• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.4
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• pp.69-75
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• 2014

We investigated flood control capacity of 484 agricultural reservoirs with storage capacity of over 1 million $m^3$ in South Korea. In general, agricultural reservoir secures flood control capacity by setting up limited water level during flood season from late June to mid-September. The flood control capacity of an agricultural reservoir during flood season can be divided into stable flood control capacity during non-flood season, stable flood control capacity associated with limited water level, and unstable flood control capacity associated with limited water level. In general, the flood control capacity significantly (P < 0.001) increased with reservoir capacity irrespective of type of spillway. The unstable flood control capacity accounted for about 20 % of reservoir capacity in the uncontrolled reservoirs. The study reservoirs showed flood control capacity of 0.60-65 billion (B) $m^3$ and stable flood control capacity of 0.43-47 B $m^3$, depending on the upper and lower limited water levels during the flood season. The stable flood control capacity of the gated reservoirs (0.29-0.33 B $m^3$) was about two times than that of reservoirs with uncontrolled spillways (0.14 B $m^3$). The ratios of stable flood control capacity to reservoir capacity for agricultural reservoirs range from 21 to 23 %, similar to that for Daecheong multipurpose dam. Moreover, the reservoirs with over 100 mm ratio of flood control capacity to watershed area accounted for 38 % of total gated reservoirs. The results indicate that many agricultural reservoirs may contribute to controlling flood in the small watersheds during the flood season.

• Journal of Korea Water Resources Association
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• v.54 no.7
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• pp.545-552
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• 2021

The burden of flood control on the dam under frequently flood due to climate change and especially heavy flood in 2020 year are come to the forward and increased. The objective of the study is therefore to establish the method to estimate capacity and target water level for flood control in actual dam management. Frequency matching method was applied to establish a pair of cumulative distribution function (CDF) based on daily dam inflow and discharge records. The relationship between dam storage and discharge volume represented as a percentage of inflow volume was derived and its characteristics was analyzed. As the result, the Soyanggang (45%) and Chungju Dam (39%) contributing to flood control with temporarily storing flood runoff. The method and diagram to estimate flood control capacity and target water level for flood control in the dam were established. The result of the study could be used as a supplementary data for flood control of the dam according to the rainfall prediction on the Korea Meteorological Administration.

• Journal of Korean Society on Water Environment
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• v.29 no.6
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• pp.754-761
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• 2013

Urban floods are usually caused by the lack of drainage capacity. Hence, sewer capacity expansion methodology by replacing small pipes with bigger ones is primarily applied as a flood control measure. However, this approach is often unreasonable because of the costs and time involved. Thus, the installation of underground rainwater storage tanks with the two advantages of flood control and water conservation is proposed. This study compared the effectiveness of flood control by both the sewer expansion methodology and rainwater storage tanks using the Storm Water Management Model. Three cases were simulated in this study. The first case analyzed flood reduction by the storm sewer expansion methodology. The simulation results indicate that the overflow volume from manholes was reduced by 49% with this methodology. The second case analyzed flood reduction by installation of rainwater storage tanks. The simulation results indicate that the overflow volume was reduced by 62%. However, these two cases could not prevent urban floods completely. Hence, the third case analyzed the joint application of the storm sewer expansion methodology and rainwater storage tanks. In this simulation, flooding did not occur. Consequently, the results of this study clearly show that underground rainwater storage tanks are more effective for flood control than capacity expansion of storm sewer. Furthermore, the joint application of these two flood control measures is more effective than their separate application.

• KIEAE Journal
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• v.10 no.4
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• pp.9-17
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• 2010

The purpose of this study is to draw out objective bases for selecting various applicable facilities in case of the establishment of rainwater management strategies. To do so, sixteen facilities were selected from decentralized rainwater management systems that induce rainwater infiltration and detention as well as centralized end-of-pipe type infiltration and detention facilities in local areas. With these facilities, it attempted to evaluate them in terms of sustainability, pollutant elimination, flood control capacity and costs and subsequently analyzed correlations between each characteristic. The outcomes of the analysis were as follows: First was the analysis of characteristics between decentralized rainwater management systems and end-of-pipe rainwater management systems. From the decentralized rainwater management systems, the mulden-rigolen system and grass swale at street level had the highest in the total of the four items while the totals of the underground detention tank and temporary detention site were highest in end-of-pipe rainwater management systems. After analyzing the correlation between different types of facilities and each variable, it can be said that decentralized rainwater management systems have a higher correlation than end-of-pipe rainwater management systems in terms of sustainability whereas the latter are better in flood control capacity than the former. Second, the analysis of correlation in variables of each facility is as follows: first, there is a negative correlation between sustainability value and flood control capacity value; and there is a positive correlation between flood control capability and pollutants elimination. In addition, it revealed that the higher the flood control and pollutant elimination capability the higher the facility costs. Based on these assessments, it is possible to use them as objective selection criteria for facility application in case of site development project or complex plan.

• Journal of Korean Society of Water and Wastewater
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• v.18 no.3
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• pp.343-350
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• 2004

For the last two decades, Seoul has always been affected by large floods. As climate change causes more frequent localized heavy rains exceeding the capacity of sewer or river to discharge water, flood damage is expected to increase. Under the situation, detention facilities for lacking capacity of sewers can control stormwater runoff to reduce flood damage in urbanized areas. In this study, in order to reduce flood damage in Cheonggyecheon areas, the capacity of detention facilities was decided to make up for the lacking capacity of main sewers in case of the rainfall in July, 2001 as large flood. The average amount of stormwater detained in eight Cheonggyecheon drainage areas is $235.09m^3/ha$. Location and size of stormwater detention facilities is designed to have effects in short term by targeting the reduction of flood damage. Schools and parks are suggested as optimal locations where detention facilities are constructed in drainage areas.

