Search

The watershed scale Soil and Water Assessment Tool (SWAT) model divides watersheds into smal- ler subwatersheds for simulation of rainfall-runoff and sediment loading at the field level and routing through stream networks. Typically, the SWAT model first needs to be calibrated and validated for accurate estimation through adjustment of sensitive input parameters (i.e., Curve Number values, USLE P, slope and slope-length, and so on). However, in some instances, SWAT-simulated results are greatly affected by the watershed delinea- tion and Digital Elevation Models (DEM) cell size. In this study, the SWAT ArcView GIS Patch II was developed for steep sloping watersheds, and its performance was evaluated for various threshold values and DEM cell size scenarios when delineating subwatersheds using the SWAT model. The SWAT ArcView GIS Patch II was devel- oped using the ArcView GIS Avenue program and Spatial Analyst libraries. The SWAT ArcView GIS Patch II improves upon the SWAT ArcView GIS Patch I because it reflects the topographic factor in calculating the field slope-length of Hydrologic Response Units in the SWAT model. The simulated sediment value for 321 subwater- sheds (watershed delineation threshold value of 25 ha) is greater than that for 43 subwatersheds (watershed delineation threshold value of 200 ha) by 201% without applying the SWAT ArcView GIS Patch II. However, when the SWAT ArcView GIS Patch II was applied, the difference in simulated sediment yield decreases for the same scenario (i.e., difference in simulated sediment with 321 subwatersheds and 43 subwatersheds) was 12%. The simulated sediment value for DEM cell size of 50 m is greater than that for DEM cell size of 10 m by 19.8% without the SWAT ArcView GIS Patch II. However, the difference becomes smaller (3.4% difference) between 50 and 10 m with the SWAT ArcView GIS Patch II for the 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. Thus, the results obtained in this study show that the SWAT ArcView GIS Patch II should be used when simulating hydrology and sediment yield for steep sloping watersheds (especially if average slope of the subwatershed is >25%) for more accurate simulation of hydrology and sediment using the SWAT model. The SWAT ArcView GIS Patch II is available at http://www.EnvSys.co.kr/~swat for free download. (KEY TERMS: ArcView GIS Patch; DEM; slope-length; subwatershed; SWAT; watershed delineation.)

The alpine agricultural activities are usually performed at higher and steep areas in nature. Thus, significant amounts of soil erosion are occurring compared with those from other areas. Thus, the soil erosion induced environmental impacts in these areas are getting greater. The Doam watershed is located at alpine areas and it has been well known that the agricultural activities in the watershed are causing accelerated soil erosion and water quality degradations. Many modeling approaches were employed to solve soil erosion and water quality issues. In this study, the Soil and Water Assessment Tool (SWAT) model was utilized to simulate the hydrologic and sediment behaviors in the Doam watershed. In many previous modeling studies, the digital soil map and its corresponding soil properties were used without modification to reflect soil conditioning at many agricultural fields of the Doam watershed. Thus, the soil sample was taken at the agricultural field within the Doam watershed and analyzed for its physical properties. In this study, the digital topsoil properties in the agricultural fields within the Doam watershed were replaced with the soil properties for reconditioned soil analyzed in this study to simulate the impacts of using soil properties for reconditioned soil in hydrologic and sediment modeling at the Doam watershed using the SWAT model. The hydrologic component of the SWAT model was calibrated and validated for measured flow data from 2002 to 2003. The value was 0.79 and the EI value was 0.53 for weekly simulated data. The calibrated model parameters were used for hydrologic component validation and the value was 0.86 and the EI value was 0.74 for weekly data. For sediment comparison, the value was 0.67 and the EI value was 0.59. These statistics improved with the use of soil properties of the reconditioned soil in the field compared with the results obtained without considering soil reconditioning. The simulated sediment amounts with and without considering the soil properties of the reconditioned soil were 284,813 ton and 158,369 ton, respectively. This result indicates that there could be approximately 79% of errors in estimated sediment yield at the Doam watershed, although the model comparison with the measured data gave similar satisfactory statistics with and without considering soil properties from the reconditioned soil.

In order to assess hydrologic and nonpoint source pollutant behaviors in the watershed with the Soil and Water Assessment Tool (SWAT) model, accuracy evaluation of the SWAT model should be conducted prior to the application of it to the watershed. When calibrating and validating hydrological components of the SWAT model, the Nash-Sutcliffe efficiency coefficient (EI) has been widely used. However, the EI value has been known as it is affected sensitively by big number among a range of numbers. In this study, the Web-based flow clustering EI estimation system using K-means clustering algorithm was developed and used for the SWAT hydrology evaluation. Even though the EI of total streamflow was high, the EI values of hydrologic components (i.e., direct runoff and baseflow) were not high. Also when the EI values of flow group I and II (i.e., low and high value group) clustered from direct runoff and baseflow were computed, respectively, the EI values of them were much lower, negative EI values for some flow group comparison. The SWAT auto-calibration tool estimated values also showed negative EI values for most flow group I and II of direct runoff and baseflow although EI value of total streamflow was high. The result obtained in this study indicates that the SWAT hydrology component should be calibrated until all four positive EI values for each flow group of direct runoff and baseflow are obtained for better accuracy both in direct runoff and baseflow.

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.

We fabricated the CdS semiconductor quantum dots(QDs) embedded in the polyvinyl alcohol. By measuring the absorption spectrum of PVA with CdS, we could determine the radius of QDs. We confirm that as it increasing the mole ratio (CdCl2/RSH) in the mixture, the mean radius of the QDs decreased and the band gap energy increased. When added the RSH, absorption peak energy was 3.67eV and without the RSH it was 3.20 eV. The radius was 18 A with the RSH and it was 23 A without the RSH. As a result of comparing the low temperature absorption spectrum line with the normal temperature absorption spectrum line, the intensity of absorption was increased and the absorption line moved to the long wave.