Nakdong Estuary Research Articles

Pace of heavy metal pollution in the anthropogenically altered and industrialized Nakdong River Estuary, South Korea: Implications for the Anthropocene

Estuaries, vital coastal ecosystems, face growing threats from industrialization. To understand the pace of sedimentary changes and heavy metal pollution at the anthropogenically altered and industrialized Nakdong River Estuary in South Korea, we used sediment coring to reconstruct environmental change. Estuarine dam construction in 1934 shifted the sedimentary system from sand to mud, coinciding with a post-1930s mercury increase due to coal burning. Mercury concentrations in other South Korean regions surged in the 1970s, indicating proximity to emission sources matters. However, most heavy metal levels (Cu, Cd, Zn, Ag) sharply rose in the 1960s and 1970s with regional industrialization. Modern heavy metal concentrations doubled pre-industrial levels, underscoring human activities as the primary driver of Nakdong Estuary environmental changes. This emphasizes the need for a balanced approach to development and environmental preservation.

Seawater intrusion effects on nitrogen cycling in the regulated Nakdong River Estuary, South Korea

Research on the impact of seawater intrusion on nitrogen (N) cycling in coastal estuarine ecosystems is crucial; however, there is still a lack of relevant research conducted under in-situ field conditions. The effects of elevated salinity on N cycling processes and microbiomes were examined in situ seawater intrusion experiments conducted from 2019 to 2021 in the Nakdong River Estuary (South Korea), where an estuarine dam regulates tidal hydrodynamics. After the opening of the Nakdong Estuary Dam (seawater intrusion event), the density difference between seawater and freshwater resulted in varying degrees of seawater trapping at topographically deep stations. Bottom-water oxygen conditions had been altered in normoxia, hypoxia, and weak hypoxia due to the different degrees of seawater trapping in 2019, 2020, and 2021, respectively. Denitrification mostly dominated the nitrate (NO3-) reduction process, except in 2020 after seawater intrusion. However, denitrification rates decreased because of reduced coupled nitrification after seawater intrusion due to the dissolved oxygen limitation in 2020. Dissimilatory nitrate reduction to ammonium (DNRA) rates immediately increased after seawater intrusion in 2020, replacing denitrification as the dominant pathway in the NO3- reduction process. The enhanced DNRA rate was mainly due to the abundant organic matter associated with seawater invasion and more reducing environment (maybe sulfide enhancement effects) under high seawater-trapping conditions. Denitrification increased in 2021 after seawater intrusion during weak hypoxia; however, DNRA did not change. Small seawater intrusion in 2019 caused no seawater trapping and overall normoxic condition, though a slight shift from denitrification to DNRA was observed. Metagenomic analysis revealed a decrease in overall denitrification-associated genes in response to seawater intrusion in 2019 and 2020, while DNRA-associated gene abundance increased. In 2021 after seawater intrusion, microbial gene abundance associated with denitrification increased, while that of DNRA did not change significantly. These changes in gene abundance align mostly with alterations in nitrogen transformation rates. In summary, ecological change effects in N cycling after the dam opening (N retention or release, that is, eutrophication deterioration or mitigation) depend on the degree of seawater intrusion and the underlying freshwater conditions, which constitute the extent of seawater-trapping.

Characteristics of sedimentation based on data from the Nakdong estuary information service system (NEISS), South Korea

The sedimentary environment of the Nakdong River Estuary (NRE) in Busan, South Korea, is governed by natural erosion, sedimentation, and various anthropogenic factors (e.g., the NRE Dam, completed in November 1987). In the present study, we assessed sedimentation processes during 2015–2021 using data from the Nakdong Estuary Information Service System (NEISS) to clarify land–sea interactions and characterize the brackish water zone around the NRE barrier island system. The data included periodic observations of sediment distributions (n = 90). Sand dominated the seaward side of the barrier islands, whereas muddy sand dominated the lagoon side. The depth-integrated net suspended sediment load over one tidal cycle showed seaward movement of 1698 kg m−1 of sediment; the net suspended sediment fluxes at the surface, middle, and bottom layers of the water column were −2.1 × 10−3, −2.0 × 10−3, and 3.3 × 10−3 kg m−2 s−1, respectively. Stratification index analysis revealed a distinctive saltwater wedge with strong stratification in both ebb and flood currents in the mainstream of the NRE. Overall, the NEISS enabled effective analysis of the changes in the sedimentary environment of the NRE over the study period. And the NEISS data collected after May 2015 were used to support Marine Spatial Planning (MSP) in the brackish water zone. This system will be useful for monitoring future changes in the NRE following partial opening of the dam after February 18, 2022.

