Woon-Kwang Yeo

Numerical Analysis for Bed Changes due to Sediment Transport Capacity Formulas and Sediment Transport Modes at the Upstream Approached Channel of the Nakdong River Estuary Barrage

The effects of the selection for sediment transport equations and advection-diffusion equations according to different sediment transport modes on the modeling results of bed changes were analyzed using the CCHE2D and compared with field data in this paper. The most suitable sediment transport equation and sediment transport mode for advection-diffusion equation were suggested for the upstream approached channel of the Nakdong River Estuary Barrage. The bed changes simulated by the Engelund and Hansen formula were very small in the modeling case for the low and high flow discharges compared with the case of the Ackers and White formula. Also, the numerical modeling with the actual hydraulic event in 2002 presents that the bed change result with the bed load transport type for advection-diffusion equation was close to the field measurement more than the suspended load type.

Analysis for the Effectiveness of Sedimentation Reduction Using the Channel Contraction Method at the Estuary Barrage

In this study, the methods of sedimentation reduction for the estuary barrage were analyzed using the CCHE2D bed change model. Especially, the effectiveness of sediment dredging currently applied in the field was evaluated quantitatively and also the channel contraction method which is a substitute method was analyzed for the Nakdong River Estuary Barrage (NREB). The numerical model was calibrated and validated for the sediment transport equations and transport modes. In the NREB case, the Ackers and White formula and bed load type was the most similar to the field condition. As a results of the dredging simulation, there was the sedimentation reduction effect of 0.2 m in the bed changes. Furthermore, the analysis result of the channel contraction method represented that the sedimentation reduction effects of the average 0.4 m and the maximum 2.0 m were produced.

An Experimental Study for the Empirical Equation to Quantify the Subsidence of Riprap Scour Protection at Downstream of Vertical Drop Structures

낙차공은 하천의 경사를 완화시키기 위해 설치하는 대표적 횡단구조물로써 국내 하천에서 쉽게 볼 수 있다. 낙차공물받이부(apron)는 낙차공 본체와 일체화된 구조물로 설치하는 것이 일반적이며 물받이부의 하류부에 바닥보호공을 설치하여 낙차공과 물받이를 보호하도록 설계된다. 이에 본 연구에서는 낙차공 물받이부에서의 세굴현상과 사석보호공을 설치함으로써 발생하는 침하량에 대한 실험을 수행하였다. 세굴은 낙차공에 유입되는 유량이 증가함에 따라 세굴심은 증가하지만 낙차공 하류부의 수심이 증가할수록 세굴심은 감소하는 것으로 나타났다. 또한 낙차공 물받이부 사석보호공을 포설두께에 따른침하량을 산정하여 세굴심을 제어하고 구조물의 안전을 확보할 수 있는 가능성을 확인하였으며 최종적으로 필터가 없는 사석보호공의 무차원 침하량 산정식을 제안하였다. 【Drop structures that span the entire width of channels are installed to alleviate channel grades and have been constructed widely in Korean rivers. Aprons are normally installed and integrated with drop structures and bed protections are added on the downstream part of aprons to protect both drop structures and aprons. Scour occurring on aprons is reported to provide various habitats such as ripples and pools in natural rivers. This study focuses on the scour characteristics on an apron integrated with a drop structure and the subsidence of a riprap protection. The scour depth on the downstream part of the drop structure is found to increase with the increase of unit discharge; however, to decrease as the tail water depth gets deeper. Based on the experimental measurements, the subsidence of the riprap scour protection is calculated with respect to the thickness of riprap. Finally, the dimensionless empirical equation to quantify the subsidence of the riprap scour protection without filters at downstream of the vertical drop is suggested.】

Risk Assessment and Potentiality Analysis of Soil Loss at the Nakdong River Watershed Using the Land Use Map, Revised Universal Soil Loss Equation, and Landslide Risk Map

The land use map of the Nakdong River watershed was classified by each land use contents and analyzed to rank the risk of soil loss and erosion. Also, the soil loss and erosion was evaluated in the Nakdong River watershed using Revised Universal Soil Loss Equation (RUSLE) and the subbasin with high risk of soil loss was evaluated with the analysis results of land use contents. Finally, the analyzed results were also compared with the landslide risk map, hence the practical application methods using developed and analyzed results were considered in this study. As a result of land use analysis and RUSLE calculation, it was represented that the Naesung Stream watershed had the high risk for soil loss among the subbasins of the Nakdong River watershed. It was also presented that the high risk area identified by computation of RUSLE was corresponding to the landslide risk area. However, the high risk of soil erosion by land use near the river or wetland was confirmed only through the calculation results of RUSLE.

