Impacts Of Hydraulic Engineering On Hydrological Connectivity Based On Ecology Health

River ecosystem is one of the most important ecological systems,providing various ecological service functions.Water-mediated transfer of matter,energy and organisms within hydrological cycle constitute hydrological connectivity.River ecosystem is a complete organic integrity,and hydrological connectivity ensure the transport of matter,energy,information and species,which determine the amounts,effectiveness and complexity of habitats and create suitable habitat conditions for river ecosystem.Hydraulic engineering make hydrological connectivity damaged,which threat the health and stability of river ecosystem directly.In the process of maintaining and repairing river ecosystem,it is need to make watershed as a whole,studying the impacts of hydraulic engineering on hydrological connectivity comprehensively and deeply,thus maintaining the health and stability and protecting ecological service function of river ecosystem while getting social and economic interests.This paper made Xitiaoxi Watershed in the upper reaches of Taihu Basin as study area,applying GIS spatial analysis,hydrological model and hydraulic model,analyzing the impacts of sluices on river network connectivity,effects of reservoir regulation on longitudinal connectivity and influences of hydraulic engineering on hydrological connectivity between river and floodplain.The purpose of this paper is to explore the methods of evaluating hydrological connectivity influenced by hydraulic engineering quantitatively,and these methods could provide theory basis and decision support for hydraulic engineering planning,design and operation.On the other hand,the results of this study also could provide references for river ecosystem maintenance and repair in Xitiaoxi Watershed and others with similar natural and social economy characteristics.The main research contents and conclusions of this paper are as follows:(1)Impacts of sluices on river network connectivity in study area.Making Dipuxi Watershed in the upper reaches of Xitiaoxi Watershed as a whole,using spatial analysis,longitudinal continuity index and dendritic connectivity index to analyze river network connectivity influenced by sluices,and the effects of amount,passability and location of sluices on river network connectivity were also discussed.The results show that compared with spatial analysis and longitudinal continuity index,dendritic connectivity index could analyze the impacts of different quantities of sluices with various passabilities and placed at different locations more effectively,which could be applied to compare different planning programs.On the other hand,the amount and location of sluices have significant influences on river network connectivity.As the amount increases,river network connectivity decreases gradually but more and more slowly.The impacts of sluices located at different locations vary:upstream and downstream sluices have smaller impacts than those located in midstream.(2)Effects of reservoir regulation on longitudinal connectivity in study area.By utilizing HSPF(Hydrologic Simulation Program-FORTRAN),natural hydrological processes without reservoir regulation above Fushi Reservoir,Laoshikan Reservoir and Hengtangcun Hydrological Station in Xitiaoxi Watershed were simulated.IHA(Indicators of Hydrologic Alteration)which reflect ecological relevant flow characteristics including magnitude,frequency,duration,predictability and rate of change of flow were used to measure the differences between actual and natural hydrologic regime,while RVA(Range of Variability Approach)were applied to identify reservoir management targets.In addition,by comparing the differences between actual and natural hydrologic regime among Fushi Reservoir,Laoshikan Reservoir with similar water-collecting area and different regulation and power generation capacities compared with Fushi Reservoir,and Hengtangcun Hydrological Station in the downstream of these two reservoirs,the influence ways,degrees and ranges of reservoir regulation on hydrological regime were discussed.The results show that the biggest changes in hydrologic regime by reservoir regulation in Xitiaoxi Watershed include monthly flow in low water season,annual maxima flow for short duration,frequency and duration of high and low pulses,rate and frequency of water condition changes,and these changes in hydrologic regime would affect river habitat in study area in various ways.On the other hand,Fushi Reservoir with higher regulation and power generation capacities has more influence on hydrological regime than Laoshikan Reservoir with similar water-collecting area,and the hydrological alterations in these two reservoirs are more significant than downstream Hengtangcun Hydrological Station,which illuminate that the impacts of the reservoir regulation on longitudinal connectivity has certain range.Compared with traditional method which compares hydrological sequences before and after reservoir construction,simulating natural hydrological processes by hydrological model and measuring the differences between actual and natural hydrologic regime could overcome the limits of climate change,land use and land cover change(LUCC),representativeness of hydrological station and length of hydrological sequences.On the other hand,making use of hydrological model to simulate hydrological processes and obtain hydrological regimes for various scenes could provide reservoir regulation with powerful reference.(3)The impacts of hydraulic engineering on river-floodplain connectivity in study area.Combining HSPF with HEC-RAS(Hydrologic Engineering Center's River Analysis System),this study applied flood inundation areas and water depths for specific flood,lateral connectivity areas,and floodplain development coefficients to analyze river-floodplain connectivity for current situation,the scene only with levees,the scene only with reservoirs and natural scene,and combined influences of reservoir regulation and levees on river-floodplain connectivity were discussed.The results showed that reservoir regulation reduce flood flow,while levees weaken the connection between river and floodplain.Reservoir regulation and levees influence on river-floodplain connectivity in different ways,and the impacts of reservoir regulation were less than levees.Reservoir regulation and levees greatly reduce floodplain area exchanging material,energy and information with river,which destroy the structure and function of river ecosystem.