Melbourne Water commissioned Alluvium Consulting Australia to assess the ecohydrology of a significant (EPBC listed) seasonal herbaceous wetland (SHW). The wetland, adjacent to Kororoit Creek, has been identified through the Melbourne Strategic Assessment for urban development.

The wetland is listed in the impact of Melbourne’s growth on ‘seasonal herbaceous wetlands (freshwater) of the temperate lowland plains – Melbourne Strategic Assessment’. Approximately 7.5 Ha of the wetland area is considered to be SHW, which is listed under the Environment Protection and Biodiversity Conservation (EPBC) Act 1999. The wetland (including a buffer and proposed GGF wetlands between the wetland and Kororoit Creek) has a protection overlay in the Melbourne Strategic Assessment (MSA).

In this project, we undertook modelling and investigation of the hydrologic regime of the wetland. This focussed on changes to the hydrology likely to occur if the wetland’s catchment is urbanised. Using the outputs from the model we identified a range of management options to mitigate the impacts on this EPBC vegetation community. We developed high-level management options to mitigate the deleterious impacts on the ecological values of the wetland identified from changes in the hydrologic regime. This involved developing a hydrological model and water balance for the wetland that considered different development scenarios and climate change impacts.

Ecohydrological modelling involves assessing the intra-seasonal variations in water availability at a location and how that meets the ecological requirements of the resident flora & fauna communities. This requires a different focus from traditional hydrological modelling used for flood modelling as it needs to consider seasonal changes within tight parameters of inundation duration and depth.

The project highlighted that a business as usual approach to drainage design would negatively affect the SHW and that novel design approaches needed to be considered. The mitigation options proposed will manage the threats to the biodiversity values of the wetland and:

  • Provide a hydrological regime that provides seasonal water availability to support Seasonal Herbaceous Wetland vegetation.
  • Allow for adjustment of the water flows to respond to seasonal water requirements and/or water level monitoring information.
  • Provide the Stormwater treatment from the catchment flows to mitigate sediment and dissolved nutrient flows to the wetland.