Efficacy of Synthetic Sediment Graph Developed using Various Modified Time-Area Methods

Abstract

Suspended sediment (SS) is an essential indicator for assessing watershed health. However, the temporal variation of SS, called sediment graph (SG) using readily available data, is not always considered, particularly in un-gauged watersheds, which are many in developing countries. Since field measurements of SS are time-consuming and costly, the synthetic SG seems to be a promising alternative. Therefore, it is essential to have reliable SS data for watershed management. This study aimed at simulating SGs through conceptual analysis of soil erosion and sediment yield at the watershed scale. To that end, soil erosion, sediment yield, and sediment routing were modeled using 38 storm events collected during 2011 and 2019 at the Galazchai Watershed in West Azerbaijan Province, Iran. Initially, the Time-Area Method (TAM) was applied, and then two strategies were considered to improve the TAM performance, including RUSLE and sediment delivery ratio (SDR) using gradient ratio and WaTEM/SEDEM methods. Comparing simulated SGs with recorded ones showed that the SDR-based method had the lowest relative error in time to peak and base time, but the peak value had the highest relative error. Results also showed that TAM developed using the spatially distributed travel time method had a better performance than the channel longitudinal profile method. Overall, TAM could not simulate the temporal variation of sediment and needs further research.