Environmental flows support waterways that receive less water than they need. Flow recommendations are therefore typically based on the minimum requirements to maintain functioning ecosystems, in the face of water scarcity. Urbanising catchments, however, have an abundance of flows. So, can we use these to reduce environmental flow shortfalls? And can we define ecological and physical thresholds to characterise the maximum beneficial flows for waterways?
This project investigated the maximum beneficial flow recommendations for Jacksons Creek, Sunbury. An expert panel was asked to assess the conditions under which waterway values may be impacted by flow changes. The maximum flow recommendations were then based on the disturbance thresholds for key values in the system.
Since the Millenium Drought, Jacksons Creek has experienced a step change decline in stream flow. If managed appropriately, urbanisation and increasing stormwater volumes can reduce system shortfalls. For this, maximum flow thresholds need to be set to limit harm. In Jacksons Creek, flow thresholds were predominately driven by vegetation and geomorphology. The development of these recommendations demonstrated the need to align with ecological limits at a finer scale than minimum environmental flow recommendations are made. For example, a more conservative maximum flow was recommended during the primary vegetation growth and recruitment period; ensuring flow variability is maintained even when “baseflow” conditions are set.
The new recommendations allow waterway managers maintain the benefits of environmental flows, while also managing the threats posed by increasing urban runoff. They allow more flexibility to increase the potential environmental demand, catering for greater volumes of water to be released in times of abundance. This increases the agility of stormwater harvesting schemes, while also protecting waterways. Many catchments across the landscape are experiencing rapid urban development. Catchment managers can apply this methodology to manage harvested stormwater for environmental benefit.