Bottleneck too costly to remove
THE proposal that the bottleneck in the Mary River at Fishermans Pocket be removed to ease flooding in Gympie has been rejected as unviable and potentially devastating to the environment.
Aurecon examined the possible downstream mitigation idea, but found that opening up the "chokes" at Fishermans Pocket could cost as much as $1.2 billion and would involve the excavation and removal of some 55 million cubic metres of material, a large proportion of which would be rock.
"The cost would run into the hundreds of millions of dollars," the study says.
"At a very generous rate of $10 per cubic metre, this would cost some $550 million to complete (but more likely three to five times this cost)."
Even if economically and environmentally feasible, opening up the bottleneck at Fishermans Pocket would reduce flood levels at Kidd Bridge by only 1.5 metres in a major, one-in-100-year flood, the study found.
"And it is likely to yield lesser benefit at lower flood levels," the report says.
"It should be noted that there would be a significant worsening of flooding downstream from the works, as the effect of the current restriction is to act like a detention basin, with temporary storage upstream and lower flows and flood levels downstream."
Getting the multiple departmental approvals to blast the river bank would be "onerous".
"With only 1.5m of flood relief at Gympie, clearly such a scheme is not viable on any measure and is not worthy of any further consideration."