Younshik Park

Comparison of Soil Loss Estimation using SWAT and SATEEC

Soil erosion is a natural process and has been occurring in most areas in the watershed. However, accelerated soil erosion rates have been causing numerous environmental impacts in recent years. To reduce soil erosion and sediment inflow into the water bodies, site-specific soil erosion best management practices(BMPs) need to be established and implemented. The most commonly used soil erosion model is the Universal Soil Loss Equation(USLE), which have been used in many countries over 30 years. The Sediment Assessment Tool for Effective Erosion Control(SATEEC) ArcView GIS system has been developed and enhanced to estimate the soil erosion and sediment yield from the watershed using the USLE input data. In the last decade, the Soil and Water Assessment Tool(SWAT) model also has been widely used to estimate soil erosion and sediment yield at a watershed scale. The SATEEC system estimates the LS factor using the equation suggested by Moore and Burch, while the SWAT model estimates the LS factor based on the relationship between sub watershed average slope and slope length. Thus the SATEEC and SWAT estimated soil erosion values were compared in this study. The differences in LS factor estimation methods in the SATEEC and SWAT caused significant difference in estimated soil erosion. In this study, the difference was -51.9%(default threshold)～-54.5%(min. threshold) between SATEEC and non-patched SWAT, and -7.8%(default threshold)～+3.8%(min. threshold) between SATEEC and patched SWAT estimated soil erosion.

Analysis of Soil Erosion Reduction Effect of Rice Straw Mat by the SWAT Model

The purpose of this study is to evaluate sediment yield reduction under various field slope conditions with rice straw mat. The Vegetative Filter Strip Model-W (VFSMOD-W) and Soil and Water Assessment Tool (SWAT) were used for simulation of sediment yield reduction effect of rice straw mat. The Universe Soil Loss Equation Practice factor (USLE P factor), being able to reflect simulation of rice straw mat in the agricultural field, were estimated for each slope with VFSMOD-W and measured soil erosion values under 5, 10, and 20 % slopes. Then with the regression equation for slopes, USLE P factor was derived and used as input data for each Hydrological Response Unit (HRU) in the SWAT model. The SWAT Spatially Distributed-HRU (SD-HRU) pre-processor module was utilized, moreover, in order to consider spatial location and topographic features (measured topographic features by field survey) of all HRU within each subwatershed in the study watershed. Result of monthly sediment yield without rice straw mat (Jan. 2000 - Aug. 2007) was 814.72 ton/month, and with rice straw mat (Jan. 2000 - Aug. 2007) was 526.75 ton/month, which was reduced as 35.35 % compared without it. Also, during the rainy season (from Jun. to Sep. 2000 - 2007), when without vs. with rice straw mat, monthly sediment indicated 2,109.54 ton and 1,358.61 ton respectively. It showed about 35.60 % was reduced depending on rice straw mat. As shown in this study, if rice straw mat is used as a Best Management Practice (BMP) in the sloping fields, rainfall-driven sediment yield will be reduced effectively.

Development and Application of SATEEC L Module for Slope Length Adjustment Based on Topography Change

Severe sediment-laden problem has been the hot issue in Korea. It was assumed that agricultural activities and landslides were the primary causes of these problems in watersheds. The USLE-based systems have been widely used in soil erosion studies. However the GIS-based USLE modeling system has limitation in USLE L factors. In this study, the SATEEC L module was developed to reflect the slope length segmentations in the fields. The SATEEC L module was applied to the study watershed to analyze the effects of using the SATEEC L module on estimated sediment. As shown in the comparisons between SATEEC estimated sediment with SWAT values, the SATEEC GA-SDR module derives the SDR with reasonably acceptable accuracies. However, it is worthy to note that the soil erosion using the SATEEC L module for the study watershed was lower than that without using the SATEEC L module by 25%, although the SATEEC estimated sediment values with and without using L module match the SWAT sediment values with similar accuracies. This is because the SATEEC GA-SDR module estimates lower SDR in case of greater soil erosion estimation without the L module and greater SDR in case of lower soil erosion estimation with the L module. This indicates that the SATEEC input parameters, especially L factor, need to be prepared with care for accurate estimation of SDR at a watershed scale and for accurate evaluation of BMPs in the watershed.

