• Journal of The Korean Society of Agricultural Engineers
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• v.58 no.5
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• pp.11-18
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• 2016

The objective of this study was to develop the simple method to estimate ungauged river section for flood stage analysis. Damage prediction should be prioritized using hydrological modeling to reduce flood risk. Mostly, the geographical data using hydrological modeling depends on national river cross-section survey. However because of the lack of measured data, it is difficult to apply to many local streams or small watersheds. For this reason, this study suggest the method to estimate unguaged river cross-section. Simple regression equations were derived and used to estimate river cross-section by analyzing the correlation between the river cross-sectional characteristics (width, height and area). The estimated cross-sections were used to simulate flood level by HEC-RAS (Hydrologic Engineering Center's River Analysis System). The applicability of this method was verified by comparing simulated flood level between measured and estimated cross-section. The water surface elevation of the flood stage analysis was 6.56-7.24 m, 5.33-5.95 m and 6.12-6.75 m for measured cross section, for estimated cross section and for estimated cross section based on DEM elevation, respectively. Further study should consider other factors for more accurate flood stage analysis. This study might be used one of the guidelines to estimate ungauged river section for flood stage analysis.

• Journal of Korea Water Resources Association
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• v.48 no.4
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• pp.309-319
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• 2015

River characteristics in South Korea has been affected by seasonal climatic variability due to climate change and by remarkable land cover change due to rapid economic growth. In this regard, the roles of river management is getting more important to eco-system and human community in watersheds of South Korea. Understanding river characteristics including direct runoff and baseflow, the first step of river management, can give a significant contribution to sustainable river environment. Therefore, the objective of this study is to quantify the contributions of the direct runoff and baseflow to river streamflow. For this, we used the BFLOW and WHAT programs to conduct baseflow separation for 71 streamflow gauge stations in Han River system, South Korea. The results showed that baseflow index for 71 stations ranges from 0.42 to 0.78. Also, gauge stations which have baseflow index more than 0.5 occupied 76% of a total stations. However, baseflow index can be overestimated due to human impacts such as discharge from dams, reservoirs, and lakes. This study will be used as fundamental information to understand river characteristics in river management at the national level.

• Journal of Korea Water Resources Association
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• v.48 no.10
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• pp.793-806
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• 2015

The simulation of natural streamflow at ungauged basins is one of the fundamental challenges in hydrology community. The key to runoff simulation in ungauged basins is generally involved with a reliable parameter estimation in a rainfall-runoff model. However, the parameter estimation of the rainfall-runoff model is a complex issue due to an insufficient hydrologic data. This study aims to regionalize the parameters of a continuous rainfall-runoff model in conjunction with a Bayesian statistical technique to consider uncertainty more precisely associated with the parameters. First, this study employed Bayesian Markov Chain Monte Carlo scheme for the estimation of the Sacramento rainfall-runoff model. The Sacramento model is calibrated against observed daily runoff data, and finally, the posterior density function of the parameters is derived. Second, we applied a multiple linear regression model to the set of the parameters with watershed characteristics, to obtain a functional relationship between pairs of variables. The proposed model was also validated with gauged watersheds in accordance with the efficiency criteria such as the Nash-Sutcliffe efficiency, index of agreement and the coefficient of correlation.

• Journal of Korea Water Resources Association
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• v.53 no.spc1
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• pp.755-764
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• 2020

In South Korea, 850 standard watersheds and 7,807 KRF catchment areas have been used as basic maps for water resources policy establishment, however it becomes necessary to set up new standard maps with a more appropriate scale for the integrated managements of surface water-groundwater as well as water quantity-quality in the era of integrated water management. Since groundwater has a slow flow velocity and also has 3-D flow properties compared to surface water, the sub-catchment size is more effective than the regional watershed for the evaluation of surface water-groundwater interaction. The KRF catchment area, which has averagely a smaller area than the standard watershed, is similar to the sub-catchment area that generally includes the first-order or second-order tributaries. Some KRF catchment areas, which are based on the surface reach, are too small or large in a wide plain or high mountain area. Therefore, it is necessary to revise the existing KRF area if being used as a unit area for integrated management of surface-water and groundwater. A unit watershed with a KRF area of about 5 to 15 ㎢ can be effective as a basic unit for water management of local government considering a tributary composition and the location of groundwater wells, and as well it can be used as a basic tool for water demand-supply evaluation, hydrological observation system establishment, judgment of groundwater permission through a total quantity management system, pollution assessment, and prioritizing water policy, and etc.

