Sang Min Jun

Effects of Agricultural Reservoir Rehabilitation on their Flood Control Capacities

About 74 % of reservoirs in Korea are older than 40 years and their storage capacities have been decreased substantially. As part of reservoir reinforcement, the dam heightening project has been ongoing for about 110 reservoirs. The main purpose of the dam heightening project is to secure additional environmental water, while improving flood control capacity by gaining additional storage volume. The objective of this study was to evaluate reservoir flood control capacity changes of dam heightening reservoirs for effective management of additional storage volume. In this study, 13 reservoirs were selected for reservoir simulation of 200 year return period floods. Rainfall data of 1981-2100 were collected and divided into 4 periods (1981-2010; 1995s, 2011-2040; 2025s, 2041-2070; 2055s, 2071-2100; 2085s). Probability rainfalls and 200yr design floods of each period were calculated using FARD2006 and HEC-HMS. Design floods were used as inputs of each reservoir simulation using HEC-5. Overall, future probability rainfalls and design floods tend to increase above the past 1995s. Control ratios were calculated to evaluate flood control capacities of reservoirs. As a result, average flood control ratios were increased from 32.6 % to 44.2 % after dam heightening. Control ratios were increased by 12.7 % (1995s), 12.4 % (2025s), 10.3 % (2055s) and 10.9 % (2085s). The result of this study can be used as a basis for establishing the reservoir management structure in the future.

Statistics and Probability Distribution of Total Coliforms in Wastewater

Probability distribution of microbes in wastewater is a crucial factor to be determined for microbial risk assessment associated with its reuse. The objective of this study was to investigate probability distribution of an indicator microorganism in wastewater. Daily total coliform counts measured from nationwide wastewater treatment plants in 2010 by the Ministry of Environment were used for statistical analysis. Basic statistics and probability distributions were estimated in the three different spatial scales using the MS Excel software and FARD2006 model. Overall, wastewater from manure and livestock treatment plants demonstrated greater median coliform counts than from sewage and village treatment plants. Generalized logistic (GLO) and 2-parameter Weibull (WBU2) appeared to be the two probability distributions that fitted best for total coliform numbers in wastewater. The study results of microbial statistics and probability distributions would provide useful data for quantitative assessment of microbial risk from agricultural wastewater reuse.

Evaluation of the Tank Model Optimized Parameter for Watershed Modeling

The objective of this study was to evaluate of the Tank model in simulating runoff discharge from rural watershed in comparison to the SWAT (Soil and Water Assessment Tool) model. The model parameters of SWAT was calibrated by the shuffled complex evolution-university Arizona (SCE-UA) method while Tank model was calibrated by genetic algorithm (GA) and validated. Four dam watersheds were selected as the study areas. Hydrological data of the Water Management Information System (WAMIS) and geological data were used as an input data for the model simulation. Runoff data were used for the model calibration and validation. The determination coefficient (R), root mean square error (RMSE), Nash-Sutcliffe efficiency index (NSE) were used to evaluate the model performances. The result indicated that both SWAT model and Tank model simulated runoff reasonably during calibration and validation period. For annual runoff, the Tank model tended to overestimate, especially for small runoff (< 0.2 mm) whereas SWAT model underestimate runoff as compared to observed data. The statistics indicated that the Tank model simulated runoff more accurately than the SWAT model. Therefore the Tank model could be a good tool for runoff simulation considering its ease of use.

Effects of Controlled Drainage and Slow-release Fertilizer on Nutrient Pollutant Loads from Paddy Fields

The objective of this study was to investigate the effects of farming methods on mass balance from paddy rice. The experiment fields were established at Chunpo-myeon, Iksan-si in the Saemangeum watershed. Experiment was performed during the growing season to assess water and mass balances of the study field in 2013. The three different farming practices were applied: conventional (TR-A), drainage outlet heighten (TR-B) and slow release fertilizer use (TR-C). Drainage amount from TR-B was reduced by 28.5 % compared to the TR-A, while the amount from TR-C was similar to that of TR-A. Overall, nutrient concentration of paddy water were similar among the treatments except for T-P. Mean T-P concentration from TR-C was lower than that from TR-A (p-value