Development of a SWAT ArcView GIS Patch for Accurate Analysis of Soil Erosion and Sediment Yield at Steep Sloping Watershed

Abstract: The watershed scale SWAT model divides the watershed into smaller subwatersheds for rainfall-runoff and pollutant generation at the field level and routing though stream networks. The SWAT model first needs to be calibrated and validated for accurate estimation through adjustment of various input parameters. However, in some instances the SWAT simulated results are greatly affected by the watershed delineation and DEM cell size. In this study, the SWAT ArcView GIS Patch II was developed for steep sloping watershed and its performance was evaluated for various threshold value and DEM cell size scenarios when delineating subwatersheds using SWAT. The SWAT ArcView GIS Patch II was developed using the ArcView GIS Avenue program and Spatial Analyst library. The SWAT ArcView GIS Patch II is better than the SWAT ArcView GIS Patch I by Lim et al. (2007) because it reflects the topographic factor in calculating the field slope length of the HRU in the SWAT model. The simulated sediment value for 321 watershed (threshold value of 200 ha) is greater than that for 43 subwatershed (threshold value of 25ha) by 201% without applying the SWAT ArcView GIS Patch II. However, when the SWAT ArcView GIS Patch II was applied, the difference decreases (12% difference) for the same scenario. The simulated sediment value for DEM cell size of 50m is greater than that for DEM cell size of 10m by 19.80% without the SWAT ArcView GIS Patch II. However, the difference becomes smaller (3.41% difference) between 50m and 10m DEM scenarios. As shown in this study, the SWAT ArcView GIS Patch II can reduce differences in simulated sediment values for various watershed delineation and DEM cell size scenarios. Without the SWAT ArcView GIS Patch II, variations in the SWAT simulated results using various watershed delineation and DEM cell size scenarios could be greater than those from input parameter calibration. The results obtained in this study show that the SWAT ArcView GIS Patch II needs to be used when simulating hydrology and water quality for steep sloping watersheds (especially if average slope of the subwatershed is greater than 25%) for accurate simulation of hydrology and water quality using the SWAT model. The SWAT ArcView GIS Patch II is available at http://www.EnvSys.co.kr/~swat for free download.

Development of the SWAT DWDM for Accurate Estimation of Soil Erosion from an Agricultural field

준분포형 모형인 SWAT 모형은 소유역내 수문학적 반응단위 별로 유출, 유사 등의 발생을 평가하는데 이때 Hydrological Response Unit (HRU)의 지형정보가 활용된다. 현재 SWAT 모형의 인터페이스 구조는, 각 소유역의 평균 지형인자 값이 각 소유 역내의 모든 HRU의 지형정보로 사용된다. 그러므로 각 소유역내의 HRU에 있는 지형인자를 정확하게 추출하기 위해서는 수계 를 자세하게 나누어야 하며, 이를 위해서 더욱 자세한 소유역 수계 인터페이스가 필요하다. 현재 SWAT 모형 인터페이스에서는 수계를 나눌 때 임계값의 최소값은 최대 flow accumulation 값의 0.1 %가 사용된다. 따라서 HRU의 지형인자를 추출하기 위해 아주 자세한 정도로 소유역의 수계를 나눈다는 것은 불가능하다. 본 연구에서는 사용자가 원하는 임계값과 농경지 경계를 근거 하여 소유역 경계를 추가로 수계를 나눌 수 있는 Dual Watershed Delineation Module (DWDM) 을 개발하였다. 기존 SWAT의 수 계추출 모듈로 유량을 모의한 결과 27,219 m/month 가 산정되었고, DWDM 을 적용한 결과 26,172 m/month 로 약 3.8 %의 미 미한 차이가 생겼다. 하지만 유사의 경우 DWDM을 적용하기 전에는 0.779 ton/month, 적용 후에는 2.688 ton/month 로 약 245 % 의 차이를 보였다. 즉 농경지를 추가적으로 수계를 나눌 때 유사의 가장 민감한 요소인 경사장을 실제지형에 맞게 고려함에 따 라 좀 더 정확한 유사 산정을 할 수 있었다. 농경지에서의 정확한 수문 및 유사 평가 시 본 연구에서 개발한 모듈이 적용 되어 야 한다고 사료된다.

