Flood Frequency Analysis For Lower Awash Subbasin Tributaries From Northern Wollo High Lands Using Swat 2005 Model

Flood frequency analysis provides vital information for the planning and design of manyrnhydraulic structures and risk assessment in flood plain use.rnThe objective of flood frequency analysis is to estimate a flood magnitude corresponds tornany required recurrence interval. The resulting relation between flood magnitudes and returnrnperiod is referred to as Q-T relation (Flood Frequency curve). This study is based on peakrndischarge, in particular the annual maximum floodrnFlood frequency Analysis, the determination of flood flows at different recurrence interval,rnis a common problem in hydrology. The standard procedure to determine probabilities ofrnflood flows consists of fitting the observed stream flow record to specific probabilityrndistributions. However, this procedure only works for basins: That have ‘long enoughrn‘stream flow records to warrant statistical analysis (gauged catchments) because a reliablernestimates of the Q-T relationship cannot be obtained from small samples of at-site datarnbecause of the high variability involved and where flood flows are not appreciably alteredrnby reservoir regulation, channel improvements (levees) or land use change.rnThe majority section of this study contains the procedure of generating stream flow datarnfor Mille and logiya watershed using rainfall –runoff model approach for use in floodrnfrequency analysis. This thesis describes a spatially distributed watershed model of LowerrnAwash basin (Mille and Logiya watersheds) that has been developed using SWAT 2005 torndescribe stream flow generation for Mille and Logiya watershed at Mille stationrn(Gauge033021) and Logiya, (Gauge033027). The Soil and Water Assessment Toolrn2005(SWAT2005) was developed by the Agricultural Research Service of the United StatesrnDepartment of Agriculture and distributed by the US Environmental Protection Agency forrnwatershed management. SWAT2005 Simulates through time the daily soil water balance.rnXIIrnThe spatially distributed nature of SWAT 2005 means that the hydrological surface runoffrnprocesses are represented independently in different regions across the basin. There are 52rnand 29 different regions called HRU (hydrological response units) for Mille and Logiyarnriver watershed respectively in this modeling application (shown at Appendix G and H forrnMille and Logiya watershed respectively).rnA set of SWAT2005 input representative of the basin has been developed from a wide arrayrnof data and the flow simulation is successfully tested against measured flow data. For thernMille and Logiya river basin, SWAT2005 model was calibrated and validated over a fourrnyear on a daily time base for daily peak surface runoff from January 1990 to December 1994rnfor calibration and January 1995 to December 1998 for validation period. Sensitive modelrnparameters were adjusted within their feasible ranges during calibration to minimize modelrnpredictive error for daily peak flows.rnModel performance testes were evaluated to test the model accuracy during the validationrnand calibration period .These measures included percent differences, coefficient ofrncorrelation (R2) and Nash-sutcliffe measures (ENs). A summery of the statistical results forrnhydrological calibration and validation of Mille and Logiya watershed at Mille and Logiyarnstations is summarized in table5.9 and table5.11 for Mille and table5.10 and table5.12 forrnLogiya. The daily ENs , R2, and the percentage difference values range from 0.69 to 0.79 ,rn0.71 to 0.83 and 15.8% to 27.5% respectively for both watersheds at the gauging stationsrnduring the calibration and validation period. These hydrology performance test resultsrnranges indicate the model is effectively simulating in the watershed. The results fulfilled thernrequirements suggested by Santhi et al. (2001) for R² >0.6 and ENS > 0.5.rnContinuous hydrologic simulation is a valuable tool to determine flood frequencies inrnUngauged watershed and in gauged watersheds that have short stream flow records or arernheavily regulated. Since hydrologic simulation models the rainfall-runoff relationship in thernbasin, it can also be used to check the validity of the probabilistic distribution selected forrngauged unregulated watersheds with long stream flow records.rnXIIIrnStream flow records, if available at all, are often much shorter and most of the subrnwatersheds are unguaged. The SWAT2005 continuous hydrologic simulation was used thernmonthly metrological data as an input for weather generator input file (.wgn file) thatrncontains the statistical data needed to generate representative daily climate data for the subrnbasins and soil, land cover and DEM data layers for simulation and extend the existingrnshort stream flow records form a few years to 50 years data for the watersheds.rnThe objective of the research is to use the watershed (Mille and Logiya) SWAT2005 modelrngenerated Annual maximum flow data for determining the best fit distribution for eachrnwatershed and Comparative analysis of flood frequency results. The extended records werernfitted to a probabilistic distribution using “Easyfit” Statistical application Software and thernGamma three parameter distribution was the best fit distribution for both Mille and Logiyarnwatersheds among many distributions presented within the softwar

Get Full Work

Report copyright infringement or plagiarism