Application of the WEPP model to determine sources of run-off and sediment in a forested watershed

Abstract

This study investigates critical run‐off and sediment production sources in a forested Kasilian watershed located in northern Iran. The Water Erosion Prediction Project (WEPP) watershed model was set up to simulate the run‐off and sediment yields. WEPP was calibrated and validated against measured rainfall–run‐off–sediment data. Results showed that simulated run‐off and sediment yields of the watershed were in agreement with the measured data for the calibration and validation periods. While low and medium values of run‐off and sediment yields were adequately simulated by the WEPP model, high run‐off and sediment yield values were underestimated. Performance of the model was evaluated as very good and satisfactory during the calibration and validation stages, respectively. Total soil erosion and sediment load of the study watershed during the study period were determined to be 10 108 t yr−1 and 8735 t yr−1, respectively. The northern areas of the watershed with dry farming were identified as the critical erosion prone zones. To prioritize the subwatersheds based on their contribution to the run‐off and sediment production at the watershed's main outlet, unit response approach (URA) was applied. In this regard, subwatersheds close to the main outlet were found to have the highest contribution to sediment yield of the whole watershed. Results indicated that depending on the objective of land and water conservation practices, particularly, for controlling sediment yield at the main outlet, critical areas for implementing the best management practices may be identified through conjunctive application of WEPP and URA. Copyright © 2014 John Wiley & Sons, Ltd.

Subdividing Large Mountainous Watersheds into Smaller Hydrological Units to Predict Soil Loss and Sediment Yield Using the GeoWEPP Model

“…As literature has stated, the degradation of both forests and grasslands mostly due to illegal logging, opennings, forest roads, and overgrazing has been known as a common practice in the region [1]. A similar outcome has been reported by Saghafian et al [11] as they concluded that converting natural land use into other uses, particularly dry-farming, played the dominant factor in increasing the amount of sediment load within the Kasilian Watershed in Iran. In another study, the results of a GeoWEPPapplied experiment on a hilly watershed in southern China indicated that land use type changing from forest to agriculture caused sediment amount to increase by 42.6% [32].…”

“…However, the sub-watersheds were still too large (total surface area of 1 st , 2 nd , and 3 rd sub-watersheds were 1,413.27 ha, 936.54 ha, and 2,948.4 ha, respectively) to be properly run with the GeoWEPP program as our attempts failed several times. Therefore, as applied in previous studies [11,[20][21], in order to both run the program easily and obtain detailed data on soil loss and sediment yield in the GCW, all three sub-watersheds were further sub-divided into smaller hydrological units (SHUs) using the hydrologic In this subdivision approach, we believe that running each SHU with GeoWEPP resulted in better and more detailed soil loss and sediment yield data [22] since we could enter detailed soil, land cover, and management data for each SHU specifically compared to entering one large data set (e.g., climate) for the whole study area. In addition, this method allowed us to better evaluate the areas experiencing soil loss and sediment amounts as we can easily see some basic characteristics (land use, soil properties, slope, elevation, and bedrock type, etc.)…”

“…Parallel results of soil loss and sediment yields were reported by other studies that also took place in watersheds with similar features (e.g., mountanious, hilly, steep terrain). For example, two pieces of research initiated in the same mountanious and mostly forested Kasilian Watershed in Iran [11] found that the average erosion rate was 1.2 t ha Overall, the distribution of soil loss amounts within the GCW can be seen in Fig. 4a, revealing that the whole watershed experiences some degree of soil erosion even though approximately 84% of the GCW is covered with natural vegetation (forests and meadows).…”

“…Thus, recently, several prediction models have been developed and universally applied on estimating and/or predicting soil loss/sediment yeild of an area [9][10][11][12][13], including scenarios used to compare present and prehistoric times [14][15]. However, previous studies [12,14] indicated that, especially in large watersheds, these prediction models may not properly measure soil loss and/ or sediment amounts in some cases.…”

Application of GeoWEPP for Evaluating Sediment Yield in a Mountain Area: Agatsuma Watershed, Japan

“…The WEPP model describes physical processes that dictate water and sediment dynamics in a watershed, including infiltration, surface runoff, soil erosion, and sediment transport . WEPP also incorporates components for weather generation, winter processes, plant growth, residue decomposition, and irrigation [Saghafian et al ., 2015]. In this study, the following processes were examined to obtain optimal results.…”