Jonggun Kim

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 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.

Development of Web-based SWAT System

Non Point Source Pollution (NPSP) load had been arising as a significant environmental issue. Especially excessive NPS input to the water bodies is causing serious impacts on river or stream ecosystems worldwide. To develop efficient best management practices for water quality improvement, hot spot target areas first need to be identified and understood to develop proper action plans to restore river ecosystem. For simulation of NPSP influences on watershed, the Soil and Water Assessment Tool model (SWAT) has been widely used in many countries, by many researchers. But the SWAT model is a desktop-based system. Therefore there are many disadvantages over advantages of desktop-based system, especially when it is used for watershed management related decision making processes. In this study, the Web GIS-based SWAT system was developed, which provides Web GIS interface for the SWAT model installed on the server-side. The Web GIS-based SWAT provides simple-to-use interface to allow users to change the subbasin and HRU level input parameters, such as filter strip width, surface cover management, main channel slope, initial SCS CN II value, and so on. The Web-based SWAT system will provides valuable scientific information for watershed decision makers with ease-of-use Web GIS-based interface.

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.

Development of Web-based Load Duration Curve for Analysis of TMDL and Water Quality Characteristics

Abstract: The total maximum daily load (TMDL) program has been established for water quality restoration and management in watershed. The Load Duration Curve (LDC) has been used for appropriate TMDL targets determination. However, the related personals had to first learn to develop the LDC, and then collect flow and water quality data for a site of interest to generate LDC which is very much time-consuming. Thus, the web-based Load Duration Curve (LDC) System was developed using the Perl/CGI, GNUPLOT, JavaScript, and Google Map script for analysis of TMDL and water quality characteristics in watershed. This system provides users with various interfaces (flow and water quality input and uploading) for flow and water quality input to the system for generating LDC. Also, Google Map based interface is developed to retrieve daily stream flow data from remote USGS-server. Then the LDC is generated using these data automatically in 3-4 seconds. The Web-based LDC system (https://engineering.purdue.edu/~ldc; http://www.envsys.co.kr/~ldc), developed in this study, is an useful tool for characterizing the problem according to flow condition and proving a visual display to easily understand the problem and the TMDL targets. In addition, this system will be able to help decide appropriate BMPs with generated result for the watershed.

Development of Optimization Module in the WHAT System for Accurate Hydrograph Analysis and Model Application

Over the last years, significant areas in the watershed have been converted into impervious areas with human-induced development activities.xa0 These activities resulted in changes in the hydrologic response characteristics and pollutant generation trends.xa0 Thus, many hydrologic and water quality computer models have been developed and used to assess hydrologic and water quality impacts of land use changes.xa0 However, these models have to be first validated prior to the application in environment-friendly land use planning.xa0 The direct runoff estimation module of the Long-Term Hydrologic Impact Assessment (L-THIA) ArcView GIS system was validated using the Web GIS-based Hydrograph Analysis Tool, called WHAT (http://pasture.ecn.purdue.edu/~what).xa0 The L-THIA model was applied to the Little Eagle Creek (LEC) watershed and compared with the BFLOW filtered direct runoff values.xa0 The R2 value was 0.68, Nash-Sutcliffe coefficient value was 0.64.xa0 Also, the L-THIA estimates were compared with those separated using the Eckhardt digital filter (w/ default BFImax value of 0.80).xa0 The R2 value was 0.66, Nash-Sutcliffe coefficient value was 0.63.xa0 Although these results could indicate that the L-THIA model is good in estimating the direct runoff reasonably well, the filtered direct runoff values using the BFLOW and Eckhardt digital filter with the default BFImax value do not reflect hydrological and hydrogeological situations in the LEC watershed.xa0 Thus, the hydrograph recession curve analysis was automated using CGI programming and optimization module was developed. These two modules were integrated into the WHAT system for determinination of the optimum BFImax parameter of the Eckhardt digital filter. The recession curve analysis method was used to separate baseflow because the shape of hydrograph reflects hydrological and hydrogeological situations in the LEC watershed.xa0 With automated recession curve analysis method and optimization module of the WHAT system, the optimum BFImax value of 0.597 was determined.xa0 The comparison of the L-THIA estimates with filtered direct runoff using optimized BFImax value of 0.597 resulted in the R2 value of 0.66 and the Nash-Sutcliffe coefficient value of 0.63.xa0 However, the L-THIA estimates calibrated with optimized BFImax increased by 17% and the L-THIA estimated NPS pollutant loadings increased by more than 20%.xa0 This indicates the L-THIA model direct runoff estimates can be wrong by 17% and NPS pollutant loading estimation by more than 20% if accuracy of baseflow separation method is not validated for the study watershed.xa0 This study shows the importance in baseflow separation in hydrologic and water quality modeling using the L-THIA model.

