The fluvial geomorphology of the Murray River : the role of inheritance

Abstract

The complex meandering and anabranching course of the Murray River on the Riverine Plain of South-eastern Australia reflects inheritance of characteristics left by its ancestral precursors active during Late Quaternary time. In this study the historical development of the Murray forms a basis for explaining its modern characteristics.Radiocarbon dating supported by a comparison of ancestral river morphology and sediments permits a reconstruction of their evolution and palaeohydrology. Between 16,000 and 13,000 B.P. a major reduction of water and sediment discharge occurred while ancestral rivers changed to predominantly suspended load initiating the smaller Edward and Goulburn Rivers within their floodplains. Derived from these, the Murray formed its present course by a series of diversions around 8 500 B.P. Rates and patterns of pointbar sedimentation and morphologic adjustments related to this event demonstrate the stability of the Murray to the present time. Hydrologic behaviour of the river continues to reflect inheritance from the Edward and Goulburn Rivers in its downstream variations as well as in the adjustments to 45 years regulation. The morphology and sediments associated with the. Murray and its meander pattern demonstrate inheritance also from older ancestral rivers. Those active between 13,000 and 20,000 B.P. were responsible for the large flood­ plains which are traversed by the Murray. The sediments of these now form the banks of the river and exert a major influence in association with discharge on the size, shape and sediment type of the channel and its pointbars. Although visually apparent differences exist between meander patterns along its course, spectral analysis does not discriminate between these. Moreover relationships of its discharge to meander wavelength and those relating channel shape to sediment type are different for the Murray than those developed for North American rivers. Murray data cast doubt on a number of former notions of channel morphologic adjustments to river discharge. The controlling effects of sediment load as well as type on the Murray and its palaeochannels suggest these factors must be included in relationships between morphology and discharge. Otherwise such relationships do not have universal applicability. Show more