Estuary Barrage Research Articles

Effective Flood Control Method in River Downstream Affected by Tidal Effect Using Optimal Operation of Estuary Barrage

This article introduces an effective flood control method in the downstream of a river through the optimal operation of a barrage that is connected with a sea. A new operating model for flood control of an estuary barrage that can comprehensively evaluate the intensive discharge through the floodgates at the estuary barrage during low tide and the flood propagation process in the downstream river system is proposed. The optimization method applied to the operating model of the barrage combines a one-dimensional hydrodynamic model to analyze the flood propagation process in river channels and a search algorithm based on an iterative method to organize the maximum discharge at the estuary barrage during the ebb tide periods. The proposed method was applied to the flood control of the Taedong River downstream in the Democratic People's Republic of Korea, and its effectiveness was shown and evaluated through modeling results. By imagining the downstream boundary of the river before and after the construction of the West Sea Barrage, the inundation simulation at the Taean gauging station in the downstream of the Taedong River for floods of different average recurrence interval (ARI) was achieved by employing the proposed method.

Complementary Modeling Approach for Estimating Sedimentation and Hydraulic Flushing Parameters Using Artificial Neural Networks and RESCON2 Model

Accurate prediction of reservoir sediment inflows (Min) and adaptation of feasible sediment management strategies pose challenges in water engineering. This study proposed a two-stage complementary modeling approach for comprehensive reservoir sediment management. In the first stage, artificial neural network-based models provide real-time Min predictions using water inflow, water head, and outflow as input parameters. In the second stage, the parameter estimation method of the RESCON model is applied to hydraulic flushing in a reservoir. This approach was applied to the Sangju Weir and Nakdong River Estuary Barrage (NREB) in South Korea. Results from the RESCON model revealed that hydraulic flushing was effective for sediment management at both the Sangju Weir reservoir and the NREB approach channel. Efficient flushing at the Sangju Weir required a flushing discharge of 100 m3/s for 6 days and 40 m of water head. Efficient flushing at the NREB required a flushing discharge of 25 m3/s for 6 days with 1.8 m of water-level drawdown. The proposed approach is expected to prove useful in reservoir sediment management.

Movement Patterns and Diel Activity of Anguilla japonica in the Middle Part of a Large River in South Korea.

Simple SummaryAnguilla japonica is an IUCN red list species facing a natural reduction in population due to environmental changes and artificial decline due to various human activities (disturbance in foraging, river, etc.). While many of these disturbances mainly occur in freshwater areas, studies on the ecology of A. japonica in the freshwater environment are limited compared to those of Anguilla anguilla and Anguilla rostrata. Freshwater is an important habitat for eels to grow to the spawning period. With insufficient numbers of adults supplied to the sea for spawning, eels may eventually become extinct. This study aimed to provide ecological information of the continental phase in the freshwater ecosystem by examining diel activity along with the movement patterns of eels in the pure freshwater environment based on the results of monitoring. In the future, it is necessary to establish a protection and management strategy for the conservation of eels living in rivers based on the results.To investigate movement patterns and diel activities of Anguilla japonica in the freshwater ecosystem, we applied acoustic telemetry on A. japonica in the Geum River, a large river in South Korea. The acoustic tags were attached on 19 individuals of A. japonica (12 with a depth sensor) in May and October 2015 and tracked at approximately 100-km sections from an estuary barrage by 20 automatic listening stations. Only four individuals showed longitudinal movement (mean, 5.2 km), and others were detected by the receivers at release sites; therefore, A. japonica showed high site fidelity. We did not identify seaward migration during the study period (May to November). Conversely, A. japonica showed active diel movement. The number of detections (p = 0.002) and movement distance (p = 0.004) were higher at night-time (18:00–06:00). As most individuals were actively moving at nighttime, we confirmed that A. japonica is nocturnal, although few individuals also showed daytime movement. Although the population and habitats of A. japonica have been decreasing simultaneously, the East-Asian countries are still severely exploiting rivers and streams to use water resources, and result in habitat simplification generated. Therefore, these results contribute to effective A. japonica management regarding habitat and population conservation and restoration.

