Abstract
The Soil and Water Assessment Tool (SWAT) model has been used worldwide for many hydrologic and Non-Point Source (NPS) Pollution analyses on a watershed scale. However, it has many limitations in simulating the Vegetative Filter Strip (VFS) because it considers only ‘filter strip width’ when the model estimates sediment trapping efficiency and does not consider the routing of sediment with overland flow which is expected to maximize the sediment trapping efficiency from upper agricultural subwatersheds to lower spatially-explicit filter strips. Therefore, the SWAT overland flow option between landuse-subwatersheds with sediment routing capability was enhanced by modifying the SWAT watershed configuration and SWAT engine based on the numerical model VFSMOD applied to South-Korean conditions. The enhanced SWAT can simulate the VFS sediment trapping efficiency for South-Korean conditions in a manner similar to the desktop VFSMOD-w system. Due to this enhancement, SWAT is applicable to simulate the effects of overland flow from upper subwatersheds to reflect increased runoff volume at the lower subwatershed, which occurs in the field if no diversion channel is installed. In this study, the enhanced SWAT model was applied to small watersheds located at Jaun-ri in South-Korea to simulate a diversion channel and spatially-explicit VFS. Sediment can be reduced by 31%, 65%, and 68%, with a diversion channel, the VFS, and the VFS with diversion channel, respectively. The enhanced SWAT should be used in estimating site-specific effects on sediment reduction with diversion channels and VFS, instead of the currently available SWAT, which does not simulate sediment routing in overland flow and does not consider other sensitive factors affecting sediment reduction with VFS.
Highlights
In recent years, sediment transport in runoff has been considered one of the serious environmental problems in South-Korea as well as other countries [1,2], there are many methods to prevent soil erosion and sediment inflow into water bodies, through structural and non-structural best management practices (BMPs) to prevent or manage sediment transport
To simulate the effects of Vegetative Filter Strip (VFS) and diversion channels with Soil and Water Assessment Tool (SWAT), subwatersheds need to be configured as shown in Figure 1, and the flow type needs to be modified so it is described as either overland flow or channelized flow, or sometimes both flow types, depending on the field flow condition
Because it cannot simulate the sediment routing with overland flow type between single landuse subwatersheds, and the filter strip module of the current SWAT is only based on the filter strip width
Summary
Sediment transport in runoff has been considered one of the serious environmental problems in South-Korea as well as other countries [1,2], there are many methods to prevent soil erosion and sediment inflow into water bodies, through structural and non-structural best management practices (BMPs) to prevent or manage sediment transport. The dimension of VFS needs to be determined from experimental data under various field and rainfall conditions to obtain the desired pollutant removal results. These data are rarely available for site-specific design of VFS. If a diversion channel is not installed, the chances are that soil erosion in the agricultural area will be increased by runoff from the forest Both VFS and the diversion channel are often utilized together to increase sediment deposition and reduce runoff flowing into agricultural areas from upper forest areas. The effects of VFS and diversion channel need to be evaluated before installation in fields to maximize the effects of sediment reduction and to determine the best places and dimensions of VFS and diversion channels
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