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In this study, analysis of reliability of sewer network was progressed with the number of overflow nodes and overflow volume simultaneously for urban areas considering sedimentation. Reliability analysis shows that it is possible to quantify the difference in the phenomenon of the destruction of sedimentation in urban sewer system under the same design frequency. It is proposed as one of the indicators evaluated as full reliability for sewer system. To analyze detailed changes in conduit designs in urban sewer networks, tried to reduction of sedimentation in sewer networks using modified pipe slope in Bujeon-dong catchment, Busan. The various sewer designs were applied and then, the most effective improvement of reliability over 10%. Suggested reliability process can produce the quantitative evaluations about sewer systems using the results of the system simulations and use of possible the objective function for the sewer network designed with a relative evaluation.

Recently, Flood damage in river is mainly occurring in medium and small streams. In case of national river or large scale local rivers, disaster management such as river improvements were established. Whereas, In case of medium and small stream, disaster management for flood damage is insufficient. Among medium and small streams of the streams passing urban areas if flood damage occur, the focus of management is required to large scale damage of human and infrastructure. In this study, it proposed selection criteria of medium and small streams that flood damage is recently increased and medium and small streams that passes through the urban area that classification criteria of urban basin proposes using impervious area.

In this study, we effectively reduce the flood damage through a revise the border for district unit urban drainage system and propose a design technique over the configuration of the sewer network. It was selected in adjacent urban drainage system, analysis the results for the revise of the watershed boundary and inundation reduction effect. The main nodes were chosen to generate a flood damage, the flood mitigation effect was verified. It proposed a emphasis point for revise the border for urban drainage system.

The storm sewer is designed to pass the inflow rate depending on the design frequency smoothly. However, taking a look at the exam-ple of flooding generated in urban area shows that an increase in the generation and damage of flooding can be often caused by thedeposition of sediment in the sewer. This is a problem in the maintenance of sewers, but this implies that the effect of sediment dep-osition should be considered to some degree for the design of a conduit itself in another aspect. Thus, it is necessary to realize designin a direction to reduce flood damage pursuant to it by considering the deposition aspect of sediment in a conduit when designing astorm sewer. This study conducted an analysis on the current storm sewer for the Bujeon stream basin at Busan in order to analyze thedeposition aspect of sediment in a sewer network at an actual urban area and the effect of the generation of flooding damage due tothis. The applicable sewer is a box type, which has appeared to be able to discharge capacity enough to discharge a design rainfallover 30, 50, 80 and 100 years for a duration time such as 60, 120, 180 and 240 minutes when not considering the deposition of soil inthe sewer network. On the other hand, when considering the deposition of sediment in conduit, flooding took place for all the abovedesign rainfall. In addition, as a result of adjusting the slope of the conduit section arbitrarily for the current conduit, it was analyzedthat the deposition of sediment can be reduced and the generation of overflows for the design rainfall applied according to this can bereduced by maximum about 65%. From these analysis results, it appeared as necessary to consider the deposition aspect of sedimentwhen designing a sewer network, and design it in a direction to secure the discharge capacity pursuant to this as much as possible.Key words : Sedimentation, Sewer network, Inundation, Discharge capasity

Reduction of discharge capacity due to sedimentation in sewer increase danger of the inundation risk because of occurrence of fre-quent localized heavy rainfall, we need to find the fundamental solution for sewer design and maintenance. However, internalresearches considering sedimentation in sewer designs are very insufficient, should be urgently required by considering the charac-teristics about future research and design standards. In this study, examines the design concept for discharge capacity and reduction ofsedimentation in sewer networks. The virtual sewer networks are designed to analysis and distribute the sedimentation of depositionalpatterns in the sewer conduits, while considering the sedimentation diameter, in order to reduce the inundation risk. Accordingly, toanalyze detailed changes in conduit designs in urban sewer networks, tried to reduction of sedimentation in sewer networks usingmodified pipe slope in Bujeon stream catchment, Busan. The various sewer designs were applied to Bujeon stream catchment andthen, the most effective reduction of sedimentation volume over 30%. Just, total sedimentation depth separately intended the variationcases contrary to total sedimentation volume, we need to consider about entirely adequate aspect of related to design safety. So,including both the volume and the depth consideration through estimating the reliability of sewer network systems.Key words : Sedimentation, Sewer network, Inundation, Discharge capasity, Depositional pattern

