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

Abstract

Sediment discharge monitoring can be used to detect sediment disasters in upstream areas in order to enable prompt countermeasures. Sediment disaster signals should be easily differentiated from ordinary sediment discharge. This study examined the application of the geospatial interface for the Water Erosion Prediction Project (GeoWEPP) for the assessment of baseline sediment discharge in a mountain watershed to allow early detection of upstream sediment disasters. When compared to detailed observation-based data from the Agatsuma watershed, GeoWEPP successfully reproduced continuous sediment discharge in subwatersheds of varying size, topography, and land use. GeoWEPP parameter settings corresponded to actual conditions and processes involved in water and sediment dynamics. Additionally, the introduction of a restrictive layer and improved settings for evapotranspiration rate were critical for predicting surface runoff and subsequent surface erosion in hillslope sections. The depth to non-erodible layer was important for determining the overall sediment discharge at the study site, as it was the only parameter that varied over time and could not be obtained from the actual depth of bed material. This parameter should be interpreted as a conceptual index that represents the spatial distribution of bed material and its erodibility, and requires an initial adjustment period. Therefore, GeoWEPP calculations should eliminate the first year in order to obtain optimal results in a mountain watershed with a significant depth of bed material in a channel section.

Soil Erosion, Sediment Yield, and Runoff Modeling of the Megech Watershed Using the GeoWEPP Model

“…The GeoWEPP model combines three functions: the Topographic Parameterization Tool (TOPAZ) for topographic evaluation, drainage identification, watershed identification, watershed segmentation, and sub-catchment parameterization; the PRISM (Parameterelevation Regressions on Independent Slopes Model) for editing existing climate data; and the WEPP (Water Erosion Prediction Project) for soil erosion calculation [62]. The GeoWEPP successfully reproduced the continuous sediment discharge in watersheds of varying size, topography, and land use [44,49,63,64]. The GeoWEPP also has the ability to determine where the sediment yield and runoff occur and locates possible deposition places and also indicate when they happened.…”

“…The geospatial Water Erosion Prediction Project of the GeoWEPP model is a GIS-based model and is applicable in estimating sediment yield, soil loss, and runoff successfully for varying size, topography, and land use. It was tested [47][48][49] and its computational performance was compared with other soil erosion models. For example, [50][51][52] compared WEPP with empirical USLE or RUSLE and WEPP produced better results [53][54][55] compared with the Soil and Water Assessment Tool (SWAT) conceptual model, indicating the WEPP simulation was nearer to measured values [44].…”

Study on the Preparation of GeoWEPP Model Input Data for Erosion Prediction in Cikeruh-Citarik Sub-watershed

“…Menurut Effendy et al, (2019), hasil prediksi GeoWEPP berupa distribusi variasi erosi secara spasial dalam bentuk peta yang besaran kuantitatifnya diambil dari setiap unit lereng (hillslope). Hal tersebut memungkinkan GeoWEPP untuk dapat memprediksi sebaran erosi baik secara spasial maupun temporal dalam kurun waktu yang bervariasi dari mulai harian, bulanan hingga tahunan pada kondisi topografi, hidrologis dan tutupan vegetasi yang bervariasi (Amaru & Hotta, 2018) Sub-DAS Cikeruh-Citarik sebagai bagian hulu dari DAS Citarum memiliki karakteristrik tersendiri yang membedakannya dari bagian DAS yang lain. Menurut (Asdak, 2018), DAS bagian hulu secara biofisik memiliki ciri-ciri diantaranya: merupakan wilayah konservasi dengan vegetasi utama berupa hutan, memiliki kerapatan drainase yang tinggi dan kemiringan lereng yang besar.…”