Hydrologic Process And River Health In Qinhuai River Basin In The Context Of Urbanization

Hydrology and Water resources research under changing environment is one of the current hot issues of hydrological sciences.The two main factors that impact hydrological processes change are climate change and human activities.With the socio-economic development and intensified human disturbances to the natural environment,there has been increasing external disturbances to the river system structure evolution,hydrological processes and river health.During the urbanization process,human activities have drastically changed regional land cover and profoundly modified local river system,thus breaking the equilibrium of nature.The modification of land surface and rivers by urbanization inevitably results in the changes of hydrological processes in the watershed,causing growing regional floods,and water resource and environment problems.Therefore,the evolution of river systems and changes of hydrological process as well as the consequent river health problems in rapid urbanization areas are in urgent need of further research.Qinhuai River basin is located in Nanjing and Zhenjiang City at the lower reach of Yangtze River.From half a century on,with the expansion of the city and construction of development zones in this basin,high-intensity human activities have resulted in increasingly prominent and severe flooding and water environmental problems.And the river network showed a trunk treading with the urban development,flood storage function declined;flood water level remains high,which highlighted the phenomenon of catastrophe caused by small flood;ability of self-healing of urban rivers has been wakening,and river health displayed a worrying state.Therefore,it is both theoretically and practically significant to explore and study the river system and structure river hydrological effects as well as the river health management in Qinhuai River Basin middle-downstream plain river network district under the influence of rapid urbanization.Based on physical geography,river geomorphology,hydrology and other theories,the river system changes and their influence on hydrological processes in the rapid urbanization area was analyzed by integrated use of RS and GIS,time series analysis,hydrological simulation and other methods.Using the river network maps of 1960s,1980s,2000s as well as the long-term hydrometeorology data,we analyzed the effects of human activities featured by urbanization on the river network,river regulation,rainfall and water level.Using the distributed hydrological model(HEC-HMS model),the rapid urbanization influenced the storm flood process in Qinhuai River Basin was analyzed quantitatively.Based on a comprehensive assessment of the river health in Qinhuai River Basin,management measures were proposed at three different levels of city,region and watershed.Firstly,the variations of underlying surface and river system under the urbanization background were analyzed.Through the ERDAS software,the land use maps of several periods were acquired by interpreting remote sensing images.By calculating the land use transition matrix and urban land expansion intensity index,the water conservancy area was divided into high,medium and low-grade urbanized areas,which was set as a preliminary basis to determine the level of urbanization.From 1979 to 2014 the overall changes in the underlying surface,in terms of temporal variations,were intense urbanization,which showed a tendency of the leap urban construction land,slightly increase of water area and paddy fields,slightly decline of dry land and other agricultural land,and a significant decrease of woodland.In terms of spatial variations,urbanization and the distances to Qinhuai River and Dongshan were negatively correlated.Three digital drainage maps of 1960s,1980s and 2000s were extracted based on high resolution remote sensing images and digital terrain maps(1:50000)to further explore the changes of river system structure and its storage capacity.The results showed that,with the increase of urbanization level,the river structure was simplified and trunked,the stability of river was weakened,and the river network flood storage capacity maintained an inverse relationship with levels of urbanization in general.Secondly,changes of hydrological process of Qinhuai River basin in the context of urbanization were analyzed.Based on the hydro-meteorological data from 1960s to 2000,a statistical analysis of the difference of the rainfall indicators in urban and suburban areas were analyzed and compared.Based on the daily data of the Dongshan Station and Wudingmen Station,we,by using the change range method,analyzed the water level changes before and after human activities so to explore the influence of urbanization to watershed hydrological regimes.Results showed that monthly average water level changed moderately while flood season changed significantly;and that annually minimum water level changed drastically while annually maximum water level changed only slightly;and that there were moderate or slight changes in the time of extreme water level events,frequency and delay of high/low water level events,as well as the rate and frequency of water level changes.Our results suggest that the regional hydrological regimes have changed to varying extent.By a comprehensive rainfall-runoff simulation model,the rain-runoff process under different river patterns in urbanized area was dynamically modeled,thereby quantitatively predict the effects of river network change on storm flood and drought,providing support for analyzing the hydrological rules in changing environment.Finally,a comprehensive assessment of the watershed hydrological environment and river health was conducted.Following theories in multidiscipline like hydrology,river geomorphology,landscape ecology and environmental science,and based on the analysis of impacts of river network changes on hydrological cycling elements and processes,we investigated the hydrological environment in the studied urbanized watershed.,Based on the traditional entropy weighting method,combining the Matter-Element Model which using correlation functions,we established the entropy weighting matter-element method for assessing river health.Subsequently,the spatial-temporal variations of river health in Qinhuai River Basin were studied.Based on the influencing factors and underlying mechanisms of river health,several countermeasures were proposed to improve river health at three levels of city,region and watershed,which can provide a reference for river health management of Qinhuai River basin.In conclusion,this research,by a case study of the Qinhuai River basin where the urbanization developed rapidly and floods occurred frequently,analyzed the changes of river network and hydrological processes,revealed the influenced factors that affected river patterns and features of hydrological processes under the influence of urbanization and other human activities.A hydrological model was established to dynamically simulate the storm and flood process after urbanization and to provide the scientific basis for flood mitigation.The comprehensive evaluation of river health under urbanization background was further conducted and the countermeasures of river health management in Qinhuai river basin were proposed,which provided a reference for studies of the river management under changed hydrological situations in other urbanized area.