• Journal of Environmental Science International
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• v.15 no.8
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• pp.775-784
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• 2006

In this study, CN value was estimated by using detailed soil map and land cover characteristic against upper basin of Kumho watermark located on the upper basin of Kumho river and the hydrologic morphological characteristic factors were extracted from the basin by using the DEM document. Also the runoff analysis was conducted by the WMS model in order to study how the assumed CN value affects the runoff characteristic. First of all, as a result of studying the soil type in this study area, mostly D type soil was Identified by the application of the 1987 classification criteria. However, by that in 1995, B type soil and C type soil were distributed more widely in that area. When CN value was classified by the 1995 classification criteria, it was estimated lower than in 1987, as a result of comparing the estimated CNs by those standars. Also it was assumed that CN value was underestimated when the plan for Geum-ho river maintenance was drawn up. As a result of the analysis of runoff characteristic, the pattern of generation of the classification criteria of soil groups appeared to be similar, but in the case of the application of the classification criteria in 1995, the peak rate of runoff was found to be smaller on the whole than in the case of the application of the classification criteria in 1987. Also when the statistical data such as the prediction errors, the mean squared errors, the coefficient of determination and other data emerging from the analysis, was looked over in total, it seemed appropriate to apply the 1995 classification criteria when hydrological soil classification group was applied. As the result of this study, however, the difference of the result of the statistical dat was somewhat small. In future study, it is necessary to follow up evidence about soil application On many more watersheds and in heavy rain.

• Journal of Korean Society for Geospatial Information Science
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• v.18 no.4
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• pp.21-30
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• 2010

In this paper, the parallel distributed rainfall runoff model(K-DRUM) using MPI(Message Passing Interface) technique was developed to solve the problem of calculation time as it is one of the demerits of the distributed model for performing physical and complicated numerical calculations for large scale watersheds. The K-DRUM model which is based on GIS can simulate temporal and spatial distribution of surface flow and sub-surface flow during flood period, and input parameters of ASCII format as pre-process can be extracted using ArcView. The comparison studies were performed with various domain divisions in Namgang Dam watershed in case of typoon 'Ewiniar' at 2006. The numerical simulation using the cluster system was performed to check a parallelization effectiveness increasing the domain divisions from 1 to 25. As a result, the computer memory size reduced and the calculation time was decreased with increase of divided domains. And also, the tool was suggested in order to decreasing the discharge error on each domain connections. The result shows that the calculation and communication times in each domain have to repeats three times at each time steps in order to minimization of discharge error.

• Journal of Environmental Health Sciences
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• v.35 no.6
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• pp.517-525
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• 2009

The water quality of Lake Shihwa had been rapidly deteriorating since 1994 due to wastewater input from the watersheds, limited water circulation and the lack of a wastewater treatment policy. In 2000, the government decided to open the tidal embankment and make a comprehensive management plan to improve the water quality, especially inflowing stream water around Shihwa and Banwol industrial complex. However, the water quality and microbial community have not as yet been fully evaluated. The purpose of this study is to investigate the influent water quality around the industrial area based on chemical and biological analysis, and collected surface water sample from the Siheung Stream, up-stream to down-stream through the industrial complex, Samples were collected in July 2009. The results show that the downstream site near the industrial complex had higher concentrations of heavy metals (Cu, Mn, Fe, Mg, and Zn) and organic matter than upstream sites. A combination of DGGE (Denaturing Gradient Gel Electrophoresis) gels, lists of K-WQI (Korean Water Quality Index), cluster analysis, MDS (Multi-Dimensional Scaling) and PCA (Principal Component Analysis) has demonstrated clear clustering between Siheung stream 3 and 4 and with a high similarity and detected metal reducing bacteria (Shewanella spp.) and biodegrading bacteria (Acinetobacter spp.). These results suggest that use of both chemical and microbiological marker would be useful to fully evaluate the water quality.

