Sydney is a big place. It can drizzle for days on the coast while the catchment area in the highlands remains bone dry. At other times, certain weather patterns see days of soaking rain fall across the entire system, the ground becomes sodden, drains are full and water has nowhere to go. The four major river systems within the Sydney basin become swollen and threaten to burst banks as they’re unable to effectively take sufficient water to sea.
A number of years ago, Sydneys’ major water supply, Warragamba Dam was down to around 40% of the 2.5 million mega-litre capacity. The threat of us running out of water became real enough for the government of the time to build a desalination plant to convert seawater to fresh, then pump it into the water supply network. That was done in quick time, with great expense and of course it seemed to trigger immediate rain!
Warragamba Dam today keeps relatively full and large rain events now make her overflow. While large amounts of water may be released, excess can still spill over the top, becoming uncontrollable. At its’ worst, residents on low
