• Ecology and Resilient Infrastructure
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• v.9 no.3
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• pp.131-140
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• 2022

The magnitude and frequency of extreme floods are increasing owing to the effects of climate change. Therefore, multipurpose flood management techniques incorporating nature-based solutions have been introduced to mitigate the limitations of flood management and river design methods relying on existing observation data. Nature-based solutions to prepare for such extreme flooding events include ways to retreat the embankment, expand the floodplain, and reduce flood damage. To apply these technologies, adopting appropriate location selection methods based on various evaluation factors, such as flood damage reduction effects, sustainable ecological environments, river connectivity, and physical channel structure enhancements, should be prioritized. Therefore, in this study, the optimal location for implementing the multipurpose floodplain construction project was determined by selecting the location of the floodplain expansion with objectivity in the river waterfront area upstream of Daecheong Dam to downstream of Yongdam Dam. Through the final location determination, the Dongdaeje and Jeogokje sections were included in the optimal location considering both flood damage reduction and water environment improvement.

• Ecology and Resilient Infrastructure
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• v.3 no.4
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• pp.322-326
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• 2016

The distribution of floodplain vegetation is mainly affected by hydrological and hydraulic processes. In this study, we investigated changes in the vegetation distribution due to flood discharge alteration, and the relationship between the vegetation types and the flood frequency during the last ten-year period in the Cheongmi-cheon Stream. Flood discharge of the Cheongmi-cheon Stream tended to decrease from 2006 to 2016. It has greatly decreased to less than $160m^3/s$ since 2013. This resulted in the settlement of Phragmites japonica to the wide sand bar at the Cheongmi-cheon Stream, even though it had sparse vegetation before 2013. The sand bar was fully covered with P. japonica in 2016. Vegetation communities in the floodplain were classified by dominant species, i.e. the annual-hygrophytic, the perennial hygrophytic and the mesophytic communities. Analysis of the relationship between the vegetation communities and the flood frequency shows the annual hygrophytes, perennial hygrophytes and the mesophytes communities distributed in the range of under 1 year, 1-10 year and over 7 year flood inundation area, respectively. In conclusion, distribution of the floodplain vegetation is closely related with the flood discharge and frequency in the Cheongmi-cheon Stream.

• Economic and Environmental Geology
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• v.30 no.3
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• pp.263-275
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• 1997

Compound calcrete deposits are recognized from the Dadaepo Formation in Dusong peninsula, Pusan, and their textures, structures, morphology, and stratigraphic distribution are examined. The Dadaepo Formation in study area consists of fluvial plain deposits including floodplain-lake deposits, and the compound calcrete deposits occur above floodplain deposits and below lacustrine deposits. The compound calcrete deposits are composed of nodular to massive (micritic), laminar, nodular, nodular to massive (marly), and marly calcrete deposits. In these calcretes, circumgranular and curved cracks, alveolar structures, fitted peloids, tubular fenestrae with laminar micrite wall (rootlet casts), microstalactic calcite, and tepee structures are observed, which indicates that they are calcic paleosols. Considering their stratigraphic occurrences and pedogenic origin, compound calcrete deposits are interpreted to have formed on distal fluvial plain to palustrine environment by the repetetion of deposition and subsequent calcification due to alternation of lake expansion and contraction. The repetetion of calcrete formation suggests that arid climatic condition was alternated with humid condition in short-term period. Such alternated paleoclimatic condition is similar to those of the Sindong and Hayang groups, and indicates that short-term fluctuations from arid to humid climate were prevailing in overall Gyeongsang Basin. In stratigraphic sense, the compound calcrete deposits can be used as a marker deposit for the correlation of the Dadaepo Formation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.6
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• pp.735-747
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• 2023

In recent times, the sharp increase in extreme flood damages due to climate change has posed a challenge to effectively address flood-related issues solely relying on conventional flood management infrastructure. In response to this problem, this study aims to consider the effectiveness of nature-based flood management approaches, specifically levee retreat and relocation. To achieve this, we utilized a 1D numerical model, HEC-RAS, to analyze the flood reduction effects concerning floodwater levels, flow velocities, and time-dependent responses to a 100-year frequency flood event. The analysis results revealed that the effect of creating a flood buffer zone of the nature-based solution extends from upstream to downstream, reducing flood water levels by up to 30 cm. The selection of the flow roughness coefficient in consideration of the nature-based flood buffer space creation characteristics should be based on precise criteria and scientific evidence because it is sensitive to the flood control effect analysis results. Notably, floodwater levels increased in some expanded floodplain sections, and the reduction in flow velocities varied depending on the ratio of the expanded cross-sectional area. In conclusion, levee retreat and floodplain expansion are viable nature-based alternatives for effective flood management. However, a comprehensive design approach is essential considering flood control effects, flow velocity reduction, and the timing of peak water levels. This study offers insights into addressing the challenges of climate-induced extreme flooding and advancing flood management strategies.

