Flood Rains !

  A lot of New South Wales residents are mopping up and trying to get their lives back in order after the worst flood in living memory and they will be astonished to learn that while Warragamba dam was overflowing and contributing to their misery, the Sydney desalination plant was running at full tilt and adding fifty milllion litres of water a day to the flood.

There is a lot of criticism levelled at the water authorities because this heavy rain event was predicted and the Warragamba level could have been lowered beforehand to reduce the risk of flooding.  That would have been a risky option if the rainfall had been less than expected because Warragamba is the key  source of Sydney's drinking water.

This big rain event actually delivered  1212 gigalitres to the Warragamba catchment area, which is sixty percent of the dams capacity.  For those not familiar with the gigalitre term, that is 1,212,000,000,000 litres so a major overflow was inevitable.

It was not so long ago that Sydney had water restrictions imposed because of falling catchment levels and today Warragamba is near full capacity.  There is a plan in place to  raise the wall level to increase storage but that would inundate a lot of farmland and historic sights  and we would still get flooding if we had a repeat of this recent rain event.

Keeping that $2.3 billion desalination plant running when the dam was overflowing does make a lot of sense when you consider what the floods left behind.  Flooded home owners are dealing with mud that washed into their homes and in many areas there is a critical shortage of safe drinking water.

A lesson was learned from the disastrous  2013 Brisbane flood which so contaminated the water supply that drinking water was being drawn from a desalination plant on the Gold Coast as a health initiative. There was no shortage of drinking water in Sydney during this flood, despite the water flowing into Warragamba being polluted to below a safe level.

Science tells us that one of the effects of global warming will be intermittent rain variations.  This unusually heavy rain event is part of that pattern, just as we can expect more droughts over a longer period of time.  Given time, the sediment contained in the flood will settle to the bottom of the Warragamba catchment and the inflow will be safe to drink, but until that settles the flow from the desalination plant will be critical.

It is doubtful if weather prediction will ever become reliably accurate.  Drinking water is as essential for human life and if Australia is to receive a drier climate because we live in a warmer world, keeping the taps flowing will probably depend on more desalination plants.

The tricky bit will be how we deal with excess rain like this recent flood event.  If the scientists are right we may have to deal with it on a more regular basis  !