Downstream hydrogeomorphic changes along the Macquarie River, southeastern Australia, leading to channel breakdown and floodplain wetlands

摘要: Abstract Floodplain wetlands and floodouts in the Macquarie Marshes are fed by numerous anastomosing distributary channels on lower reaches of River, southeastern Australia. River discharge is seasonally annually variable affected both interannual interdecadal climatic trends, related to ENSO IPO. A downstream comparison hydrologic data shows that flows decrease significantly magnitude stream power along allogenic as outflows not matched tributary inputs. Intrinsic geomorphic thresholds lead breakdown trunk into smaller distributaries, with disintegration channelised development extensive low-gradient, dryland alluvial floodplain-fan. Cross-sectional analysis morphology morphometry change accordingly, adjustments planform cross-sectional shape marked reductions channel capacity bed width. Despite monotonic declines river discharge, gross area, there a threshold response. Channel width-to-depth ratio decreases middle then increases, while sinuosity increases until immediately upstream core rapidly straight enter areas breakdown. width greatest plain, allowing broader area floodplain develop, characterised fine cohesive sediments. connection where form Marshes. wetland formation distinct examples nonequilibrium response declining power, which an inherent condition many Australian rivers during Holocene.