Prediction of Water Level and Water Quality Using a CNN-LSTM Combined Deep Learning Approach

A Convolutional Neural Network (CNN)-Long Short-Term Memory (LSTM) combined with a deep learning approach was created by combining CNN and LSTM networks simulated water quality including total nitrogen, total phosphorous, and total organic carbon. Water level and water quality data in the Nakdong river basin were collected from the Water Resources Management Information System (WAMIS) and the Real-Time Water Quality Information, respectively. The rainfall radar image and operation information of estuary barrage were also collected from the Korea Meteorological Administration. In this study, CNN was used to simulate the water level and LSTM used for water quality. The entire simulation period was 1 January 2016–16 November 2017 and divided into two parts: (1) calibration (1 January 2016–1 March 2017); and (2) validation (2 March 2017–16 November 2017). This study revealed that the performances of both of the CNN and LSTM models were in the “very good” range with above the Nash–Sutcliffe efficiency value of 0.75 and that those models well represented the temporal variations of the pollutants in Nakdong river basin (NRB). It is concluded that the proposed approach in this study can be useful to accurately simulate the water level and water quality.

Application of a Marine Environmental Information System (MEIS) Data to Marine Spatial Planning (MSP) in the Nakdong River Estuary, Busan Metropolitan City, South Korea

Lee, J.-H.; Woo, H.J.; Jung, H.-S.; Jeong, J.B., and Park, H.N., 2020. Application of a Marine Environmental Information System (MEIS) Data to marine spatial planning (MSP) in the Nakdong River Estuary, Busan Metropolitan City, South Korea. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 860–864. Coconut Creek (Florida), ISSN 0749-0208.The Nakdong River in South Korea is nearly 526 km long, and has a drainage basin of around 23,817 km2. It is subject to natural erosion and sedimentation, and there is also the potential for disturbance by various human activities, including water diversion and reservoir construction, and other large construction projects in the river estuary. The Noksan dike, built in April 1934, blocks the flow of the west Nakdong River. The Nakdong River Estuary (NRE) barrage in Busan Metropolitan City was completed in November 1987 to regulate the flow of the Nakdong River. In this study, Marine Environmental Information System (MEIS) data collected after May 2015 were used to support marine spatial planning (MSP) in the brackish water zone. The NRE and surrounding locations can be divided into areas managed by the government, protected marine areas, areas for sand mining, areas for the development of tourist attractions, areas of research conservation, areas where an environmental risk assessment would be required prior to use by ships, military areas, and coastal areas subject to safety management measures. Data on environmental changes in the estuarine watershed were used during the preparation of the NRE for partial opening and drainage extension in 2019. Data supporting MSP in the target area should be collected, processed, and analyzed to facilitate future decision-making, and databases should be established based on geological field surveys. Furthermore, protected areas should be designated according to governmental guidelines. All scientific data used in these processes should be validated, and spatial data to facilitate MSP should be produced.

Study on the Characteristics of the Hydraulic Environment in the Downstream Area According to the Discharge of Changnyeong-Haman Weir

Kim, T.W.; Kim, Y.J.; Cho, W.C.; Park, B.W., and Yoon, J.S., 2019. Study on the characteristics of the hydraulic environment in the down-stream area according to the discharge of Changnyeong-haman weir. In: Lee, J.-L.; Yoon, J.S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp.151-155. Coconut Creek (Florida), ISSN 0749-0208.This study refined the reproducibility of a stream cross section of the Nakdong River using the Modified EFDC model and examined the salt water flow from the external sea to the river upstream according to the changing gate open rate of Nakdong River estuary barrage and the influent flow and tide level conditions in the Changnyenong-Haman Weir using a numerical model. Furthermore, numerical simulations were conducted and the hydraulic characteristics were examined to investigate the flushing effect according to the changing discharge of the Changnyenong-Haman Weir in the event of a salt wedge.

Prediction of Topographic Change in the Estuary of Nakdong River and Analysis of Its Contribution by External Force Condition

It is very important to understand the mechanism of estuary topographic changes for the study of estuary management and treatment methods. In this study, the effects from the land-side, such as rainfall, river discharge, sediment discharge, and sea side, such as tide, tidal current, wave and surface sediments related to the topographic changes of the Nakdong river estuary were investigated and analyzed. Based on the analyzed data, topographic modeling was performed to analyze the topographic change and contribution of external force conditions. As a result of numerical modeling, the topographic change showed that erosion that predominates in the water directly affected by the discharge of the estuary barrage. The deposition predominates in the indirectly affected tideland. As sediments moved along the water way being sorted and distributed by the wave, the deposition predominated in the front of the barrier island. Compared with the deposition dominance, which is the result of the topographic change prediction, the impact of each external force condition gives larger erosion. However, the combined impact of each external force condition showed deposition dominant. Therefore, the topographic changes of the Nakdong river estuary are considered to be the result of various complex external factors. The impacts of each external force condition show the different contribution to each comparison area. These results should be considered when establishing the estuary management method. It must be understood that this is the result of complex interactions.