Assessment of Future Climate Change Impact on Groundwater recharge, Baseflow and Sediment in Steep Sloping Watershed

RegionalInfrastructureEngineering,KangwonNationalUniversity,Korea*EnvironmentalResearchCenter,KangwonNationalUniversity,Korea**DepartmentofAgriculturalandBiologicalEngineering,PurdueUniversity***DepartmentofCivilEngineering,Inhauniversity,Korea요 약기후변화로인해폭우및재해들이일어나고있다. 특히강우강도가커짐에따라토사유출도심해지고있다. 이에따라효율적인수자원및수질관리를위해지하수함양량과기저유출, 그리고토사유출현황을평가하는것이필요하다. 이에본연구에서는대표적인급경사지유역인양구해안면유역에미래기후변화시나리오를적용하여지하수함양량, 기저유출량, 유사량을전망하였으며, 또한유역의경사도를완만하게줄임으로서지하수함양량, 기저유출량, 유사량의변화를분석하였다. 모의기간을2013~2040년, 2041~2070년, 2071~2100년으로나누었으며, 급경사지유역보다유역의경사도를완만하게줄인경우가지하수함양량이평균50% 증가되었으며, 기저유출량도약42% 증가되었다. 유사량은급경사지유역보다경사도를완만하게줄였을경우가72% 유사량이줄어드는것으로나타났다. 본연구의결과에서보이는바와같이경사도를완만하게적용하면유역내지하수함양량및기저유출량이증가하고, 유사량을저감시킬수있는것으로분석되어향후탁수에긍정적인영향을미칠것으로판단된다.핵심용어:SWAT, 유사량, 기저유출, 지하수함양량, 기후변화AbstractClimate change has caused detrimental phenomena such as heavy rainfall which could aggravate soil erosion. Accordingly, itis needed to evaluate the groundwater recharge, baseflow, and soil erosion for the efficient management of water resourcesand quality. In this study, future climate change scenarios were applied to the Haean-myeon watershed which is a steepsloping watershed in South Korea to analyze groundwater recharge, baseflow, sediment. Also, the variation of groundwaterrecharge, baseflow, sediment was analyzed according to the change of slope (5 %). Simulated periods were divided intothree terms (2013 ~ 2040 years, 2041 ~ 2070 years, 2071 ~ 2100 years). As a result of this study, average groundwaterrecharge and baseflow increased by 50 %, 42 %, and sediment decreased by 72 %, respectively. In these regards, thesuggested method will positively contribute to hydro-ecosystem and reduction of muddy water at a steep sloping watershed.Keywords:SWAT, Sediment, Baseflow, Groundwater recharge, Climate Change+ Corresponding Author: jung.younghun@gmail.com

Development of Web GIS based VFSMOD System to Simulate Sediment Reduction Efficiency with Vegetative Filter Strip

