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

Abstract Wetland classification has become a primary tool to characterize and inventory wetland landscapes, but wetlands are difficult to classify because they straddle the terrestrial and aquatic boundary and occur in a variety of hydroclimatic and topographic settings. Presently, many ecological wetland classification schemes are focused on the 'hydrogeomorphic' unit, which attempts to account for the physical setting of a wetland. In many cases topographic terms (e.g. flats, slopes) rather than geomorphological terms (e.g. oxbow, floodplain) are used to characterize landforms, and little attempt is made to characterize the process-landform relationships within wetland landscapes. The current misrepresentation of product geomorphology (i.e. topographic rather than landform description) and underrepresentation of process geomorphology (i.e. lacking process-landform relationships) means that many current wetland classification schemes represent an incomplete and static attempt to characterize geomorphologically dynamic wetland landscapes. Here, we use examples from wetlands in the drylands of Africa, Australia, and North America to identify the capacity for adjustment (i.e. form and timescale of adjustment) of wetland landforms and we relate this capacity to the geomorphological concepts of sediment connectivity and landform sensitivity. We highlight how geomorphological insights into process-landform relationships and timescales of landform adjustment can add value to wetland classification efforts, with important implications for wetland management and ecosystem service delivery. We submit that geomorphology has a much larger role to play in wetland characterization and can enhance existing wetland classification schemes. More participation by the geomorphology community in wetland science and more awareness by the ecology community in recognizing and characterizing wetlands as dynamic landscapes will facilitate more effective wetland research and management. Graphical abstract Unlabelled Image Highlights • Hydrogeomorphic wetland classification schemes fail to recognize landform dynamism. • Geomorphological processes determine the capacity for wetland landform adjustment. • Sediment connectivity and landform sensitivity control wetland landform adjustment. • Wetland landform adjustment is a key control on ecosystem service delivery. • Wetland classification should incorporate process geomorphology to aid management. [ABSTRACT FROM AUTHOR]

Abstract This study derives a new function describing the relationship of channel bankfull discharge (Q bf) to channel width in modern rivers of the Murray-Darling Basin (MDB) of southeastern Australia and applies this to dated palaeochannels of seven rivers to quantify late Quaternary discharge history in this important basin. All rivers show high MIS3 and MIS2 Q bf , declining in the Holocene. The Q bf of modern MDB rivers is correlated with total catchment precipitation but comparison with palaeochannel Q bf estimates shows that while enhanced runoff efficiency is necessary to account for much larger late Pleistocene palaeochannels, either lower or higher precipitation rates could have prevailed. A strong association between relative palaeo- Q bf enhancement and temperature suggests a temperature-mediated mechanism controlling river discharge, such as the fraction of precipitation stored as snow and thawing in spring, the enhancement of orographic rainfall, or CO 2 feedbacks with vegetation cover. Significantly enhanced MIS3 Q bf requires an additional mechanism, such as increased rainfall. These findings are consistent with others that increased moisture availability was associated with past colder climates, although this was not necessarily the result of enhanced precipitation. Highlights • Dated palaeochannels of the Murray-Darling basin, Australia, reveal late Quaternary hydrological history. • A regime equation based on modern rivers is used to predict palaeo-discharge. • Discharge of MIS2 and MIS3 palaeochannels was 3–270 times equivalent modern rivers. • MDB palaeochannel discharge follows Antarctic temperature, which determines catchment runoff. • Relatively larger MIS3 MDB palaeochannels require additional moisture sources. [ABSTRACT FROM AUTHOR]

[Display omitted] • Geomorphic river diversity can be explained by a mix of catchment scale controls. • Imposed controls (slope and valley bottom) do not adjust over geomorphic timeframes. • Flux controls (bed material and stream power) are interactions between fluxes. • Assessing controls along long profile can explain the pattern of river diversity. A mix of catchment-scale controls operate to determine geomorphic river diversity in a catchment. These are contextualised here as imposed and flux controls. Imposed controls do not adjust over geomorphic timeframes and produce the environmental setting in which a river functions. Flux controls are dynamic interactions between flow and sediment that heavily influence geomorphic river diversity. We measure and statistically analyse the network scale mix of imposed and flux controls occurring along longitudinal profiles of various shape. We use this to explain the diversity, pattern and sequence of river types at different positions in a catchment. Using the Richmond River catchment, New South Wales, Australia, as our case study we analyse the imposed controls of slope and valley bottom width and the flux controls of bed material size and gross stream power for five river types, ranging from confined continuous rivers in headwaters to laterally unconfined discontinuous rivers in lowland plains. We find that slope and gross stream power are strong, positively correlated controls on all river types, but act most strongly on rivers with continuous channels. In contrast, bed material size is a dominant control on rivers with discontinuous channels. Slope and gross stream power are also critical for determining the downstream pattern of river types along longitudinal profiles. However, the relationship between these controls is complex as not all rivers are influenced by these controls in the same way. Understanding the mix and patterns of controls operating along longitudinal profiles can be used to explain the variability and pattern of river types we see in the landscape. [ABSTRACT FROM AUTHOR]