Spawning nests of six goby species in a newly-established fish-way on the Onga River estuary barrage

Spawning nests of six goby species in a newly-established fish-way on the Onga River estuary barrage

Impact of estuary barrage construction on fish assemblages in the lower part of a river and the role of fishways as a passage

The construction of an estuary barrage, an instream structure in the lower reaches of a river, causes significant physical changes in water flow patterns and river morphology, and results in altered environmental conditions. Here, we examined the impact of the Geum River estuary barrage, completed in 1990, on fish assemblages by using a literature search and fresh surveys of fishways in the barrage. We found that fish assemblages upstream and downstream of the barrage were altered following its completion. After construction, more species were found in the freshwater area, with a particularly great increase in freshwater species. Conversely, estuarine and marine species were only consistently caught in the downstream salt-water area, although the number of species increased. In total, 15,829 fish from 47 species and 20 families were identified at the three types (pool and weir, rubble type, and boat passage) of fishways in the barrage. The dominant species were Chelon haematocheilus, an estuarine species, Coilia nasus, a diadromous species, and Erythroculter erythropterus, a freshwater species. The mean total length of fish (101.9 ± 76.0 mm) in the boat passage fishway was approximately 100 mm lesser than those in the pool and weir (207.2 ± 112.8 mm) and rubble type (205.8 ± 112.7 mm) fishways. The boat passage fishway was the most efficient for fish movements. The current fishway system is not sufficient for fish migration, and thus additional ways are required to improve the system such as the boat passage. Few estuarine or diadromous species were found in both freshwater and salt-water areas, but freshwater fishes that accidently moved to salt-water area actively used fishways. Therefore, fishway management in the Geum River estuary barrage has to focus on freshwater fish; however, this may need to change to a focus on migratory fishes depending on ecological life cycles of migratory fish.

The Investigation of Sea Water Intrusion Length on Opening of Nakdong River Estuary Barrage Using Numerical Simulation Model

The Investigation of Sea Water Intrusion Length on Opening of Nakdong River Estuary Barrage Using Numerical Simulation Model

Numerical modeling of sedimentation control scenarios in the approach channel of the Nakdong River Estuary Barrage, South Korea

The effects of sedimentation reduction at the Nakdong River Estuary Barrage (NREB) in Korea were quantitatively analyzed with respect to different sediment control methods using the calibrated and validated two-dimensional model. The countermeasures of sediment dredging, sediment flushing, channel geometry change, and a combination of flushing and channel geometry change were examined for the approach channel of the NREB. The flood event and channel geometries of the 3.8km section upstream of the NREB surveyed before and after dredging in 2007 were used for modeling conditions. As a result, the half of sediments dredged in 2007 could be eliminated naturally by floods without dredging. The numerical simulation of sediment flushing indicated that the deposition height decreased in the entire simulation section with the minimum and maximum reductions from 0.3m to 1.3m in deposition height. The channel contraction method produced quantitatively the largest amount of sedimentation reduction and sediment flushing and dredging followed. Sedimentation reduction by a combination of flushing and channel contraction was up 10% compared to the individual method of channel contraction.

Changes of fish assemblages after construction of an estuary barrage in the lower Nakdong River, South Korea

In the Nakdong River, an estuary barrage was constructed in 1987, and it divided the freshwater and the seawater, resulting in a change in the ecosystem. To estimate the impact of barrage construction on fish assemblages, we evaluated 20 years of monitoring data before and after the construction of the estuary barrage, and evaluated the role of fishways. The barrage construction generated entire changes of fish assemblages. After construction, the number of fish species dropped sharply, and 36 species disappeared. Conversely, 18 species appeared at this site, including eight freshwater species, seven of which were exotic or translocated species. Barrage construction affected freshwater fish more severely than it did estuarine and marine species because of the existence of an estuarine environment below the barrage. We did not detect any evidence of recovery of fish assemblages. A total of 31 species were collected at fishways, and the number of individuals collected at each fishway was positively correlated with the amount of discharge from the estuary barrage, mean daily tide level, and water temperature. Migratory fish using a fishway had obvious occurrence periods. Therefore, the efficiency of fishway use can be increased if an appropriate management plan is prepared and implemented.

