The measuring point of the Hangang Bridge affected by tide has some special topographic characteristics due to Nodle Island. Furthermore the submerged weirs located on the upstream and downstream. Therefore flow is separated and joined by Nodle Island. Discharge measurement at the point of the Hangang Bridge is very important, because Hangang Bridge is key station in managing the discharge and flood forecasting. In the past, it was too difficult to measure discharge in tidal conditions. HRFCO(Han River Flood Control Office) installed automatic discharge measurement facilities for solving this problem. Measuring equipments operates and measures discharge every 10 minutes at 2 points(southern and northern section close to Nodle Island), and calculates flow discharge using Chiu`s velocity law(Chiu, 1988). In order to verify the results of automatic discharge measurements, manual discharge measurements were carried out by ADCP. In addition, the monthly discharge were also compared.

In this paper a heuristic method for identifying individual pipes in water pipe networks to determine specific sections of the pipes that need to be replaced due to deterioration. An appropriate minimum pipe length is determined by selecting the pipe length that has the greatest variance of the average cumulative break number slopes among the various pipe lengths used. As a result, the minimum pipe length for the case study water network is determined as 4 m and a total of 39 individual pipe IDs are obtained. The economically optimal replacement times of the individual pipe IDs are estimated by using the threshold break rate of an individual pipe ID and the pipe break trends models for which the General Pipe Break Prediction Model(Park and Loganathan, 2002) that can incorporate the linear, exponential, and in-between of the linear and exponetial failure trends and the ROCOFs based on the modified time scale(Park et al., 2007) are used. The maximum log-likelihoods of the log-linear ROCOF and Weibull ROCOF estimated for the break data of a pipe are compared and the ROCOF that has a greater likelihood is selected for the pipe of interest. The effects of the social costs of a pipe break on the optimal replacement time are also discussed.

Determination of optimal pressure monitoring location is essential to manage water distribution system efficiently and safely. In this study, entropy theory is applied to overcome defects of previous researches about determining the optimal sensor location. The previous studies required the calibration using historical data, therefore, it was difficult to apply the proposed method in the place where the enough data were not available. Also, most researches have focused on the locations to minimize cost and maximize accuracy of the model, which is not appropriate for the purpose of maintenance of the water distribution system. The proposed method in this study quantify the entropy which is defined as the amount of information calculated from the pressure change due to the variation of discharge. When abnormal condition is occurred in a node, the effect on the entire network is presented by the entropy, and the emitter is used to reproduce actual pressure change pattern in EPANET. The optimal location to install pressure sensors in water distribution system is the nodes having the maximum information from other nodes. The looped and branched networks are evaluated using the proposed model. As a result, entropy theory provides general guideline to select the locations to install pressure sensors and the results can be used to help decision makers.

General reliability assessment of levees embankment is performed with safety factors for rainfall characteristics and hydrologic and hydraulic parameters, based on the results of deterministic analysis. The safety factors are widely employed in the field of engineering handling model parameters and the diversity of material properties, but cannot explain every natural phenomenon. Uncertainty of flood analysis and related parameters by introducing stochastic method rather than deterministic scheme will be required to deal with extreme weather and unprecedented flood due to recent climate change. As a consequence, stochastic-method-based measures considering parameter uncertainty and related factors are being established. In this study, a variety of dimensionless cumulative rainfall curve for typhoon and monsoon season of July to September with generation method of stochastic temporal variation is generated by introducing Monte Carlo method and applied to the risk assessment of levee embankment using reliability index. The result of this study reflecting temporal and regional characteristics of a rainfall can be used for the establishment of flood defence measures, hydraulic structure design and analysis on a watershed.

Due to environmental, economical and the other limitations, it has been more difficult to construct new large hydraulic structure such as dam. For this reason, it has been tried to use small hydraulic structure such as washland as alternative of hydraulic facility. Because the flood control effect of small hydraulic structure are affected by runoff volume, hydrograph, storage capacity and weir crest elevation, and design frequency must be predetermined for the design of the hydraulic structure. Multiple washlands will be required to satisfy enough peak reduction effect so that considering washlands as a network, rather than individually, are critical to analysis of flood reduction effect. In this study, new index for determination of optimal location for washlands is presented and the existing model for this determination is modified by adopting the new index. Developed new model is applied to Ansung river basin for examination and the new model shows its` applicability as a decision making criteria for the determination of optimal location for washlands.

Levee-break Analysis model is developed to predict the variation of breach width according to time and to estimate inundation area and depth in protected lowland. This Model calculate flood depth using 4 point implicit finite difference method in river channel and analyze breach flow based on physical theory introducing soil transport equation and erosion process. Breach analysis model and channel flood model are combined into Levee-Break Model and this model is applied to actual levee break case. Then, this model can simulate reasonably many levee-break parameters such as river stage, breach width, breach formation and so on. If the applicability of this model is proved through applications to more various actual levee-break cases, the suggested model is expected to do more accurate flood analyses on levee break site.

Hwang River in South Korea, has experienced channel adjustments due to dam construction. Hapcheon main dam and re-regulation dam. The reach below the re-regulation dam (45 km long) changed in flow regime, channel width, bed material distribution, vegetation expansion, and island formation after dam construction. The re-regulation dam dramatically reduced annual peak flow from 654.7 /s to 126.3 /s and trapped the annual 591 thousand of sediment load formerly delivered from the upper watershed since the completion of the dam in 1989. An analysis of a time series of aerial photographs taken in 1982, 1993, and 2004 showed that non-vegetated active channel width narrowed an average of 152 m (47% of 1982) and non-vegetated active channel area decreased an average of 6.6 km2 (44% of 1982) between 1982 and 2004, with most narrowing and decreasing occurring after dam construction. The effects of daily pulses of water from peak hydropower generation and sudden sluice gate operations are investigated downstream of Hapcheon Dam in South Korea. The study reach is 45 km long from the Hapcheon re-regulation Dam to the confluence with the Nakdong River. An analysis of a time series of aerial photographs taken in 1982, 1993, and 2004 showed that the non-vegetated active channel width narrowed an average of 152 m (47% reduction since 1982). The non-vegetated active channel area also decreased an average of 6.6 (44% reduction since 1982) between 1982 and 2004, with most changes occurring after dam construction. The average median bed material size increased from 1.07 mm in 1983 to 5.72 mm in 2003, and the bed slope of the reach decreased from 0.000943 in 1983 to 0.000847 in 2003. The riverbed vertical degradation is approximately 2.6 m for a distance of 20 km below the re-regulation dam. It is expected from the result of the unsteady sediment transport numerical model (GSTAR-1D) steady simulations that the thalweg elevation will reach a stable condition around 2020. The model also confirms the theoretical prediction that sediment transport rates from daily pulses and flood peaks are 21 % and 15 % higher than their respective averages.