Assessment Of River Health Under The Background Of Urbanization In Taihu Lake Basin

River,as the carrier to the survival of humans,plays an important role in material and energy transfer process of the earth,river health is the basis and prerequisite for the sustainable development of river function.In recent years,however,with the deepening of the urbanization process,the stability of river system has gradually declined,and river health has gone from bad to worse,therefore,river health evaluation problems under the background of urbanization became the focus of attention.Taihu basin plain river network region is the most densely populated area with the most dynamic economy in China,river and lake in the area of are numerous,level of urbanization and industrialization development second to none in the country.For a long time,the developing mode which pursues the development of social economy at the expense of regional ecological environment in this area causes dramatic changes in natural ecological environment.Under the strong interference of human activity,the drainage pattern in this area is destroyed,most of the rivers are straightened,the trunk channel widens,small tributaries were buried,river curvature and river network development coefficient decrease obviously,rivers become backbone,simplification,and gradually deviated from its natural form.Water resources and water environment problems such as river drainage recession,blocked connection,river function decline and deterioration of water environment appear to some extent.Therefore,carrying out research on river health assessment under the background has important application value for the sustainable development of urbanization and the conservation and management of riverTaking Suzhou city which located in the abdominal region of Taihu lake watershed as the study area,based on the water system data,water quality data,3 period data of land use,social and economic data,with multi-discipline including river geomorphology,hydrology,landscape ecology,environmental science and so on as theoretical basis,according to scientific,representative,quantitative and operability principles,integrated applying RS,GIS,mathematical statistics method,time series analysis,landscape pattern analysis,entropy value method,matter-element analysis method,the paper analyzes and discusses the urbanization process and its water quality variation characteristics of the research region,and builds a set of river health assessment index system and evaluation methods and models suitable for the area,discusses the spatial and temporal variations and law of river health under urbanization in the study area,puts forward the countermeasures of river protection and management,provides reference for upper city planning and the water ecological planning.The main studies of the paper include:1.The urbanization process in the study area and water environment quality condition analysis(1)Analysis of urbanization in the study areaThrough the calculation of population urbanization rate index and land use change situation,the paper gives a detailed analysis of the urbanization process of the research region.The analysis results show that the population urbanization level of Suzhou in 1990-2008 of enhances unceasingly,and rate of the population urbanization level grow faster in the 21st century;According to remote sensing image of 1991,2001 and 2010 to analyze the underlying surface land cover condition of the research region,and the change rule of underlying surface overall is:urban area proportion increased significantly,less arable land,forest land,water area year by year,the decrease range of paddy field area in the period 2001-2010 is larger,shows that the growth of the urban area mainly comes from the transformation of paddy fields,water and forest land.(2)Analysis of water environmental quality situation in the study areaThe paper uses common water quality comprehensive index as the representation of water environment quality condition,and calculates the water quality comprehensive index according to 10 water quality monitoring site data from 2004 to 2014,the result show general trend of decreasing firstly and increasing after,the water quality of composite index is obviously on the low side in 2004～2008,and increase year by year after 2008,it means that water environment quality conditions of Suzhou improved significantly;By a comparative analysis of water quality of different levels of river,the results show that water quality of basin-wide river(first order river)is better than that of regional backbone channel(second order river),and the degree of water quality improvement is more significant.Therefore,it is urgent to protect lower level river from damage and pollution in the process of urbanization and maintain the plain river network region water environment quality condition.2.Setup of river health assessment index systemOn the basis of the research at home and abroad,taking multi-discipline including hydrology,river geomorphology,landscape ecology,environmental science and so on as theoretical support,the paper defines the connotation of river health,selects five element layer indexes,respectively,as the natural shape elements,water quantity elements,water quality elements,riparian habitat environment elements,the river social economic function elements,make full use of existing data in the study area,analyzes the influence of urbanization layer index,and selects nine river health assessment indexes at the same time,respectively,as coefficient of curvature of rivers and river development rate,water rate,water quality comprehensive index,respectively,as the arte of river curvature and development coefficient change,water surface ratio,water quality comprehensive index,green coverage,Shannon diversity index,biological primary potential productivity,water consumption per ten thousand yuan GDP,agroforestry production growth rate from the river health influence element.The index system covers the drainage structure,and is a set of river health assessment index system suitable for plain river network region.3.River health assessment methods and modelsBased on the analysis of commonly used methods of empowerment,through the analysis and compare of the subjective and objective determining weights method,in order to eliminate the subjectivity of weight decision,the paper makes improvement to traditional entropy analysis method;Based on the weighing and comparative analysis of many kinds of river health evaluation comprehensive methods about their advantages,disadvantages and scope of application,it is found that compared with other rivers health comprehensive evaluation method,matter-element analysis method is not only simple and convenient,and can effectively solve the problem of incompatibility between individual indicators,suitable for multi-factor evaluation system,but also can grasp the differentiation information of evaluation index with the aid of correlation function and correlation,and then discusses the reason and mechanism influencing the health of river health in the study area.Suzhou is located in the northeast of the plain river network region of Taihu lake watershed,and is one of the most densely populated area with highest level of urbanization and largest water area.There are numerous river and lake,the effects of urbanization on river health is much significant,the complexity of the river system directly determines the necessity of the application of matter-element model.Therefore,this article will apply matter-element analysis method covering dependent function and the correlation expression to the comprehensive evaluation of river health,and finally establish entropy matter-element model of river health.4.River health evaluation analysis of Suzhou under urbanizationOn the basis of evaluation index system building,using the entropy matter-element model,the comprehensive evaluation and comparative analysis to the river health of Suzhou in different periods and different parts of are carried on.(1)The river health evaluation results of Suzhou at different periods shows that the river health level of Suzhou in 2001,2006 and 2010 was "sick","sick" and "medium",respectively,general river health level is not high,but with the slow of urbanization process and the implementation of corresponding protection measures,the river health condition is improving little by little.In addition,seen from the size of the weight value of each index,curvature of river,the effects of water quality comprehensive index,agroforestry production growth rate to river health are more outstanding,and need to be improved.At the same time,according to the trend analysis of each index under urbanization,it can be seen that curvature of the river,river network development coefficient,water surface ratio,water quality synthetic index,biological primary potential productivity and agroforestry production growth rate are the main limiting factors.(2)River health assessment results of regions of Suzhou in 2009 show that the overall river health condition of Suzhou tend to be "healthy" level,while river health of the other four counties tend to "medium" and "the sick" level,the overall level is low.From the point of space layout,river health presents the trend of gradually reduce from inland river to urban river along the river.From the point of each index weight,the weight of curvature of the river network,agroforestry production growth rate,water quality comprehensive index and Shannon diversity index value is bigger.Although the regional limit factor influencing river health is not the same,but for each region,river network structure,water quality and the improvement of riparian habitat environment are still necessary for river health restoration.(3)According to the spatial and temporal variations of river health of Suzhou,based on the influential factors and mechanism of river health,the paper puts forward the countermeasures to improve the river health from five aspects,namely,perfecting urban planning,comprehensive realignment of river courses,improving the ability of water body restoration,formulating landscape ecological planning,consummating the river management policy,so as to provide reference for the river management in Taihu lake basin.