Study On The Concentration Model Of Fengjiageduo Watershed Based On Geomorpho-Climatic Instantaneous Unit Hydrograph (GIUH)

The Geomorpho-Climatic Instantaneous Unit Hydrograph (GIUH), as one of the important flood design methods of the middle or small catchment, has displayed a wide prospect of application in design flood calculation, flood prediction and other aspects by its unique merits, that is quantificationally introducing the geomorphological element and hydrodynamic factors into basin response and little relying to gauged data.This paper reviews the development of concentration model, especially on the development history, principle and research application status of the concentration model which take GIUH as the basic way, and introduces modern Geographical Information System application in the respect of obtaining the hydrology model parameters. At the same time, building the concentration model of GIUH basing on landform datum, according to the fact that a lot of data of precipitation and runoff are needed when determining a basin's unit hydrograph, basing on Digital Elevation Model (DEM), taking Fengjiageduo watershed as object of study, obtaining the geomorphic parameter and hydrodynamic parameters of R-V GIUH by applying GIS technology. Then simulating results, comparing with the measured flood hydrograph, analyzing characteristic of GIUH, providing reference for the flood forecasting in the data shortage region. The principal results are as follows:(1) The paper, extracts channel network of different critical support area by using Arcgis9.0 and generating continuous river network method, analyses on the effects of the critical support area on both the total length and the average slope of the extracted channel network, and determines the result that 0.05km~2 is the critical support area of Fengjiageduo watershed for channel development, and calculates out its Horton's bifurcation ratio (R_B) is 4.63, length ratio (R_L) is 2.59, area ratio (R_A) is 2.90. The proposed approach avoids extracting river network subjectively, and improves exactness of extracting geomorphic parameters.(2)This paper obtains 20 cross sectional drawings of typical river channel, by dividing river network into 20 levels, and double grading river network according to each river length level, basing on grading river network by Strahler grading method. On this basis, calculating the average river width of each flood according to the mean water level of each flood and each cross sectional drawing of typical river channel. Then, comparing the calculation results with the actual test one, and the results showed that average river width (B) increases with the increment of average net rainfall intensity (ir), and they represents exponential relationship, namely B = 0.261Ln(ir) + 3.3783. The expressions transforms the relationship between average river width and average confluence process into the relationship between average net rainfall intensity and average confluence process.(3)Building concentration model of Fengjiageduo watershed by using the geomorphic parameters and hydrodynamic parameters, and simulating the hydrological process of 4 rainfall processes in the watershed. The simulation result shows that the simulation confluence curves can be good at reflecting the effect of rainfall on flood process, and the shape, peak value, time to peak, trend of simulation confluence curves basically tally with the measured curves'. At the same time, research results show that the concentration model based on R-V GIUH is suitable for the small watersheds of Loess Plateau of western Shanxi as the prediction method to predict flood process, and it also can be used for the hydrological forecasting in the small watersheds of short of hydrological data.(4) By means of changing the main geomorphic parameters and hydrodynamic parameters in research area, this paper reveals the change law of peak value and delay time of GIUH with the changes of the above parameters and the results are as follows:â‘ R-V GIUH is different sensitivities to geomorphic parameters change. Among them, R-V GIUH is most sensitive to the changes of RL, and the peak value of R-V GIUH is decreased as the increase of RL; for the RA, the larger the RA, the higher the peak value of R-V GIUH and the shorter the delay time of R-V GIUH; R-V GIUH doesn't display the unitary change trend with the change of RB, so the change trend of R-V GIUH can't be estimated until analyzing the reason of RB change.â‘¡The change of R-V GIUH is very notable and sensitive with Manning roughness coefficients (n). The larger the n, the smaller the average confluence process (v) and the smoother the curve of R-V GIUH; conversely, the smaller the n, the larger the v and the steeper the curve of R-V GIUH.â‘¢When the other hydrodynamic parameters, geomorphic parameters and rainfall process are the same, the smaller the average river width (B), the larger the v and the steeper the curve of R-V GIUH and the larger the peak value; when the river basin is fixed, with average net rainfall intensity increasing, the B is broader, the v is larger, the curve of R-V GIUH is steeper, and the peak value is bigger.