In recent days, the Non Point Source Pollution has been arising as a big environmental issue. Especially muddy water problem is causing serious impacts on river ecosystem not only in Korea but also most of the countries. Accordingly many methods to manage and prevent this problem have been investigated such as greet chamber, reservoir or debris barrier. However, the VFS is thought to be the one of effective methods. However the effective width of the VFS first needs to be determined before VFS installation in the field. To provide ease-of-use interface with scientific VFS modeling engine, the Web GIS based VFSMOD system was developed in this study. The Web GIS based VFSMOD uses UH and VFSM as core engines to simulate rainfall-runoff and sediment trapping. The provide soil information of a point of interest, the Google Map interface to the Mapserver soil database system was developed using the Google Map API, Javascript, Perl/CGI, and Oracle DB programming. Two versions of the Web GIS based VFSMOD system were developed; one is Single Storm Event Analysis and the other is Multiple Storm Event Analysis options. With these two options in the Web GIS based VFSMOD system, the users can easily simulate the effects of filter strip under given rainfall event using the Single Storm Event Analysis mode and determine optimum filter strip width using the Multiple Storm Event Analysis mode. These two versions were applied to the study watershed located at Gangwon province in Korea to demonstrate how the Web GIS based VFSMOD system can be used in VFS analysis. It was found that the VFS efficiencies are dependant on storm amounts and filter strip width.

Modification of Sediment Trapping Efficiency Equation of VFS in SWAT Considering the Characteristics of the Agricultural Land in Korea

Abstract In this study, considering the factors that affects sediment trapping efficiency of Vegetative Filter Strips (VFS), the scenarios were designed to develop a regression equation to estimate sediment trapping efficiency of VFS for agricultural fields in South-Korea. For this, general conditions of agricultural fields in South-Korea were investigated. Then, based on these results , total 53,460 scenarios were set and simulated by Vegetative Filter Strip MODel (VFSMOD-w). Two variables were determined from the results of 53,460 scenarios. These two variables were applied to CurveExpert for development of a equation, which can estimate sediment trapping efficiency of VFS. The equation developed in this study can be used in SWAT model for estimation of sediment reduction efficiency of VFS to upland field in Korea. Moreover, it is expected that VFS will be effectively applied to agricultural fields in South-Korea. Key words : Sediment, Sediment reduction, SWAT, Vegetative filter strips, VFSMOD-w

Development of Web-based Load Duration Curve System for TMDL Analysis

ABSTRACT: Development of TMDLs requires quantification of flow duration and load duration data for the waterbody of concern. Flow and load duration curves help identify specific flow regimes for which water quality standards are violated. Similarly, load reduction strategies for point and nonpoint source pollutants to meet TMDLs can be identified using the flow and load duration curves. Traditionally, development of these curves has been a time consuming process involving downloading and processing of flow and water quality data, and plotting of the data in a format suggested by EPA. We have developed an online tool to automate this process. The on-line tool provides options to upload a user’s flow and water quality data. Alternatively, a user can select stream flow data from an existing USGS gauging station using a Google MapsTM interface for the tool. The Google Maps interface has allowed us to scale the applicability of this tool to any watershed within the continental US. We have provided training for the use of this tool to various stakeholder groups involved in TMDL development. The use of this tool has resulted in significant time savings for the groups involved in TMDL development. In addition, it provides a consistent approach of quantifying and interpreting flow and load duration curves for different watersheds.

Development and Application of L-THIA 2009 System for Accurate Direct Runoff Estimation in Doam-dam Watershed

The Long-Term Hydrologic Impact Assessment (L-THIA) model has been widely used in estimating the long-term impacts of land use change because of its ease-of-use interface. However, the current L-THIA 2.3 is developed in the ArcView 3.x platform. Thus, there have been requests for enhanced version in ArcGIS platform because of computer processing capacity and model execution time. Also, the current L-THIA 2.3 calculates CN values based on average field slope for the whole watershed to estimate direct runoff. However, when it is applied to steep mountainous areas, the CN values should be adjusted based on subdivided field slope. For these reasons, the ArcGIS-based L-THIA 2009 system was developed for ease and accurate evaluation of the L-THIA performance in this study. This enhanced system was applied to Doam-dam watershed to evaluate the accuracy of the estimated direct runoff, considering CN2s value based on slope of each HRU. As shown in the results, it is strongly recommended the CN2s values should be adjusted based on slope of each HRU, especially in steep sloping watershed. The enhanced L-THIA 2009 system has been proven as an efficient tool for various land use change studies because of it ease-of-use interface in ArcGIS platform and built-in base-flow separation module for direct runoff comparison.