Model application to assess effects of urbanisation and distributed flow controls on erosion potential and baseflow hydraulic habitat

Abstract

The catchment model SWMM was modified to include on-site flow-control devices, and then linked with models of hydraulic habitat suitability and erosive potential for specific reaches in a study catchment. Urbanisation decreased the modelled baseflow by up to 33% and reduced the area of suitable hydraulic habitat by 0.5–13.3%, depending on the reach and species. Hypothetical infiltration devices increased the baseflow to pre-development levels, with an associated increase in habitat, but other measures were not effective. Urbanisation increased the erosion potential index by a factor of 1.58–9.32, depending on the reach. Erosion-control ponds decreased the erosion potential to pre-development level in some reaches. Detention tanks reduced the erosion potential significantly, but not to pre-development levels. The poor predictive ability of the models for baseflow compromised the utility of the hydraulic habitat assessment. Predictions of the effects of urbanisation on baseflow habitat should therefore be treated cautiously.

Keywords:

• erosion
• hydraulic habitat
• low impact drainage
• stormwater modelling

Acknowledgments

The authors wish to thank the North Shore City Council for providing data on the Alexandra Stream. This study was funded by the Foundation for Research Science and Technology under contract C01X00012. Field work for habitat surveys and flow gaugings were carried out under difficult conditions by Wayne McGrath, Cindy Baker and Marganne Allen. Alistair McKerchar provided helpful discussions and considerable assistance with computations. The authors also wish to thank the reviewers of the paper who provided valuable advice.