Thesis: Performance Assessment of Flood Protection System

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Flood Assessment in the Nerang River Catchment

Performance Assessment of Flood Protection System (Floodplain Catchments)

One of the first signs of global warming will be a rise in water levels around the world. Flooding will increase in many areas already prone to flooding, in addition, new floodplains will be created, placing humans and property at risk. The escalating impact of climate change makes it necessary to reassess existing flood protection systems and to assess the need for new ones in areas that were not previously at risk for flooding. The purpose of this research is to assess the performance of the Nerang Floodplain Catchment system in the Gold Coast area of Australia.

This assessment will develop a 2D Hydraulic simulation model for the Nerang Floodplain catchment in regards to present and future estimated strain from global warning. The Nerang Floodplain will be used as an example of how such an assessment can be accomplished in other areas at risk. The study will result in the development of a model that can be used to evaluate other catchment systems in other areas of the world.

The focus of the research will be on methodology development, using the Nerang Floodplain as an example. The analysis will use five primary variables to assess the catchment system. These variables were derived from previous research and a review of existing literature on floodplain catchment evaluation. The five variables are vulnerability (ss), Reliability (I±), Resiliency (y3) (Hashimoto, 1982), Flood Risk Index (FRI) and Flood Damage Index (FDI) (Zongxue, 1998). Measurements will illustrate the overall performance of the catchment system in a spatially distributed manner for the Nerang catchment system.

The result of the project will be to evaluate the performance results to determine the actions that need to be taken to bring the Nerang Catchment up to the standards necessary to counteract the affects of rising coastal waters. The recommendations will be for the modification, upgrade, or complete replacement of the existing system as determined by the performance assessment. This research will play an important role in the performance assessment of other catchment systems. The most valuable contribution of the research project will be to provide a consistent methodology for the assessment of not only flood protection systems, but for any engineering infrastructure.

The first chapter of the research study will consist of the introduction and background material for the research study. The second chapter will explore the impact of global warming and climate change on sea levels and rainfall in selected areas. Chapter 3 will evaluate the Nerang Floodplain Catchment system using the five criteria outlined in the introduction. Chapter 4 will address adaptation strategies and recommendations for improvement of the Nerang catchment system. Chapter 5 will evaluate the hydraulic simulation model and suggestions of how to apply the model to the current system.

1.1 Background

In order to understand fully, the scope and application of the model developed in this research study, it is important to understand the basic parameters and concepts that will be presented. This section will explore the precise meanings of various terms used throughout the research study, as well as an introduction to the targeted geographic area and the current catchment system.

The definition of a floodplain refers to a flat area of land that is adjacent to a waterway and which experiences periodic or occasional flooding. The morphology of a floodplain is highly related to the hydrogeology and sediment structure of the area. The floodplain can be described as the floodway, which consists of a stream channel and areas that carry the flood flows. The floodway has current during periods of flooding. This zone typically extends beyond the normal stream or river channel. The flood fringe refers to an area that is covered by the flood, but that does not experience strong current during flooding periods.

Flood plains are created as the banks of the stream erodes. Periods of flooding accelerate the erosion of stream and riverbanks. As the banks of the stream erode, it leaves the underlying bedrock exposed. Layers of sediment build up to create the flat floodplain. They generally consist of unconsolidated sediments of heterogeneous materials (Bolton & Shellberg, 2001). They can contain layers of sand, gravel, loam, silt, or clay. These layers form a natural filtration system for the waters as they filter into local aquifers. The composition of these layers determines the nature of flooding in the area. As flooding continues in an area, stream terraces form on the sides, representing the hydro geologic history of the area (Bolton & Shellberg, 2001).

Floodplains are an important part of the ecosystem, supporting riparian zone plants. These areas are continually wet and support large quantities of microorganisms that help to break down organic material (Bolton & Shellberg, 2001). Thus, the soil in a flood plain is often fertile and well suited for growing many crops. Floodplains are often tempting area for human development. They offer flat building sites, highly fertile soil, and access to nearby water. However, these areas are risky, depending on the return period of floods in the area. Human occupation and use of floodplain areas forms the major concern of building adequate catchment systems.

Understanding the factors that influence the formation and evolution of a floodplain help engineers and land use planners to determine the best course of action for an area. The present population of the area and the projected population of an area help to determine the importance of the catchment system. Catchments located near heavily populated or agricultural areas must be given a higher priority than those in remote or wilderness areas.

The Gold Coast corner of Queensland, Australia is an area of high population concentration. It is also an important addition to the Queensland economy. Human developed occurred in an area that was once wetland. Man-made structures converted this area into a group of islands that were able to support homes. The most highly developed area is situated atop a narrow barrier sandbar that lies between the waterways and the sea. A sand bypass system stabilizes sand movement due to tides and flooding in the area, protecting upscale homes in the area (Bodwell & Murray, 2001).

The level of development and economic prosperity of the Gold Coast area make it a high priority for an evaluation of the floodplain catchment systems. Due to its local geology and location, the Gold Coast area is an area of high concern as the waters rise due to global warming. This research will play an important role in the ability to sustain this highly prized asset to the Australian people.

2.0 Global Climate Change

Current models indicate that the risks to humans in coastal areas is changing due to climate changes and social trends (Stansby, Walkden, & Dawson et al., 2009). These changes are due to rising water levels from melting ice from glaciation and the polar caps (Boesch, Fiesd, & Scavia, et al., 2001). Increased water results in increased coastal erosion, which makes conditions favorable for the development of floodplains in areas that were not previously at risk for coastal flooding conditions (Stansby, Walkden, & Dawson et al., 2009).

Coastal dynamics result in sedimentary exchange between different geographic locations. Older models of coastal flooding only considered populated areas in isolation from surrounding areas (Stansby, Walkden, & Dawson et al., 2009). However, the development of better modeling of the interdependency of coastal areas is rapidly changing this philosophy. The new paradigm in coastal floodplain modeling considers the entire coastal area as a dynamic system, rather than patches of coastal area existing in isolation (Stansby, Walkden, & Dawson et al., 2009). This is an important point in the development of flood catchment systems in the Gold Coast area. Anything that affects the Gold Coast will influence the surrounding wilderness areas as well (Boesch, Fiesd, & Scavia, et al., 2001). Likewise, surrounding areas will have an impact of the accuracy of the model of the Gold Coast flooding profile. These dynamics are quickly changing paradigms regarding the long-term management of coastal areas.

2.1. South East Queensland (Gold Coast), Australia

It is not surprising that Gold Coast is taking a proactive approach to protecting its local resources from the impact of flooding due to climate change. Currently, several mandates are in order to help mitigate future concerns. For instance, the Nerang River Flood Mitigation Strategy imposed many new requirements on development in the area. This mandate requires that any new development take into consideration its impact on either flooding to neighboring properties, downstream or upstream (Gold Coast Council, 2006). This research will serve as an important tool in the development of short, mid-range, and long-term flood planning in the area.

The Gold Coast area has been rated as one of the most vulnerable areas to flooding as a result of climate change (Mirfenderesk, 2009). Since 1924, the Gold Coast area has experienced over 45 floods (Mirfenderesk, 2009). A number of phenomenons have triggered floods in the area in the past. Flood triggers have included cyclones and… [END OF PREVIEW]

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