Study On Division Method And Layout Of Drinking Water Source Protection Area In Typical Waters Of Mountainous Cities

Chongqing is a typical mountainous city.The surface water resources are relatively poor,and their spatial and temporal distribution is uneven.The groundwater resources are very small.Without considering the transit water resources of the Yangtze River and the Jialing River,the shortage of water resources is generally moderate water shortage,and the shortage type is generally engineering type.There are more than 1200centralized drinking water sources in Chongqing,which accounts for about 85%of the total number of centralized drinking water sources in the city.It is distributed in the Yangtze River,Jialing River,Wujiang main stream and its secondary tributaries in the Three Gorges Reservoir area.According to the survey and evaluation of the latest water source environment,the overall safety of the centralized drinking water source is better,but the water source and water quality of some water sources still can not meet the national environmental protection standard"Centralized drinking water source standardization construction environmental protection technology requirements"(HJ773).The Three Gorges reservoir is a typical river type reservoir,and the main urban area of Chongqing is in its fluctuating backwater area.In the Three Gorges Reservoir's normal water storage and high water level 175m operation,the lower reaches of the Jiangjin District Huahongbao in Chongqing reservoir area are in the backwater supporting state.During the 155m period,the following sections of the Chongqing guoyuan port area are in the backwater supporting state.In the flood season,when the flood control restricted water level 145m is running,the lower reaches of Changshou District Huangchaoxia are in the backwater supporting state.When the water level is equal to or less than 155m,the Yangtze River and Jialing River Chongqing main urban area is still in the natural river state.Therefore,the initial conditions of the main hydrodynamic characteristics of the Yangtze River,Jialingjiang and its primary tributaries,the main hydrodynamic characteristics(river bed roughness,water level and flow)and the characteristics of pollutants(horizontal diffusion coefficient,degradation coefficient and concentration)are inevitably influenced by the periodic effects of the operation and scheduling of different water levels in the Three Gorges reservoir.During the 175m high water level operation of the Three Gorges project,the water depth,low velocity and lateral diffusion of pollutants in the reservoir area are obvious.When the145m low water level is running,the water depth of the reservoir area is small,the flow velocity is high and the lateral diffusion of pollutants is relatively weak.The water quality evolution process of the water level of the restricted water level of the 155m and the other 3 kinds of transitional period(the water supply in the dry period,the storage of the flood before the flood season and the water storage at the end of the flood season)are all in the range of its envelope diagram.In addition,there are 510 mountain rivers in Chongqing with a basin area of more than 50 km~2,and a large number of rivers passing through the city have become an important carrier of water intake,industrial and agricultural production,landscape tourism and other activities in coastal towns.Moreover,the contradiction between the acceleration of urbanization process and the lagging of water ecological environment protection planning is becoming more and more obvious.The water ecological environment of some urban rivers is deteriorating even gradually into black and smelly water.However,the protection area divided by the analytical solution model recommended by"the technical specification for the division of drinking water source protection zone"(HJ 338)can not meet the special needs of the dynamic changes of the different storage sites of the centralized drinking water source area in the mountain cities.The protected area of drinking water sources designated by Chinese law is facing the dilemma of over protection or inadequate protection.Therefore,the water environment model,which has been widely verified and verified at home and abroad,is selected to determine the core parameters of the river bed roughness,the horizontal diffusion coefficient and the main pollutant degradation coefficient under different water level conditions.It has been used to identify the key areas and basins of non point source and point source pollution load in the reservoir area.How to scientifically and rationally layout drinking water sources and divide the protected areas has become a environmental supervision urgent technical problem to be solved first.The MIKE 11,MIKE21 water environment model developed by DHI company and the improved depth averaged 2-D model of Tsinghua University are determined and verified by the measured data of hydrology and water quality.The localization of the core parameters is applied to the study of the centralized drinking water source protection area divison of small watershed type(Liangtan river basin),superbig river type(Yangtze River,Jialingjiang Chongqing main city section)and river type reservoir(Three Gorges Reservoir Changshou economic development zone Section).The SWAT non-point source model is applied to identify the key area and watershed of non-point source pollution load in 40 primary tributaries of Three Gorges Reservoir with different storage levels.A new scheme for optimizing the layout of drinking water sources is proposed from two levels of key administrative regions and key drainage areas for water pollution control in the Three Gorges Reservoir area.The water quality of the upstream water of the Three Gorges reservoir,the pollution load of the river inlet and the tributary and its location will affect the water quality of the Yangtze River and its tributaries back water in the reservoir area.On the basis of comprehensive use of MIKE11,MIKE21,deep averaged 2-D water environment mathematical model numerical simulation method and scientific experimental research method and combined with the synchronous monitoring results of hydrological and water quality in typical pollution discharge zones of Three Gorges Reservoir area and the results of large-scale non-point source numerical simulation of SWAT model,the distribution of key basins and river segments affected by all kinds of pollution load in the Three Gorges Reservoir area is identified.The results can be used for decision making in environmental management in divsion drinking water sources protected areas and layout of protected areas in mountainous cities.The main innovation point of the paper is to determine the core parameters,such as the river bed roughness,the initial condition of the water level,the pollutant level diffusion coefficient,the initial assignment of the pollutant degradation coefficient and so on,with the localization mathematical model leading the auxiliary decision.The initial value assignment method of the core parameters,such as the roughness of the river bed,the initial condition of the water level,the pollutant level diffusion coefficient and the initial value of the pollutant degradation coefficient,is the main innovation point of the paper.The replicable and popularized model parameters of the localized hydrology and water quality have greatly improved the simulation accuracy of the hydrological and pollutant index and provided a scientific and practical method for the scientific division of the river type drinking water source protection area in the mountainous city of the Three Gorges Reservoir area.According to the difference between the vertical and horizontal spatial differences of the riverbed height of the channel type reservoir and the minute difference of hydraulic retention time in different water storage level,the EXCEL macro file programming method is used to replace the experience value of the different elevation points in the model calculation area.The complex analysis calculation process,such as iterative trial calculation,parameter rate determination and model verification are used.Different elevation points are assigned verification test river bed roughness,water level,pollutant horizontal diffusion coefficient and degradation coefficient.At the same time,using the"Data Manager"and"Mesh generate"tools software to generate the spatial scatter distribution and the spatial continuous distribution of river bed roughness,water level,pollutant horizontal diffusion coefficient and degradation coefficient of the large water depth and large scale water body are obtained.The 4 parameter surface files obtained by the above method are applied to the prediction of the change trend of hydrology and water quality in the typical waters of the Three Gorges reservoir,and the simulation error is reduced by about 15 percentage points.