In low-lying districts of urban areas, drainage pumping stations were built to protect urban inundation by the heavy rain and, in the station, the pump operation is performed by only reservoir depth. But the effect of pump operation can be improved by various pump- ing rules. This study would like to analysis the reduction effects of urban inundation by early operation of pumps. The various design rainfall events were applied to Gasan 1 pumping station in Seoul and then, the most effective period of early operation was 10 min- utes. Also, the maximum water levels of reservoir simulated by early pump operation were 10~70 cm lower than results by the exist- ing operation rule and the overflow volumes in upstream sewer network were reduece by about 50%. Therefore, in urban areas, the flood control stability can be improved by efficient operation of the existing pumping station.

During the dry periods, many types of pollutants are being accumulated on the land surface and the accumulated various pollutants are inflowing in th the near watershed areas for the rainfall periods. Then, the monitoring study needs to analysis of the pollutant loads and an establishment of a management plan for nonpoint source. The aims of this study are the characterization of discharge from nonpoint source, the analysis of the pollutant loads and an establishment of a management plan for nonpoint source of Geum river basin. For this purpose, 7 monitoring points was selected to the investigated. During the period from April, 2008 to August, 2013, the water automatic sampler system has been installed in each monitoring points. Event Mean Concentration(EMC) of , SS was calculated based on the monitoring data of 318 rainfall events at 7 monitoring points. The land use of the studied basins were divided into forested land and grassland. As the results, a significant relationship was observed from the correlation between EMCs and rainfall characteristics. The present study is achieved to provide the correlation between rainfall events and nonpoint source pollutants. And the data which were build up in this study will contribute to establish the management policy for the nonpoint source pollutants.

Entropy theory was applied to generate standards for the assessment of the optimal water quality monitoring network. Theentropy theory considers the trans-information among both locations where water quality monitoring facilities are installed andlocations without such facilities. Therefore, the theory can support the establishment of the water quality monitoring network byreducing the uncertainty on the basis of information produced by the network. This study has been applied to Geum river systemto evaluate if the current network for each water quality item is in proper level. In the results, The order of significant sites is dif-ferent for each water quality item. It is because each water quality item has different influence factors. The pattern of informationincrease from an additional site is different from each water quality items. For some items (BOD, pH, T-N) the total informationstagnates after a certain number of sites, however, for others (COD, SS, T-P) it still increases almost linearly as a new site isadded. This means that the current monitoring network has insufficient number of sites for some water quality items.Key words : Entropy, Water quality monitoring network, Geum River system

Recently, the danger of flooding has increased due to the result of extreme climate change and urbanization around the metropolitan areas. To prevent this kind of problems, installing underground retaining facility around the metropolitan basin has been discussed. Even though the several researches related to the underground retaining facility are on progress, the general consideration of the capacity and the location is unsatisfying. Therefore, this research has developed an optimal model which would help to decide an adequate capacity and location according to the numbers of the facilities that need to be installed. For this optimal technique, Harmony Search (HS) is utilized, and SWMM (Storm Water Management Model) 5.0 DLL is constructed accordingly for the better interpretation of hydraulic, hydrological. And the sensitivity analysis was performed for SWMM parameters such as manning`s roughness coefficient and manhole loss coefficient which affect overflow in the sewer network. And this sensitivity analysis was considered to determine the optimal positions of storages. The developed optimal model has been simulated in BEXCO district in Busan, and it has determined the positions according to the different numbers of the facilities which need to be installed.

During the dry periods, many types of pollutants are being accumulated on the land surface and the accumulated various pollutants are inflowing in th the near watershed areas for the rainfall periods. Then, the monitoring study needs to analysis of the pollutant loads and an establishment of a management plan for nonpoint source. In this study, a field monitoring was conducted in order to find out the discharge characteristics of nonpoint source pollutants in Geum river basin. Event Mean Concentration (EMC) of , SS was calculated based on the monitoring data of 56 rainfall events at 7 monitoring points. The land use of the studied basins were divided into forested land and grassland. As the results, a significant relationship was observed from the correlation between EMCs and rainfall characteristics. The present study is achieved to provide the correlation between rainfall events and nonpoint source pollutants. And the data which were build up in this study will contribute to establish the management policy for the nonpoint source pollutants.