PLC(Programmable Logic Controller)와 공중통신망을 이용한 하천수위감시시스템 구축 사례 연구

A river water level monitoring system which prevents salt water damages and effectively excludes floods has been developed to contribute efficient operation of Nakdong river estuary barrage. The system can be used for monitoring upstream conditions more quickly and do appropriate responses over changes. Telemetry and telecontrols using PLCs have been built at the three sites that directly influence on the operation of barrage gates, and are linked to Nakdong river estuary barrage’s IOS (Integrated Operation System) through public communication networks. By using PLC, the system can achieve even higher reliability and versatility than before as well as easy management. By power control devices, we can remotely control the power of PLCs to treat the minor troubles instantly without going on-sites. The power control devices also save data in preparation for the cases of communication failures. The system uses ADSL (FTTH) as a main network between SCADA server and PLCs, and CDMA (M2M) as a secondary network. In order to compensate security vulnerabilities of public communication network, we have installed the VPNs for secure communication between center and the observation stations, just like a dedicated network. Generally, river water level observations have been used custom-manufactured remote terminals to suit their special goals. However, in this case, we have established a system with open architecture considering the interface between different systems, the ease of use and maintenance, security, price, etc.

낙동강 하굿둑의 배수문 증설에 따른 통합운영시스템의 구축 사례에 대한 연구

Due to the Four Major Rivers Restoration Project, Nakdong River Estuary Barrage’s designed flood quantity has been largely increased, and this has caused to construct several drainage gates at the right side of Eulsukdo island to secure the safety of downstream river area. For successful functioning of Nakdong River Estuary Barrage, such as flood control, disaster prevention, and the securing of sufficient water capacity, drainage gates at the both sides of island have to operate systematically and reliably. To manage this under restricted personnel and resources, we have implemented the IOS (Integrated Operation System) by integrating previous facilities and resources via information and communication technologies. The IOS has been designed to have higher availability and fault tolerance to function continuously even with the partial system’s failure under the emergency situation like flood. Operators can use the system easily and acknowledge alarms of facilities through its IWS (Integrated Warning System) earlier. Preparing for Integrated Water Resources Management and Smart Water Grid, the architecture of IOS conformed to open system standards which will be helpful to link with the other systems easily.

Harbor Gate와 유입하천의 영향을 고려한 만내의 2차원 수리해석

In this study, when seawall or harbor gate is installed for coastal disaster prevention, a two-dimensional water analysis in the bay is carried out to consider the flood amount of river inflow and effect of harbor gate. The Yeongsan river and the port Mokpo area are selcected for the study region. Then, by analyzing the hydraulic characteristics of flood flow of the Yeongsan river, we analysed the compatibility of the results in the two-dimensional hydrodynamic model. A tw-odimensional water analysis were conducted for the four cases considering whether a harbor gate is installed or not, and whether the inland water boundary condition is considered or not, also with open sea boundary condition. The results of the two-dimensional water analysis shows that water level change near the port Mokpo area is mainly caused by the discharge of the estuary barrage of the Yeongsan river because the harbor gate was installed. In addition, it is revealed that the volume of reservoir created by the harbor gate and the estuary barrage is too much small compared to the volume of the discharge from the Yeongsan river. Therefore, when the harbor gate is installed in the open sea, we concluded that a flexible management between the harbor gate and the estuary barrage of the Yeongsan river is required. A initial water level of the bay and outflow from the harbor gate are proposed for disaster prevention in the coastal area of port Mokpo.

낙동강 하구둑 및 보의 홍수시 운영방안

A numerical model was developed that can simulate gate openings of estuary barrage and a series of weirs as well as the unsteady flow during the flood period in the Nakdong River. It is a multiply-connected network model based on the Preissmann's four-point scheme and the Newton-Raphson method. The computational model can appropriately simulate composite flows at multi-functional weirs including weir overflow, orifice-type flow, and fluvial-type flow. Gate operation strategies for the weirs and the estuary barrage were established such that gates be closed for water level below a certain reference level and gate openings increase as the water level rises. Ad-hoc operating condition for the drainage gate of the Nakdong Estuary Barrage is to close the gates if the inner water level is lower than the sea water level. The prescribed operation conditions were well simulated by the model, and sensitivities to the param- eters of the gate operation strategy were analyzed.

