Effect of watershed geomorphological characteristics on sediment redistribution
2021
Sedighi, Fatemeh | Khaledi Darvishan, Abdulvahed | Zare, Mohamad Reza
Sediment budget is a valuable tool for describing the sediment production, transfer and storage in a watershed and its components depend on different watershed physical properties. The present study aimed to evaluate the relationship between 22 geomorphological factors and sediment budget components in a small mountainous watershed in the west of Iran, using ordinary least square, geographically weighted regression and bivariate regression. The distribution map of erosion and deposition was prepared using ¹³⁷Cs in 15 sub-watersheds and the internal area. According to the results, the maximum net erosion rates were related with the sub-watersheds with medium slope (<20%) which strongly reveals the role of landuse and its interaction with the slope steepness. In addition, the mean sediment delivery ratio for 15 sub-watersheds was 28.43%, which decreased to 12.63% by increasing the area to the whole watershed due to trapping and redepositing mainly because of low slope agricultural lands close to the outlet. This finding reflects the interaction effects of the area and slope on the reduction of sediment delivery ratio by increasing the probability of trapping and redistribution of sediment. The Gravelius's shape index, equivalent rectangular width, and order of the main river were the most related geomorphological factors with total erosion and deposition. It is possible to estimate net erosion and sediment delivery ratio using equivalent rectangular width and topographic wetness index, respectively. The most important factor on sediment budget in the study area was topographic wetness index, probably because it depends on the slope as well as hydrological properties of the sub-watersheds.
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