I wanted to start this thread, as we now watch in anticipation of potential events 22-29th January, and questions start being raised in regards to the performance, levels and possible mitigation by our dams in Qld (esp WIvenhoe and Somerset, but also the Hinze Dam).





Currently we have the following (as @ 22.01):
SOMERSET - @ 1205 - 99.04m (0.4cm above FS)- steady
WIVENHOE - @ 1229 - 64.00m (3.0m below FS) - steady

HINZE - @ 1304 - -13.22 (m below spillway) - falling

Locke - do you have the figures handy for what Somerset and Wivenhoe were going into last January's flood event?

Locke may have exact figures, but if I remember correctly it was around the 130% mark going into the weekend of January 8-9. They did very minor releases during that weekend and then the floodwater poured in on Monday and Tuesday, jumping it up as high as 191%.

The fact it's around 80% now means we'd need even more inflows into the catchment than last year to cause similar flooding. However, the risk is of course heavy rainflow below Wivenhoe or into the Bremer/Lockyer Creeks again.

It will be very interesting to watch dam levels and inflows over the coming days though.

Wivenhoe was at 101% going into last years floods. Not sure about Somerset but probably at 100%.

The total inflows for last years event were arount 2.7 million megalitres. The 25% reduction in capacity leading into the wet season has given them an additional 370,000 megalitres to play with.

Yeah somerset was constantly over the 100%. It was 102.9% on the 4 Jan and then it peaked at 189.7% on the 13 Jan. On the same dates wivenhoe was 102.1% (4 Jan) and 186.5% (13 Jan.

Just for interests sake Toowoombas dams are at 98.6%

Cooby dam - 96.5% (19,015 ML)
Cressbrook dam - 99.3% (78,333 ML)
Perseverance dam - 97.8% (26,304 ML)

Hopefully we can snag around 100mm over the next week to push all the dams over 100% again

These figures are quoted in the report for DERM/inquiry.
7:42am Thu 6 Jan 2011:
Wivenhoe: 67.31m
Somerset: 99.34m

3pm Fri 7 Jan 2011:
Wivenhoe: 68.03m
Somerset: 99.94m

1am Sun 9 Jan 2011:
Wivenhoe: 68.63m
Somerset: 100.32m

So it depends on when you consider the "start" of the flood event actually is. To my knowledge it hadn't touched 100%/67m at Wivenhoe for like a month, but it wasn't significantly above it.

More info is in the report.

I presume posters here are dismissive of the suspiciously timed article in yesterday's Australian.

SEQ rivers and Dams seem to be coping quite well. Some steady increases though.
http://www.bom.gov.au/qld/flood/seast.shtml

I think the rain over the last 24 hours would've served to prime the catchments in most cases. Very interesting to see how the river levels look if the forecast totals for the next 24-36 hours come off.

No significant inflows yet. That will change in the coming 24-48 hours if GFS is accurate.

300+ mm in the space of 24 hours would be very similar now to one of the 2 big inflow events that occurred last year. Wivenhoe should comfortably handle that with releases in the 1500m3 sec range. What impact this has down stream will depend on how much of the projected rainfalls below wivenhoe as well.

Thanks somebody - thats exactly what I was after

So looking at the current obs compared to last year and yesterday:

SOMERSET
6 Jan @ 0742 99.34m
7 Jan @ 1500 99.94m
9 Jan @ 0100 100.32m

22 Jan @ 1205 99.04m (4cm above FS) steady
22 Jan @ 1328 99.06 m (6cm above FS) rising

23 Jan @ 1008 99.00m (at FS) rising

WIVENHOE
6 Jan @ 0742 67.31m
7 Jan @ 1500 68.03m
9 Jan @ 0100 68.63m

22 Jan @ 1229 64.00m (3.0m below FS) steady
23 Jan @ 0950 64.04m (2.96m below FS) falling

HINZE
22 Jan @ 1304 -13.22 (below spillway) falling
23 Jan @ 1002 -12.88 rising

Hinze is the only one with any real increases (as would be expected), although i think we will see that change over the coming days.

