Environmental flows are provided in regulated rivers to maintain and restore riverine environments. Given the expense and political sensitivity of providing water for the environment, greater certainty regarding the expected benefits of environmental flows is required. We assessed the role of managed flows in delivering sediment and plant propagules to facilitate riverbank recovery.
Using artificial turf mats, we investigated sediment and seed deposition from 14 flow events over five years in a heavily regulated lowland river in south-east Australia. At three sites on the Goulburn River, Victoria, mats were used to assess sediment and seed deposition on different geomorphic features along an elevation gradient (bars, benches, banks and ledges).
A total of 540 kg of sediment and 134,527 seeds from 99 plant species were sampled. Mats that were inundated via managed flow releases had an order of magnitude more sediment, and around twice the richness of seed taxa, than mats that were not inundated. Longer duration of inundation was associated with the deposition of more sediment, seed taxa and abundance. More sediment and seed taxa were deposited on low-lying bars than on more elevated features, while seed composition but not abundance varied across features.
Our findings suggest that environmental flows are critical for providing sediment and seed necessary to restore geomorphic condition and promote plant recruitment in regulated rivers. Longer flow durations are likely to provide more sediment and seeds, while high flow events may be particularly important for promoting diverse native riparian plant communities across the full range of in-channel geomorphic features.