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Abstract
Floods in populated areas expose humans to serious threats to life. In light of this fact, evacuation of flood-affected populations is considered the most appropriate protective measure to minimize the negative impacts of floods. Yet, unplanned or spontaneous evacuations during flood disasters can cause severe traffic congestion that makes evacuees more vulnerable and exposes them to further risk. Therefore, efficient and effective planning of flood disaster evacuation operations is important for minimising the devastating consequences of flood disasters. In Australia, flooding caused by rainfall is the costliest natural disaster. Flood hazards range in scale and intensity from regular, planned-for events to manageable emergencies, and sometimes even to devastating disasters. Similarly, affected population evacuation modelling methods might range from simple, certain models to complicated, uncertain models, hence, not every evacuation model is appropriate for every flood hazard event. Riverine flood-related risks are usually manageable due to the gradual development of the flood and the predictability of the factors causing them, such as rainfall, floodplain locations, and flooding’s spatial and temporal distributions. Safer evacuations are possible when the evacuation is pre-warned, and evacuation can therefore be used as a protective measure for riverine flood disasters.
Therefore, the planning of evacuation operations for a riverine flood disaster is vital for minimising their negative impacts on human lives. This research’s ultimate objective is to develop a systematic method to simulate, model and optimise riverine flood evacuation trip distribution between flood-affected areas and disaster relocation shelters. To achieve this ultimate objective, three stages of this research have been devised. Stage 1 describes how to utilise the theoretical contributions that have been identified from the analysis of flood-related resources outlined in the literature review. These contributions and knowledge gaps are explained in detail in chapter 2 and are then incorporated in the proposed model. Stage 2 discusses the methodology, and the requirements of building a robust evacuation model are explained in detail. The model inputs, processing, and outputs from different data and information sources are described, including geographical information requirements, and utilisation of a strategic transport planning model (STPM). In stage 3, the adaptation of transportation problem (also known as the Hitchcock problem) is described and compared with the shortest path method for a single evacuee simulation and the gravity distribution model, which is used in strategic transport planning modelling.
Stage 3 clarifies that traditional strategic transportation planning focuses on long-term and strategic transport issues, and it does not adequately consider short-term operational issues and problems, including planning for riverine flood disaster evacuation trip purposes. Moreover, by focusing only on traffic assignment modelling, it does not take into account the effects of generated trips from flood-affected areas and the inundation of some disaster relocation shelters to which evacuees will be distributed. Stage 3 has proven the feasibility of adapting the transportation problem to optimise and plan riverine flood disaster evacuation trip distributions, achieving shorter total evacuation times than the strategic transport planning model method.
Flood-affected dynamic populations and the evacuation travel time matrix between flood-affected areas and disaster relocation shelters, as estimated and calculated in the riverine flood disaster GIS developed in stage 2, were used as inputs in the investigation of three evacuation trip distribution methods. These three methods include the 1) single evacuee method (shortest path method), 2) the gravity distribution method, which is used in strategic transport planning modelling during normal peak periods, and 3) the proposed evacuation planning and optimisation method.
These three evacuation methods are investigated using three types of evacuation time certainty environments that might coincide with different flood disaster severity levels. These three evacuation time knowledge environments are 1) the certain, 2) the approximate, and 3) the uncertain evacuation time certainty levels.
Maps and statistical analytical tools are used to analyse and compare the evacuation trip distribution methods. These analyses have indicated that the evacuation distribution optimisation method achieves shorter total and average evacuation times between flood-affected areas and disaster relocation shelters than the single evacuee and strategic transport planning methods.