I still don't think releasing water from Wivenhoe to keep it at the 75% is a good idea right now! With potentially anywhere from 200mm up to 700mm forecast for the next week, if it falls above the dams thats fine... but anything falling below the dams is already going to cause flooding, and would only be exacerbated by any releases now. If the dam cant mitigate flooding with the flood mitigation supply PLUS the extra 25% from last year, then its just not meant to be!!

And looking at the radar currently, quite a lot is falling on or below the dam. If that rain continues in the lower Brisbane catchment it'd be pretty silly to add releases to it. But can they afford to wait?

Personally - yes I think they can. Anyone who especially after last year still thinks Wivenhoe is there to "save" Brisbane from floods is mistaken. Wivenhoe was not built to stop floods, it was built to (a) store water and (b) mitigate floods - I can't understand why the powers that be won't let it function as its supposed to rather than bowing to the pressure of the public.

Not to mention, I've stopped reading the comments on the Courier Mail page about the floods today... full of people saying "let the water out of the dams" without realising the ramifications. I swear, many people still think that water let out now will be out to sea within a few hours.

But they can pull the plug out of their bath and it goes very quickly!
Gotta love the Courier Mail (and it's readers)!

You would've thought with last year that the flood peak came after 2 days of relatively rain-free weather that the time lag from release from Wivenhoe to appearing at the lower reaches would give them a clue, hey?

Conversely I have friends who are dismissive of the threat altogether. "It's not going to flood". After 1 rainy day primarily on the coast? No. But if we were to have 3-4 consecutive days like this, including catchment rain, the risk would be there.

I don't understand people panicking. And I don't understand people completely dismissing the chance of a flood at all.

This is the link that I posted in another thread.
http://www.seqwater.com.au/public/dam-levels
Its only updated once a day but shows if they are releasing water & where from.
Yesterday it showed a lower dam level but they were releasing as they are today.

They have a policy in action of keeping it at 75%. So they will continue releasing small amounts to keep it at that level. I don't necessarily agree with that given the current rainfall situation (as more water being released into the lower Brisbane river combined with runoff from the rain means higher levels, especially with current high tides)...but it is what it is.

I think thats what Locke was referring to above too Coxy, which will be interesting to see - the 75% is the new FSL essentially, so do they keep it at that, or use the manual procedures of comparing inflows and outflows etc and let the dam mitigation to a certain event take over? they couldn't possibly let it stay at 75% and keep releasing if there was the prospect of severe flooding downstream from rain fall below the dam? Locke - you know more about the damn than I do - whats your thoughts?

Sorry, i noticed my dates above were wrong too lol:
23 Jan @ 1229 64.00m (3.0m below FS) steady
24 Jan @ 0950 64.04m (2.96m below FS) falling
24 Jan @ 1433 64.06m (2.94m below FS) rising

It appears there are in fact releases happening from Wivenhoe:
24/01 0405 27.31
0419 27.35
0421 27.41
0426 27.50
0434 27.54
0453 27.57

24/01 1253 27.56
1302 27.62
1310 27.67
1456 27.69

(Refer here:http://www.bom.gov.au/fwo/IDQ65389/IDQ65389.540178.tbl.shtml)
Looked like they ceased around 5am this morning, and then began releasing again from 1300-1500. It seems to have stayed steady since then.

Yes, when they said there were no planned releases I think they meant in excess of the current small releases to keep it around 75%. Fairly misleading message they sent anyway.

The problem is the W1 strategy outlined in the manual is for use when the dam level is between 67 and 68m. I'm not too sure whether they will commence gate operations until the dam reaches 67m. I know they have started flood operations which means they are staffing for the event and preparing for action if needed but I also saw on an earlier post they have no plans for gate releases in the next 24 hours.

Its also worth noting that inflow into the dam has been minimal to this point and if the rainfall continues to remain coastal we may not see a release at all.

There would be a certain irony to having a significant rainfall event for SE QLD with no dam release and then have the dam run dry in 5 years if no follow up rain occurs.

I'm curious though, what level of rain would be needed below Wivenhoe to cause the Lower Brisbane/Bremer to break its banks? I would've thought apocalyptic levels of rainfall...but wondering if apocalyptic can be numerically defined.