The Effectiveness of Local Stormwater Treatment Devices: A Case Study of the Carrara Catchment, South-East Queensland

Abstract

With the ever-increasing focus on the environment and the adverse effects that humanity has had, there has become a need to create means of sustaining the environment rather than destroying it. The impact of urbanisation on Stormwater runoff has included increased amounts of pollutants entering the waterways, which causes problems ranging from being aesthetically unpleasing to causing immeasurable damage, such as destroying the sea grass beds in Moreton Bay. The overall aim of this research was to investigate the effectiveness of installing local catchment water quality treatment devices on the regional ‘whole of catchment’ water quality. This was investigated specifically for South-East Queensland conditions by researching the Carrara Catchment on the Gold Coast through the collection of water quality data and modelling of the water quality. The research has shown that within Queensland, water quality treatment devices will improve the local water quality. This improvement is limited to a ’background’ concentration and removal efficiency. That is, there is a point beyond which no additional treatment of the stormwater quality is possible. The local treatment devices considered were shown to have an influence on the regional water quality, but their effectiveness was limited by the untreated subcatchments. Thus to have an effective influence on the regional water quality, every sub-catchment within a regional catchment needs to have a local treatment device. It was demonstrated that a regional treatment device (i.e. a treatment device located at the catchment outlet) has the greatest influence on the regional catchment concentration rather than many local treatment devices. The research demonstrated that in South-East Queensland a treatment device design for the 3 month ARI storm will not capture up to 90% of the average annual volume. The aim in the design of treatment devices should be to determine the removal efficiency required and design a treatment device (or train) to achieve this efficiency. Unfortunately this is usually limited by constraints such as the ‘background’ concentration level, available space and cost/benefit ratio.