The Wivenhoe Dam is a duel purpose dam. It has a drinking water capacity of 1.165 million megalitres, plus a much bigger flood mitigation capacity of over 2 million megalitres. Before this rain event drinking water capacity was at less than 60%, and flood capacity was at zero. During the rain event 100% drinking water capacity was reached quickly, but flood mitigation never exceeded 90%. During this week SEQ Water will do a controlled release of stored flood water into the Brisbane River. This will not increase the flood levels, but it will prolong it for several days. The dam operated within capacity, and without it the flood situation would have been much worse.

Here on Moreton Bay we had over 700mm in 3 days, some locations received over 1300mm or more.

thinkabit,
Try thinking long-term. Think not pushing water over the range, think through it. There are many valleys & gorges that will facilitate the flow. Think towns & farming around a permanently flooded Lake Eyre as it was some millions of years ago. Think keeping the great Artesian basin full. The benefits are enormous. As I said, think long-term !

Great idea Indy.

Once my Seniors National Service is up and running, an inland tunnel about 100km long is a fantastic project for the old folk under my command. Yes, wonderful, we'll be using the "The Principle of the Ants", many hands make for light work. Two million senior natcho's, armed with nothing more than picks and shovels tunneling away deep within the Great Deviding Range, fantastic. A quick calculation, if each natcho' removes 1 cubic metre of rock per day, the tunnel will be finished in no time, say 50 years.

I got to give it to you Indy, your ldeas are brilliant, almost as good as mine.

One solution to flooding is to move the towns above any anticipated flood level where it is possible.
Another is to build massive levies and install steam pumps to remove water which falls within the town area.
A third is to raise the town entirely above flood level.
It would take a lot of money but it’d be money saved in the long term, and lots of employment.
There are plenty of examples where individuals have raised their homes above flood level, usually on a steel girder frame.

Indy, tunnels are *VERY* expensive. Just look at how much it costs to make the few kilometers of the cross-river rail train tunnel in Brisbane. And that's in the coastal plain not far below the surface where the dirt is soft, not boring through hard range rock compacted by being 100's of meters below the surface that you want to do.

However, even if you do tunnel through the high part of the range, which would require miles and miles and miles of tunnel, you still have to push water up hill to get to the western side where the farms are. Western Queensland is 100s of meters higher than the coastal side where Wivenhoe is (here's a picture to help you understand this: http://www.nationsencyclopedia.com/Asia-and-Oceania/Australia-TOPOGRAPHY.html ).

And what would you get from this project- a tunnel that you can only use a once or twice a decade for just a few weeks when there is major flooding on the Brisbane river.

Moreover, what do you do with this extremely expensive project that produces a very unreliable water supply? Well you let farmers have the water. Water which they probably don't need anyway or even want at that time- because when the Wivenhoe is spilling like it is now it is more than likely that western part of Queensland also had rain.

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And why do you want the farmer to have this undesired water? You want them to use it for farming. That is, you want them to produce low value stuff compared to the cost of input- ie., agricultural produce. There is no big money in farming- farms provide bugger all return on the cost of the inputs. Compare the profit return of your average farm business (indeed many farmers are lucky if they even make a profit each year) to that of a high value product producing business such as an engineering firm or some other professional business.

It would make way more economic sense to spend the billions you want to spend on your idea on educating the population, either in trades or professions, instead. With education spending the government would achieve a higher return from the investment.

In short your idea is completely bonkers!