The Centre For Water Research

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During spring 1998, a large flood event occurred in Lake Burragorang, the major supply to Sydney, Australia. Using a combination of numerical modelling and field data analysis, CWR was able to demonstrate the levels of insertion and dilution as well as the effect of internal seiches on advecting poor quality water past the intakes. The volumes, times and levels of insertion are shown in FIGURE 1 for the two important inflows: Werriberri, a small inflow located close to the dam wall, and Wollondilly the largest inflow to the reservoir.

FIGURE 1: Elevation/time contours of tracer (log scale) introduced by the Wollondilly (left panel) and Werriberri (right panel) inflows. The colour indicates the concentration of tracer sourced from that inflow in the water column, with the circle representing the approximate times and sizes of the inflow insertion points. Note the early arrival of the Werriberri water at depth due to its close proximity to the dam wall, and the larger insertions associated with the Wollondilly inflow eventually dominating the water quality of the bottom 60 metres of the water column.