• Journal of Korea Water Resources Association
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• v.36 no.2
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• pp.211-221
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• 2003

The objectives of this study are to analyze the effects of time-area curve on Clark's watershed runoff method in addition to propose a GIS-based objective method for creating time-area curve. For the relative comparison of the variation of time-area curve to those of travel time and storage coefficient of Clark method, runoff sensitivities are performed on Soyang- and Chungju-dam watersheds for 1990. 9. 10~9. 14 event. The dimensionless time-area curve in HEC-1 that can be utilized in the case that the curve is not supplied is also tested in this study. The important results obtained in this study are as follows: The effects of time-area curve created by either GIS-based objective method or dimensionless curve are not significant for runoff analysis; The storage coefficient (K) and travel time( t$_{c}$), Clark's other two model parameters, are more sensitive than time-area curve for peak flow simulation. Therefore, it can be concluded that the parameters K and t$_{c}$ are more carefully estimated rather than time-area curve, when Clark method is used for runoff analysis.

• Journal of Korea Water Resources Association
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• v.39 no.2 s.163
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• pp.161-178
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• 2006

Heathcote (1998) identified a systematic, seven-step approach to general watershed planning and management. It consists of 1) understanding watershed components and processes, 2) identifying and ranking problems to be solved, 3) setting clear and specific goals, 4) developing a list of management options, 5) eliminating infeasible options 6) testing the effectiveness of remaining feasible options, and 7) developing the final options. In this study the first five steps of that process were applied to the Anyangcheon watershed in Korea, which experiences streamflow depletion, frequent flood damages, and poor water quality typical of highly urbanized watersheds. This study employed four indices: Potential Flood Damage(PFD), Potential Streamflow Depletion(PSD), Potential Water Quality Deterioration(PWQD) and Watershed Evaluation Index(WEI) to identify and quantify problems within the watershed. WEI is the integration index of the others. Composite programming which is a method of multi-criteria decision making is applied for the calculation of PSD, PWQD and WEI (Step 2). The primary goal of the study is to secure instreamflow in the Anyangcheon during dry seasons. The second management goals of flood damage mitigation and water quality enhancement are also set (Step 3). Management options include not only structural measures that can alter the existing conditions, but also nonstructural measures that rely on changes in human behavior or management practices (Step 4). Certain management options which are not technically, economically, and environmentally feasible, are eliminated (Step S). Therefore, this study addresses a Pre-feasibility study, which established a master plan using Steps 1 through 5.

• Journal of Korea Water Resources Association
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• v.32 no.4
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• pp.457-467
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• 1999

No complete methods for estimating soil loss, included by rain storms, from a small watershed are available yet, and the best recommended method is to use measured data from the watershed. When no measured data is available from the watershed, empirical models for estimating the soil loss, such as the Universal Soil Loss Equation(USLE), is well recommended in practice. For using this equation, it is necessary to estimated the rainfall erosivity, commonly expressed as R, of the watershed. In this study, first we collected data of the probable rainfalls with the return periods of 2, 5, 10, 20, 30, 50, 80, 100, 200, and 500-yr and with the duration hours of 0.5, 1, 2, 3, 6, 12, and 24-hr. Using this data, we calculated the design values for R for the return period of 24-hr at each major rainfall-measuring station nationwide. Then we constructed the iso-erodent map of Korea for each return period of the 24-hr design storm. This study shows that the 24-hr duration iso-erodent map of the 5-yr return period is very similar to the annual average iso-erodent map of Korea. This study also shows that the 24-hr duration R-values of a certain return period can be estimated by multiplying certain parameters, obtained from this study, to the 24-hr duration R-values for the 5-yr return period or the annual average R-values. Finally, the R-values of the design storm with the 24-hr return period obtained from this study can be used for designing the settling basins at small watersheds.