Life cycle cost analysis of natural channel as a component of water sensitive urban design

The traditional method of urban drainage featured by a higher proportion of impervious area, concrete channels and pipes is being challenged by Water Sensitive Urban Design (WSUD), which is a more sustainable method of urban water cycle management. The history of WSUD method in Australia is about a decade old. Although this new method has significant advantages over the traditional method, the perception of greater maintenance needs of WSUD components have made many local authorities reluctant in adoption of the new technique. There has been limited research on the long-term viability of WSUD method, in particular on the life cycle cost analysis. This paper presents an investigation of life cycle cost analysis of a natural channel in an urban environment. The natural channel is an important component of WSUD and provides a number of advantages over the concrete channel; for example, reduced runoff at catchment outlet, improved stormwater quality, enhanced habitat value, and pleasant aesthetics. However, natural channels may require greater maintenance efforts, for example frequent clearing of vegetation and erosion control. The paper uses Cooks River Rehabilitation Works in South Strathfield in Sydney's inner west in demonstrating the life cycle costs of natural and concrete channels. The traditional concrete channel was perceived as expensive in regards to the capital cost but showed cheaper maintenance and management costs. Its favourability was then weakened by the higher repair and replacement cost. The natural channel had a smaller capital cost at the beginning but increased maintenance and management costs over time. At lower interest rates, the life cycle cost of natural channel was higher. For example, at 5% interest rate, the natural channel showed life cycle cost about 6% higher than the concrete channel. At 17.5% interest rate, life cycle costs of the two methods became similar. This life cycle cost analysis did not include the cost of the extra benefits that would be provided by natural channels due to limited data availability. The paper shows that despite a little higher life cycle cost of natural channel, its adoption is justified when its relative advantages are considered.