Design Flood Estimation in the Hwangguji River Watershed under Climate and Land Use Changes Scenario

Extreme floods occur more often recently as the frequency of extreme storm events increase due to the climate change. Because the extreme flood exceeding the design flood can cause large-scale disasters, it is important to predict and prepare for the future extreme flood. Flood flow is affected by two main factors; rainfall and land use. To predict the future extreme flood, both changes in rainfall due to the climate change and land use should be considered. The objective of this study was to simulate the future design flood in the Hwangguji river watershed, South Korea. The climate and land use change scenarios were derived from the representative concentration pathways (RCP) 4.5 and 8.5 scenarios. Conversion of land use and its effects (CLUE) and hydrologic modelling system (HEC-HMS) models were used to simulate the land use change and design flood, respectively. Design floods of 100-year and 200-year for 2040, 2070, and 2100 under the RCP4.5 and 8.5 scenarios were calculated and analyzed. The land use change simulation described that the urban area would increase, while forest would decrease from 2010 to 2100 for both the RCP4.5 and 8.5 scenarios. The overall changes in design floods from 2010 to 2100 were similar to those of probable rainfalls. However, the impact of land use change on design flood was negligible because the increase rate of probable rainfall was much larger than that of curve number (CN) and impervious area.

Hydrologic Modeling for Agricultural Reservoir Watersheds Using the COMFARM

Abstract The component-based modeling framework for agricultural water-resources management (COMFARM) is a user-friendly, highly interoperable, lightweight modeling framework that supports the development of watershed-specific domain components. The objective of this stu dy was to evaluate the suitability of the COMFARM for the design and creation of a component-based modeling system of agricultural reservoir water sheds. A case study that focused on a particular modeling system was conducted on a watershed that includes the Daehwa and Dangwol serial irrigation reservoirs. The hydrologic modeling system for the study area was constructed with linkable components, including the modified Tank, an agricul tural water supply and drainage model, and a reservoir water balance model. The model parameters were each calibrated for two years, based on observed reservoir water levels. The simulated results were in good agreement with the observed data. In addition, the applicability of the COMFARM was evaluate d for regions where reservoir outflows, including not only spillway release but also return flow by irrigation water supply, substantially affect the downstream river discharge. The COMFARM could help to develop effective water-management measures by allowing the construction of a modeling system and evaluation of multiple operational scenarios customized for a specific watershed.Keywords: COMFARM; agricultural water; agricultural reservoir; modeling system; hydrologic modeling *

Estimation of Design Flood for the Gyeryong Reservoir Watershed based on RCP scenarios

Abstract Along with climate change, the occurrence and severity of natural disasters have been increased globally. In particular, the increase of localized heavy rainfalls have caused severe flood damage. Thus, it is needed to consider climate change into the estimation of design flood, a principal design factor. Themain objective of this study was to estimate design floods for an agricultural reservoir watershed based on the RCP (Representative Concentration Pathways) scenarios. Gyeryong Reservoir located in the Geum Rive r watershed was selected as th e study area. Precipitation data of the past 30 years (1981∼2010; 1995s) were collected from the Daejeon meteorological station. Future precipitation data based on RCP2.6, 4.5, 6.0, 8.5 scenarios were also obtained and corrected their bias using the quantile mapping method. Probability rainfalls of 200-year frequency and PMPs were calculated for three different future spans, i.e. 2011 ∼2040; 2025s, 2041 ∼2070; 2055s, 2071 ∼2100; 2085s. Design floods for different probability rainfalls were calculate d using HEC-HMS. As the result, future probability rainfalls increased by 9.5 %, 7.8 % and 22.0 %, also design floods increased b y 20.7 %, 5.0 % and 26.9%, respectively, as compared to the past 1995s and tend to increase over those of 1 995s. RCP4.5 scenario, especially, resulted in the greatest increase i ndesign floods, 37.3 %, 36.5 % and 47.1 %, respectively, as compared to the past 1995s. The study findings are expected to be used as a basis to reduce damage caused by climate change and to establish adaptation policies in the future.Keywords: Climate change; RCP scenarios; Design flood; HEC-HMS*