A Method Based On ASTER GDEM For Water Surface Profile Calculation In River Channels At A Watershed Scale And Its Application

The surface line is an indispensable boundary condition for simulating the conversion relationship between surface and groundwater.With the development of the computer,the calculation for surface lines can be achieved by a variety of river hydrodynamic simulation software.River channel large-section data is the basic condition for building most hydrodynamic models,and its field measurement data often consumes a lot of manpower and material resources.Relying on the“12th Five-Year Plan”water special project“Key Technology and Demonstration for Water Quality Safeguarding of Songhua River Inlet Water”,the thesis will investigate the method based on ASTER GDEM for water surface profile calculation in river channels at a watershed scale,intending to provide hydrological boundary conditions for surface groundwater conversion and combined surface and groundwater simulation.The main contents of the present study is as follows:extracting calculated sections using ArcGIS based on the ASTER GDEM accuracy of elevation data,combining with a measured large-section data as checking basis;interpolating the hydrologic data using HEC-RAS for the part of relationship loss between water table and flow rate;analyzing the roughness evolution law with increasing magnitudes of flood by sensitivity analysis,so that finishing the calibration of roughness at different magnitudes of flood;ultimately,achieving the calculation of water surface line from the semi-Lashanzi water level station to Songhua River hydrological station in the Ersong watershed through MIKE11 hydrodynamics model.This research mainly obtained the following research results:(1)When applying the cross-section data extracted by ASTER GDEM to MIKE11,adjust the Manning roughness(n)parameter value to ensure that the error of calculated upstream water level and the measured water level meet the allowable error(?2 cm).At the same time,the relationship between flow rate and roughness value was determined,and the roughness parameter was optimized.The fixed value of n is between 0.014 and 0.027.When the flow rate is less than 1000 m~3/s,the value of n decreases with the increase of flow rate with an average value of 0.023.When the flow rate is greater than 1000 m~3/s,the value of n tends to be stable with an average value of 0.015.(2)In view of the uncertainty of the section caused by the accuracy of the ASTER GDEM,in this study,correction of the calculated section were completed by adjusting the section so that the shear stress and velocity of the riverbed were within a reasonable range(to satisfy the conditions of non-deposition and non-deposition).(3)On the basis of parameter calibration and cross-section correction,the ratio of the calculated water surface line to the natural river channel gradient is the same(0.1‰~0.17‰),which verifies the rationality of the calculation results.(4)The guaranteed rates of 20%,50%,75%,and 95%of the flow rate were used as the model input conditions.The calculated numerical values of bed shear stress and flow velocity were within the allowable range.The specific slope of the calculated surface line is also consistent with the ratio of the actual river channel gradient.The calculation of the surface line will provide the hydrological boundary conditions for surface groundwater conversion and the combined simulation of surface and groundwater.Furthermore,the present study can provide a feasible method for the deliberation of the surface line during the feasibility study of the lack of river channel survey data.