Relative contribution of the presence of an estuarine dam and land reclamation to sediment dynamics of the Nakdong Estuary

The Nakdong Estuary of Korea is a dramatic example of an urban estuary that has been heavily developed with the installation of two estuarine dams and approximately 17 km2 of tidal flat reclamation. This study aims to understand the relative contribution of the different physical alterations by implementing four model simulations of the COAWST modeling system: (1) present condition, (2) pre-estuarine dam construction, (3) pre-tidal flat reclamation, (4) both pre-estuarine dam construction and pre-reclamation. In Cases 2 and 4, the model grid was modified to extend the Nakdong estuary upriver about 60 km and remove the estuarine dam. In Cases 3 and 4, the model grid was modified to restore the reclaimed tidal flats. All simulations shared the same initial conditions, boundary conditions, and forcing. Then, the simulation results for current velocity, suspended sediment concentration (SSC), and deposition were used to estimate the relative contribution of each alteration. The results showed that the annual, depth-averaged currents for the pre-estuarine dam (Case 2) were 80% faster than the present condition but were 10% slower for Case 3 (no land reclamation case). Likewise, the depth-averaged SSC was higher by about 25 mg/L in the estuary for Case 2, but it was reduced by about 9 mg/L for Case 3. The increase of velocity and SSC for Case 2 resulted from the removal of the estuarine dam, which changed both the tidal properties (tidal amplitude was reduced by about 40 cm) and estuarine circulation (factor of 5 reductions in the vertical salinity gradient), while the decrease for Case 3 was induced by the reduction in sediment accommodation space (15% of water volume) without a change in the circulation. These results also revealed that the estuarine dam enhanced deposition more than the land reclamation that showed very little change. The changes in current velocity, SSC, and deposition for Case 4 (no dam/reclamation) were very similar to Case 2. Overall, this study suggests that the influence of the estuarine dam was larger than that of the land reclamation in the altered Nakdong Estuary. Moreover, the combination of estuarine alterations acted to enhance the effects. These findings can serve as analogs that can be applied to other estuaries where various human alterations have occurred.

Prey Identification of the Little Tern, Sternula albifrons (Pallas, 1764), by Applying DNA Barcoding to Fecal Materials

This study describes the prey DNA fragments found in the feces of a migratory bird species, the little tern, Sternula albifrons (Pallas, 1764), based on a DNA barcoding approach. This species is found in Nakdong Estuary, South Korea, and is a species designated as ‘Least Concern’ (IUCN Red List). Prey identification is a central issue of population conservation, and we applied DNA barcoding (using cytochrome oxidase I; COI) to fecal materials from little tern individuals. We successfully identified prey consumed by little tern individuals. All prey items comprised one phylum including three classes, six orders, and eight families based on a robust dual certification scheme (combined analysis of BLASTn searches and phylogenetic tree construction). Even though the success of identification was largely dependent on the degree of completion of the database in the genebank or BOLD systems, an increased resolution of prey identification to species level is important in predator–prey research. The current study used a small number of fecal samples to evaluate the applicability of the COI barcoding region to avifaunal feces, and more fecal samples are expected to convey increased information that can be used to infer the range of the prey species of little terns.

The relative merits of sediment transport formulas applied to the Nakdong Estuary, Korea using a coupled numerical modeling system

Three sediment transport formulas by Lund-CIRP (2012), van Rijn (1998), and Soulsby (1997) were applied for this study with field data by Yoon (2008) and several sedimentary variables of Nakdong Estuary in a coupled numerical modeling system, CMS. CMS is adopted to compare the measured depth change data and the calculated depth change data. As a result, the Lund-CIRP formula with mean grain size (0.25 mm) and multi-bottom friction coefficients based on the mean grain size distribution had higher accuracy (1.6 %) than the other formulas. The Soulsby formula has higher accuracy for multi-grain size and 0.06 of bottom friction coefficients. The van Rijn formula has high accuracy at shallow water areas such as a river. In this study, it is judged that the accuracy of the van Rijn cases was low because the water depth of the Nakdong Estuary and the nearby sea area rapidly deepens.

