Study On The Impact Of Urbanization On Stream Structure And Regulation Capacity In The Center Of Tai Lake Basin

Located in the center of Tai Lake Basin, Wuchengxiyu region is densely covered with river networks. Since Reform and Opening in1978, the process of urbanization is accelerating continuously. For the limited land resources, a large number of water surface are occupied while low-grade river and some small water bodies are landfilled. These human activities result in the decline of water surface ratio and the stream structure is becoming much simpler in urbanized area. Finally, the regulating and storage function of river networks is weakened and the flood disaster happens frequently. Therefore, in the perspective of fluvial geomorphology, research on the variation characteristics of stream structure and its storage effect in urbanized area, combined with LUCC, is of great significance.This paper is supported by the public welfare project of ministry of water resources (No:201201074). Based on landuse、water system and water level data in three different periods, it analyzed the spatial and temporal changes in landuse, stream structure and its storage effect comparatively between different periods and scales with multiple indicators. Also, this paper analyzed the driving factors of the change in stream structure with ArcGIS and SPSS, and put forward some protection countermeasure of the stream structure based on the regulating and storage function. These countermeasures will provide relevant references for the protection and management of stream structure in the future.Based on remote sensing images of landuse in1991,2001and2006, this paper analyzed the spatial and temporal changes in landuse comparatively from the perspective of total change, structural change and the intensity change. The results showed that:(1) paddy field and urban construction land were the two main landuse types, which account for more than90%of the total area;(2) In the past16years, the urban construction land increased dramatically, and the increasing rate is126.9%; The decreasing rate of water was79.8%;(3) The total amount of landuse change is increasing year by year, and the increasing speed of urban construction land is six times of its transferring speed; Water land was mainly transferred into urban construction land and paddy field;(4) Four cities in Wuchengxiyu Region with different level of urbanization showed the same change trends in landuse, a substantial increase in urban construction land and continuously decreasing in water land; But the change ranges were different, and Wuxi city showed the most prominent changes in the total change.In order to analyze the spatial and temporal changes in stream structure comparatively, this paper calculated four characterization indicators, Rd, Wp, CR and D in1960s,1980s and2009. The results showed that:(1) the total length of rivers is continuously reducing in the past50years, and its reducing rate is35.74%; The reducing rate between1980s and2009was much larger than the last period;(2) The lower river grade is, the greater the reduction rate of river total length was;(3) Water areas in Wuchengxiyu Region showed the same change trends as the total length;(4) Since1960s, four indicators, Rd, Wp, CR and D declined year by year, which indicated that the higher the urbanization level is, the simpler the stream structure is;(5) Four indicators in different cities also reduced continuously, and the reducing rate is not only related to the urbanization level, but also to its development speed;(6) The significant impact of urbanization on stream structure was futher confirmed by the correlation analysis between non-agricultural population, GDP and the water surface rate.This paper choosed four representative water level stations to analyze the spatial and temporal changes in storage effect comparatively. Four parameters, C, AC, SR and ASR were analyzed in different periods and different river grades. The results showed that:(1) the value of SR and ASR in different grade rivers were declined continuously; The lower the river grade was, the greater the reduction of storage function was;(2) Affected by the same environment change, the third-grade river showed a positive function in regulating and storage, and the higher-grade rivers mainly showed water diversion and drainage functions;(3) The value of SR and ASR in different cities were reduced year by year, and the size order is consist with the water surface ratio;(4) Regulating and storage function closely related to stream structure is futhur confirmed by the correlation analysis between SR, ASR and Wp; Therefore, we can broaden the river channel, connect the rivers and increase the artificial water body to improve regional water surface ratio.