Determination the suitable method for estimate suspended sediment load in Ilam dam watershed.

Suspended sediment load constituted the principal part of sediment yield in rivers، and custom methods were estimating sediment yield less than real sediment. The purpose of this study was assistant accuracy and precision method customs for estimate sediment yield instudied watershed. In this basis، six different methods were used، that integrated of three rating curve linear، multilinear and mean value with two mean daily and duration flow in Ilam Dam watershed. For selecting the suitable model is used of mean absolute error (MAE) index، next the rating curve with minimum error in integrate with daily was selected as a suitable method. Such as at during 40 daily of concentration sediment flood and based flows were sampling and determination real sediment yield. In next stage real sediment with sediment estimate models were compared. The results conducted that، there were significant differences between methods sediment estimation. The rating curve by mean value in compound with daily flow discharge was selected as a suitable method. The method was able to estimate 56 percent of real sediment load، but by using of flood hydrograph sediment load increased to 83 percent. In order word، using of flood hydrograph in flood days، in compared with mean daily discharge، it was increased sediment up to 2. 73 times. Such as، 96 percent of sediment at duration flood and 4 percent at base flow were delivered. In the based، increase precision sediment hydrological models are important. To accomplish this، increase sampling of sediment at duration floods and use of flood hydrograph in estimate sediment yield are proposed.