Dear All
I am a master student in hydrology. I have some questions about the methodology of my thesis. I want to create flood maps. I used HEC-HMS and HEC-RAS programs to simulate the hydrologic and hydraulic behavior of the watershed. The watershed does not have any recording gauges, so the temporal pattern of the rainfall was not defined. On the other hand flood records were full of errors. Hence, I could not optimize my models. I consulted with some hydrologists about my problems. Finally, I used a ranking method suggested by Pilgrim and Cordery (1975) to create a hyetograph for the study area. In addition, I used the hyetographs produced by Huff (1967) as another option especially in order to compare with the ranking method results. I calculated rainfall depths at various return periods for the study area based on rainfall intensity-duration-frequency (IDF) relationships for my country, Iran. I input data into HEC-HMS to simulate rainfall-runoff model of the watershed and flood hydrographs, but because I didn't have flood data, the calibration process was impossible. I decided to perform a regional flood frequency analysis (RFFA) to find extreme flows for the study area. After I found predicted flood discharges. I tried to compare these flood values with HMS results. Therefore, I optimized the peaking coefficients of the Snyder's unit hydrograph method for different return periods in HMS based on RFFA results.
I would like to know your opinions about the mentioned methods.
I don't know to what extent can I trust to RFFA results or in fat, is it acceptable to optimize a hydrologic parameter with this manner? If not what should I do?
Any idea?
Thank you.