Spatial Prioritization of Sediment Source Areas at Watershed Scale

Identification and prioritization of critical sub-watershed is essential to sediment control at watershed scale. Many studies have been carried out on the topic of identifying and prioritizing the critical source areas (CSAs); however, only few researches have been conducted to prioritize sub-watersheds in terms of their contributions to the sediment yield of the main watershed outlet. In fact, observations alone are not enough for CSAs prioritization; hence, hydrological models may be applied for prioritization of sub-watershed. Therefore, in the present study, prioritization of sub-watershed was considered based on (1) on-site effects of soil erosion: specific sediment yield at sub-watershed scale (sediment yield/area), (2) offsite effect of soil erosion: sub-watershed contribution to the sediment yield of the main watershed outlet. In this study, Soil and Water Assessment Tool (SWAT) was applied for prediction of runoff and sediment load at sub-watershed scale and the main watershed outlet. The Unit Response Approach (URA) has also been applied to prioritize sub-watersheds in terms of their contributions to the sediment yield at the watershed outlet. The proposed model was applied in Mehran watershed, in West of Tehran (capital of Iran). The study watershed was divided into 37 sub-watersheds. The results showed that the contribution of sub-watershed No.14 and No. 17 had the largest sediment contribution into the main outlet of watershed. The results of this ranking can differ entirely from those based on single sub-watershed sediment production at the sub-watershed outlet. Targeting the placement of Best Management Practices, based on the CSAs concept, will assist sediment control in watersheds.