• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1998.10a
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• pp.479-483
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• 1998

Many computer models have been used for estimating the water quality and evaluating countermeasures. The models such as QUAL2E, STREAM, WASP, CE-QUAL have been applied in the waters so far. Some modeller assumed either that the flow of the waters is steady or that the storage change of the waters is negligible. And someone excluded hydraulic part from the quality simulation. It may cause inaccurate estimations of water flow and quality, particularly when the waters have seawards boundary and more inflow than outflow, etc. In order to show the velocity vector for water quality simulation of Paldang lake in dynamic condition, RMA-2 was performed with the water quantity data in 1997.

• Journal of Environmental Science International
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• v.17 no.7
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• pp.783-793
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• 2008

The purpose of this study is to analyze the sensitivity of the RMA2 model parameters reflecting the flow characteristics of stream junction and thus understand the hydraulic characteristics of the channel confluence flow. This study dealt with the input parameters of the RMA-2 model, a two-dimensional numerical analysis model widely used for researches both at home and abroad. The parameters of the RMA-2 model are roughness coefficient, turbulent diffusion coefficient, Coriolis forces latitude, Density, and mesh size. This study those parameters estimated from actual heavy rainfall, and varied the parameter size by (-)30%${\sim}$+30% to review the characteristics of the flow characteristics of the channel section. Weobserved that when the ratio of the channel width was relatively small, the smaller the approaching angle was, the farther from the junctions became the generating place of the maximum flow velocity, however, when the ratio of the channel width was relatively large, the larger the approaching angle was, the farther the generating place of the maximum flow velocity from the junctions became. In particular, the distance between junctions and the place where the maximum flow velocity generated showed an absolute correlationover 90% of the relative channel width, but an inverse relationwas found when the distance to the place where the flow velocity generated was shortened as relative the channel width between the main channel and tributary increased.

• Journal of Environmental Science International
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• v.18 no.9
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• pp.971-981
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• 2009

An objective of this study is as follows: 1) performing sensitivity analysis and parameter estimation of RMA2 and RMA4 models for the West-Nakdong River, 2) drawing up alternatives of gates-operation for water-quality enhancement, and 3) quantitative evaluation of methodology of 'flow-restoration by gates-operation' among 'Comprehensive Plan Improving Water-Quality in the West-Nakdong River(WNR)' with the target water-quality(BOD at Nakbon-N point: below 4.3 mg/L). The parameters for the RMA2 (depth-averaged two-dimensional flow model) and RMA4 (depth-averaged two-dimensional water-quality model) were determined by sensitivity analysis. Result of parameter estimation for RMA2 and RMA4 models is $1,000\;Pa{\cdot}s$ of the eddy viscosity, 20 of the Peclet number, 0.025 of the Manning coefficient, and $1.0\;m^2/s$ of the diffusion coefficient. We have evaluated the effects of water-quality enhancement of the selected alternatives by numerical simulation technique with the models under the steady-state flow condition and the time-variant transport condition. Because of no-resuspension from river bottom and considering BOD as conservative matter, these simulation results slightly differ from real phenomena. In the case of $50\;m^3/s$ of Daejeo-gate inflow, two-dimensional flow pn results result represents that small velocity occurs in the Pyungkang Stream and no flow in the Maekdo River. In the WNR, there occurs the most rapid flow near timhae-bridge. In the WNR, changes of water-quality for the four selected simulation cases(6, 10, 30, $50\;m^3/s$ of the Daejeo-gate inflow) were predicted. Since the Daejeo-Gate and the Noksan-Gate can be opened up to 7 days, it would be found that sustainable inflow of $30\;m^3/s$ at the Daejeo-gate makes BOD in the WNR to be under the target of water-quality.

• Journal of Korea Water Resources Association
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• v.31 no.4
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• pp.491-501
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• 1998

Numerical simulations were performed to analyse the flow pattern of the approach channel and to design the spillway guidewall for stable flow conditions. RMA-2, two dimensional finite element model which can easily represent complicated geometry was used, and model parameters were estimated from the observation data of hydraulic model test. Numerical experiments were made separately for the approach region and for the upstream region, and upstream boundary position of the hydraulic model beyond which the boundary effects are negligible was determined from the numerical results. For the stable flow condition in approach channel, alternative designs for guidewall were developed, and flow analysis for alternative designs was done through the numerical simulation. From the analysis of alternative design, we can see that the flow pattern in the approach channel is stable and the lateral stage difference disappears mostly before the spillway crest.

• Journal of Korea Water Resources Association
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• v.51 no.1
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• pp.61-70
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• 2018

This study examined how to determine the optimal sediment level in dam reservoir for efficient plan and operation of dam. Currently, Korea is applying a horizontally accumulated method for sediment level estimation for the safety design of dam and so the method estimated relatively higher level than others. However, the sediment level of dam reservoir should be accurately estimated because it is an important factor in assessing life cycle of a dam. The sediment level in dam reservoir can be determined by SED-2D model linked with RMA-2, horizontally accumulated method, area increment method, and empirical area reduction method. The estimated sediment level from each method was compared with the observed sediment level measured in 2007 in Imha dam reservoir, Korea and then the optimal method was determined. Also, the future sediment level was predicted by each method for the future trend analysis of sediment level. As the results, the most accurate sediment level was estimated by the empirical area reduction method and the future trend of sediment level variation followed the past trend. Therefore, we have found that the empirical area reduction method is a proper one for more accurate estimation of sediment level and it can be validated by the results from a numerical model of SED-2D linked with RMA-2 model.

