Sensitivity analysis of parameters affecting the design flood using HecHms(A case study of Sardasht Dam)

Several factors are affecting the flood routing process, each of which has a particular weight of attenuation of flood peaks through the spillway. This paper identifies these factors and analyzes the factors affecting the sensitivity of peak discharge estimation of Sardasht dam and the effects of these factors and their sensitivity were determined through hydrograph routing from the basin and the reservoir. At the first stage, after the construction of the basin model with full elements in Hec-Hms, one available storm event with corresponding runoff, simulated then affecting parameters in the different subbasins were calibrated. In the second stage, the probable maximum precipitation (PMP) hyetograph converted to probable maximum flood (PMF) and routed in the reservoir. At the last stage, the sensitivity of CN, amount of rainfall design, lag time of channel and lag time of basin and also flood routing of the reservoir were investigated. The results show that the design flood is most sensitive to the amount of precipitation as with 30% change in precipitation, CN and channel lag time the flooding amount changed linearly about 40%, 25%, and 8%, respectively, but with changing ±30% of basin lag time the flood peak changed non-linearly by 5 in over estimating and 16% in the underestimating.