| Hydrology response and its feedback of changing physical and social environment is one of the hotspots of the current hydrology research. Floods-waterlog are increasing in Taihu Lake basin, one of most Developed region in China, with the urbanization process and land use change and river stream change. There are great theoretical and practical significance to research the change of river network pattern and its hydrologic response.Hangzhou-Jiaxing-Huzhou Plain region is located in the southern part of the Taihu Lake Basin, accounting for about 1/5 of the entire watershed area. Floods intensified. Floods and waterlog are increasing under urbanization. The main reasons of flood and waterlog in Hangzhou-Jiaxing-Huzhou Plain region are blocked hydrological connectivity and poor drainage. And river systems decay make the blocked hydrological connectivity exacerbated under urbanization. Therefore, the connectivity of river network and its hydrological response are an urgent need in current research. In this paper, river system historical evolution and nearly 50a changes, hydrological process changes, river system storage, and hydrological connectivity are in-depth researched in Hangzhou-Jiaxing-Huzhou Plain region based on the techniques and methods of GIS spatial analysis, hydrological time series analysis, elasticity analysis, Indicators of Hydrologic Alteration (IHA) analysis, as well as the parameters analysis of river systems. (1) Characteristics and development history of Taihu lake basin river systemTo provide basic background information for the influence of modern urban development on river network, structure characteristics, as well as development historical of Taihu basin river network were reviewed.(2) Change of river system characteristic and river network patternThe water system characteristics and patterns of change were analyzed and comparatively studied in sub are near 50a with the parameters of drainage density, water area rate, development coefficient one-line river, ration area-length of two-line River, box dimension, river sinuosity etc. The study area then are divided several typical subarea by urban, river network and Lakes subarea. The characteristics of different subarea are described respectively. And the relationship of these parameters of river network is described too. The results show that the drainage density and water area rate are decreased nearly 50a, and the stream pattern showed a trend of attenuation and this trend are intensified. The differences of river system changes are obvious in different subarea. In typical urban subarea the water rate is smaller than other regions, and there is the much important urban flood control after 1980s. In typical river network subarea the dense of river network are bigger, which are significantly decreased nearly 50a. In typical Lakes subarea the water area rate are decreased but not obviously. And there is a certain correlation between the parameters of river network.(3)Change of hydrological and river network connectivityThe change of hydrological connectivity is calculated based water level difference of stations, and the river network connectivity is evaluated based on the hydraulic resistance and graph theory. The result show that the hydrological connectivity increases in the backbone river while decreased without backbone river; the river network connectivity of Jiaxing region increases after South-drain dredging. The result also shows that the evaluation method of river network connectivity proposed by this paper is feasible and effective.(4) Hydrological process changeThe hydrological process change are researched and the hydrological changes in urban and suburban are comparative analyzed based on Linear regression, Spearman’s test, ordered cluster analysis, spatial and temporal changes in the method of the Range of Variability Approach (RVA) analysis of different time scales. The results show that there are increase tended of water level in the past 50a, and maximum, average, minimum water level are growth by 0.03m/10a,0.05m/10a and 0.09m/10a; and more than 90% series mean after urbanization of monthly minimum(maximum) water level are higher than before urbanization; there are increase mean and Cv in suburbs while increase mean and decreased Cv in urban; the median and outliers of all 16 sites are increased by box-plot; there are low hydrological variability and concentrated IHA in unban station while high variability and discrete IHA in suburbs station.(5) Storage capacity and flood-waterlog influenced by the change of river systemThe cause of hydrological process change are analyzed by regression analysis, the elastic method etc. On this basis, storage capacity and flood-waterlog influenced by the change of river system are researched.The results show that human activities are an important cause of water level changes. The contribution ate of human activities on highest, average, and the lowest water level changes are 39.0%,56.2% and 82.9%, respectively. Before urbanization the elasticity coefficient of precipitation on water level are 0.23～0.81, urbanization on water level are-0.01 to 0.03, and the main reason of the water level changes are precipitation change but its sensitivity decline. After urbanization the elasticity coefficient of precipitation on water level are 0.21-0.47, urbanization on water level are -0.1～0.74, and it show that with the urbanization process, the impact of human activities on water level is gradually increasing. Water level response to precipitation and urbanization are positive, and the sensitivity of the precipitation is slightly higher than the sensitivity of urbanization.The storage capacity are decreased under the change of river system, and the decreased of one-line single line is more obvious.The time of disaster caused by rainstorm become shorter, and the ability reduce of the storage-discharge of river network systems is an important reason. And bigger the water area and more densely the river network, more slowly water level of the river rise. |
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