• Water for future
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• v.28 no.6
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• pp.169-181
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• 1995

No correction has been made for the rating curve of Goan Station since 1986 even though there has been a severe bed degradation until now. Furthermore, it was informed to Han River Flood Control Center that there was a difference between the discharge released from Paldang dam and the discharge observed at Goan station during 1990 flood. By considering such river bed changes, hydraulic model experiment with 1/100 scale was performed for the range of 2.2 km, which covers from Paldang dam to the downstream of Goan station. From this experiment, the rating curve was obtained by considering the discharges from Paldang dam and the corresponding water levels at Goan station. Also, the exsitingand the proposed rating curves were compared with those by computational method of RMA-2V.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.2
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• pp.119-127
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• 2008

The flow characteristics and the aspects of riverbed changes were analyzed for the upstream and downstream sections of Gongju Bridge. The upstream and downstream had complex topography, and the sections had the confluence of tributaries and several structures. In order to simulate the flow characteristics of the target sections, 1D HEC-RAS and 2D RMA2 were applied. As a result, the longitudinal water level of the target sections matched the results of simulated 1D and 2D samples. Also, 2D SED2D were applied to predict riverbed changes. As a result of the simulation, quantitative analysis was able to be performed for longitudinal riverbed changes from the sections of sudden change, bridges, the confluence of tributaries, and bends. Also, the distribution of riverbed changes on the main sections was in close relation to flow velocity. As a result of evaluating the sensitivity of SED2D, the concentration of suspended sediment, the thickness of sand beds, and the size of sand grains affected riverbed changes sensitively. These results will be used to apply the models of riverbed changes in the future.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1874-1878
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• 2008

본 연구에서는 물고기 서식처의 수리조건을 조사하기 위한 현장조사와 대상지에서의 미시서식처의 분포를 파악하기위한 수치계산을 실시하였다. 현장조사는 미호천과 금강이 합류되는 지점으로부터 약 24km 상류에 위치한 동경127도26분-북위36도41분 충북 청원군 오창면의 미호천 일부구간을 대상으로 수리학적 특성 조사, 지형측량 및 서식처별 대표어종 조사를 수행하였으며, 수치실험은 하천에서의 흐름거동을 2차원적으로 해석하는데 많이 사용되고 있는 상용프로그램인 SMS (Surface - Water Modeling System)의 RMA2 모형에 현장조사로부터 얻은 결과들을 입력함으로서 진행하였다. 그 결과 유속과 수심에 따른 서식처 구분이 가능하였으며, 현지특성을 재현한 수치모형 결과는 대상하천에서의 서식지 분포를 정량적으로 나타내었다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.6B
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• pp.589-598
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• 2010

When the hydraulic structures, such as bridge and weir, are consecutively installed to a short section of a river with complicated cross section, analyzing the flow characteristics and the riverbed change modality of the river is very important. In the 250 m section of the Taehwa river near the Samho-bridge, which passes through Ulsan city, three bridges has been installed, and the tributary water is flowing into both up and downstream of the section. Due to these factors, when the flood occurs, the cross section of the river changes vastly by the water level change and scour. Even so, due to the fact that the Samho-bridge divides the section into two parts, the national river and the regional river, each part is being analyzed separately by the onedimensional model. In this study, the flow characteristics due to the bridge concentration and the tributary water inflow were jointly analyzed for both up and downstream by using the one-dimensional HEC-RAS model and the two-dimensional SMS model, such as RMA2. The riverbed change modality of the section was also investigated by using the SED2D model. The results showed that the water level difference between the HEC-RAS and RMA2 was 0.87 m when applied to the three consecutive bridges. The riverbed change simulation using SED2D showed that the maximum scour was 0.231 m and it occurred at the Samho-bridge, which located in the middle and has short pier distance. In conclusion, when planning the river maintenance for the regions with concentrated bridges or the sections with severe changes in cross-section and flow, estimating the flood elevation by two-dimensional model and establishing countermeasures for the scouring of the bridge are required. In addition, an integrated analysis on both the national river and the regional river is necessary.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.351-351
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• 2016

본 연구는 최근 기후변화로 인해 유출량이 많이 증가하고 있으며, 또한 하도의 제내측에 많은 피해가 발생하고 있다. 우리나라의 하도는 산지위치하고 있으며, 만곡의 형상을 많이 지니고 있다. 또한 유출량의 증가로 하도 만곡부에 하상의 퇴적으로 인해 월류 및 제방이 파괴 되는 현상도 발생되고 있다. 만곡부의 흐름은 만곡도의 수공구조물을 설치하므로 유수의 흐름에 민감하게 변화하여 흐름변화를 예측하기 어렵다. 그래서 자연하고 만곡부에 하상의 변화에 따른 수리학적 문제와 제내측의 안정성을 확보하기 위해 만곡지점에 수제를 설치하여 하도의 흐름과 하상의 안정성에 필요하다고 사료되어 연구를 하였다. 본 연구는 만곡지점에 수리실험 모형을 설치하여 결과를 도출하는 방법도 있으나, 축소모형은 하도의 특성을 반영하기 결과도축에 제약이 있어 금회 연구는 수치모형은 2차원 수치모형인 RMA-2를 사용하여 하도의 특성을 파악하고자 한다. 먼저 만곡형상이 뚜렷한 지점을 파악하고 하천설계기준의 수제를 설치하여 흐름의 변화 및 유속변화를 분석하고 만곡부에서 기준수제의 길이를 여러 CASE로 변화를 주어 수리학적 특성을 분석하고자 하며, 이에 따른 수제부에서 발생하는 퇴적구간과 범위, 최대유속지점과 세굴지점에 대한 연구를 진행하여 하도 만곡부에 수제를 설치하여 합리적인 결과를 제시 할 수 있으며, 설계실무와 하천방재 관련 문제에서도 반영하여 이용 될 수 있을 것이다.