Water sensitive urban design for the Spring Creekcatchment and MUSIC sensitivity analysis

In recent times, water sensitive urban design (WSUD) has been used extensively in large cities such as Brisbane and Melbourne. As a city, Toowoomba has not been exposed to the benefits of stormwater management provided by WSUD. In Australia, WSUD is thought of as the implementation of planning and design techniques which are sensitive to water sustainability and environmental protection. Obvious benefits of WSUD include the ability to reduce stormwater runoff flows and increase stormwater quality. WSUD uses specifically designed systems for the management of stormwater. As the Spring Creek catchment (Toowoomba, Queensland) has undergone extensive urban development in recent years, there has been an increasing need to manage stormwater that is released from the catchment. WSUD will aid in the management of these stormwater issues. An important aspect is selecting WSUD systems is soil characteristics such as saturated hydraulic conductivity. The model for urban stormwater improvement conceptualization (MUSIC) is an industry standard in the assessment of stormwater characteristics and WSUD systems. Generic (default) input parameters for the model have been developed by the creators of MUSIC in order for users to model the catchment without extensive knowledge of the local conditions (e.g. soil characteristics). These generic parameters have been proved to provide inaccurate results when used in MUSIC. By comparing a model using generic parameters against a model using local parameters, the relative inaccuracy of the results obtained from the models can be evaluated. A soil investigation of the Spring Creek catchment was completed. This investigation involved single ring infiltrometer testing within the field and disturbed soil core testing in the laboratory. In addition, the results from the soil investigation have led to the development of localized soil input parameters for the MUSIC model. Generic input parameters and local input parameters were applied in separate models. The results of these models were compared in order to determine if MUSIC is highly sensitive to a change in soil input parameters. The results from the soil investigation have revealed low saturated hydraulic conductivity soils within the catchment. Hence, ponds and wetlands were deemed most suitable for the catchment due to the soils water ponding ability. The results of the sensitivity analysis demonstrated that the local parameters were generally greater than the generic parameters. As a result the generic model achieved much greater stormwater runoff containing larger amounts of total suspended solids. The effectiveness of WSUD systems was evaluated in both models. Generic model WSUD systems generally had to increase in size by 8% in order to have the same treatment ability as the systems in the local model. It was concluded that the local parameters were preferred for modelling in MUSIC compared to generic parameters.