• Journal of Korea Water Resources Association
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• v.40 no.1 s.174
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• pp.1-10
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• 2007

Reallocation procedure of multipurpose reservoir storage capacity between flood control and conservation is presented as an alternative to secure more water resources. Storage reallocation is an adaptive management mechanism for converting existing normal pool level of reservoirs to more beneficial uses without requirement for physical alteration. This study is intended to develop a reservoir storage reallocation methodology that allows increased water supply storage without minimizing adverse impacts on flood control. The methodology consists of flood control reservoir simulation for inflows with various return periods, flow routing from reservoir to a potential damage site, analyzing river carrying capacity, and reservoir yields estimation for reallocated storages. For the flood control model, a simulation model called Rigid ROM(Reservoir Operation Method) and HEC-5 are used. The approach is illustrated by applying it to two reservoirs system in Geum River basin. Especially with and without new project conditions are considered to analyze trade-offs between competing objectives.

• KCID journal
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• v.17 no.2
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• pp.57-70
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• 2010

This study was performed to analyze the affect of water supply capacity followed by allocating flood control volume in heightening reservoir, of which Baekgog reservoir was selected as a case study in here. Baekgog reservoir is located in Jincheon county, Chungbuk province, of which full water level will be heightened from EL. 100. 1m to EL. 102.1m, and total storage from 21.75M $m^3$ to 26.67M $m^3$. Flood inflow with 200year frequency was estimated to 997 $m^3$/s in peak flow and 22.54M $m^3$ in total volume. Reservoir flood routing was conducted to determine flood limited water levels, which was determined to have scenarios such as EL 97-98-99m in periods of 6.21.-7.20., 7.21.-8.20., and 8.21.-9.20., respectively, EL 97-97-97m, EL 98-98-98m in present reservoir, and EL 99-100-101m, EL 99-99-99m, and EL 100-100-100m in heightened reservoir. Reservoir inflow was simulated by DAWAST model. Annual paddy irrigation requirement was estimated to 33.19M $m^3$ to 2,975ha. Instream flow was allocated to 0.14mm/d from October to April. Operation rule curve was drawn using inflow, irrigation and instream flow requirements data. In case of withdrawal limit reservoir operation using operation rule curve, reduction rates of annual irrigation supply before and after flood control by reservoir were 2.0~4.3% in present size and 1.5~3.6% in heightened size. Reliability on water supply was decreased from 77.3% to 63.6~68.2% in present size and from 81.6% to 72.7~79.5% in heightened size. And reduction rates of water storage at the end of year before and after flood control by reservoir were 7.3~16.5% in present size and 7.7~16.9% in heightened size. But water supplies were done without any water deficiency through withdrawal limit reservoir operation in spite of low flood regulating water level.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.6
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• pp.57-68
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• 2013

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.

• Journal of The Korean Society of Agricultural Engineers
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• v.48 no.2
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• pp.27-35
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• 2006

Large dams are managed with operation standard and flood forecasting systems, while small dams do not have management method generally. Shortage of water resources and natural disasters due to drought and flood raised public concerns for management of small dams. Most of small dams are irrigation dams, which need diversified water uses. However, the lack of systematic management of small dams have caused serious water wastage and increased natural disasters. Storage management method and system were developed to solve these problems in small dams. The system was applied to Seongju dam for effective management. The storage management method was established considering hydrology simulation and statistical analysis using the system. This method can bring additional available water, even in the same conditions of the water demand and the supply conditions of watershed. It can improve the flood control capacity and water utilization efficiency by' the flexible operation of storage space.

• Journal of The Korean Society of Agricultural Engineers
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• v.63 no.5
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• pp.49-62
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• 2021

The objective of this study was to evaluate the flood control capacity of the agricultural reservoir based on state-of-the-art climate change scenario - SSP (Shared Socioeconomic Pathways). 18 agricultural reservoirs were selected as the study sites, and future rainfall data based on SSP scenario provided by CMIP6 (Coupled Model Intercomparison Project 6) was applied to analyze the impact of climate change. The frequency analysis module, the rainfall-runoff module, the reservoir operation module, and their linkage system were built and applied to simulate probable rainfall, maximum inflow, maximum outflow, and maximum water level of the reservoirs. And the maximum values were compared with the design values, such as design flood of reservoirs, design flood of direct downstream, and top of dam elevation, respectively. According to whether or not the maximum values exceed each design value, cases were divided into eight categories; I-O-H, I-O, I-H, I, O-H, O, H, X. Probable rainfall (200-yr frequency, 12-h duration) for observed data (1973~2020) was a maximum of 445.2 mm and increased to 619.1~1,359.7 mm in the future (2011~2100). For the present, 61.1% of the reservoirs corresponded to I-O, which means the reservoirs have sufficient capacity to discharge large inflow; however, there is a risk of overflowing downstream due to excessive outflow. For the future, six reservoirs (Idong, Baekgok, Yedang, Tapjung, Naju, Jangsung) were changed from I-O to I-O-H, which means inflow increases beyond the discharge capacity due to climate change, and there is a risk of collapse due to dam overflow.