• Ecology and Resilient Infrastructure
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• v.7 no.4
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• pp.238-247
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• 2020

This study aims to examine the causes of the rapid expansion of riparian vegetation in river channels in recent years. Accordingly, the changes in the monthly rainfall were analyzed at 19 locations over the period of 1984 to 2018. Moreover, the changes in the water levels of the target river sections of Seom River, Cheongmi River, and Naeseong River were analyzed. The results showed that rainfall increased by 30% in April and decreased by up to 49% in the May-September period since 2012. Between 2012 and 2018, when rainfall decreased, the inundation time of the floodplains of the target rivers decreased considerably. The floodplains of Seom River and Cheongmi River were not inundated since 2012 and 2013, respectively. In the case of Naeseong River, the inundation time of the low-water channel drastically decreased since 2013, and there was no inundation in 2015. Consequently, riparian vegetation settled rapidly on the floodplain without any disturbance and continued to expand. The settling and expansion of riparian vegetation reduce the flood capacity of the river channel and can also lead to the loss of the water ecosystem due to terrestrialization.

• Ecology and Resilient Infrastructure
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• v.2 no.3
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• pp.255-263
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• 2015

Biological invasion of alien plants is considered to be one of the most serious threats to biodiversity in riparian zones. The effects of two invasive alien plants, Sicyos angulatus and Paspalum distichum var. indutum, on the flora and community structure of the riparian vegetation were investigated at 22 sites at streams in Korea. Sicyos angulatus has invaded the central Korean Peninsula. This alien plant has caused problems to stream managers because of its aggressive vining growth. It had suppressed native vegetation such as trees, shrubs and tall grasses on bank slope and higher floodplains. Paspalum distichum var. indutum has become more widespread in the southern part of Korea. This invasive plant has shallow rhizomes and creeping, extensively branched stolons. It forms a dense mat over lotic or slowly-flowing water and threatens submerged and short emergent hydrophytes. In order to control the introduction and expansion of alien plants, limitation of artificial disturbances and appropriate alien plant management are needed in riparian areas.

• Korean Journal of Environment and Ecology
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• v.30 no.4
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• pp.684-693
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• 2016

Daemyung retarding basin located near the confluence floodplain of the Nakdong and Kumho River is a large spawning site for the endangered Kaloula borealis, and needs for protecting the habitat of the endangered species are increasing. However, scientific studies are rarely conducted on the population characteristics and ecological knowledge on the species in the basin. This paper aims to estimate the population size and spatial distribution of the species that inhabited at the Daemyung retarding basin, using the capture-recapture method. Also, pitfall traps were installed in each habitat types classified with micro-topographic features, slope aspects, and vegetation communities to identify the spatial distribution characteristics of the Kaloula borealis of each habitat in the retarding basin. Field survey on the species was conducted from May 2013 to October 2014, showing that the species emerged in May, became more active during July and August and started to hibernate at the end of October. Using capture-recapture method, the first survey was carried out from July to August, 2014. Ninety-eight toads were captured, marked, and released back into the site. In the second survey, 68 toads including 5 marked toads of the previous survey were captured. Based on these two-sample surveys, around 535-2,131 individual toads are estimated to inhabit the Daemyung retarding basin. Fifty-seven pitfall traps were installed in four habitat types: mounded and vegetated flatland, lowland swamps, and slope areas of both the southern and western parts of the basin in order to delineate spatial abundance of the endangered Kaloula borealis during the rainy season when the species is actively spawning. Pitfall traps at the spatially explicit array indicated that the species gradually move to the slope areas near the Daemyung stream, showing high occurrence density of the Kaloula borealis compared to the lowland swamps after the spawning season. The emergence of Kaloula borealis in the lowland swamps appeared to be comparatively higher during the spawning season. However, after the spawning season the toads species rapidly moved into the neighboring land of relatively high elevation such as the slope area towards the Dalsung protected wetlands and Daemyung River. These results are closely related to the migration patterns that toads tend to return to the sheltering sites and/or hibernating grounds after the spawning season. Also, the Kaloula borealis moved to the nearest high-level vegetated areas as the lowland swamps of their spawning grounds deteriorated with the expansion of permanent ponds due to the rise in the groundwater level.