Calculation of a Climate Change Vulnerability Index for Nakdong Watersheds Considering Non-Point Pollution Sources

As a response to climate change, South Korea has established its third National Climate Change Adaptation Plan (2021–2025) alongside the local governments’ plans. In this study, proxy variables in 22 sub-watersheds of the Nakdong River, Korea were used to investigate climate exposure, sensitivity, adaptive capacity, and non-point pollution in sub-watersheds, a climate change vulnerability index (CCVI) was established, and the vulnerability of each sub-watershed in the Nakdong River was evaluated. Climate exposure was highest in the Nakdong Estuary sub-watershed (75.5–81.7) and lowest in the Geumhogang sub-watershed (21.1–28.1). Sensitivity was highest (55.7) in the Nakdong Miryang sub-watershed and lowest (19.6) in the Habcheon dam sub-watershed. Adaptive capacity and the resulting CCVI were highest in the Geumhogang sub-watershed (96.2 and 66.2–67.9, respectively) and lowest in the Wicheon sub-watershed (2.61 and 18.5–20.4, respectively), indicating low and high vulnerabilities to climate change, respectively. The study revealed that the high CCVI sensitivity was due to adaptive capacity. These findings can help establish rational climate change response plans for regional water resource management. To assess climate change vulnerability more accurately, regional bias can be prevented by considering various human factors, including resources, budget, and facilities.

The Dataset of UAV Based High-resolution Tidal Topography at the Nakdong Estuary: Focusing on Jin-u Island and Shin-ja Island

In the tidal flats of the Nakdong Estuary, eight weirs were installed as part of the Four Major River Restoration Project in 2011, and the environment changed from a flowing stream to a still water stream. As the Nakdong River’s weir was permanently opened in February 2022, the topography and ecological environment are expected to large change. In this study, Unmanned Aerial Vehicle (UAV) photogrammetry was conducted on the tidal flats of the Nakdong Estuary in November 2021, the environment before the Nakdong River floodgates were opened. The study area was surveyed using the Network-RTK (Real-Time Kinematic) method to obtain Ground Control Point (GCP), and using an UAV, orthographic image and digital elevation model were generated for an area of 3.47 ㎢ near Jin-u island and 2.75 ㎢ near Shin-ja island. A result of spatial resolution of 1.8 cm was obtained, the result was verified using checkpoints, and results with accuracy exceeding 1 cm were obtained in both Sin-u Island and Jin-woo Island. In the future, changes in the topography and sedimentation environment of this area are expected, so it will be useful data for various research and conservation management.

Morphological Analysis of Barrier Islands in the Nakdong River Estuary, South Korea

Youn, S. and Zarillo, G., 2022. Morphological analysis of barrier islands in the Nakdong River Estuary, South Korea. Journal of Coastal Research, 38(3), 475–490. Coconut Creek (Florida), ISSN 0749-0208. The Nakdong Estuary system and the associated barrier island system near Busan, South Korea, consists of dynamic shorelines characterized by morphological transformations that result from natural disasters (typhoons and flooding), rising sea levels, and construction projects (the Nakdong Estuary Dam and the Busan Newport). This study aims to synthesize existing water level, wave, meteorological, and morphological data obtained from various institutions with the objective of identifying major factors that influence shoreline and area change over time. These objectives were met by analyzing the shoreline and area with direction analysis from center point (DACP) to consider the influence of river discharge and sea-level rise and to determine shoreline shifts in barrier island orientation over time. From DACP, it was determined that the Nakdong barrier islands rotated clockwise because of erosion and deposition. Offshore shorelines of barrier islands advanced by 0.1 to 2 km between 1972 and 2013. The area change rate between 1972 and 2013 was 20.85% from 100 to 180° because of the Maenggeummeori-do channel construction and discharge from the Nakdong Estuary Dam. Morphological changes and shifts in shoreline positions were caused by alteration of flow patterns because of construction of the Nakdong Estuary Dam and sea-level rise in the Nakdong Estuary system based on the timeline of the shoreline and area change rates. This study exemplifies the need for a preconstruction development plan in a study area to ensure that the results of a project are environmentally sound with respect to the potential impacts of project construction and sea-level rise.