Evaluation of channel-forming discharge for the abandoned channel restoration design of Cheongmi stream.

구하도 및 폐천복원은 하천에서의 이수와 치수적인 기능뿐만 아니라 환경 및 생태 서식처 기능을 강화하고 개선하기 위한 여러 방법들 중 하나이며 이러한 구하도를 복원하기 위해서는 주수로와의 하도 안정성을 고려하여 횡단면 형태를 결정하고 하도선형을 설계하게 된다. 이러한 하도설계시 기준이 되는 유량이 반드시 필요하며 이 기준유량을 하도형성유량 또는 지배유량이라고 한다. 일반적으로 하도형성유량을 산정하는 방법으로는 만제유량, 특정 재현기간별 유량, 유효유량을 계산하여 결정하는 방법이 있다. 본 연구에서는 구하도 복원 사업이 시행되는 청미천 구간에 대해 만제유량, 특정 재현기간별 유량, 유효유량을 산정하여 상호 관계를 분석하고 과거의 하상변동 특성 자료와 비교하여 연관성을 평가하였다. 청미천 구하도 복원구간의 만제유량은 HEC-RAS 자료를 이용하여 만제수위에 해당되는 유량으로 산정하였으며 488

An Experimental Study to Evaluate the Subsidence Stability of Riprap Protection without Filters

m^3/s

The Analysis of Characteristics of Swell in Korea using the Ubiquitous Measurement System

인 것으로 나타났고 이는 1.5년과 2년 빈도 사이의 유량에 포함되는 것으로 나타났다. 또한 유사량 자료와 과거 일유량 자료를 이용하여 계산된 유효유량은 만제유량보다 큰 값을 갖는 것으로 나타났다. 과거 측량자료 분석에 의하면 청미천의 대상구간 하도는 1994년에 비해 2008년 현재 하도가 침식된 것으로 나타났으며 이는 유효유량을 소통시킬 수 있는 형태로 하도가 진화하고 있다는 것을 의미하며 곧 하천이 안정한 상태로 변화하고 있다는 것을 의미한다. 【The abandoned channel restoration is one of methods to enhance the environmental function and ecological habitat as well as the functions of water-utilization and flood control. The channel-forming or dominant discharge must be evaluated and defined to design the cross-sectional and plane geometries of the stable and equilibrium channel for the abandoned channel restoration project. In general, bankfull discharge, specified recurrence interval discharge, and effective discharge have been used to decide the channel-forming discharge. In this study, bankfull discharge, specified recurrence interval discharge, and effective discharge were calculated and compared for the abandoned channel restoration site of Cheongmi Stream and their relations to historical bed changes were analyzed. The bankfull discharge, 488

Analysis for the effectiveness of sediment dredging in the approach channel at the Nakdong River estuary barrage

m^3/s

Determination of Bridge Scour Depth Considering Flow Conditions and Bed Characteristics

, of the abandoned channel restoration site of Cheongmi Stream was calculated using HEC-RAS data and ranged between 1.5-year and 2-year recurrence discharges. Also, the effective discharge evaluated with the sediment rating curve and mean daily discharge data is greater than the bankfull discharge. According to the survey data of 1994 and 2008, the bed elevation of the study reach was decreased over time. It is indicated that the channel bed is changing to the stable condition to allow the effective discharge.】

Automatic Real-Time Coastal Bridge Scour Measurements

Many countermeasures for local scour at bridge piers constructed on the river and sea have been developed and researched to protect piers against local scour. The most commonly employed method is riprap protection, which is sometimes required the filter installation between riprap and base layers. However, the construction of stone filters are really hard to perform in the field, require the high cost, or sometimes are impossible. The experimental modeling is conducted to analyze the riprap failure modes and the stability of riprap protection without filters based on the different approach velocity and riprap layer thickness conditions. Also, the stability index to evaluate the performance of riprap protection is developed using the experimental results. The cover and thickness of the riprap layer play a very important role in the stability and thicker riprap layers can prevent a total disintegration of the riprap layer effectively, especially due to winnowing failure. keywords : pier scour, riprap protection, winnowing failure, riprap subsidence ..............................................................................................................................................................................................