Water Environment Simulation And Total Amount Control Based On SWAT Model In Gan River Basin

At present, total amount control of water pollution in our country is given priority totarget gross control, and the capacity gross control is still in the preliminary stage. Inthe process of “total amount control in control unit”, there are several prominent issues:First, the concept of the control unit, connotation and the indicator system of controlunits division is controversial; second, quantitative methods are too simple, and thetechnology of reducing non-point source pollution lag behind; third, insufficientattention has been paid to dynamic change of water environment capacity because ofoversimplified water environment capacity models; finally, the non-point sourcepollution and the total dynamic allocation have not been taken into account in theprocess of total allocation. Therefore, it is of theoretical significance and practical valueto carry out water environment simulation and total gross control in Gan River basin.In this paper, various means such as field investigation, laboratory analysis andquerying historical data and literature outcomes were applied in building basicdatabase in Gan River basin and typical research area (Jin River basin). Moreover,using the GIS (Geographic Information System) technology, the spatial superpositionanalysis with multiple criterion and the expert decision-making methods, we describethe principles, the criterion system and the technical route of the control unit divisionat different basin levels. And then, the SWAT model was employed to implementhydrological and water environmental simulations, and to identify the Critical SourceAreas (CSAs) in the typical study area. In addition, Best Management Practices(BMPs) have been performed and evaluated based on the simulations. At last, TotalAmount Control of water pollution was carried out. The results showed as follows:(1) The control unit is proposed in this present study, which is water quality targetmanagement unit based on the concept of "Total Amount Control in Control Unit"artificially divided for the realization the purposes of computing, allocation andmanagement of water environment capacity by considering hydrology, waterenvironment, water ecology and water use function and other factors. Taking theGangjiang and Jinjiang Basins as examples, Ganjiang Basin can be divided into17control units at Grade1and even57control units at Grade2, while Jinjiang Basincontains4control units. (2) The SWAT model has been calibrated and validated using observed data from2001—2008.The evaluation results show that the calibrated model can satisfy the accuracy ofrunoff, sediment yield and water quality simulation, indicating the validity of themodel for water environmental simulation in the study area. Moreover, based on therainfall data from2001—2008, the calibrated SWAT model was applied inquantitative simulation, temporal-spatial distributions and BMPs of non-point sourcepollution. The results show that in rainy season the loss of runoff, sediment yield andnutrients account for59.4,76.9and60percentage of the year, respectively.Additionally, the correlation between rainfall/runoff and the other factors presents ahigher value in rainy season, revealing that heavy rainfall is the main driving force ofsediment and non-point source pollution.(3) The CSAs identification results demonstrate that the higher grade areas of soilerosion and nutrient loss mainly locate in urban intensive or agriculture developedareas, and these areas contribute much more than other areas. Thus, human activity isthe important cause of soil erosion and non-point source pollution, and the fifth gradeareas were chosen as CSAs of non-point source pollution.(4) The evaluation results of BMPs show that COD, TN, ammonia nitrogen, nitratenitrogen and total phosphorus loads can decrease by﹣10.26%,﹣23.10%,﹣21.80%,﹣13.60%and﹣22.40%by reducing30%fertilizer, respectively. Moreover, thebuffer has a lower reduction rata of non-point source pollution, whereas with a higherreduction (21.20%) of sediment yield. Therefore, a mix scheme can be taken intoaccount to reduce soil erosion and non-point source pollution at a time.(5) The water environment capacity of COD and ammonia nitrogen in rainy seasonaccounts for63.4%and60.6%, respectively, suggesting that the dynamic waterenvironment capacity can more efficiently utilize the natural resource. The optimal schemeof the total dynamic allocation obtained by the gini coefficient method was test itsfeasibility by the calibrated SWAT model with distributed amount of ammonia nitrogen.