낙동강하류 생태공원의 조류 현황

The estuary of the Nakdong River is the largest habitat for migratory birds in Korea, and it is an area with high conservation value due to its wide tidal flats and wetlands with high biodiversity and abundant fishery resources. However, many changes are taking place, such as the destruction of migratory bird habitats due to urban expansion and development. In this study, the role and impact of ecological parks are analyzed by analyzing the current status of birds in the Nakdong Estuary Ecological Park, and furthermore, it is intended to be used as data for ecological management. Migratory birds visiting the estuary of the Nakdong River use the ecological park, but the birds found in the ecological park had a high proportion of resident birds. Also, the species richness index and biodiversity index (species diversity) were lower in the ecological park compared to the Nakdong River estuary.

Characteristics and Satisfaction Analysis of Eco-Tour Ships at Ecotourism Sites: Focusing on the Cases of the Nakdong River Estuary, Suncheon Bay Wetland, and Goesan Lake and Sanmagi-Yetgil in Korea

This study investigated eco-tour ships at Nakdong estuary, Suncheon wetland, and Goesan and Sanmagi-yetgil, 3 of the 26 ecotourism sites in Korea, by analyzing the characteristics and level of ecotourist satisfaction. The field investigation focused on eco-tour ship image, facilities, landscape observed from eco-tour ship, course, and operations. The results of the satisfaction analysis can be summarized as follows. First, there was no significant difference in satisfaction of eco-tour ship image between Nakdong estuary and Sanmagi-yetgil (p > 0.01), while Suncheon wetland showed a significant difference (p < 0.01). It is assumed that the fact that the ship was built using timber which better suits the natural environment and coastal ecosystem had a positive impact on the visual image. No significant difference in satisfaction with facilities on eco-tour ships was found between Nakdong estuary and Suncheon wetland, while Sanmagi-yetgil showed a significant difference. Second, satisfaction of the landscape observed from the eco-tour ships showed significant differences in the mean scores of landscape evaluation the three target sites: Sanmagi-yetgil (8.40), Suncheon wetland (7.20), and Nakdong estuary (4.67). These values are based on the qualitative evaluation of the landscape as seen from the eco-tour ship. It is presumed to have been influenced by the diversity of the landscape and the width of the river. The eco-tour ship course satisfaction also showed significant differences in the mean scores: Sanmagi-yetgil (7.37), Suncheon wetland (6.57), and Nakdong estuary (5.00). The landscape and tour course evaluations of the respondents seem to be correlated. In particular, the variety of courses available to visitors in Sanmagi-yetgil was relatively high compared to Nakdong estuary and Suncheon wetland. Third, satisfaction analysis for eco-tour ship operations found that Suncheon wetland and Sanmagi-yetgil did not differ significantly in terms of satisfaction (p = 0.634), but Nakdong estuary showed a significant difference. The relatively low satisfaction with the eco-tour ship operation at Nakdong estuary is due to the low scores for eco-tour ship commentary, reservation system, and with the facilities, while it is shown that the operation time as well as the landscape observed from the eco-tour ship and the tour course had a combined influence on satisfaction. In the comparative analysis of the impact of eco-tour ships on ecotourism, Nakdong estuary showed a significant difference. This finding indicates a greater influence of eco-tour ships on ecotourism in Suncheon wetland, Sanmagi-yetgil, and Nakdong estuary. Enhanced ecotourism satisfaction improves the probability of return visits. Thus, there is a need to incorporate the characteristics of ecological resources with well thought out operation and increased functional suitability of eco-tour ships to improve ecotourism satisfaction. The eco-ships in the three places in this paper have elements promoting and enhancing their potential. Our findings showed the satisfaction level of the users with the theme of ecotourism.

