A Study on the Mixing Characteristics According to the Flow Structure and Saltwater Wedge in Estuary

다국어 초록 (Multilingual Abstract)

The river mouth is the point where the river and the coast contact, and it refers to the waters where the fresh water and seawater are mixed together. In river mouth, the water flow has the movement characteristics of two fluid flows which the vertical structure is divided into two structures, due to the difference in density of the freshwater and seawater. The two fluid flows phenomenon occurs due to the difference in salinity, water temperature, or density distribution of suspended solid, causing the significant difference in density of upper level and the lower level. In Korea, the management system for the river mouth is not clearly set, and the domestic study of the brackish water zone is insufficient.
In this study, Suyoung river, the “opened” river mouth, and Nakdong river, the “closed” river mouth, were selected as the target area. For Suyoung river, the 3.5km section from Minrak bridge to Oncheon stream confluence was selected as the study range and analyzed the water quality and the status of the brackish water zone through high-level analysis using the DEM, irrigation, and water quality field measurement. The EFDC was used to conduct the flow analysis, applying the scenarios of minimum flow, storage, ordinary water flow, ninety-five-day flow inflow in spring and neap tide period. The same methods used in Suyoung River were used in the study of Nakdong river mouth, and the study range was selected as the 42km section starting from the Nakdong river estuary bank to Chang-am water intake station to conduct the study on the seawater intrusion when the estuary bank floodgate is opened.
In the numerical simulation, the Suyoung river mouth did not show significant change because the influence of the seawater is dominant in this section. When the tidal gap period models are applied, applying the ninety-five-day flow showed the gradual decrease of the salinity density, and it appears that the influence of freshwater can be in effect in the brackish water zone only when the inflow over 5.59㎥/s is secured. When the ninety-five-day flow is applied to the Nakdong river mouth, the result showed no seawater influence to all water intakes located within the Nakdong river mouth. However, when the minimum flow was applied, it was confirmed that water intakes in Maery, Wondong, Moolgeum, and Sindosi were affected.

국문 초록 (Abstract)

하구는 하천과 해안이 접하는 지점으로 담수와 해수가 서로 혼합되는 수역을 말한다. 담수와 해수간의 밀도차이로 연직구조를 둘로 나누는 이층류의 거동특성을 갖게 되며, 이층류 현상은 염분이나 수온의 차이 또는 부유물질의 농도분포 등에 의해 상층부와 하층부 간의 확연한 밀도차로 인해 나타난다. 국외에 비해 국내에서는 하구에 대한 관리 체계가 명확하게 설정되어 있지 않으며, 기수역에 관한 국내연구가 부족한 실정이다.
본 연구에서 열린하구인 수영강 하구와 닫힌하구인 낙동강 하구를 연구 대상지역으로 선정하여 진행 하였으며, 수영강의 경우 민락교 ~ 온천천 합류점 까지 약 3.5 km로 연구범위로 선정하여 DEM을 활용한 고도 분석과 수리 및 수질 현장계측을 통해 기수역 내의 수질 및 현황을 분석하였고, EFDC를 활용하여 대조기와 소조기에 기존갈수량, 저수량, 평수량, 풍수량 유입유량 시나리오를 적용해 해수의 유동분석을 진행하였다. 수영강에서 진행한 방법들을 활용하여 낙동강하구에 적용시켰으며, 낙동강하구둑 ~ 창암 취수장까지 약 42 km로 연구범위를 선정하여 하구둑 수문을 개방하였을 시 해수침투 영향 범위에 대한 연구를 진행하였다.
수치모의 결과 열린하구인 수영강 하구의 경우 해수의 영향이 지배적인 구간이기에 큰 변화가 나타나지 않는 것으로 나타났으며, 대조기 및 소조기 모델 구동시 풍수량을 적용하였을 경우 점차 염분도 농도가 감소하는 것으로 보아 유입유량이 5.59 ㎥/s 이상 확보를 하여야 기수역에 담수의 영향이 미칠 것으로 판단된다. 낙동강 하구의 경우 풍수량을 적용시 낙동강 하구 내에 위치한 모든 취수장에 해수의 영향이 미치지 않는 것으로 나타났지만, 갈수량 적용시 매리, 원동, 물금, 신도시 취수장까지 영향이 미치는 것으로 확인이 되었다.

목차 (Table of Contents)

• Table of Contents
• Table of Contents ⅰ
• List of Tables ⅲ
• List of Figures ⅳ
• Abstract ⅵ
• 1. Introduction 1
• 1.1. Purpose of Study 1
• 1.2. Study Background 3
• 2. Theoretical Backgrounds 6
• 2.1. Characteristics of River Mouth and EFDC Program 6
• 2.1.1. Characteristics of River Mouth 6
• 2.2. EFDC Modeling 9
• 2.2.1. EFDC Model 9
• 2.2.2. EFDC Model’s Structure 11
• 2.2.3. Governing Equation of EFDC Model 16
• 3. Experimental Method 26
• 3.1. Study Target Area 26
• 3.1.1. Suyoung River 26
• 3.1.2. Nakdong River Mouth 29
• 3.1.3. Operation Rule of the Nakdong River Estuary bank 31
• 3.2. Study Target Range 34
• 3.2.1. Suyoung River 34
• 3.2.2. Nakdong River Mouth 35
• 3.3. Water Quality and Hydraulic Analysis of Suyoung River Mouth 36
• 3.3.1. Hydraulic Measurement Sensor (ADCP) 36
• 3.3.2. Water Quality Measurement Sensor (YSI-6600) 37
• 3.3.3. Water Quality and Hydraulic Analysis of Suyoung River 38
• 3.4. EFDC Model Application 40
• 3.4.1. Topographical Data Establishment and Input Data Analyzation 40
• 3.4.2. Elevation Analysis of Suyoung River Channel Section 40
• 3.4.3. Lattice Division of Study Target Range 43
• 3.4.4. Input Data 45
• 3.4.5. Model Verification 47
• 4. Result Analysis 51
• 4.1. EFDC Analysis Result 51
• 4.1.1. EDFC Analysis Result in Spring Tide (Suyoung RIver) 51
• 4.1.2. Neap Tide Period EFDC Analysis Result (Suyoung River) 54
• 4.1.3. EFDC Analysis Result Per Opening of Left-Right Flood
• Gate (Nakdong River Mouth) 57
• 4.1.4. EFDC Analysis Result Per Opening of Left Flood
• Gate (Nakdong River Mouth) 62
• 5. Conclusion 67
• 6. Reference 70