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Flood Planning for Dummies


It has taken me some time to comprehend that with different sea level rise policies the sea is going to rise faster in the Eurobodalla than it is in the Shoalhaven. Imagine a Durras Beach that is a few hundred millimetres deeper at the Eurobodalla end than it is at the Shoalhaven end.

Now, while live-streaming last week’s Council meeting I learned that the flood planning level for a development in Orient Street Batemans Bay is 2.64 metres AHD. Just across the estuary mouth at Surfside, it is 3.5 metres AHD. The question must be asked how we are going to stop this flood that is 760 mm higher in Surfside side of the river from flowing downhill and causing a 3.5 metre flood a few hundred metres away in the main street.

To top this off I went to a meeting recently where an ESC planner announced a 5.65 metre AHD flood planning level for Broulee. For anyone who cannot convert AHD to a normal tide reading, add just under a metre. So Broulee’s flood planning level is the height of a two storey house above the high tide level in Candalagen Creek. There can’t be too many properties in Broulee that will be classified “flood free” after this piece of classic flood modelling.

We could all have a laugh if these flood planning levels were not taken seriously by our insurers. Find yourself in a flood prone area and you could be denied flood insurance, or asked to pay a prohibitive premium for full cover. When you try to sell your house, you will find that banks are reluctant to loan money on flood prone properties, and sales will fall through. This impediment will eventually be reflected in the value of houses in your flood prone area.

We don’t want people to be misled into buying houses are genuinely flood prone, but there is evidence of excessive flood planning levels being determined by today’s town planners. A good example is Mummaga Lake in Dalmeny where Council’s consultants modelled peak flood levels in the absence of any recorded flood levels. When challenged by people who did have evidence of the peak levels reached in a number of locations, it was found that the computer models exaggerated those peak levels by up to 1.25 metres.

If our town planners are intent on playing games with computer models and determining flood levels that do not reflect known flood behaviour, we need the State Government to intervene and set flood susceptibility levels that are based on proven flood records.

Viv Sethi


A Guide to adopting a Sea Level Model to suit your agenda

#Opinion #Council #LocalStateFederal

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