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Yea G.-G.,Sambu Construction Co. | Kim T.-H.,Korea University | Kim J.-H.,Korea Institute of Water and Environment | Kim H.-Y.,Sambu Construction Co.
Journal of Performance of Constructed Facilities | Year: 2013

This paper provides a detailed study of remediation work on the core zone of a damaged earth-fill dam. The relevant material includes a review of the dam surface survey data, leakage monitoring data, drilling method, grouting material, and drilling and grouting procedure. A compaction grouting method was selected as the remediation technique. In addition, the reduction and prevention of leakage and settlement were assessed. Compaction grouting was successful for filling voids, closing channels, and compacting the disturbed core soils. The loose or voided zones were properly filled, and the leakage was reduced after compaction grouting. Verification of the compaction grouting work was performed by evaluating the grouting pressures and volumes injected internally and by monitoring the dam leakage rate and tracer externally. All of these factors provide a good indication of changes inside the core of the dam, including reduction or closure of the leakage channels in the dam core. © 2013 American Society of Civil Engineers.

Lee G.,Chungnam National University | Kim J.-C.,Korea Institute of Water and Environment
Journal of Hydrologic Engineering | Year: 2010

Identifying the optimal drainage network based on digital elevation models (DEMs) is a fundamental task in rainfall-runoff modeling. Rapidly improving geographic information system technology enables hydrologists to use a variety of DEM-based hydrologic models that yield spatially concrete outputs. However, reliable drainage networks are still difficult to represent due to insufficient information about the dynamic behavior of water movement on catchment hillslopes. This study proposes an efficient method for drainage network identification through a comparative analysis of geomorphologic characteristics, such as drainage density, length of hillslope flow path, source area, etc., using area threshold and slope-area threshold criteria that incorporate scaling properties between the local slope and the contributing area. The results demonstrate that both criteria yield different drainage networks from "blue lines" based on topographic map from the Korean National Geographic Information Institute. Although the drainage networks obtained from the two criteria are visually similar, the area threshold yields an incorrect drainage structure due to excessive constraint of the draining source area size. In contrast, use of the slope-area threshold produces a relatively acceptable drainage structure in terms of preserving constant geomorphologic similarity to the study catchment. The proposed drainage network identification procedure may be used to describe landscape evolution for channel initiation in catchment hydrology. In addition, the comparative analysis of geomorphologic characteristics is found to provide important preprocess information for selecting a threshold value to generate reliable drainage networks based on DEMs before the application of hydrologic models. © 2011 ASCE.

Jang B.S.,Korea Institute of Water and Environment | Oh B.H.,Seoul National University
Cement and Concrete Research | Year: 2010

The purpose of this study is to explore the effects of non-uniform corrosion on cracking behavior of concrete cover. The effects of non-uniform corrosion distribution, cover-to-rebar diameter ratio, and concrete compressive strength on the cracking pressure of concrete cover were studied. The present study indicates that the pressures to cause cracking of concrete cover under non-uniform corrosion conditions are much smaller than those under uniform corrosion case. The cracking pressure decreases up to about 60% depending upon the types of non-uniform corrosion distributions. It was also shown that cover-to-rebar diameter ratio and concrete compressive strength affect greatly the cracking pressure of concrete cover. Realistic equations on the cracking pressure of concrete cover were derived. The comparisons of analysis results with the test data on the cracking pressure of concrete cover show fairly good agreement. Finally, the effect of non-uniform corrosion on the service life of concrete structures was discussed. © 2010 Elsevier Ltd. All rights reserved.

Choi Y.,Chungnam National University | Lee G.,Chungnam National University | Kim J.,Korea Institute of Water and Environment
Journal of Hydrologic Engineering | Year: 2011

This study presents a new method to estimate the Nash model parameters on the basis of the concept of geomorphologic dispersion stemming from spatial heterogeneity of flow paths within a catchment. The proposed method is formulated by including physically meaningful characteristic velocities for channel and hillslope and also takes account of the effect of complex interactions between channel and hillslope hydrological behaviors on catchment responses. We applied the proposed formulas to the Bocheong watershed, an experimental area established under the International Hydrological Programme (IHP) in Korea, with several storm events to assess the individual effect of channel and hillslope on hydrological responses in the study site. The characteristic velocities were estimated by topographic data based on a 20×20 m digital elevation model (DEM) from a 1:25000-scaled topographic map and statistical features of the historical events. We then calculated the Nash model parameters by substituting the estimated characteristic velocities into the new formulas proposed in this study. The sensitivity analysis results of the Nash model parameters and instantaneous unit hydrograph (IUH) shape of the characteristic velocities indicated that the scale parameter of the Nash model was more sensitive to the hillslope velocity than the channel velocity, whereas all of the Nash model parameters were determined by the relative difference between the hillslope and channel characteristic velocities. The rising limb of IUH and time to peak were dependent mainly on the channel velocity, whereas the recession limb of the IUH reacted very sensitively to the variation of the hillslope velocity. In addition, the skewness of the IUH varied with the ratio of characteristic velocities. Finally, the IUHs, estimated from regional analysis of the characteristic velocities, led to acceptable and constant hydrological responses for the catchment scale. If the improved regional analysis, modeled on hydrodynamic (or physical) approaches, is performed, the proposed formulas for the Nash model in this study can be a useful tool to simulate rainfall-runoff processes in ungauged basins. © 2011 American Society of Civil Engineers.

Park J.H.,Korea Institute of Water and Environment | Hur Y.T.,Water Resources Operation Center
KSCE Journal of Civil Engineering | Year: 2011

A lumped model, in general, is expressed by ordinary differential equations, which does not take into account the spatial variability of processes, input, boundary conditions and watershed geometric characteristics. For this reason, recently distributed run-off models have been developed to represent the variability in physical watershed characteristics such as topography, land use, and rainfall properties. However, the distributed rainfall-runoff model requires a lot of time and effort to generate input data. Also, it takes a lot of time to calculate the discharge using a numerical analysis based on kinematic wave theory in runoff process. Therefore, most river basins that use the distributed model are of limited scales, such as small river basins. Especially, the necessity for an integrated watershed management system has been increasing due to changes in watershed management concepts and discharge calculations for whole river basins, including the upstream and downstream of dams. In this study, a distributed rainfall-runoff model using Message Passing Interface (MPI) technique was developed to decrease the calculation time needed for the application of large scale watersheds. This model, which uses a parallelized based K-water hydrologic & hydraulic Distributed RUnoff Model (K-DRUM), can simulate temporal changes and the spatial distribution of flood discharge by taking into consideration radar grid rainfall and grid based hydrological parameters. The model was applied to the Geum River Basin, which include the Yongdam and Daecheong Dam Watersheds located on the Korean Peninsula. The results were calculated between a single domain and a divided small domain. They were compared to analyze the application effects of the parallelization technique. As a result, a maximum of 10 times the amount of calculation time was saved by using parallelization code rather than a single processor. Also, problems related to the running time and inaccurate settings that typically occurred using the existing trial and error method were solved by applying an auto calibration method in setting initial soil moisture conditions. As the result, the calculation results showed a good agreement with the observed data. © 2011 Korean Society of Civil Engineers and Springer-Verlag Berlin Heidelberg.

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