Year

2016

Degree Name

Master of Philosophy

Department

School of Earth and Environmental Sciences

Abstract

Australian rivers are generally considered to have high flow variability with large differences between baseflow and flood flows as well as large differences in the volume of floods of various return periods. This comparative study systematically assesses the hydrology of Snowy Mountain rivers to determine whether snowmelt rivers demonstrate similar discharge characteristics to their non-snowmelt counterparts. Historical and current gauging data was used to investigate flood frequency and flow scaling relationships for unregulated alluvial and semi-alluvial rivers in eighteen Snowy Mountain rivers and fifteen temperate east coast and semi-arid non-snowmelt rivers.

The results demonstrate that Snowy Mountain rivers do not exhibit the same hydrological variability as non-snowmelt rivers. By comparison, snowmelt rivers were found to have a strong seasonal discharge pattern and a higher baseflow index. The flash flood magnitude index for the snowmelt rivers (0.27) was lower than the global mean (0.28) and lower than the comparison east coast (0.74) and semi-arid (0.62) rivers. Snowy Mountain rivers demonstrated low inter-annual flow variability through low coefficient of variation values (0.38) that contrasted with those of the east coast (1.19) and semi-arid (1.41) rivers. These results were reflected by Snowy Mountain rivers having the flattest flood frequency ratio curves, the least vertical spread between predicted flow levels of varying average recurrence intervals within a given cross-section and less variability in event-based runoff coefficients. This has implications for unit-discharge relationships, which in turn affects the magnitude of flow scaling by catchment area. Floods were found to become proportionally larger (scaled to catchment area) at all recurrence intervals in Snowy Mountain rivers, but not to the extent that they did in comparison rivers. The drivers of the low inter-annual hydrological variability include a regular, seasonal climate with local conditions that keep the ground moist for months at a time. The baseflows in the Snowy Mountain rivers are higher than in the non-snowmelt settings which works to decrease the difference between mean daily and flood flow rates and volumes.

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