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https://theconversation.com/when-floodwater-reaches-the-sea-it-can-leave-a-50-metre-thick-layer-of-brown-water-and-cause-real-problems-213548>
"Over this wet summer, Melburnians and Sydneysiders have had to think twice
about cooling off at their local beach. Heavy rainfall has swollen rivers and
pumped pollutants, nutrients and murky fresh water far out to sea. Swimmers at
Port Phillip Bay beaches are emerging coated in brown goo, while Sydney’s seas
were contaminated last week.
During 2022, floods repeatedly hit Australia’s eastern seaboard, causing an
estimated A$3.5 billion in damage and tragic loss of life. In Sydney, it was
the wettest year on record, with 2.2 metres of rain falling in the year, twice
as much as usual. The heavy rainfall event in March–April dropped more than 600
millimetres of rain alone.
We don’t normally think about what happens to floodwater once it pulses out to
sea. But we should. Floodwater is fresh. When it hits the sea in large volumes,
it lowers the coastal ocean’s salinity. In our new research, we found
floodwaters in 2022 led to 116 extreme low salinity days off Sydney – ten times
more than the annual average. Extreme low salinity days are those that fall
into the bottom 5% of salinity values ever measured at this location.
Normally, this effect clears within six days. But in 2022, extreme low salinity
persisted for months in the coastal ocean. These plumes of freshwater extended
as far as 70 kilometres offshore – five times further than original estimates.
You could see them from space. For fish, this is confusing and dangerous. For
kelp forests or sponge gardens, it can be lethal."
Cheers,
*** Xanni ***
--
mailto:xanni@xanadu.net Andrew Pam
http://xanadu.com.au/ Chief Scientist, Xanadu
https://glasswings.com.au/ Partner, Glass Wings
https://sericyb.com.au/ Manager, Serious Cybernetics
