Assessing and Mitigating the Hydrological Impacts of Urbanisation in Semi-Urban Catchments Using the Storm Water Management Model

Urbanisation causes a range of adverse impacts on stream physical and ecological conditions due to increases in catchment runoff caused by increased imperviousness. Developing ways to reduce these impacts on in-stream ecosystems is a major challenge and requires innovative catchment specific, high-time-resolution modelling methods. We employed a combination of high-time-resolution data collection, analysis and modelling methods to understand the underlying hydrological processes and evaluate a potentially significant management option - stormwater harvesting. A set of sensitive parameters of the Storm Water Management Model (SWMM) were optimised using an automatic calibration method and hourly data in eight catchments in South East Queensland, Australia. Systematic investigation of the effects of urbanisation and its mitigation through stormwater harvesting was achieved by modelling the impacts of increasing impervious area for three of the relatively undeveloped catchments. As the extent of impervious areas across the catchments increased we typically found increases in the duration of high flow spells together with increases in mean flow and the frequency of runoff events. However, many hydrologic responses to increasing imperviousness were specific to the physical characteristics of catchments, and to the spatio-temporal pattern of urbanisation. By implementing stormwater harvesting options the hourly flows were reduced by up to 60 % but the maximum flow was unchanged. Thus the option was able to reduce, but not totally ameliorate, the negative hydrological impacts of increasing imperviousness.