Sediment transport mechanisms in altered depositional environments of the Anthropocene Nakdong Estuary: A numerical modeling study

The Nakdong Estuary, Korea, is a dramatic example of an Anthropocene estuary. Over the last century, the construction of two dams has divided the estuary into two discharge energy regimes with the East Nakdong Estuary receiving discharge and the West Nakdong Estuary receiving no discharge. The mean-flow sediment flux gradient during high discharge was the main mechanism for deposition in the East Nakdong Estuary. Because of limited observations, the sediment transport mechanisms for the entire estuary remained unclear. To complement previous observations that were limited to a high discharge event of the East Nakdong Estuary, this study aimed to better understand the spatiotemporal variation of sediment transport and the mechanisms of deposition throughout the Nakdong Estuary. Sediment fluxes and bed level changes were estimated by utilizing the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST). Results confirmed that the East and West Nakdong Estuaries had different depositional patterns. The East Nakdong Estuary was characterized as a river-dominated environment with a high influence of river discharge that experiences rapid deposition. The West Nakdong Estuary was characterized as an environment mainly influenced by tides and waves that contribute to gradual deposition throughout the year. The mean-flow sediment flux by river discharge was a main mechanism of deposition in the East Nakdong Estuary after the construction of dam. The continuous landward mean-flow flux by tides and waves through the inlets was the dominant mechanism for deposition in the West Nakdong Estuary. These model results suggest that the Nakdong Estuary may serve as an analogue for a microtidal estuary altered by an estuarine dam, particularly those for which there is a monsoonal climate or anthropogenically reduced river discharge.

Applying the resilience principles for sustainable ecotourism development: A case study of the Nakdong Estuary, South Korea

When studying sustainable ecotourism, the ecotourism system can be better understood as a complex association of various elements that affects the local society and wildlife habitats. The purpose of this study is to plan an ecotourism system for the wise ecotourism resource management of estuary wetlands by using a resilience principle-based systems thinking approach. This study suggests an integrated management plan that considers diversity, connectivity, learning, participation, and polycentric governance to solve universal and important issues, such as estuary dam removal, urbanization, and natural resource use in the estuary's social-ecological system. The ecotourism system plans suggested in this study include minimizing ecological conflict and load through an improved sense of responsibility among stakeholders and strengthened protective activities. The results of this study suggest appropriate roles for various stakeholders in the management of tourism resources that can be used to establish new guidelines for ecotourism destination planning.

Variation in Phytoplankton Community Due to an Autumn Typhoon and Winter Water Turbulence in Southern Korean Coastal Waters

We evaluated changes in the phytoplankton community in Korean coastal waters during October 2016 and February 2017. Typhoon Chaba introduced a large amount of freshwater into the coastal areas during autumn 2016, and there was a significant negative relationship between salinity and nutrients in the Nakdong estuarine area, particularly in the northeastern area (Zone III; p < 0.001). The abundance of diatom species, mainly Chaetoceros spp., increased after this nutrient loading, whereas Cryptomonas spp. appeared as opportunists when there was relatively low diatom biomass. During winter, biotic and abiotic factors did not differ among the surface, middle, and lower layers (p > 0.01; ANOVA), implying that water mixing by winter windstorms and low surface temperature (due to the sinking of high-density water) physically accelerated mixing of the whole water column. Diatoms predominated under these conditions. Among diatoms, the centric diatom Eucampia zodiacus remained at high density at the inshore area and its abundance had a negative correlation with water temperature, implying that this species can grow at cold temperatures. On the other hand, the harmful freshwater diatom Stephanodiscus hantzschii mainly appeared in conditions with low salinity and high nutrients, implying that it can persist even in the saltwater conditions of the Nakdong Estuary. Our results indicate that hydro-oceanographic characteristics, such as river discharge after an autumn typhoon and winter water turbulence, have major effects on the composition of phytoplankton communities and can potentially affect the occurrence and characteristics of harmful algal blooms in southern Korean coastal waters.

Monitoring Variation in Sea Surface Temperature in the Nakdong River Estuary, Korea, Using Multiple Satellite Images

Eom, J.; Park, W.; Syifa, M.; Lee, C., and Yoon, S., 2019. Monitoring variation in sea surface temperature in the Nakdong River estuary, Korea, using multiple satellite images. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Remote Sensing and Geoscience Information Systems of Coastal Environments. Journal of Coastal Research, Special Issue No. 90, pp. 183-189. Coconut Creek (Florida), ISSN 0749-0208.Annual and monthly sea surface temperatures (SSTs) of the coastal waters around Nakdong River, Korea, were analyzed using data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Landsat. SST values derived from MODIS data were consistent with the in-situ data (R2 = 0.63), whereas Landsat-derived SST values were moderately correlated with in-situ data (R2 = 0.44). The mean annual SST over 18 years was 21.7 °C. The coldest temperatures were recorded in 2001, and the warmest were recorded in 2016. SSTs were higher during the summer than in the winter, mainly because of higher air temperatures in summer. Across all years, March was the coldest month, with a mean SST of 14.4 °C, whereas August was the warmest month at 28 °C. As MODIS data have a spatial resolution of 4 km, it cannot be used to detect SST variation at fine spatial scales (least 100 m or less). However, it can be monitored temporal trends in SST. Spatially detailed SST variation was monitored using Landsat data. According to the Landsat data, warm SSTs were measured in the area extending from the southwest to northeast of the Nakdong Estuary, which is an area affected by the Kuroshio Current. Climate data are needed in addition to image data to accurately monitor SST variation in the future.

