# Case Study of HEC-RAS 1D–2D Coupling Simulation: 2002 Baeksan Flood Event in Korea

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## Abstract

**:**

## 1. Introduction

## 2. HEC-RAS Flood Model

#### 2.1. One-Dimensional River Flow Modeling

#### 2.2. Two-Dimensional Flood Inundation Modeling

#### 2.3. Coupled 1D–2D Method

## 3. Data and Methods

^{2}of agricultural land and 80 houses were flooded [6], and 24 of those were completely destroyed. The negative effect of the event lead to further interest in developing efficient dam breach flood models. This event also provides reliable field data suitable for verification, which previous research has used for flood analysis [6,14,15].

#### 3.1. Research Domain

#### 3.2. Methodology

#### 3.3. Pre-Simulation Conditions

## 4. Results and Analysis

^{2}) compared to that of FLUMEN and Gerris (3.13 and 3.51 km

^{2}, respectively).

^{2}for FLUMEN and 3.5 km

^{2}for Gerris, which remained constant until the end of the simulation. For HEC-RAS, however, an inconsistent increase in flooded area can be observed, where the maximum area simulated is 3.93 km

^{2}at 2200, and then this starts to decrease in size afterwards. The flooded area for HEC-RAS reached 75% after 7 h and 97% after 16 h. This behavior was not observed in the other two models. The reason for this might be because Gerris and FLUMEN model simulations considered the levee break as a topographical misalignment, in which the flow of water is only one way, while the HEC-RAS 1D–2D coupled method considers the interconnection between the 1D river flow and the 2D flood inundation. The recedence of water back into the river was considered in HEC-RAS, which is more realistic compared to the other models. Another reason may possibly be the difference in the threshold level for the three models. The models have different threshold values on which they count the wet and dry grid.

## 5. Conclusions

## Author Contributions

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 2.**(

**a**) Upstream discharge and (

**b**) downstream water level boundary conditions calculated using the U.S. Army Corps of Engineers Hydrologic Engineering Center River Analysis System (HEC-RAS) 1D model.

**Figure 3.**Baeksan levee failure flood domain showing elevation and constructed mesh (33 × 33 m resolution).

**Figure 4.**HEC-RAS coupled 1D–2D lateral structure (

**a**) and breach data (

**b**) of Baeksan flood simulation.

**Figure 5.**Extent of flood inundation from (

**a**) observed data (red line), FLUMEN (blue), Gerris (purple) and (

**b**) HEC-RAS model (yellow).

**Figure 6.**Topography and location of gauged points (

**a**) (Points G1 and G2 are located in the river side and flooded area side of the levee, respectively) and water level at points G1 and G2 from Gerris (

**b**), FLUMEN (

**c**) and HEC-RAS models (

**d**).

**Figure 7.**Simulated flood depth (m) comparison of Gerris (

**a**) and HEC-RAS models (

**b**) at 3, 5, 12 and 48 h after the levee breach.

**Figure 8.**Simulated flow velocity vector (m/s) comparison of Gerris (

**a**) and flow velocity particle tracking in the HEC-RAS (

**b**) model at 3, 5, 12 and 48 h after the levee breach.

**Figure 10.**Gerris, FLUMEN and HEC-RAS models’ simulated surface water elevation values at 1, 12, 24 and 48 h after the levee breach.

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**MDPI and ACS Style**

Dasallas, L.; Kim, Y.; An, H. Case Study of HEC-RAS 1D–2D Coupling Simulation: 2002 Baeksan Flood Event in Korea. *Water* **2019**, *11*, 2048.
https://doi.org/10.3390/w11102048

**AMA Style**

Dasallas L, Kim Y, An H. Case Study of HEC-RAS 1D–2D Coupling Simulation: 2002 Baeksan Flood Event in Korea. *Water*. 2019; 11(10):2048.
https://doi.org/10.3390/w11102048

**Chicago/Turabian Style**

Dasallas, Lea, Yeonsu Kim, and Hyunuk An. 2019. "Case Study of HEC-RAS 1D–2D Coupling Simulation: 2002 Baeksan Flood Event in Korea" *Water* 11, no. 10: 2048.
https://doi.org/10.3390/w11102048