Comparison and evaluation of spatial changes of sediment connectivity and sediment delivery ratio in Marcheshme watershed (Semnan province)

Watershed sediment yield estimation is an important process in watershed management. Because of limited information on sediment yield in small watersheds, empirical methods are developed in different watersheds. Sediment connectivity is an important characteristic of watershed sediment yield and is compared for better estimation of sediment delivery ratio (SDR). This research aims to compare and evaluate the spatial changes of SDR values and connectivity index on a small watershed scale. This study was conducted in the Marcheshme watershed of Semnan province with an area of 2418 ha. At the outlet of this watershed, an earthen dam was built by the natural resources and watershed management organization of the province (1995). No conservation and management measures were carried out in the watershed. In 2013, the amount of sediment trapped behind the dam was measured by the research center of Semnan province. It should be noted that there isn’t any overflow of the earth dam between 1995 and 2013. The WaTEM/SEDEM model was calibrated to calculate the SDR using the measured amount of sediment, and the SDR values for the entire watershed were distributed. A distribution map of the sediment connectivity index was prepared. The highest value of the SDR map was close to 0.5, the lowest value was close to zero, and the sediment connectivity index varied from -6.71 to 3.04. SDR and IC indices show that the amount of sediment transport and delivery near the outlet is higher than the average value in the watershed area. In the upper part of the watershed, erosion is more than the one in other parts, although SDR and the possibility of sediment connection are less than the ones in other parts. These two indicators and distribution of them can be important for prioritizing areas in terms of soil erosion and sediment management. This study shows the up-to-date application of available data and develops their potential for further analysis.