Matthew Lambourne, Mullumbimby
I thank Jim Mangelson for confirming (letters, last week) what I said the week before (letters, September 10), that Council asked the developers to restore access along the track at the site of the temporary flood outlet they built in 1973, but did not ask or order them to close the outlet.
It was the developers’ decision to close the outlet, although they probably had little choice – the Shire engineer’s report of 22 June 1976 refers to the company agreeing to ‘restore the ground to its original condition in accordance with its agreement with the Department of Lands’.
In the same report the Shire engineer agrees that Council might be responsible for any increase in flooding caused by the work the developers had done (the early parts of North Ocean Shores), and estimated this might be one to three inches (25–75mm).
In 1995 a flood outlet similar to, and at the site of, the 1973 outlet was modelled. The reduction in flood levels for a one-in-100-year flood was 28mm at the Capricornia Canal, 19mm at Balemo Drive and 24mm at New Brighton.
When the modelled outlet was increased to more than three times the size of the 1973 outlet, the respective reductions were 69mm, 36mm and 59mm.
If such an outlet could be responsibly built (it can’t) it would cost millions of dollars, and the benefit/cost ratios would be minuscule.
This was recognised by Council when they adopted the Marshalls Creek Floodplain Management Plan, without a flood outlet, in 1997, and will no doubt be acknowledged again in the current management plan process.