Temporal Variation of Bed Load to Suspended Load Ratio in Kojour River, Iran

Abstract

Analysis of the river sediment transport variability under different temporal and hydrological conditions is important in hydraulics, hydrological, and soil and water conservation science and engineering. However, few studies have been conducted to study bed load (BL) and consequently BL to suspended load (SL) relationships and temporal variation of this ratio. The present study was, therefore, conducted to evaluate the temporal variation of the BL–SL ratio in the main river of the Educational and Research Forest Watershed of Tarbiat Modares University (Kojour), Iran. BL, SL, and discharge were simultaneously measured from July 2011 to June 2012, under different hydrological conditions, at a flume located at the main outlet of the watershed. The BL–SL ratios were then analyzed under different conditions, which showed that the discharge, SL, BL, and BL–SL ratio during the study period varied between 60 and 780 L s−1, 2 and 2786 mg L−1, 0.0005 and 13 mg L−1, and 0.01–8.1%, respectively. The mean ratios of the BL–SL ratio in summer, autumn, winter, and spring were 0.16, 0.86, 4.6, and 0.8%, respectively, with standard deviations of 0.067, 0.95, 2.73, and 0.56%, respectively. The mean ratio of BL–SL was about 1%, which is very low compared to figures off‐reported. Flow discharge, precipitation, and sand and gravel mining were also recognized as important factors affecting the temporal variability of BL–SL ratio in the study area.