• Ecology and Resilient Infrastructure
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• v.9 no.4
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• pp.237-246
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• 2022

Owing to their high bioproductivity and unique physical environment, estuarine wetlands are gaining importance in national biodiversity management and habitat conservation. With regard to conservation and management of estuarine wetlands, this study analyzed the ecological characteristics of Gahwacheon Estuarine Wetland, an open estuary with various habitat types. Data from vegetation and biotic surveys have shown that 12 plant communities of five physiognomic vegetation types, including lentic herbaceous vegetation, halophytic herbaceous vegetation, and chasmophytic herbaceous vegetation. Due to the discharge of Namgang Dam and the effect of the tide, vegetation are distributed along the narrow waterside area. In terms of biodiversity, a total of 715 species, including 12 endangered wildlife species, were identified. Species diversity was relatively high in sections I and III where various riverbed structures and microhabitats were distributed. Due to the effect of the brackish water area following the inflow of seawater, endangered wildlife of various functional groups were also found to be distributed, indicating the high conservation value of that area. The collection of ecological information of the Gahwacheon Estuarine Wetland can be used as a framework for establishing the basis for conservation and management of the estuarine ecosystem and support policy establishment.

• Journal of Korea Water Resources Association
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• v.45 no.5
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• pp.445-454
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• 2012

The present study aims to investigate the long-term channel morphological changes derived from channelization, embankment and levee construction works in unregulated fluvial channel of the Jiseock River. Analyses of aerial photographs taken past (Year 1966) and recent (Year 2002) showed the temporally remarkable changes in channel planform such as channel shape, bar migration, vegetation encroachment in bar. During the period, the natural single threading changed into braided types together with decreasing sinuosity by 9.2%, increasing vegetation occupied bar ranged 97% of total bars area. Because such channel morphological changes are closely similar to those in dam downstream channels, we assume that both/either flow regime alteration and/or sediment transport discontinuity may be critical for the fixed channel and spread of vegetated bars even in unregulated river without dam reservoir upstream. We found more reduced frequency and magnitude of flooding water level comparing with past, but no significant alteration of inter annual water level variation. Bed material has been coarsened by 4~5 times and the riverbed has been degraded in overall channel but aggraded locally in conjunction reach of tributaries. The results indicates that reduced sediment dynamics in fluvial channel which derived by bed material coarsening, river bed degradation and unbalanced sediment transport capacity between tributary and mainstem can be a causal factor to trigger channel morphological changes even in unregulated rivers.

• Journal of the Korean association of regional geographers
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• v.16 no.2
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• pp.85-99
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• 2010

This study analyzes the geomorphic environments of river channels and properties of sediments in the Naeseong-River basin, a branch of Nakdong-River. While the area at NU1 located in the uppermost reaches indicates the landscapes with the gravel riverbeds, the sand riverbeds can be seen in the downstream of NU2 whose basin consists mostly of the granite regolith. The downstream of NU2 has the braided channels in the beds and this may be due to the large quantities of sand particles supply to the bed under the favorable geologic and geomorphic conditions, properties of river flowing within the floodplains less resistant to the erosion and great fluctuations of discharges. Whereas the river at NU2 may seem that sand particles are actively eroded during the high water-level periods, the particles may be actively deposited during the periods at NM2 and NL2. Moreover, in the reaches of NU2 to NM1 and NL1 to NL2, the mean grain sizes of sediments increase downstream suggesting the other supplies of coarse sediments from the lower order streams running the steep slopes because the river flows in the areas consisting of the metamorphic rocks rather than the granites and shows the properties of incised meander.

• Journal of Korean Society of Forest Science
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• v.102 no.2
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• pp.176-181
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• 2013

The impacts of habitats changes of benthic macroinvertebrae species and individuals of the torrents due to construction of torrent structures can be summarized as follows. Approximately 16 to 40 species and 352 to 4,333.3 individuals of benthic macroinvertebrae were found around the local position of the torrent structures. Construction of torrential structures can increases the stability in the riverbed by preventing vertical corrosion and reducing the flow rate. However, if pond is created due to increase flow rate of rainfall, the temporal confusion of micro-habitats may lead to decrease in the number of species and induce reduced number of diversity as well as cause simplification in the community structure. Therefore, erosion control structures in torrent cause influence on the habitual ecosystem, though there are differences in the degree per distance depending on the types and heights of the structure. Before establishing torrent erosion control structure in mountainous torrent area, ecosystem status should be studied carefully from the planning stage and torrent habitats should be protected by deciding type, height and scale of structure, to minimize the influence on local habitants.

• Journal of the Korean Geographical Society
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• v.42 no.6
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• pp.879-897
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• 2007

The Royal District in Gyeungju-city was placed in lower surface of alluvial fan that was formed during the Last Glacial Age. During the Holocene, Bukcheon-river was reached in the dynamic equilibrium status and the form of river channel was similar or same to the present. The cases of dying people and carrying houses away by flood for ancient history in Gyeongju were six times, in 131, 160, 350, 496, 657 and 703. Like this big flood was happened at interval of $150{\sim}200$years. A period of big flood appearance in Bukcheon-river was extremely long. Therefore the people who had lived in Gyeongju for ancient history perceived that most part of riverbed of Bukcheon-river was a safety place from flood damages. Not only private houses. In east part of Bunhwangsa temple, that is, west side of Bukcheon-river where the river energy is maximum, a pillow block was built to prevent a lateral erosion but any artificial riverbank was not. In spite of high flood possibility in Bukcheon-river, there was no facility to prevent floods in this section. Also, deposits of flood are not identified. This point is very suggestive that Bukcheon-river did not flood for ancient history.

