to the length of each channel,the initial roughness of all channels was set to be 0.03 with reference to the Holden roughness table.The actual measured water level data at the two representative sections(Fengshanzha Station and Luoshe Station)in 2013 were compared with the hydrodynamic simulation data,and the model parameters were determined accordingly.The results showed that the roughness values of the rivers in the Liangxi River and the surrounding river network were approximately 0.020-0.025.The local river network was used as the verification of the hydrodynamic and water quality parameters.The verification results proved that the parameters are accurate,and the average relative error between the calculated and the measured value is only 0.15%.Based on the Liangxi River mesh water system,different water diversion and drainage conditions were designed.12.5%,25%,and 37.5%,and 50%of water was added or subtracted on the basis of basal diversion and drainage condition.Comparing the water quality in the eight operating conditions and the actual measured baseline values selected from the already established hydrodynamic and water quality models,the Liangxi River Network was evaluated by comparing the changes in the water quality parameters under these eight conditions.The most suitable water diversion and drainage condition was determined for the Liangxi River.The following conclusions are drawn:(1)If the water quantity is adjusted by water diversion and drainage to reduce the TN,it is recommended that the water diversion and drainage volume is 30%of the baseline water quantity.(2)If the water quantity is adjusted by water diversion and drainage to reduce NH3-N,it is recommended that when the water diversion and drainage volume is 25%of the reference water volume.(3)If the water quantity is adjusted by water diversion and drainage to reduce the TP,it is recommended that the water diversion and drainage volume is about 38%of the standard water volum.