Those earlier posts about the possible mass coral bleaching of the Great Barrier Reef are alarming not just in their own right, but because it’s extra worrying that such things are possible in a La Niña year.
Globally, La Niñas are typically cooler and, for northern Australia, stormier. If we can get mass coral bleaching in such years, we can get them pretty much any year. The next El Niño year might not be pretty at all.
Anyway, as we noted earlier, there is a chance we’ll get a third La Niña year in a row, which won’t provide much comfort to flood-hit areas, or those that might just have missed out lately.
Dams, for instance, might stay full for a while, and spill too. During the recent floods near Sydney, Warragamba dam – the city’s largest by far – spilled for more than two weeks and technically continues to spill, WaterNSW tells us.
As of Friday, it was still 100% full, and the spill rate was about 14 gigalitres a day.
There will be more precise figures later, but Warragamba’s total spill was about 1200GL, or close to 2.5 Sydney Harbours. At its peak rate, the dam was spilling at the pace of about 355GL a day.
While some parts of the Hawkesbury-Nepean River rose more than during the March 2021 floods, the actual spill rate and totals from Warragamba were higher then than during this month’s floods. (At its peak last year, the spill rate reached about 440 GL/day and about 1300GL ended up spilling, WaterNSW says.)
Those figures are a reminder that a lot of water enters the floodplain downstream of the dam, so raising the dam wall by 14m at the cost of $2bn or more, won’t remove the “flood-prone” descriptor for that region.