Palaeohydrology of lowland rivers in the Murray-Darling Basin, Australia. (15th November 2018) - Hesse, Paul P.
Abstract: This study derives a new function describing the relationship of channel bankfull discharge (Qbf ) 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 Qbf, declining in the Holocene. The Qbf of modern MDB rivers is correlated with total catchment precipitation but comparison with palaeochannel Qbf 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- Qbf 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 CO2 feedbacks with vegetation cover. Significantly enhanced MIS3 Qbf 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.