عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Appropriate estimates of flows for different return periods are important for floodplain management in designing canal, bridges, culverts and levees. In general, there are two common approaches to determine design flows at ungaged sites: Rainfall-runoff models, which are often costly and time consuming, and regression models, in which design flows of various return periods are related to watershed characteristics such as drainage area, topographic features, soils and climate. In the present study, bankfull-geometry data as well as flashiness index are used as effective independent variables in regression models to evaluate design flows relationships at 41 streamflow-gauging sites in Gara-Gum basin of Khorasan-Razavi province located in an arid and semiarid region. The bankfull geometry regression is found to be useful to predict design flows and comparable with flow estimates developed by traditional approaches for ungaged sites in the same basin. As, in three stations in this study area, the error in computations, compared with the method of frequency analysis, was 8% for bankfull hydraulic geometry relationship.