The frequency and intensity of disaster is increasing by climate change and the establishment of disaster management policy and its application in practice is necessary. for that, it is important to define the risk and assess estimate the degree of the risk in a region. In this study, to assess the risk by damage by storm and flood in a region, three disaster indices(occurrence, vulnerability and damage analysis index) were developed. And a method for estimate risk environment was suggested using the indices. The developed method were applied at 230 regions to assess locality risk. The results of this study are expected to utilize to disaster management policy.

As the urbanization proceeds, the extent of impermeability has expanded due to the increase of land use changes and pavement percentage of the road. These facts have aggravated the danger of inundation such as the increase of urban efflux and the decrease in time of reaching permissible range. To handle the increasing amount of inundation, numbers of retarding basins and drainage pump stations are already constructed or under contemplation in the urban areas. Consequently, due to the fact that the damage caused by the inundation might fluctuate according to the technique of drainage pump operation, the importance of appropriate management in detention storage and drainage pump system has aroused, despite of the identical constructional condition of the retarding basins. However, this may work effectively when the efflux from the upper stream is predicted and the pump is activated beforehand. Therefore, for more effective management of drainage pump stations, the following research provides the method of selecting an adequate monitoring spot in the sewer system for the urban basins. Utilizing the entropy methods and linear regressions, the model provided below suggests a method of selecting monitoring spots considering the efflux of each basins and the concentration time to the outlet.

One of the researches about the reliability of storm sewer network defined the sewer system failure as the overflow occurrence for the rainfall events and suggested the reliability evaluation method of storm sewer network, RSDMM(Reliability of Sewer system using DMM). In this study, the parameters to estimate the reliability are the overflow volume and the number of the overflow manholes in the storm sewer network. In order to estimate the reliability, this method used the Distance Measure Method (DMM) to estimate the distance between the parameters while the units and dimensions of each parameter are different. But, the frequency boundary of applied rainfall events was not clear although the reliability results can be different when the boundary of rainfall event`s frequency is different. That is, the RSDMM is estimated as the average of overflows for each excessive rainfall event although the overflow occurrences are different according to applied rainfall frequencies. Therefore, to solve these problems and improve the RSDMM, in this study, the frequency boundary of applied rainfall events was defined clearly and the scale control between the number of overflow nodes and overflow volume was organized. Then, the reliability of sewer network is estimated as the quantitative evaluation and this new suggested method improved the RSDMM of Lee`s study.

Recently, the danger of flooding has increased due to the result of extreme climate change and urbanization around the metropolitan areas. To prevent this kind of problems, installing underground retaining facility around the metropolitan basin has been discussed. Even though the several researches related to the underground retaining facility are on progress, the general consideration of the capacity and the location is unsatisfying. Therefore, this research has developed an optimal model which would help to decide an adequate capacity and location according to the numbers of the facilities that need to be installed. For this optimal technique, genetic algorithm is utilized, and SWMM(Storm Water Management Model) 5.0 DLL is constructed accordingly for the better interpretation of hydraulic, hydrological. The model has been simulated in Sungnae district in Seoul, and it has determined the adequate capacity and the location according to the different numbers of the facilities which need to be installed. Furthermore, by adapting various situations of exceeding rainfall, it has also analyzed the method of reducing inundation while installing the underground retaining facilities.

In this study, Entropy method and PROMETHEE(Preference Ranking Organization METHod for Enrichment Evaluations) which is one of the multi criteria decision making methods are applied to estimate the relative inundation risk of the urban subcatchment. For this purpose, several factors which have an effect on the inundation risk are selected and used to perform PROMETHEE. Those are elevation average, slope average, width and population, density of conduit of each subcatchment. Based on them, PROMETHEE is performed and the relative urban inundation risk for each subcatchment is estimated. For the validation of the suggested method, the results from the suggested method are compared with the historical inundation records occured on 1990 and the relative urban inundation risk estimated. From the comparison, it is found that the suggested method may generate better results to estimate the relative urban inundation risk of each subcatchment than the method considering sediment yields per unit area only. Also, it can be applied to establish a rehabilitation order of subcatchments for mitigating the inundation risk.

