Development of synthetic unit hydrograph for northern Iranian watersheds using physiographical characteristics

Application of unit hydrographs as one of flood estimation techniques requires hydrometry stations and observed data collection. Application of watershed physiographical characteristics is therefore supposed as an applicable substitution because of their accessibility and accuracy. The present research has been conducted to regress different shape and time components of unit hydrograph into physiographical characteristics of the some selected watersheds in northern Iran with an area of ca. 177000 km2 extended in Golestan، Mazandaran and Guilan Provinces. For this purpose، 9 physical characteristics of the watersheds and 8 characteristics of unit hydrograph were taken into account. Different statistical analyses of bivariate and multivariate regressions using simple and transformed forms of data، clustering and principle components were applied to study the relationships. The obtained models were evaluated with the help of relative error، root mean square error and efficiency coefficient. The results verified the possibility of development of synthetic unit hydrographs by using watershed physiographical characteristics emphasizing on watershed perimeter for estimation of hydrograph components and watershed mean slope for prediction of time related factors. The priority of bivariate and multivariate models was also ascertained for estimation of time and discharge components of the 2h unit hydrographs، respectively، with an average value of efficiency coefficient of 0. 52 ± 0. 32.