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 . . .

Time and tides

In John Oxley and the chain of ponds, I questioned whether Oxley could have found freshwater ponds downstream from Gregory Park, given that this part of the Western Creek is subject to regular inundation by the brackish tidal waters of the river. The tidal limit of the creek (or at least the drain) is no longer visible, being hidden somewhere underneath Frew Park, Gregory Park, or even further upstream. An article from The Brisbane Courier in 1896 reveals that tidal waters were entering Red Jacket Swamp, where they “killed the vegetation, and so caused it to fester and give off unhealthy odours”.1 Correspondence between Council engineers in the 1930s shows that at that time the tide even reached underneath Baroona Road.

But what about in 1824, when Oxley visited? Could it have been much different then? Since Oxley’s time, the river bed has been extensively dredged, and the bar at the river mouth cut away. Some of the narrower channels have been widened, and most of the riverbank (except in the upper reaches) has been cleared. Changes such as these, particularly the dredging and cutting of the bar, can be expected to affect the tidal dynamics of the river. The question is, how, and how much? Might the tidal limit of Western Creek have been very different in 1824 to what it is now, or even what it was in 1896 (given that dredging began in the 1860s2)?

The Wikipedia page for the Brisbane River, citing the 2001 State of South-east Queensland Waterways Report,3 states that “Historically, the Brisbane River contained upstream bars and shallows and had a natural tidal limit of only 16 km. The current tidal limit now extends 85 km upstream due to continual channel dredging”. If this is true, then the tidal dynamics of the river have changed dramatically indeed.

I’d really love to hear from someone with some insights, or even just some leads, regarding how these changes might have affected the tidal limit of Western Creek. Three things do make me wonder if whether it was indeed lower than Gregory Park. First, there is the way this part the creek is typically drawn on the old maps. The section from McKellar’s 1895 map shown below is a good example. Through the flats of Milton the creek is wide and winding, much like the river itself. Then after it crosses Milton Road, it thins and straightens as it enters Red Jacket Swamp. Second, there is the quote above from The Brisbane Courier, describing how the tidal water killed the vegetation in Red Jacket Swamp. If the swamp was naturally (i.e. historically) tidal, wouldn’t the vegetation in it be adapted to the salty water? And third, Red Jacket Swamp (Gregory Park) is marked on some of the early maps as ‘Water Reserve’. I’m not sure if this means it was seen as a potential water supply, or merely that it was a waterlogged chunk of government-owned land. If it was the former, then surely this land can’t have been much affected by the tides. Can somebody help??

A section of McKellar's 1895 map of Brisbane (retrieved from the Queensland Historical Atlas)

A section of McKellar's 1895 map of Brisbane (retrieved from the Queensland Historical Atlas)

The tides of Toowong

Just over a week ago I took a trip to Toowong Creek, where at Perrin Park you can see a “natural” mangrove-lined channel (though it is clearly not the original channel) giving way to a freshwater stream. The tide was low at the time, but I inferred (okay, guessed) its reach from the character of the vegetation and the quality of the water. Then quite fortuitously, while at the State Archives just the other day, I found a map made by the Queensland Survey Office in 1901 titled “Sketch plan showing position of bridge over Toowong Creek”,4 a portion of which is shown below.

Part of a sketch from 1901 indicating the tidal limit of Toowong Creek (Queensland State Archives Item ID620230)

Part of a sketch from 1901 indicating the tidal limit of Toowong Creek (Queensland State Archives Item ID620230)

Near the centre of the picture is the label “Tidal limit”, pointing to a line drawn across the creek. How does it compare to where it is today? By my reckoning, the limit today is somewhere near the hairpin bend just after the word “Toowong” on the map above. (I will report back once I have actually visited at high tide!) This is about 200 metres further upstream (as the crow flies) than the limit marked on the 1901 sketch.

What does this mean? I’m not sure, since we are not even comparing the same channel. As well as being straighter, the channel through the park today could well be deeper than the old one, which would result in the tide coming further upstream. Without knowing these sorts of specifics, it is hard to draw anything conclusive from this observation. Interesting though, isn’t it?

Notes:

  1. The Brisbane Courier, 24 July 1896, p7.
  2. G.R.C. Mcleod, “A short history of the dredging of the Brisbane River, 1860 to 1910”. This document is available online, and appears to be a chapter of a book, but unfortunately I cannot tell which book this is.
  3. Ivan Holland, Paul Maxwell and Angela Grice, ‘Tidal Brisbane River’, Chapter 12 in State of South-east Queensland Waterways Report 2001, Moreton Bay Waterways and Catchments Partnership, p.75.
  4. Queensland State Archives Item ID620230

A trip to Toowong Creek

Wanting to take advantage of a perfect autumn afternoon, I hopped on the train and went to look at Toowong Creek. My report is here.

The key word is ‘mangroves’. I had no idea there was an intact tidal section of Toowong Creek until this afternoon, so discovering it was a bit of a thrill.

Then again, the creek at Perrin Park isn’t really intact at all is it? It’s dead straight while the original creek was as winding as the rest of them. Can someone tell me about the history of this place?

New page – John Olxey and the chain of ponds

Happy Easter!

Though I’m feeling slightly guilty for being inside when the weather is so stunning, I’m glad to announce that I’ve posted a new page to the site. John Oxley and the chain of ponds explores Oxley’s trip up the Brisbane River in September 1824, during which he landed near Western Creek and discovered a “chain of ponds watering a fine valley”. I’ve done my best to explore not only what Oxley’s observations can tell us about Western Creek, but also what our knowledge of Western Creek can tell us about just where Oxley may have landed and discovered the chain of ponds.

I hope you enjoy it. And as ever, please let me know if you have any insights to share, any questions to raise, or if you simply happen to find a mistake!

-Angus