MWRPP Report 14.5: The feasibility of maintaining ecologically and geomorphically important elements of the natural flow regime in the context of a superabundance of flow: Stage 1 – Kororoit Creek study.

This project is testing the extent to which ecologically and geomorphically important flow metrics can be maintained at their pre-development level in the context of an increase in flow volume due to urbanisation. In this first stage of the project, we tested this question for the ephemeral Kororoit Creek catchment. The results demonstrated that each of the flow metrics is drastically changed by the level of urbanisation proposed for the catchment. The testing undertaken demonstrates that it is not possible to return these flow metrics to near their pre-development state without achieving total runoff volume reductions in the range of 70-90% below the fully urbanised state. It should also be noted that only a limited number of stormwater management strategies within that volume reduction range maintain flow metrics close to their natural values.The results of the Kororoit Creek catchment modelling indicate that, at least for ephemeral streams, unless a water balance close to natural is achieved, hydrologic and geomorphic characteristics key to ecological processes and functions will not be retained and the waterway will thus be significantly altered. In any case, the stream's ephemerality and the particular ecological values that are unique to ephemeral stream in Melbourne will be lost.