Pollution Intensity Assessment of Sediments Obtained Near Nakdong Estuary Using Pollution Index For Heavy Metals

The goal of this study was to determine pollution intensity of the points for heavy metals according to elemental analyses and concentrations of heavy metals on eight sediments samples obtained from Nakdong estuary. As a result of enrichment factor analyses, cadimum was evaluated as minor enrichment on 8 points but rest of the heavy metals were evaluated as no enrichment. Cadimum was evaluated as unpolluted to moderately polluted at N1 and N4 points and unpolluted at the rest points according to geoaccumulation index analyses. All the other heavy metals except cadimum were classified as unpolluted at all points. For potential ecological risk factor analyses, all heavy metals except cadimum were classified as low risk at 8 points, but cadimum showed considerable risk at 8 points. Probability of toxicity by heavy metals was 8% for N5 and N6 points. The rest of the points showed probability of toxicity of 21% by heavy metals. Key words: Sediments, Heavy Metals, Nakdong Estuary, Pollution Assessment, Ecological Risk

낙동강 하구 진우도 갈대군락의 서식환경 특성

낙동강 하구 진우도 갈대군락의 서식환경 특성

낙동강 하구의 용존 메탄 분포와 메탄 플럭스의 계절변화

낙동강 하구의 용존 메탄 분포와 메탄 플럭스의 계절변화

Environmetal Characteristics of Reed Habitat in Nakdong Estuary Saltmarsh

In this paper, as a basic research for the restoration and construction of easuary saltmarsh, To observe the habitat environment for reed, we observed sediment environment (Particle size, water content, pH, nutrient analysis (, )), ground water level, ground level, individual numbers of reed, maximum reed height. As a result of this study, sediment particle size and moisture content of soil on the study area not effected reed habitat, pH showed no difference in each site. and concentration also no difference in each site. Ground level of reed habitat area is more higher than none reed habitat. However Ground water level of reed habitat area is more lower than none reed habitat. As a results of analyzing the influence factors for reed habitat in Nakdong estuary saltmarsh, ground water level and ground level is most influenced factor for reed habitat.

Mechanism for sediment convergence in the anthropogenically altered microtidal Nakdong Estuary, South Korea

Abstract Previous sedimentological work has shown that throughout the last half-century, average sediment accumulation of 2–6 cm yr− 1 occurred due to the emplacement of estuarine dams and land reclamation in the Nakdong Estuary of South Korea (Williams et al., 2013). To investigate the timing and rate of sedimentation, two sonar altimeters were deployed for nearly a year. In the West Nakdong River, where there is no freshwater discharge from the dam, 4 cm of gradual sedimentation was observed, corresponding to the long-term average accumulation. On the other hand, episodic sedimentation of 6 cm, which also corresponds to the long-term accumulation rate, was observed during two months of summer discharge in the main East Eulsuk Channel. To examine the mechanisms of sedimentation, Acoustic Doppler Current Profilers at three sites measured current velocity and acoustically-derived suspended sediment concentration during increased discharge and wave activity events, and through spring and neap tidal cycles. Sediment flux was decomposed into tidal pumping and advection terms to determine the primary factors controlling sedimentation throughout the estuary. Downstream sediment fluxes were dominated by mean advection, particularly during large discharge events. The difference in the magnitude between the upper and lower stations has been determined to be the main mechanism for convergence of flux (deposition) in the central estuary. In the absence of strong discharge, residual sediment transport caused a flux into the estuary, suggesting the primary mechanism for gradual deposition throughout the year in the West Nakdong River where discharge is entirely blocked.