An event-based approach to the hydrology of arid zone rivers in the Channel Country of Australia

Channel Country rivers drain very large basins, have extremely variable annual flows, and experience very high relative flood magnitudes. Regional relationships describe how mean annual discharge, the average number and length of zero-flow periods, and event duration vary as power functions of drainage area. Flood flows (Q2, Q5, Q10, Q20) vary in a more complex way with drainage area, relationships changing from positive to negative because of increased transmission losses in the larger catchments. An event approach based on three distinct types of event—single, multiple, compound—provides an appropriate vehicle for analysing hydrologic variability. Single events have significantly smaller magnitudes, shorter durations and more rapid times-to-peak. Multiple events, although more akin to compound events than single ones overall, tend to occupy a middle ground, behaving more like single events at smaller runoff volumes and in smaller basins but more like compound ones at the other end of the scale. Generally there is a progressive increase in magnitude, duration, time-to-peak and level of unpredictability from single to compound events. Travel time, a more elusive variable to analyse, decreases log-linearly with increasing discharge in upper reaches but varies nonlinearly with discharge further downstream, reaching an intermediate maximum that is equated with the onset of floodplain flow.