Effect of slope steepness and its aspect on sediment and surface runoff; case study in Gonbad Watershed

Erosion is always a major concern for farmers, engineers and policy makers due to economic and environmental impacts. Slope is one of the most important indicators on soil erosion, therefore, the aim of this study is investigation of slope steepness and its aspect on sediment and surface runoff on Gonbad Watershed located in Hamadan, Iran. To this regard, three standard experimental plots installed at southern, northern, and eastern aspects of the basin. The plot dimensions were 1.8×24 meters installed in the relatively uniform slope with different values. Runoff and its sediments were collected in spatial containers. 16 rainfall events (2010-2013) were sampled. Effect of slope steepness, its aspect as well as their interactions were analysed using a factorial experiment by SAS 9.4 software. Results indicated significant roles of slope, its aspect and their interactions in surface runoff volume. Based on the results, small slope has carried out slope steepness significantly on runoff rate, that have more significant effect on smallest steep compared to higher steepness. This is because of land use and vegetating cover and also higher average infiltration rate as well as the recent soil moisture content on the high steep. This is important to note that the slope steepness have not significant effect on runoff sediment rate. The aspect also has significant effect just on 6.25% of the events. The interaction of slope steepness and its aspect also was significant on 18.75% of the events.