The effect of altered flow regime on the frequency and duration of bankfull discharge: Murrumbidgee River, Australia

Abstract

On meandering rivers with well-developed floodplains, bankfull stage has geomorphological and ecological significance because it approximates the level of connection between the channel and the floodplain. As a river rises to bankfull stage, sediment begins to be deposited on the floodplain, wetlands are progressively inundated and organisms migrate between the channel and floodplain habitats. On many rivers large headwater dams have reduced the frequency and duration of floodplain inundation downstream. However, the lack of reliable pre-regulation flow data has made it difficult to quantify the effects of river regulation. This study used historical regulated and modelled matural flow data to determine the effects of regulation of the frequency and duration of bankfull flows on the Murrumbidgee River, on of Australia's largest and most heavily regulated rivers. In combination with floodplain surveys the flow data show that regulation has halved the frequency and duration of bankfull flows. This reduction in channel-floodplain connection has implications for the ecological health of the Murrumbidgee River.