The reliability of storm sewer network is estimated by the probability of system failure as the general structure systems. And the current researches for the system reliability have been based on the uncertainty analysis. However, these researches consider only the failure probability based on mathematical analysis in the sewer design but does not consider the situations caused by the system failure. In this study, the suggested method, RSDMM(Reilibility of Sewer system using DMM), evaluates the reliability of storm sewer network considering the situation of the network failure. In this method, the system failure was defined as the overflow occurrence in the sewer system for the rainfall events. And the parameters to estimate the reliability are the overflow volume and the number of the overflow manholes in the storm sewer network. In order to estimate the reliability, this method used the Distance Measure Method (DMM). DMM is the method to estimate the distance between the parameters while the units and dimensions of each parameter are different. Therefore, the suggested RSDMM can produce the quantitative evaluations about the relative superiors among the sewer systems using the results of the system failure simulations.

The increasing incidence of torrential rain and the increment of impervious area caused by urbanization has increased the surface flow and decreased the time of concentration. Therefore, the peak outflows and urban inundation risks are increased in urban areas, so that the sewer system must be designed to minimize the inundation risk in urban areas. In this reason, the suggested Optimal Sewer layout and Watershed division Model (OSWM) determines the optimal sewer layout and basin boundary considering "minimum peak outflow" at outlet in the sewer network to reduce the urban inundation risk. The OSWM determines the optimal design considering peak outflow at outlet and rehabilitation cost of sewer network. Then, the peak outflow and rehabilitation cost are minimized, so that the urban inundation risk is decreased due to the peak outflow reduction. In this model, NSGA-II (Non-dominated Sorting Genetic Algorithm) which is one of the multi-objective optimal techniques was used to solve this multi-objective problem. The OSWM was applied to a multi-outlet urban area containing two sub-basins in Seoul, South Korea. According to the basin boundary and sewer networks determined from OSWM, the peak outflows at each sub-basin outlet were decreased by 26.6% for the design rainfall event of 10-year frequency.

It is general to design the sewer network in current urban basin to calculate the minimum construction cost depending on sewer route setting of the shortest distance, and precedent researches on optimal design of sewer network is focused on cost-benefit of sewer network. Also, regional torrential rains currently occurred frequently increase the risk of local heavy rainfall in the urban basin with increasing of impermeable areas due to urbanization while exceeding of discharge capacity in the urban basin sewer network, so limitations on existing sewer design have came to the fore. Thus, this study has control the flow changes in pipes as the function objective that can be controlled depending on configurations of sewer through controlling of superposition effects between runoff hydrograph to determine the minimum overflow volume optimal sewer network focusing on that optimal sewer network to maximize the flooding prevention effect, and through application of excessive rainfall events by design frequency 10 years, reduction effects of inundation have been analyzed. Resulting in that, in case of overflow volume minimum sewer network, among 33 nodes, 20 sewers were connected to other direction than current sewers, and overflow volumes for each point about excessive rainfalls show that reduction rate against current sewer network was between 24% and 46%.

Generally, inundation risk should be estimated to establish the flood disaster prevention policy in urban areas. In this study, a new method was suggested to estimate urban inundation risk. To develop the suggested method, we selected the five factors such as surface elevation, surface slope, pipe density, population and sediment in pipe, which have influence on the urban flood risk. Although the contribution of each factor to increase the risk must be considered at the same time, it is difficult to combine those contributions because each factor has different units. For this reason, the new method adopts the Fuzzy C-Means (FCM) algorithm which is one of the fuzzy cluster algorithms and makes it possible to consider the contribution of those factors that increase urban inundation risk at the same time. To verify the applicability of the suggested method, we applied the suggested method to Gunja basin in Seoul, Korea. Firstly, we collected the five factors for each sub-basin and used them to perform the FCM to estimate the inundation risk of each sub-basin. Then, the results obtained from the analysis were compared with the inundation history of Gunja basin. Comparison results showed that the high-risk sub-basins were in good agreement with the sub-basins which have the inundation history. Thus, the inundation risk estimation using FCM can be applicable to establish the disaster prevention policy for urban flood.