• Journal of Korea Water Resources Association
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• v.49 no.10
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• pp.809-821
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• 2016

The study area is local river of 671 (total length 3,741 km) in Gyeongnam prefecture, the results are as follows. Total number of river-crossing structures was investigated as 7,730, and it was found that structures were installed in 2.1 sites per 1 km (river length) on average. Diversion weirs for agriculture were 4006 (51.82%) and drop structures for channel bed maintenance were 3670 (47.48%), but the rest (riverbed road etc.) were 54 (0.70%). The number of high structures (height > 1.0 m) that affect many impact in upstream and downstream was investigated as 3,897 (51%), and the number of low structures (height < 0.5 m) that affect negligibly was 1109 (14%). Fish ladders have been installed on 640 (8%) structures in 153 (23%) rivers. In flood control and environment conservation, river-crossing structures brought about various impact that flood water level is raises and the eco-corridor is intercept. In order to improve these problems, we proposed a few engineering measures that can be realize with respect to river-crossing structures.

• Journal of Korea Water Resources Association
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• v.52 no.7
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• pp.493-503
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• 2019

This study presents a new method of estimating the size distribution of river bed gravel through image processing. The analysis was done in two steps; first the individual grain images were analyzed and then the grain particle segmentation of river-bed images were processed. In the first part of the analysis, the relationships (long axes, intermediate axes and projective areas) between grain features from images and those measured were compared. For this analysis, 240 gravel particles were collected at three river stations. All particles were measured with vernier calipers and weighed with scales. The measured data showed that river gravel had shape factors of 0.514~0.585. It was found that the weight of gravel had a stronger correlation with the projective areas than the long or intermediate axes. Using these results, we were able to establish an area-weight formula. In the second step, we calculated the projective areas of the river-bed gravels by detecting their edge lines using the ImageJ program. The projective areas of the gravels were converted to the grain-size distribution using the formula previously established. The proposed method was applied to 3 small- and medium- sized rivers in Korea. Comparisons of the analyzed size distributions with those measured showed that the proposed method could estimate the median diameter within a fair error range. However, the estimated distributions showed a slight deviation from the observed value, which is something that needs improvement in the future.

• Journal of Korea Water Resources Association
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• v.52 no.2
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• pp.163-172
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• 2019

The linear and cross-sectional shapes of the natural river channel are subjected to continuous changes in time and space due to the interaction with the flow of water and sediment transport. This study aims to investigate the morphological characteristics and change patterns of river channel quantitatively for the middle reach of Nakdong River, which has undergone large scale riverbed dredging and construction work, as Four Major River Restoration Project. A series of bathymetry and near-river survey has been conducted to obtain the detailed terrain information for the study area. The properties related to the linear and cross-sectional characteristics of river channel have been calculated based on the filed survey data and analyzed with comparing the survey data obtained in 2012 for the project completion. Since there has not been enough time for meaningful terrain change to take place, it was not possible to extract special tendency in the degree and aspect of terrain change. However, it is necessary to make regular examinations to the patterns and degree of river channel change using the proposed methodology.

• Ecology and Resilient Infrastructure
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• v.6 no.1
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• pp.23-33
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• 2019

Naeseong Stream is a sand-bed river that flows through the northern area of Gyeongbuk province. It is characterized by dynamic sandy bedforms developed in response to the seasonal hydrological fluctuation and by its unique riverine landscape called "white river." However, changes including construction of Yeongju Dam from 2010 and the extensive vegetation establishment around 2015 occurred along the Naeseong Stream. This paper aims to analyze climate, hydrology, and water quality as factors and to examine the possibility of channel changes accordingly. The second least precipitation during the last 60 years happened in 2015, which led to the lowest peak discharge in 50 years. The sediment characteristics of Naeseong Stream were not significantly different along the upstream and downstream reaches, but it was confirmed that annual minimum water level of the stream decreased continuously regardless of the dam construction. This suggests that intermittent drought and change in water quality are likely to provide favorable conditions for riparian vegetation establishment and the resulting physical changes have affected riverbed degradation. Therefore, it is necessary to conduct diversified monitoring in connection with river vegetation change in order to analyze the causes of river changes.

• Korean Journal of Soil Science and Fertilizer
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• v.31 no.2
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• pp.170-176
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• 1998

Nitrogen and phosphorus loads from an agricultural watershed of the Yulmun-chon tributary in the Buk-Han River Basin were quantified based on total amounts of water stream flow. The water quality and soil loss were estimated. Levels of the stream were recorded automatically using the water level meter. The flow velocities, along with the cross-sectional areas of the riverbed, were measured to estimate total amounts of water flow at three monitoring sites in this tributary. Water samples were collected at nine sites with two weeks interval from May to August and analyzed for the water quality parameters. Amounts of soil loss were estimated by the USLE. The size of the Yulmunchon watershed was 3,210 ha, of which paddy and upland soil areas were composed about 41%. The total amounts of soil loss from the watershed areas were estimated to be $13,273Mg\;year^{-1}$, showing 53%, 46% and 0.7% of the soil loss ratio from upland, forest, and paddy areas, respectively. Electrical conductivities and Nitrogen concentrations of the stream water were higher in the lower watershed area than in the upper area. Increments of N were higher for $NO_3-N$ than $NH_4-N$. Nitrate nitrogen was the major N form to pollute the water due to the agricultural activity. Total runoff was about 72% of the total precipitation in the watershed. The maximum loads of T-N and T-P due to the runoff were estimated to be 1,500 and $5kg\;day^{-1}$, respectively. Concentrations of $NO_3-N$ and $NH_4-N$ in the runoff were 13.5 and 1.8 times higher than those in precipitation. The N loads were mainly from soil loss, application of fertilizer, and livestock wastes, which were 52% of total N load. Results demonstrated that reduction of fertilizer use and the soil loss would be essential for water quality protection of the agricultural watershed.