SWAT 모형을 이용한 낙동강 유역의 장기 유출에 따른 유사량 분석

Abstract Sediment discharge by long-term runoff in the Nakdong River watershed should be predicted for the maintenance and management of the Nakdong River newly changed by the four major river restoration project. The data establishment by the analysis of runoff and sediment discharge using the long-term watershed model is necessary to predict possible problems by incoming sediments and to prepare countermeasures for the maintenance and management. Therefore, sediment discharges by long-term runoff in the main points of the Nakdong River were calculated using SWAT(soil and water assessment tool) model and the relations and features between rainfall, runoff, and sediment discharge were analyzed in this study. As a result of sediment discharge calculation in the main points of the Nakdong River and tributaries, the sediment discharge at the outlet of the Naesung Stream was greater than the Jindong Station in the Lower Nakdong River from 1999 to 2008 except the years with low precipitation. The sediment discharge at the Nakdong River Estuary Barrage (NREB) was corresponding to 20% of the Jindong Station which is located about 80 km upstream from NREB.

Status of wintering populations of the baikal teal (Anas formosa) in Geumgang River, Korea

This study investigated the daily changes of individual numbers of the baikal teal migrating in Geumgang River from November in 2008 to March in 2009 and from November, 2011 to February, 2012. The finding from 2008 to 2009 showed that the highest number of 500,000 individuals (November, 2008) with an average of 146,582 ± 123,705 individuals were recorded. The finding from 2011 to 2012 indicated that the highest number of 250,000 individuals (January, 2012) with an average of 61,696 ± 63,407 individuals. The baikal teal's population was increased in the early wintering period was not observed in the mid-wintering period when the Geumgang River became frozen. On the other hand, the population tended to increase again in the late wintering period when the river began to thaw. As the baikal teals prefer flat water areas without currents, they were mainly observed in the upper stream of Geumgang estuary barrage but not in the downstream.

Analysis for the effectiveness of sediment dredging in the approach channel at the Nakdong River estuary barrage

The upstream channel of the Nakdong River Estuary Barrage (NREB) has experienced sedimentation problems requiring annual dredging operation after the construction. The main purpose of sediment dredging is to prevent flooding during late summer. Numerical simulation and volume analysis using field surveying data for the Lower Nakdong River have been conducted to quantify the bed changes with and without dredging operation and to analyze the effectiveness of dredging at the NREB. As a result, it is presented that the bed change rate (sedimentation rate) after dredging is much faster than the bed condition without dredging. The water surface rising of the maximum 10 cm was generated in case the dredging was not considered in the modeling. Volumetric analysis of bed changes using field surveying data presented that 41 percent of total sediment erosion was eliminated by natural flushing and 59 percent was dredged in the field. Because it is noticeable that dredged section is redeposited rapidly after dredging during low flow through the 2D simulation, it is expected that most of total sediment erosion (at least more than 41% of total sediment erosion) is caused by natural flushing due to the floods. Therefore, it is highly recommended to use natural flushing or intentional sluicing techniques for sedimentation control methods at the NREB.

낙동강 하류의 퇴사저감을 위한 하폭축소방법이 홍수위변화 및 하상변동에 미치는 영향 분석

Sediment from the upstream channel has been deposited near the Nakdong River Estuary Barrage (NREB) due to the mild slope and decreased velocity. The annual mechanical dredging to ensure the flood capacity has been performed to remove the deposited sediment. However, the dredging method is not considered as an effective countermeasure due to high cost and long time to operate. Therefore, many methods for sedimentation reduction have been proposed for NREB. Especially, the channel contraction method to mitigate sedimentation problem by changing the channel geometry from 2 km to 3 km upstream of NREB has been recently suggested as an effective countermeasure. However, there is the possibility that the channel contraction method induces flood level increase compared to original condition. Therefore, it is necessary to investigate quantitatively the flood level changes in the upstream and downstream section due to the channel contraction method for NREB. In this study, water level changes by 10% channel contraction of whole width has been evaluated using the HEC-RAS model and simulated with and without channel contraction for various flood discharge. As a result, water level in the section where the channel was contracted was decreased by 0.02 m and flood level at the upstream of channel contracted was increased up to 0.015 m for the 500-year flood.