To perform a long-term simulation which can be used for the estimation of annual runoff or other analyses, a long-term rainfall-runoff simulation relies on a continuous daily- or monthly-rainfall data. For this purpose, sufficient observed rainfall time series data must be used to satisfy the reliability of runoff analysis. In Korea, many rainfall stations have enough observed rainfall data for the reliable statistical analysis. However, as the characteristics of rainfall change due to urbanization and climate change, using all the rainfall data including older ones may average out their effects. Therefore, in this study, the year of the rainfall characteristic change was determined by the statistical analysis, and the long-term rainfall data was then generated by the Neyman-Scott model using the more recent rainfall data after the year of the rainfall characteristic change. For the observed rainfall data of 48 years(1961~2008), the Year 1990 was determined as the year of the rainfall characteristic change. Based on this finding, the 100- year daily-rainfall time series were generated by the Neyman-Scott model using the rainfall data observed from 1990 to 2008. Finally, the simulated daily-rainfall time series were verified for the statistical reliability by comparing with the more recent observed data.

In order to manage a sewer system effectively, flow conditions such as flux, water quality, Infiltration and Inflow (I/I), Combined Sewer Overflows (CSOs), etc need to be monitored on a regular base. Therefore, in sewer networks, a monitoring is so important to prevent the river disaster. Monitoring all nodes of an entire sewer system is not necessary and cost-prohibitive. Water quality monitoring points that can represent a sewer system should be selected in a economical manner. There is no a standard for the selection of monitoring points and the quantitative analysis of the observed data has not been applied in sewer system. In this study, the entropy method was applied for a sewer network to evaluate and determine the optimal water quality monitoring points using genetic algorithm. The entropy method allows to analyze the observed data for the pattern and magnitude of temporal water quality change. Since water quality measurement usually accompanies with flow measurement, a set of installation locations of flowmeters was chosen as decision variables in this study.

Previously most of flood prevention efforts have been made for relatively large watersheds near to channel flow. However, as economical development and the expansion of leisure areas to mountainous region, human casualty by flash flood occurs frequently, requiring additional prevention activity. Therefore, to reduce the damage of human lives and property by flash flood, we develop an assessment method for flash flood occurrence for mountainous areas considering various factors involving it. PROMETHEE(Preference Ranking Organization METHod for Enrichment Evaluations) which is one of the MCDM(Multi-Criteria Decision Making) was adopted to assess the contribution of each factor to the risk of the flash flood in the mountainous area. The main evaluation criteria are classified into three categories, namely, the regional and rainfall characteristics, and geographical features. Also, the Entropy method is used to determine the weight of each evaluation criteria without survey. The suggested method based on PROMETHEE with Entropy method is applied to BongHwa region to verify its applicability. After applied, the method successfully assesses the relative risk of flash flood occurrence of each sub region in the BongHwa region. Out of the seventeen sub-regions, five, seven and five of them are evaluated as high-risk, medium-risk, and low-risk, respectively. To verify the results, we searched the historical data of flash flood and the flash flood had occurred in one of high-risk sub-regions at 2008.

Although many researches have been carried out concerning the watershed division in natural areas, it has not been researched for the urban watershed division. If the boundary between two urban areas is indistinct because no natural distinction or no administrative division is between the areas, the boundary between the urban areas that have the different outlets (multi-outlet urban watershed) is determined by only designer of sewer system. The suggested urban watershed division model (UWDM) determines the watershed boundary to reduce simultaneously the peak outflows at the outlets of each watershed. Then, the UWDM determines the sewer network to reduce the peak outflow at outlet by determining the pipe connecting directions between the manholes that have the multi-possible pipe connecting directions. In the UWDM, because the modification of the sewer network changes the superposition effect of the runoff hydrographs in sewer pipes, the optimal sewer layout can reduce the peak outflow at outlet, as much as the superposition effects of the hydrographs are reduced. Therefore, the UWDM can optimize the watershed distinction in multi-outlet urban watershed by determining the connecting directions of the boundary-manholes using the genetic algorithm. The suggested model was applied to a multi-outlet urban watershed of 50.3ha, Seoul, Korea, and the watershed division of this model, the peak outflows at two outlets were decreased by approximately 15% for the design rainfall.