Flow regimes influencing riparian vegetation on an unregulated sand-bed stream in the Hunter Valley, NSW

Widden Brook in the Hunter Valley, NSW, is an unregulated active sand-bed stream characterized by high flood variability. The dominant riparian tree on Widden Brook is Casuarina cunninghamiana (River Oak). Successful establishment of River Oaks require bankfull flows that gradually build bars into benches, reducing the frequency of flood scour, and sub-bankfull flows that deposit fine sediment on the benches, enhancing Oak survival and growth. Although River Oaks do not require floods to germinate, seedlings are highly susceptible to water-stress and need a subsequent moist period to establish. The rate at which the water-table falls also influences River Oak survival. Overbank flows are important for the replenishment of soil water and the alluvial aquifer. Many riparian trees use groundwater opportunistically and access during extended dry periods may be critical to their survival. River Oaks on the floodplain and the benches were most likely able to access the water-table during 2006-2008