Case Study: Hydraulic Model Study for Abandoned Channel Restoration

Recently, a paradigm of river restoration is recognized as the importance of flood plan involving abandoned channel. Hence, effort which abandoned channel area by improvement project will become the territory of river area is trying. This study is a part of river restoration project. In this study, hydraulic model experiment and numerical simulation were performed to understand the flow characteristic and bed change for abandoned channel restoration. The target area of the hydraulic model was the midstream of the Hampyeong Stream (stream length: 1.3 km). Horizontal scale was 1/50 and vertical scale was 1/40. For numerical simulation, the FESWMS model was used. Cases of hydraulic and numerical models were frequency flood discharge (50 and 100 years) and channel formation discharge (100 m3/s and 120 m3/s). Flow characteristics were analyzed in fixed condition using hydraulic and numerical models. Bed change on abandoned channel restoration was analyzed on deposition trend using sediment supply from upstream in hydraulic model, and was compared with results of bed shear stress in numerical model. Results velocity profile and bed shear stress of numerical model were similar with trends of measured velocity and deposition of hydraulic model. The results of this study will be applied to restoration design of abandoned channels.

Assessment of Habitats according to Groyne Types (Using Pale Chub)

A groyne zone formed by installing groynes functions as habitat or shelter for aquatic organisms during a flood. Since flow characteristics over a groyne zone are affected directly by groynes, understanding flow patterns due to shapes and types of groynes is of importance for designing groynes. In order to use groynes as an eco-friendly river structure, the ecological effects should also be considered at the design stage. In Korea, the ecological effects of groynes have rarely been examined or included for the actual design. In this study, a set of experiments were carried out to investigate flow pattern changes depending on different types of groynes. Based on the flow characteristics in the groyne zone, the scales of habitats and shelters by the groyne types were estimated. In addition, to test the applicability of a habitat evaluation model to the ecological design of groynes, River2D was used for a virtual river. For assessment of the groyne’s function of ecological habitat, the suitability index of a habitat for pale chub, one of the popular fishes in Korea, was used and the habitat areas by the groyne types were analyzed. The flow changes depending on the groyne types simulated by River2D show the applicability for the simulation of an ecological habitat to the groyne design.

Habitat Evaluation on Scour Hole Downflow Low Drop Structure Types Using Large-Scale Experiment

This study sought to review whether large-scale experimentation can apply to actual rivers concerning the effect of topographical change by scour in the downstream area of natural-type low drop structures on the fish habitat. The large-scale applicability experiment performed in this study installed low drop structures as the study object within the experiment channel and precisely surveyed topography in the downstream area of drop structures along with the hydraulic amount including water level and flow velocity under certain flow conditions. Based on topographical data acquired through the survey after the experiment ended, this study reviewed the change of suitability index and difference of weighted usable area by performing 2D habitat simulation. Ultimately, through the habitat simulation results in cases of considering and not considering scour in the downstream area of drop structures, this study analyzed the effects of topographical change in actual rivers on the habitat.

An Experimental Study on a Characteristics of Flow around Groyne Area by Install Conditions

In designing group groynes, the space of the groynes is an important factor, and the flow between the groyne areas will vary along the space. Since the flow in the groyne field significantly affects the flow change, the bed change, the bank erosion and the condition of the habitat, an assessment of the flow along the space of the groynes will yield important data needed to diversify the object of the groyne installation. To provide basic data for the determination of the proper space of groynes in a groyne group, the flow in the channel and groyne field, which varies with the installation of the groyne, is herein analyzed. The space of the groynes was set from the same length to 12 times the length of the groyne, and the flow range was measured using the LSPIV method and ADV. The influence of the angle of the installation was also analyzed. As a result, through the flow configuration in the groyne field and the flow range at the center of the groyne field against the space of the groyne, the decreasing influence of groyne erosion was suggested by the analysis of the shelter effect of aquatics and the countercurrent in the bank line.

Analysis of the Cause for the Collapse of a Temporary Bridge Using Numerical Simulation

The purpose of this study was to suggest the measures and methods for securing the stability of temporary bridges by analyzing the cause for the collapse of the temporary bridge built for the construction of the GunNam flood control reservoir located at the main channel of the Im-Jin River. Numerical simulations (one-, two-, and three-dimensional) were performed by collecting field data, and the results showed that the collapse occurred because the height of the temporary bridge was lower than the water level at the time of the collapse. Also, the drag force calculation showed that when the guardrail installed on the upper deck structure was not considered, there was no problem as the calculated values were lower than the design load, whereas when the guardrail was considered, the stability was not secured as the calculated values were higher than the design load, 37.73 kN/m. It is thought that the actual force of the water flow applied on the bridge increased due to the accumulation of debris on the guardrail as well as the upper deck.

Experimental Study on Local Scour in the Downstream Area of Low Drop Structure Types

Although ecologically disadvantageous since a river is interrupted because of drop structure installation, such structure installation is also deemed ecologically advantageous in terms of scour and complex flows in the direct downstream area. This study started from the premise that scour hole carries value as a habitat and sought to analyze quantitatively the local scour adjustment possibility in the downstream area through drop structure type change and to offer a habitat through scouring. This study provided changes in drop structure types, such as straight line type and V type. For local scour analysis impacting the downstream area by drop structure type, quantitative analysis of scour scope, depth, and length was comparatively performed for a tentative physical habitat through hydraulic experiments. As a result of the experiments, this study found that scour scope increases and various water depth conditions are offered as the angle of the drop structure’s apex becomes smaller. Future studies accompanied by various fish habitation evaluations are considered useful in finding an alternative to upgrade the ecological environment.