Distributed Nonpoint Source Polution Modelling

With the development of economy and society as well as the aggravation of the urbanization process, the issues on water and city become one of the great challenges that the international society faces this century. It is an important measure to solve the regional shortage of water for protecting current clean water sources from pollution while developing new resources and reducing wastes. Miyun Reservoir, the mere surface water source for drinking water in Beijing presently,is facing serious threat of eutrophication in recent years. The improvement of water quality in the reservoir is related with the safety of drinking water and the sustainable development of economy and society in Beijing. On the basis of the theories and methods such as watershed management, conjunctive control of both point and nonpoint sources, land use and management, etc., a distributed hydrological model SWAT was developed by using GIS (Geographic Information System) technique to investigate the water source protection on the Miyun Reservoir. The main conclusions are as follows:(1) For the purpose to develop the weather generator in SWAT model, a method to estimate daily solar radiation was proposed on the basis of relationship between sunshine duration and solar radiation. The interpolation method was used to make the soil grain size conversion, and the soil water characteristics were estimated by the SPAW program to build up soil property database. The result shows that the weather generator accurately reflects the climate characteristic and the estimated soil property parameter value can describe the soil spatial distribution in the basin. It is proved that the SWAT model can be used in the upland areas in northern Hai Basin.(2) The sensitive parameters were identified through sensitive analysis and the calibration and validation for streamflow, sediment and nutrients were performed. A scientific platform was built to investigate NPS (Nonpoint source) pollution in the Miyun Reservoir basin. The spatio-temporal distribution features of NPS pollution in the Miyun Reservoir basin were revealed. NPS pollution mainly takes place in flood season, and it is more serious in the Cao River watershed than that in Bai River watershed.(3) The nutrition contributing ratio in the Miyun Reservoir was estimated. The study shows that one third of the total TN and TP load are produced by the human activity in the Miyun Reservoir basin, and other pollution load was produced by the soil background value which is related to landuse. Nearly four fifth of the pollution load which is controlled by people is attributed to NPS. Therefore, the emphasis of basin management should be put on the NPS control in the Miyun Reservoir basin.(4) The critical areas of soil erosion and nutrient loss were identified. According to the simulation result the soil erosion module were calculated in each subbasin and their soil erosion intensities were classified. For the purpose to protect people health and biological safety, the concentration of nitrate and soluble phosphorus were calculated at the outlets of each subbasin. The result shows there may be potential risks in too high concentration of soluble phosphorus at some outlets of subbasins in upstream of the Miyun Reservoir basin.(5) The spatio-temporal features of land use changes in the Miyun Reservoir basin during 1990s were analyzed. The result shows that the centric shift and transition between different landuse were intensive, and agriculture activity was major driving forces for the changes. Comparatively, the land use in 1995 was beneficial to reduce the NPS pollution load into the Miyun Reservoir.(6) The environmental capacity of TN and TP in the Miyun Reservoir were calculated by using Dillon model during the period from 1991 to 2003. Compared with the inflow load, there is no margin for TN load even in the early 1990s. With the increase of fertilizer use and the development of poultry and livestock breeding, the inflow load will increase too and lead to the water quality below to meet the national standard II of water environment. It is same for TP, but there still have some margin for it. Measures must be taken to prevent the entering load from exceeding the capacity.(7) The pollution loads were assigned by the contribution ratio. The preliminary allocative decision is to build sewage treatment plants in both Chicheng and Dage towns and decrease 2/5 pollution load from poultry, livestock and fertilizer. The simulation result shows that these measures are feasible.(8) Eight scenarios were proposed to find the best management practices, from which one or different combination of these scenarios may be selected to prevent NPS pollution. The main innovations in this study include:The spatio-temporal features of land use changes in the Miyun Reservoir basin during the 1990s and its effects on water resources have been analyzed;The method to set up SWAT model has been proposed;The field of SWAT model application has been extended to water source protection.