Il Hong

A Study on the Channel Planform Change Using Aerial Photographs and Topographic Map in the Mangyoung River

River is able to change by various environmental factors. In order to conduct river restoration design, it is necessary to evaluate the stable channel through the analysis of past and present river channels. River evaluation requires various data, such as geometry, hydraulic and hydrology, but there is a lot of difficulty to understand topographical information of river change on time and space due to a lack of past data by domestic conditions. This study was analyzed abandoned channel formation, changes in the vertical-section and cross-section length of rivers, and micro-landform changes etc using an image analysis technique. Purpose of this research is to evaluates the stable channel through a river channel morphology change from past and present river channels image. Mangyoung river was conducted artificial river maintenance through straight channel consolidation form 1920 to 1930 year. In the result river maintenance, mangyoung river length was decreased by 15 km and abandoned channels of six points were made. Since then, weir was continuously increased to control bed slope and use water. Install of weir was to be the reason of changes on channel width, thalweg, vegetated bar, sand bar, water area. Present Mangyoung river show that water area was temporary increased in upper and middle reach because of weir installation. Total sand bar was only decreased in upper channel. The change of vegetated bar and sand bar was slight recently. In this result, Mangyoung river is inferred to reach stabilized channel although there is some difference to the lower reach.

Effect of Climate Change on Environmental Flow Components and Physical Habitats

The quantity and timing of runoff are critical components for the water supply, water quality, and ecological interaction of river systems (Poff, et al., 1997). Five components of the flow regime (magnitude, frequency, duration, timing, and rate of change) can directly and indirectly impact an aquatic ecosystem. (Karr, 1991; Poff, et al., 1997). Due to the recent phenomenon of climate change, the timing and pattern of rainfall has changed and affected the flow regime of certain basins. Hence, in this research, the future impact of climate change on the river flow regime and aquatic ecosystem of the Mangyeong River, a medium-sized basin in Korea, has been quantified by analysis of environmental flow components and physical habitat modeling. Consequently, it is predicted that there will be crucial changes in the material conditions related to the river flow regime, and the risk of ecological environmental changes will greatly increase. KeywordsClimate Change; EFCs; CSI; Environmental Flow Components

Application of the LISFLOOD-FP model for flood stage prediction on the lower mankyung river

LISFLOOD-FP model in which channel flows are resolved separately from the floodplain flows using either a kinematic or diffusive wave approximation has been used to analyze flooding behavior on the lower Mankyung River influenced by backwater. A calibration and validation process was applied using the previous flood events to assess the model performance. Sensitivity analysis was conducted for main calibrated parameters, such as Manning roughness coefficient and downstream boundary condition. Also, we examined the effect of warm-up for the initial conditions. The results show that the computed hydrograph is in good agreement with measured data on the study reach, even though it was a hydrologic kinematic wave model. The sensitive analysis show that the difference between the computed results may be greater depending on the used calibrated parameters and that the sufficient calibration/validation process against various flood events is necessary. If the flood inundation simulation is performed using the validated model, it is expected to be able to contribute about river planning and policy decision-making for flood damage reduction.

A Study on Ecotope Diversity Transition Analysis in the Middle of the Mankyung River, South Korea

An ecotope is an environment where an ecological niche and habitat are combined. Ecotopes are the smallest habitat units that are homogeneously classifiable on maps. Since the diversity of classified ecotopes i closely related to biodiversity, analysing ecotope diversity should be useful for indirectly presuming ecological healthiness. In this study, ecotopes in the middle of the Mankyung River were classified by time period (1918~2014), and the changes of their diversity before and after the construction of dikes were analyzed. Based on this analysis, the ecological healthiness of the environments of the Mankyung River was evaluated. The results of this study show that, after the construction of dikes in 1948, riverside lands formed intensive ecological environments, but the ecotope diversity index of protected lowlands declined sharply due to the artificial development of roads, farmlands, houses, and rural villages. KeywordsEcotope; Diversity; Stream Environment; Habitat; Aerialphoto

A Study on Evaluation of Ecological Function before and after River Improvement

In this study, the assessment scheme has been developed to evaluate the ecological function of rivers which were changed by the river improvement project. The evaluating factors are composed of physical structure in river channels and ecological connectivity in river areas, and each value of the factors is quantified based on 4 and 2 variables, respectably. This scheme was applied to past (1918, before artificial river improvement) and present Mankyung River area. A GIS model was adopted for calculating, analysing, and presenting river ecological conditions using the 204 grids and 7 reaches in study area. Comparison results show that the evaluation grade was decreased in both factors after river improvement. The main causes of lower grade (from II to IV) for physical structure are the river straightening and crossing structures. The reduction (from II to III) in ecological connectivity grade effected by linear fragmentation due to roads and rails is found to be greater than areal fragmentation due to land-use. In particular, it is also found that a high degree of ecological connectivity in 1918 was distributed along the river, but that one in 2007 showed a tendency to scatter because of the construction of levee and increase of urbanized area.

Channel Evaluation for Abandoned Channel Restoration Using Image Analysis Technique

River is able to change by various environmental factors. In order to conduct restoration design of abandoned river channels, it is necessary to evaluate the river through the analysis of past and present river channels. River evaluation requires various data, such as geometry, hydraulic and hydrology, but there is a lot of difficulty to understand topographical information of river change on time and space due to a lack of past data by domestic conditions. This study analyzes the changes in past and present river channels and examines the applicability of river channel evaluation through image analysis using aerial photographs and 1918 year`s map. Aerial photograph analysis was conducted by applying the image analysis method and GIS analysis method on Cheongmicheon. As a result of this analysis, we have quantitatively identified the form and size of abandoned channels, changes in the vertical-section and cross-section length of rivers, and micro-landform changes. More importantly, we verified that morphological changes in sandbars due to artificial straightening are important data in identifying the state of current river channels. In these results, although image analysis technique has limitations in two-dimensional information from aerial photographs, we were able to evaluate the changes in river channel morphology after artificial maintenance of the river.