A floodgate for Western Creek

A sign announcing the construction of a backflow valve at the mouth of Western Creek.

A sign announcing the construction of a backflow valve at the mouth of Western Creek. It is erected on the gate to the footbridge under Coronation Drive. (Photo: S. Cowley)

So, it’s really happening. If this sign is to be believed, then Western Creek is finally going to have its floodgate. The photo was snapped at the entrance to the footbridge under Coronation Drive at the mouth of Western Creek (otherwise known as the Milton Drain) a few weeks ago by Steven Cowley, who has been my eyes on the ground at Western Creek ever since I moved to the southside last year.

The sign doesn’t mention a floodgate, but that is essentially what the ‘devices to be installed’ as part of the ‘Backflow Program’ are. They are contraptions of varying designs that ‘mitigate river water from flowing back up stormwater pipes when the river is in flood’. Such devices have already been installed just downstream near Cribb Street and the Go-Between Bridge. The City Council’s website has a page listing all of the places where backflow devices have been, or might soon be, installed. The page also provides links to the technical reports about these devices that the council commissioned in the wake of the 2011 flood. Continue reading

When waters collide

Just over a week ago I posted about the ‘tidal limits’ of Milton Drain, noting that at a very high tide, the drain is pretty much full to the brim.

Today, I braved weather that ranged between miserable and awful in order to see how the drain held up when it had more than just a high tide to contend with. With the remnants of Cyclone Oswald looming over South East Queensland, Seqwater began releasing water from Wivenhoe Dam on Friday evening, and according to the Seqwater website, the releases are expected to continue for several days. So we have the tides coming in from downstream, the dam releases coming from upstream, and the stormwater from the Western Creek catchment racing through the drains towards the river. What happens when the waters collide?
Continue reading

Milton Drain’s tidal limits

Last Saturday (the 12th of January) we had a particularly high tide. According to willyweather.com, high tide at the Port Office was 2.7m at 10:51am. The Bureau of Meteorology’s tide tables suggest that we won’t get another tide this big (give or take a few centimetres) until the 26th of May.

Tides at the Brisbane Port Office for the week of 8 January 2013, according to willyweather.com.

Tides at the Brisbane Port Office for the week of 8 January 2013, according to willyweather.com.

I was aware of this only because a couple of weeks earlier I had passed by the Milton Drain and noticed that it was unusually full. When I looked up the tide tables to see how that tide rated, I found that an even higher one was coming. So I made a point of visiting the drain at high tide on the 12th of January. I even put a reminder in my phone. Yes, this is the sort of thing that I do.

Here is what I saw:

Milton Drain at high tide on 12 January 2013.

Milton Drain at high tide on 12 January 2013.

The water level must have been barely half a metre below Milton Road. At the other end of Milton Park, the water was just a few centimetres from the top of the concrete:

Milton Drain at high tide on 12 January 2013.

Milton Drain at high tide on 12 January 2013.

Milton Drain at high tide on 12 January 2013.

Milton Drain at high tide on 12 January 2013.

Not much room to move, is there?

I’m not sure how much higher the tides get than this; I’ve never studied them before. Next January, BoM’s tide tables predict a tide about 10cm higher than this one, and the maximum last year was just as high. So it looks like Milton Drain is built more or less exactly to the height of the highest high tide that typically occurs. This is all well and good, unless of course there happens to be stormwater flowing through the drain as well. If a tide like this coincided with heavy local rain, the drain would spill over into Milton Park (as I’m sure it has on many an occasion). And if the river is already swollen from rain further upstream — well, we know what happens then.

What I didn’t think to do was to see if the water was visible through any of the drains in Gregory Park or even Rosalie, as a tide like this would have surely reached that far. I did, however, get down to the river later that afternoon, and saw clear signs that the water had spilled over onto the bike track just downstream of the old floating restaurant. But I didn’t have my camera with me. Perhaps in May . . .

Floods aniversary special

Two years ago today, Rosalie and many other parts of Brisbane were underwater. Any misconceptions we had about the power of Wivenhoe Dam to save us from ever being flooded again were swept away, and before long, attention turned to what, if anything, we could do to stop this from happening again.

In a post in The Forum (actually the first!), a visitor named Barry noted that the Council plans to install a floodgate at the mouth of Western Creek (Milton Drain) to mitigate future flooding in Milton and Auchenflower. As in many other parts of Brisbane in January 2011, the floodwaters that inundated the Western Creek catchment did not spill over the riverbanks, but entered instead via the stormwater drains that discharge to the river. The diagram below, taken from the Council’s fact sheet on backflow flooding, illustrates how this kind of flooding occurs.

Concept diagram of backflow flooding, taken from the Brisbane City Council's <a href="http://www.brisbane.qld.gov.au/downloads/environment_waste/water/Backflow%20Fact%20Sheet%20June%202012.pdf">factsheet</a>.

Concept diagram of backflow flooding, taken from the Brisbane City Council’s factsheet.

The Council has indeed stepped up to the plate and has already started building backflow prevention devices in Milton and elsewhere. And among the areas that have been flagged for future attention is the mouth of Western Creek.

This is a laudable idea, but the Council can hardly claim credit for it. The idea of using floodgates to protect Milton and Rosalie has been doing the rounds for over a century. In a new page entitled Backflow to the Future, or: How we learned to stop worrying and love the floods, I present a retrospective of these past proposals, courtesy of newspaper clippings from The Brisbane Courier and The Courier Mail that I have found while trawling through Trove.

The title of the essay is strictly tongue-in-cheek, and I’ll admit, downright cheeky. I’m not suggesting for a minute that we really enjoy the floods, and I don’t want to offend anyone who has suffered from them. But I do hope to put into stark focus the question of why, after all these years, we have not adopted such simple measures as floodgates to ease the pain. And I confess, the temptation to structure an essay around Dr Strangelove was just too much for me to resist.

I hope you enjoy the new page. It has been a fascinating journey to write.

-Angus

The moon, the drain and the diving bats

I haven’t found the time to do any real research recently, so I thought I’d post some photos instead. I took these back in January and they have been gathering virtual dust on my hard drive ever since. According to the SunSurveyor app on my phone, this was the last time in a while that a full moon would hover over Milton Drain at a low enough angle to catch it reflected on the water. Exactly why I felt the need to capture this event is a good question… probably something to do with seeing the beauty in an otherwise ugly piece of suburban infrastructure. At any rate it made for an interesting photographic challenge.

While I was taking these photos, I occasionally saw what looked like a flying fox (fruit bat) swoop down towards the water and emit a strange sound before skimming the water and flying back to a tree. It looked an awful lot like they the bats were fishing, but I thought that flying foxes only ate fruit. On top of that, I’m not even sure that flying foxes use echolocation (they have big, sensitive eyes instead). So, either they were doing something other than fishing, or they weren’t flying foxes at all. Any ideas???