| Integrated demonstration area of Changzhou city river network composes of 15 rivers. The aim of water protection in the "12th five-year plan" in Changzhou requires that the water quality of the control sections would reach the National Standard Ⅳ grade, and cut the load of ammonia nitrogen and COD by 20%~30%. Through in-situ monitoring and modeling method, this thesis calculated the load of pollutant, the effect of emission reduction and the total maximum daily loads(TMDL) of the river network in the integrated demonstration area.The water quality and hydrological contition of the control sections in Xinzaogang River and Dawanbang River were monitored from May 2013 to October 2013 during 29 rainfalls. The non-point source load into the river for each rainfall was also analyzed. Based on the BP neural network model, we predicted the annual non-point source pollutant for a single river. By analyzing the relationship of non-point source pollution between a single river and the entire river network, the annual non-point source pollution loads in the demonstration area for TN, NH4+-N, TP and CODCr were approximately 29 t, 47 t, 3t, and 517 t, respectively. Combined with the point source load during 2013, the emissions of TN, NH4+-N, TP, and CODCr in 2013 in this area were 729 t, 103 t, 18 t, 1641 t, respectively.The water quality model of river network in the demonstration area of Changzhou city was developed using the WASP(The water quality analysis simulation program software). Based on the water quality monitored data of river network in the study area, the water environmental capacity in the area was calculated for each month during July 2012 to October 2013. The whole process of water pollution control model in the study area was developed using the CE-QUAL-W2 model. The effects of the load reduction were assessed when the sluices of connected river were opened, or closed. The water quality could be improved under the conditions of the sluice-closed case during low-flow period and of the sluice-opened case in rainy days. In the sluice-closed case, the maximum reduction values at the section of Changxin Bridge in the low-flow period for TP, NH4+-N, CODCr and TN were approximately 0.018mg/L, 0.17mg/L, 0.19mg/L, 0.18mg/L, respectively. In the sluice-opened case, the maximum reduction values at the section of Changxin Bridge in rainy days for TP, NH4+-N, CODCr and TN were approximately 0.022mg/L, 0.32mg/L, 4.8mg/L, 5.5mg/L, respectively.According to the principle of TMDL plan, the daily maximum allowable discharge load of the river in the study area was calculated during the rainy season and the dry season. The monthly average flows for the minimum flow in dry season and the normal flow in rainy season for the 3 years(2011 to 2013) at the sluice of Zaogang were used as the design flow conditions. Water quality concentrations under 90% guaranteed in both the rainy and dry seasons were used as the design water quality condition. Using the CE-QUAL-W2 water quality model developed in the study area, the daily maximum allowable discharge load of Xinzaogang River, Dawanbang River, Dongzhi River, Laozaogang River,Beitang River were calculated. The CODMn allowable emissions of TMDL for all Rivers in dry season were 4195kg/d, 4116kg/d, 1749kg/d, 1296kg/d, 296kg/d, respectively. The TP allowable emissions of TMDL in dry season were 0kg/d, 0kg/d, 11kg/d, 11kg/d, 2kg/d, respectively. The NH4+-N allowable emissions of TMDL in dry season were 16kg/d, 0kg/d, 14kg/d, 25kg/d, 0kg/d, respectively. The CODMn allowable emissions of TMDL in rainy season were 7020kg/d, 0kg/d, 6908kg/d, 1847kg/d, 574kg/d, respectively. The TP allowable emissions of TMDL in dry season were 52kg/d, 40kg/d, 37kg/d, 0kg/d, 0kg/d, respectively. The NH4+-N allowable emissions of TMDL in dry season were 42kg/d, 0kg/d, 14kg/d, 0kg/d, 0kg/d, respectively. There is no available capacity for total nitrogen in all the Rivers over the whole year. |
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