Chounghyun Seong

Assessing Irrigation Water Capacity of Land Use Change in a Data-Scarce Watershed of Korea

AbstractThe objective of this study is to assess stable irrigation water capacity and erosion on the basis of water and sediment balance analysis of land use change. The reservoir water balance analysis is calculated by the daily irrigation reservoir operation model (DIROM) for simulating daily inflow and release rates for irrigation reservoirs. The reservoir capacity change for assessing the sediment flux is predicted using the universal soil loss equation (USLE), sediment delivery ratio (SDR), and trap efficiency. To analyze soil erosion changes according to land use changes, Landsat-5 images were selected. Spatial distribution of deposited sediment is estimated by the U.S. Bureau of Reclamation (USBR) method and the hydrodynamic, sediment and contaminant transport model (HSCTM-2D), which is a finite-element model for simulating surface water flow and sediment transport. The model performance was verified by comparing simulated and observed data. The simulated results, which were validated using an inte...

Effects of Reclaimed Wastewater Irrigation on Paddy Rice Yields and Fertilizer Reduction using the DSSAT Model

The objectives of this study were to assess the rice yields and evaluate fertilizer reduction effect of reclaimed wastewater irrigation in paddy fields using the Decision Support System for Agrotechnology Transfer (DSSAT) v4.5 model. The experimental plots were designed, which was located near the Suwon wastewater treatment plant in Gyeonggi-do, Korea. The rice yield, irrigation amount, irrigation water quality and soil data were monitored and collected between 2006 and 2009. The DSSAT model was calibrated and validated with observed data. The methods that were used to evaluate this model were the root mean square error (RMSE), normalized root mean square error (nRMSE), and index of agreement (d). The values of RMSE, nRMSE, and d ranged from 145 to , 3.0 to 13.3 %, and 0.90 to 0.95 for the calibration period, respectively and represented from 91 to , 2.0 to 10.4 %, 0.94 to 0.98 for the validation period, respectively. Overall, this model showed good agreement with observed data of rice yields irrigated with reclaimed wastewater. The fertilizer reduction effect in paddy field of reclaimed wastewater irrigation was assessed about 60 % in 2008 and 40 % in 2009.

Feasibility Study of Wastewater Reuse for the Vegetable Farming in Jejudo

The objective of this study is to assess the feasibility of wastewater reuse for the vegetable farming. The study region, about 250 ha in size, is located on the west coast of Jejudo, Korea. Major agricultural products of the study area are the cabbage, broccoli, garlic and onion. To confirm the feasibility of wastewater reuse, the drought duration and the water requirement analysis were conducted respectively. The average annual precipitation of the study region (1,121 mm) was smaller than that of Jeju island (1,975 mm). The drought duration for a ten-year return period in October through November was more than 20 days. The water requirement for irrigation was calculated by the FAQ Penman-Monteith method which took into account the cultivated crops, planting system, and meteorological conditions of the study region. The water requirement for a ten-year return period was estimated 4.7 mm/day and the water demand for irrigation was . As a result, the irrigation water for the crops was insufficient during their breeding season, especially in October through November. Thus, the result indicated that the study region required the alternative water supply such as wastewater reuse during the non-rainy season. As drought continues to place considerable stress on the availability of fresh water supplies in the study region, irrigation with reclaimed wastewater will play an important role in helping to meet future water demands.

A Comparative Study of Unit Hydrograph Models for Flood Runoff Simulation at a Small Watershed

In this study, three different unit hydrograph methods (Snyder, SCS, Clark) in the HEC-HMS were compared to find better fit with the observed data in the small agricultural watershed. Baran watershed, having in size, was selected as a study watershed. The watershed input data for HEC-HMS were retrieved using HEC-GeoHMS which was developed to assist making GIS input data for HEC-HMS. Rainfall and water flow data were monitored since 1996 for the study watershed. Fifty five storms from 1996 to 2003 were selected for model calibration and verification. Three unit hydrograph methods were compared with the observed data in terms of simulated peak runoff, peak time and total direct runoff for the selected storms. The results showed that the coefficient of determination () for the observed peak runoff was and root mean square error, RMSE, was for calibration stages. In the model verification, for the observed peak runoff was and RMSE was , which were slightly less accurate than the calibrated data. The simulated flood hydrographs were well agreed with the observed data. SCS unit hydrograph method showed best fit, but there was no significant difference among the three unit hydrograph methods.

Alternative CN Averaging Methods for Determining the Representative CN of a Watershed

AbstractA representative curve number (CN) of a catchment is often calculated from the area-weighted average of CN values of unique land use and soil combinations. While convenient for implementation, this method is known to underestimate direct runoff depth. This paper investigates the mathematical mechanism of the expected underestimation and proposes alternative CN averaging methods called the quadratic and exact averaging methods, to handle the underestimation problem. Results suggest that the quadratic method could reduce the level of underestimation in direct runoff depth; further, the exact method could provide the same direct runoff depth as that of the area-weighted direct runoff depth averaging method. A representative CN is found to be a function of rainfall size and catchment landscape, and the underestimation is relatively large for small and mid-sized storm events. The improvement in runoff estimation with the newly proposed averaging methods is particularly beneficial to stormwater manageme...

Calibration of HSPF Hydrology Parameters Using HSPEXP Model Performance Criteria

The purpose of this study was to test the applicability of the HSPEXP model performance criteria for calibrating hydrologic parameters of HSPF. Baran watershed, located at Whasung city, was selected as a study watershed in this study. Input data for the HSPF model were obtained from the digital elevation map, landuse map, soil map and others. Water flow data from 1996 to 2000 was used for calibration and from 2002 to 2007 was for validation. Using the HSPEXP decision-support software, hydrology parameters were adjusted based on total volume, then low flows, storm flows, and finally seasonal flows. Suggested criteria for each model performance variables were referenced from the previous research. For the calibration period, all the HSPEXP model performance criteria were satisfied while two criteria were slightly violated for the validation period.

A Study on the Economic Analysis of Wastewater Reclamation and Reuse Systems for Agriculture using a System Dynamics Approach

Abstract. Many studies have reported additional treatment is needed to use wastewater for agricultural purpose. Economic considerations should be taken into account to establish infrastructure for agricultural reuse because of a large amount of water use in irrigation and relatively low water quality requirement. The objective of this study was to conduct economic analysis of wastewater reclamation and reuse systems for agriculture. A system dynamics approach considering complexity and dynamics in the wastewater reuse systems was used for the economic analysis, which are related with social, environmental, and economic problems. Sensitivity and benefit cost analysis for wastewater reuse systems was conducted through the established economic assessment model. The result of sensitivity analysis showed that water resources development and installation cost were the most sensitive for total benefits and costs, respectively. The scenario-based test of the organized economic assessment model shows marginal cost ranges and enables decision-makers to decide reasonable cost for the wastewater reuse systems for agriculture.