Palaeochannels of the Namoi River Floodplain, New South Wales, Australia: the use of multispectral Landsat imagery to highlight a Late Quaternary change in fluvial regime

Abandoned channels of ancient rivers are clearly visible on aerial photographs of the Namoi River floodplain in northern New South Wales, Australia. However, the spatial distribution of these palaeochannel systems over many tens of kilometres makes their broad-scale mapping with air photos difficult. Satellite imagery has previously been used to a limited degree in the identification of palaeochannels in many areas, but typically only in single image bands. This study finds that combining and enhancing multiple bands of Landsat 7 ETM+ data improves subtle differences in the spectral reflection of soil moisture and vegetation, aiding palaeochannel identification. These results are much better than using single band data alone in this important agricultural area, one suffering strong water and soil resource pressures. There are several generations of palaeochannels visible on this floodplain, and analysis shows they were very different from the modern rivers; they had greater discharges, longer meander wavelengths and flowed along different courses to the modern rivers. This study supports other recent investigations of the geomorphology and chronology of the Namoi River floodplain that showed that these changes only occurred during the Late Quaternary. These historical changes were not fully recognised until recently, and are different from what was assumed from studies of other riverine plains in south-eastern Australia.