Flood mapping under an extreme event in a large shallow lake influenced by flood pulse in Southeast Asia

Sokly Siev,Chihiro Yoshimura,Hideto Fujii,Vannak Ann,Takashi Nakamura,A Soleh Setiyawan,M Sonny Abfertiawan,H Dwi Ariesyady,A Nastiti,D Roosmini

doi:10.1051/e3sconf/202014806004

Abstract

Tonle Sap Lake (TSL) in Cambodia is the largest shallow lake in Southeast Asia. Influenced by flood pulse system of the Mekong River, TSL provides diverse benefits including ecosystem services, ecological functioning, and flood water storage in the floodplains. However, extreme events (e.g., flooding) due to rising water level caused by dam break and/or heavy rainfall in the Mekong River Basin could threaten the ecosystems of the lake, community health and economic growth in the region. Flood mapping under such extreme event could be informative in the flood risk and emergency management. In this study, we aim to develop a flood risk boundary map in TSL using an existing 2D hydrodynamic model (Caesar-Lisflood, CL) with rising water levels estimated by Gumbel distribution. As a result, the extreme water level of 1% chance (or 100-year flood return period) exceeding the annual maximum water level at Prek Kdam station was approximately 11.38 m resulting in the largest inundation area of 15193 km2. Overall, the employed method and flood risk mapping are useful for the decision makers to manage flood risks and emergency in the lake. This is to anticipate the consequences of a possible rising water level by an extreme event.

Highlights

Quantifying the risk of flooding is the central challenges for planning regulation, insurability standards and pricing, and disaster management
The employed method and flood risk mapping are useful for the decision makers to manage flood risks and emergency in the lake
The study composed of two main components including flood frequency analysis (e.g., Gumbel distribution) and application of 2D hydrodynamic model (Caesar-Lisflood, Caesar Lisflood (CL))

Summary

Introduction

Quantifying the risk of flooding is the central challenges for planning regulation, insurability standards and pricing, and disaster management. Flood frequency analysis is a one of the quantitative assessment methods for the flood risk management by quantifying the magnitude of flood water levels in terms of nominal return-periods, like the 1 in 100-year flood. This information is essential for the “design floods” in the planning regulation, and other flood risk management policy making [1]. Unless additional analysis is applied, such as overlying the flood water level over the topography map of the investigating area, the area under flood water level (flood water level > topography) can be quantified This simple application does not represent physical processes of flood or hydraulic meaning (e.g., movement of flood water level, flood duration, time-lag) and could overestimate the flood extent area when the investigating area is large.

Objectives

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Results

Conclusion