Environmental character and history of the Lake Eyre Basin, one seventh of the Australian continent

One of the world\u27s largest internally drained (endorheic) basins, the 1.14 million km2 Lake Eyre (hydrological) Basin (LEB), covers nearly 15% of the Australian continent. Palaeoclimatic and associated flow regime variations are recorded in an archive of fluvial, aeolian and lacustrine sediments that are particularly accessible for deposits from the past ~ 300 ka, and are especially relevant for the past ~ 50 ka during which humans have inhabited Australia. Due to its great size, economic resources and diverse latitudinal extent, it has for over six decades been the focus of environmental, scientific and resource-based studies across numerous disciplines. With an emphasis on assessing the scientific and environmental research over this period, this paper is divided into four parts: Part A provides an introduction and background. Part B provides the geological history, including evidence of substantial Tertiary and Quaternary climate change. Part C covers the contemporary environmental conditions, and Part D presents a conclusion and summary. This not only represents the first comprehensive review of current knowledge of any of the world\u27s truly large dryland drainage basins, but also highlights how more multi-disciplinary research is required. Key remaining questions revolve around the impact of global weather systems on the LEB; the lake-level story in relation to a more precise picture of Late Quaternary climate change; the role of humans and climate in the demise of the megafauna; modern hydrological changes; the role of vegetation in altering channel morphology and flow efficiencies; and nature of flood transmissions

Anabranching and maximum flow efficiency in Magela Creek, northern Australia

Anabranching is the prevailing river pattern found along alluvial tracts of the world's largest rivers. Hydraulic geometry and bed material discharge are compared between single channel and anabranching reaches up to 4 times bank-full discharge in Magela Creek, northern Australia. The anabranching channels exhibit greater sediment transporting capacity per unit available stream power, i.e., maximum flow efficiency (MFE). Simple flume experiments corroborate our field results showing the flow efficiency gains associated with anabranching, and highlight the prospect of a dominant anabranch, which is found in many anabranching rivers. These results demonstrate that anabranching can constitute a stable river pattern in dynamic equilibrium under circumstances in which a continuous single channel would be unable to maintain sediment conveyance. We propose the existence of a flow efficiency continuum that embraces dynamic equilibrium and disequilibrium (vertically accreting) anabranching rivers

Continental aridification and the vanishing of Australia\u27s megalakes

The nature of the Australian climate at about the time of rapid megafaunal extinctions and humans arriving in Australia is poorly understood and is an important element in the contentious debate as to whether humans or climate caused the extinctions. Here we present a new paleoshoreline chronology that extends over the past 100 k.y. for Lake Mega-Frome, the coalescence of Lakes Frome, Blanche, Callabonna and Gregory, in the southern latitudes of central Australia. We show that Lake Mega-Frome was connected for the last time to adjacent Lake Eyre at 50-47 ka, forming the largest remaining interconnected system of paleolakes on the Australian continent. The final disconnection and a progressive drop in the level of Lake Mega-Frome represents a major climate shift to aridification that coincided with the arrival of humans and the demise of the megafauna. The supply of moisture to the Australian continent at various times in the Quaternary has commonly been ascribed to an enhanced monsoon. This study, in combination with other paleoclimate data, provides reliable evidence for periods of enhanced tropical and enhanced Southern Ocean sources of water filling these lakes at different times during the last full glacial cycle. © 2011 Geological Society of America

Stream channels of the Illawarra

Streams that flow from the IIlawarra escarpment are mostly small and may not flow all year, but because of regional topography, climate, and their rather unusual geomorphology, they are capable of flooding in a manner unrepresentative of their small size (Neller, 1980). This problem of flooding is made all the more important because of the extent of agricultural and residential development on the region\u27s floodplains (Fig. 1)

Why some alluvial rivers develop an anabranching pattern

Anabranching rivers have been identified globally, but a widely accepted and convincing theoretical explanation for their occurrence has remained elusive. Using basic flow and sediment transport relations, this study analyzes the mechanisms whereby self-adjusting alluvial channels can anabranch to alter their flow efficiency (sediment transport capacity per unit of stream power). It shows that without adjusting channel slope, an increase in the number of channels can produce a proportional decrease in flow efficiency, a finding particularly relevant to understanding energy consumption in some braided rivers. However, anabranching efficiency can be significantly increased by a reduction in channel width, as occurs when vegetated alluvial islands or between-channel ridges form. The counteracting effects of width reduction and an increasing number of channels can cause, with no adjustment to slope, an otherwise unstable system (underloaded or overloaded) to achieve stability. As with other river patterns, anabranching can be characterized by stable equilibrium or accreting disequilibrium examples

Macrochannels and their significance for flood-risk minimisation, West Dapto, New South Wales

A prominent characteristic of streams draining catchments in West Dapto, New South Wales, are well developed macrochannels that have formed within alluvial terraces in mid-catchment zones. A detailed hydraulic modelling study using HEC-RAS, HEC-GeoRAS and Arcview GIS indicates that these macrochannels are scaled to accommodate high magnitude floods. They offer a significant degree of natural protection from flood events up to and in excess of 100 years recurrence interval, essentially by operating as \u27bankfull\u27 channels during such events. Macrochannel landforms can be clearly distinguished and mapped on fine-scale digital elevation models (DEMs) and other GIS data sources such as rectified aerial photography, offering the opportunity to integrate analyses of fluvial landforms and channel processes into hydraulic modelling studies, and ultimately, flood-risk avoidance strategies. Such an approach has the potential to improve on traditional flood risk avoidance methods that are focussed primarily on design-flood heights by enabling the interpretation of hydraulic modelling outputs in the context of fluvial landforms that exert a significant control on flood behaviour

Temporal and spatial adjustments of channel migration and planform geometry: Responses to ENSO driven climate anomalies on the tropical freely-meandering Aguapeí River, São Paulo, Brazil

Two reaches of Aguapeí River, a left-bank tributary of the Paraná River in western São Paulo state, Brazil, were studied with the objective of assessing the role of bend curvature on channel migration in this wet-tropical system and examining if land-use changes or ENSO (El Niño Southern Oscillation) driven climate anomalies over nearly half a century have changed migration behaviour and planform geometry. Meander-bend migration rates and morphometric parameters including meander-bend curvature, sinuosity, meander wavelength and channel width, were measured and the frequency of bend cutoffs was analysed in order to determine the rate of change of channel adjustment over a 48year period to 2010. Results show that maximum average channel migration rates occur in bends with curvatures of about 2-3 r c /w, similar to other previously studied temperate and subarctic freely meandering rivers although not as pronounced and with a tendency to favour tighter curvature. From 1962 to 2010 the Aguapeí River has undergone a significant reduction in sinuosity, a shift from tightly curving to more open bends, an overall decline in channel migration rates, an associated decrease in the frequency of neck-cutoffs and an overall increase in channel width. As the majority of the drainage basin (96%) was already deforested in 1962, channel form and process changes were, unlike an interpretation for an adjacent river system, not attributed to altered land-use but rather to a sharp ENSO-driven increase in the magnitude of peak flow-discharges of some 32% since 1972. In summary, this research revealed that recent climate and associated flow regime changes are having a pronounced effect on river channel behaviour in the Aguapeí River investigated here