An Environmental Impact Study for a proposed fancy new resort here in Cairns was released on Friday.

http://eisdocs.dsdip.qld.gov.au/Active%20Projects/Aquis%20Resort%20at%20the%20Great%20Barrier%20Reef/EIS/Aquis%20EIS_DIGITAL_Executive%20Summary.pdf

The basis of the resort, as can be seen in the following image, has a moat around it.

The study states:

The main design-related constraint to groundwater is the lake that is required to be constructed on the eastern lots as a flood mitigation solution. The water quality needs of this lake require it to be some 4 m deep and this will intersect the upper aquifer and therefore interact with groundwater. The lake water quality solution requires that seawater be pumped into the lake constantly.

Over a very short period of time, the water in the lake will become saline, approaching the salinity of Richters Creek at most times. Without mitigation, this water has the potential to interact with adjacent groundwater and make it saline.

The adopted design solution is to quarantine the lake from groundwater, either by lining its base and sides, or by constructing waterproof cut-off walls beside the lake down to the impermeable clay layer that exists at a depth of about 7-10 m. Both of the solutions are practical and the preferred approach will be determined during detailed design.

They seem to be going to a lot of effort and expense to use seawater, when I would have assumed fresh water would allow for a much nicer environment and lower maintenance. So why aren’t they? And how does a lake assist in flood mitigation in the first place?

Thanks for that CS.

Looks like it’s time to make a cup of tea and not mow the lawn :)

Unless they drain the lake just before a cyclone or decent low, I can’t see it buffering the vast amounts of water that comes down through that system. Even then, It’d fill in the fist day and then be pretty much useless.

Those crazy Queenslanders.

> The lake water quality solution requires that seawater be pumped into the lake constantly.

Not such a good idea, unless they want to guests to have a place to fish for salt-water fish without leaving the resort.

I would guess that the decision to use salt water came about because it was originally planned with fresh water but evaporation rates are high and there’s no catchment area available for free fresh water refill.

The shape of the buildings imitates the shape of a cyclone – are they trying to send a message to tourists? The actual performance of the buildings in a cyclone would depend on the details, but the shape doesn’t seem to be chosen with minimising wind speeds and forces in mind.

> how does a lake assist in flood mitigation in the first place?

The most obvious is that perhaps the material dredged from the lake is used to raise the foundations of the resort to lift the whole of the built-up part of the resort above flood level.

mollwollfumble said:

> how does a lake assist in flood mitigation in the first place?

The most obvious is that perhaps the material dredged from the lake is used to raise the foundations of the resort to lift the whole of the built-up part of the resort above flood level.

I think you are on to something, the resort is going to be 5m above natural ground level.

Given the tidal variance up that way; twice daily it could end up being less of a moat and more of a mud flat…

This is an interesting little read and very relevant to the site. The comments about the Barron silting up with the result of more water being forced through Thomatis creek are very true. At low tide the other week, I walked from Machans Beach to the Southern bank without getting my feet wet.

http://www.cairnsblog.net/2009/09/moratorium-on-development-in-barron.html

I haven’t finished reading the EIS yet, but I’m seeing a lot of issues already.