USING A GEOSPATIAL INTERFACE (GeoWEPP) TO PREDICT SOIL LOSS, RUNOFF AND SEDIMENT YIELD OF KOKOLET CREEK WATERSHED

Soil loss and sedimentation processes currently stand as one of the most serious environmental issues in Turkey. Improper use and conversion of lands along with recent shifts in precipitation and runoff frequencies caused by the global climate change are thought to be the main reasons for these issues. However, in order to take necessary precautions against these problems, firstly, both the amount and the degree of soil erosion must be determined. Recently, the efforts on obtaining data on soil erosion have shifted towards using prediction models including GeoWEPP, a geospatial interface software integrating the WEPP (Water Erosion Prediction Project) with GIS. In this research, soil loss, runoff and sediment yield from the Kokolet Creek Watershed (4057.02 ha) were predicted using GeoWEPP. Required soil, climate, management and slope files were established and the watershed was subdivided into 15 smaller hydrological units (SHUs) for an easier run. The results showed that the annual total soil loss amount was 23559 tons for the watershed. While the total sediment reaching to the channels was around 10225 ton/yr, the sediment yield was 2.52 ton/ha/yr, over the trash hold value of 1 ton/ha/yr. Moreover, the GeoWEPP predicted about 735 mm of total annual precipitation for the watershed and almost no runoff generated in the SHUs containing more than 70% forest and/or grassland areas. On the other hand, 209.73 mm of runoff was produced within SHUs where the majority of the land was converted to agriculture. The sediment delivery ratio (SDR) was around 0.782 for the watershed.