Won-Seok Jang

Development of new R, C and SDR modules for the SATEEC GIS system

Soil erosion is a natural phenomenon, but accelerated soil erosion is occurring with increased construction activities and intensive agricultural cultivation within many watersheds in recent years. To develop efficient soil erosion control best management practices, the soil erosion status in the target areas first needs to be understood spatially and temporally. The SATEEC system has been widely used for soil erosion studies because of its ease-of-use and limited input data requirement. However, SATEEC cannot be used for spatiotemporal analysis of soil erosion studies. Thus, the time-variant R, C, and GA-SDR modules were developed and integrated with the SATEEC system. The enhanced SATEEC 2.0 system estimated sediment yield values were compared with measured data for the Imha watershed. The R^2 value and the Nash-Sutcliffe coefficient were 0.72 and 0.72, respectively for calibration and 0.91 and 0.88, respectively for validation with the time-variant R, C and GA-SDR modules. The statistics indicate the enhanced SATEEC 2.0 system with these modules can be used for spatial and temporal analysis of soil erosion and sediment yield with higher accuracy and a limited input dataset, which is the primary philosophy of the SATEEC ArcView GIS system. Since the daily USLE C database was obtained from SWAT runs using the climate data and agricultural management data in Korea, the daily USLE C database should be adjusted depending on the climate condition and agricultural management when the SATEEC is applied to other watersheds having different climate and agricultural management systems.

Water Quality Prediction at Mandae Watershed using SWAT and Water Quality Improvement with Vegetated Filter Strip

Mandae watershed in Gangwon province has been known as one of soil erosion hot spot watersheds within Hanggang basin. Thus numerous efforts have been made to reduce soil erosion and pollutant loads into receiving watershed. However, proper best management practices have not been suggested because no monitoring flow and water quality data were available. Thus, modeling technique could not be utilized to evaluate water quality issue properly at Mandae watershed to develop and implement the best management practices. In this study, the SWAT model was applied to the Mandae watershed, Gangwon province to evaluate the SWAT prediction ability and water quality improvement with vegetated filter strip (VFS) in this study. The Nash-Sutcliffe model efficiency (NSE) and Coefficient of determination () values for flow simulation were 0.715 and 0.802, respectively, and the NSE and values were 0.903 and 0.920 for T-P simulation indicating the SWAT can be used to simulate flow and T-P with acceptable accuracies. The SWAT model, calibrated for flow and T-P, was used to evaluate water quality improvement with the VFS in agricultural fields. It was found that approximately 56.19 % of T-P could be reduced with vegetated filter strip of 5 m at the edge of agricultural fields within the watershed (34.86 % reduction with VFS of 1m, 48.29 % with VFS of 3 m). As shown in this study, the T-P, which plays key roles in eutrophication in the waterbodies, can be reduced with proper installation of the VFS.

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 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.

Evaluation of Effects of Soil Erosion Estimation Accuracy on Sediment Yield with SATEEC L Module

SATEEC ArcView GIS system was developed using the Universal Soil Loss Equation (USLE) and sediment delivery ratio (SDR) modules. In addition, time-variant R and C modules and module were developed and integrated into the SATEEC system in recent years. The SATEEC ArcView GIS 2.1 system is a simple-to-use system which can estimate soil erosion and sediment yield spatially and temporarily using only USLE input data, DEM, and daily rainfall dataset. In this study, the SATEEC 2.1 system was used to evaluate the effects of USLE LS input data considering slope length segmentation on soil erosion and sediment yield estimation. Use of USLE LS with slope length segmentation due to roads in the watershed, soil erosion estimation decreased by 24.70 %. However, the estimated sediment yield using SATEEC GA-SDR matched measured sediment values in both scenarios (EI values of 0.650 and EI 0.651 w/o and w/flow segmentation). This is because the SATEEC GA-SDR module estimates lower SDR in case of greater soil erosion estimation (without flow length segmentation) and greater SDR in case of lower soil erosion estimation (with flow length segmentation). This indicates that the SATEEC soil erosion need to be estimated with care for accurate estimation of SDR at a watershed scale and for accurate evaluation of BMPs in the watershed.

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 Composite Soil Quality Index Evaluation System based on Web GIS

It has been known that torrential rainfall events have been occurring worldwide due to climate change. The accelerated soil erosion has caused negative impacts on water quality and ecosystem of receiving waterbodies. Since soil security issues have been arising in various areas of the world, intensive interests have been given to topsoil management in Korea. Thus in this study, Web GIS-based computing system of physical, chemical, and biological topsoil quality indices were developed. In this study, five soil quality maps at national scale and top soil erosion potential were prepared for evaluation of soil quality based on soil erosion potential. For this system, the open source Web GIS engine, OpenGeo, was used as core engine of the system. With this system, decision makers or related personnel in areas of soil erosion Best Management Practices (BMPs) would be able to find the most appropriate soil erosion BMPs based on soil erosion potential and soil quality at the area of interest. The Web GIS system would be efficiently used in decision making processes because of ease-of-use interface and scientific data used in this system. This Web GIS system would be efficiently used because this system could provide scientific knowledge to decision makers or stakeholders. Currently various BMP database are being built to be used as a decision support system in topsoil management and topsoil quality areas.

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.