Year

2011

Degree Name

Bachelor of Environmental Science (Honours)

ANZSRC / FoR Code

05 ENVIRONMENTAL SCIENCES

Department

School of Earth & Environmental Sciences

Abstract

Lake Illawarra, located on the south east coast of New South Wales, Australia, plays an important role in the lives of many people living in the region. It has economic value through the support of commercial fisheries and the tourism trade as well as providing an area that is aesthetically appealing and supports a range of recreational activities. Maintaining the ecological health of Lake Illawarra is imperative if the Lake is to continue providing these resources. The primary reason for the degradation of Lake Illawarra’s ecological health is an increase in the human population living in the catchment area, especially since early European settlement. Over the past 50 years, and continuing to the present day, extensive urban development is the greatest threat to the Lake’s ecological health. High rates of sediment and nutrient discharges have led to enhanced algal growth, higher turbidity in the water column and loss of aquatic habitat.

This project aims to develop knowledge to facilitate the management of the Lake Illawarra catchment by characterising areas with a high risk of sediment and nutrient discharge. This was done by modelling soil erosion processes within the catchment and, by also taking into account nutrient levels associated with the soils, providing an evaluation of soil erosion and nutrient export risk within the catchment. Soil erosion modelling was based on the Revised Universal Soil Loss Equation (RUSLE), and incorporated the use of a Geographical Information System (GIS). GIS has been increasingly relied upon for catchment scale modelling of soil erosion as it provides the most efficient and accurate method for the calculation of factors at the necessary scale, namely slope steepness and slope length. It also helps to provide a geographically accurate spatial representation of risk areas found during the modelling procedure.

It was found that risk areas of concern were strongly linked to factors relating to slope, which is not uncommon in soil erosion models at this scale. The Lake Illawarra catchment is characterised by the steep rise of the Illawarra Escarpment, where the coastal plain rises up to a maximum elevation of nearly 800 metres above sea level. Nutrient export risk was modelled based on the nutrients associated with mobilised soil particles, and so is strongly linked with the results found from soil erosion modelling. Extensive new developments have been approved in West Dapto and Calderwood, both of which cover areas of high erosion risk. In order for Lake Illawarra to remain as an ecologically, economically and aesthetically important resource for the people of the Illawarra region, in light of the new developments and population growth within the catchment, improvements in the application of sediment and erosion control measures and stormwater runoff management are of the utmost importance.

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