MWRPP Report 20.2: Billabongs of the lower Birrarung: native wetland vegetation responses to watering.

Melbourne Water is investigating ecological, social, and Indigenous cultural values of billabongs along the lower Yarra River. The project aims to develop a monitoring program to assess vegetation response to natural and managed watering events, informing adaptive management.Permanent quadrats were established at six priority billabongs with varying connectivity to the Yarra. 'Big old' River Red Gums were surveyed for condition and reproductive output. Environmental watering at Banyule Billabong in spring 2019 reduced exotic plant cover and promoted native wetland plant growth. Billabongs flooding more frequently generally have greater native wetland plant cover and lower exotic plant prevalence.While the required frequency and duration of wetting to maintain native wetland vegetation is unclear, short-duration flooding events (e.g., one month) appear sufficient to kill off above-ground terrestrial vegetation. However, without subsequent flooding, terrestrial vegetation can recover within two to three years.River Red Gum condition was similar across all billabongs, possibly due to groundwater access. A mass flowering event at Banyule suggests flooding may promote reproductive output.Recommendations include continued seasonal monitoring, inclusion of Annulus billabong, annual monitoring of tree flowering, repeated environmental watering where possible, investigation of long-term solutions for certain billabongs, and collaboration with the Wurundjeri Council's Narrap Team to better consider Indigenous cultural values and engage in joint vegetation surveys.