Development of ArcGIS-based Model to Estimate Monthly Potential Soil Loss

Soil erosion has been issued in many countries since it causes negative impacts on ecosystem at the receiving water bodies. Therefore best management practices to resolve the problem in a watershed have been developed and implemented. As a prior process, there is a need to define soil erosion level and to identify the area of concern regarding soil erosion so that the practices are effective as they are designed. Universal Soil Loss Equation (USLE) were developed to estimate potential soil erosion and many Geographic Information System (GIS) models employ USLE to estimate soil erosion. Sediment Assessment Tool for Effective Erosion Control (SATEEC) is one of the models, the model provided several opportunities to consider various watershed peculiarities such as breaking of slope length, monthly variation of rainfall, crop growth at agricultural fields, etc. SATEEC is useful to estimate soil erosion, however the model can be implemented with ArcView software that is no longer used or hard to use currently. Therefore SATEEC based on ArcView was rebuild for the ArcGIS software with all modules provided at the previous version. The rebuilt SATEEC, ArcSATEEC, was programmed in ArcPy and works as ArcGIS Toolset and allows considering monthly variations of rainfall and crop growth at any watershed in South-Korea. ArcSATEEC was applied in Daecheong-dam watershed in this study, monthly soil erosion was estimated with monthly rainfall and crop growth variation. Annual soil erosion was computed by summing monthly soil erosion and was compared to the conventional approach to estimate annual soil erosion. The annual soil erosion estimated by the conventional approach and by summing monthly approach did not display much differences, however, ArcSATEEC was capable to provide monthly variation of soil erosion.

A Study to Develop Monthly Cover Management Factor Database for Monthly Soil Loss Estimation

Soil loss is an accompanying phenomenon of hydrologic cycle in watersheds. Both rainfall drops and runoff lead to soil particle detachment, the detached soil particles are transported into streams by runoff. Here, a sediment-laden water problem can be issued if soil particles are severely detached and transported into stream in the watershed. There is a need to estimate or simulate soil erosion in watersheds so that an adequate plan to manage soil erosion can be established. Universal Soil Loss Equation (USLE), therefore, was developed and modified by many researchers for their watersheds, moreover the simple model, USLE, has been employed in many hydrologic models for soil erosion simulations. While the USLE has been applied even in South-Korea, the model is often regarded as being limited in applications for the watersheds in South-Korea since monthly conditions against soil erosion on soil surface are not capable to represent. Thus, the monthly USLE factors against soil erosion, soil erodibility and crop management factors, were established for four major watersheds, which are Daecheong-dam, Soyang-dam, Juam-dam, and Imha-dam watersheds. The monthly factors were established by recent fifteen years from 2000 to 2015. Five crops were selected for the monthly crop management factor establishments. Soil loss estimations with the modified factors were compared to conventional approach that is average annual estimations. The differences ranged from 9.3 % (Juam-dam watershed) to 28.1 % (Daecheong-dam watershed), since the conventional approaches were not capable of seasonally and regionally different conditions.