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 natural flow data to determine the effects of regulation on the frequency and duration of bankfull flows on the Murrumbidgee River, one 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.
River regulation by headwater dams has altered the flow regime of rivers worldwide. For floodplain rivers, reduced connectivity between the main channel and floodplain wetlands has led to a decline in ecological health. Current river restoration theory advocates a return towards a more natural regime of floodplain wetland inundation. However, for many rivers, a poor understanding of the natural floodplain wetland inundation regime has hampered effective restoration management. This paper describes a technique for quantifying the effect of flow regulation on the inundation regime of floodplain wetlands on an extended reach of the Murrumbidgee River, Australia. A series of Landsat Thematic Mapper (TM) images, captured before and after a set of floods, was analysed to describe the relationship between flow and inundation for a 640 km river reach. These data were combined with historical regulated and modelled natural daily flow data to show that river regulation has reduced the duration and frequency of wetland inundation by ∼40%. For the majority of wetlands the capture of small and medium floods in the headwater dams reduced wetland inundation substantially. However, for low connecting wetlands in reaches upstream of the main irrigation off-takes, summer irrigation flows have increased inundation.Extra keywords: integrated quantity quality model, IQQM, Landsat Thematic Mapper, modelled natural flow, remote sensing.
Current high-resolution remote sensing provides the means to accurately map upland swamp boundaries and vegetation communities in eastern Australian coastal woodlands. The aim of this study was to develop baseline methods for upland swamp definition and change detection that can be routinely applied in an operational setting.
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