Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Najafi, Mohammad Reza

Abstract

Compound flooding refers to flood events caused by multiple factors, including marine processes (e.g. storm tides and waves), hydrometeorological signals (e.g. rainfall and river flows) among others. Saint Lucia is a tropical island in eastern Caribbean Sea, which is frequently affected by weather-related extreme events such as tropical storms and the associated risks are exacerbated due to its mountainous topography and high concentrations of infrastructure and human communities close to the coast. At the southern coast of Saint Lucia, significant infrastructures such as Hewanorra International Airport and Vieux Fort Seaport, and human settlements such as towns of Vieux Fort and La Tourney are located at low-lying areas and are at risk of compound flooding. A hydrologic model (i.e. HYdrological MODel) and a two-dimensional hydrodynamic model (i.e. LISFLOOD-FP) are set up and calibrated to investigate the combined effects of storm tides, wave run-up, rainfall, and river flows on flood risks in Saint Lucia. Results indicate the necessity to consider multiple contributing factors as well as to characterize the effects of uncertain boundary conditions. In flood-prone areas, there are infrastructures supporting major services in the study area, and by extension, the economy of the Island. A network-based model, which considers direct and indirect connections between infrastructures, is set up to explore risks of assets in conditions of non-flooding and flooding. Modelling results reveal the fundamental importance of various components including electricity distribution, flood control, information and communication services, transportation, housing and human settlements, tourism, and particularly the normal operations of Hewanorra International Airport. Prioritization of risks is critical for developing effective mitigation methods for infrastructure networks.

Summary for Lay Audience

Compound flooding has multiple contributing factors, including marine processes (e.g. storm tides and waves) and hydrometeorological signals (e.g. rainfall and river flows). They can interact with each other and generate more severe flooding, which has not been recognized until recent years. The study area is located at the southern coast of Saint Lucia, which is highly exposed to hurricanes and tropical storms, such as Hurricane Dean in 2007, Hurricane Tomas in 2010, and Hurricane Matthew in 2016. The compound flooding risks are exacerbated due to the mountainous topography and high concentrations of infrastructures and human communities. The most important infrastructure is Hewanorra International Airport, whose failures in several extreme events severely impacted local and international transportation as well as the local economy. Other assets that support major services in the study area and the economy of the island include Vieux Fort Seaport as well as the towns of Vieux Fort and La Tourney. They are interdependent and the failure of one asset in flooding can propagate through the network, leading to failures of other assets and more severe consequences. To understand compound flooding and its associated risks in the study area, a hydrological model (i.e. HYdrological MODel) and a two-dimensional hydrodynamic model (i.e. LISFLOOD-FP) are set up and calibrated to investigate the combined effects of storm tides, wave run-up, rainfall, and river flows on flood risks in the study area. A network-based risk analysis model is set up to explore risks of interdependent assets. Results indicate that it is important to consider multiple factors in flood analysis. Hewanorra International Airport has the fundamental significance in the study area, along with other high-risk assets in flooding such as electricity distribution, flood control, information and communication services, transportation, housing and human settlements, and tourism. This study provides insights of compound flooding and helps prioritize risks of infrastructures in local flood management.

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