Close to the brink

| No Comments
Brisbane's flooding came very close to being a lot worse -- from the Melbourne Herald Sun:
A few more inches and heaven help Brisbane

brisbane.jpg


Here�s how close to utter disaster Brisbane came during last month�s floods. This is the Wivenhoe dam, built to save the city from flooding, at the moment its operators were desperately trying to lower the levels before it overtopped and parts of the dam gave way.

Reader Bruce explains:
Not many people have seen this picture yet. This is Wivenhoe Dam at its peak, i.e. at 191+% capacity.

Note that the main 5 floodgates are fully open. Note also the spray / white water just visible above the trees beyond the right hand end of the dam wall. This is from the spillway which is cut into the base rock and is out of sight to the right (west) of the wall you can see.

Brisbane dodged a very big wet bullet in those 24 hours, no thanks to Anna Blight and her minions in Queensland water.
This is why those floodgates were turned on full:
These calculations, yet to be tested by SEQWater, show that the urgent release from the dam of huge volumes at unprecedented rates of flow of up to 7500 cubic metres per second, when the operators were gravely concerned late on January 11 that the dam�s rising levels could trigger a collapse of the system, produced most of the flood in the Brisbane River....

Wivenhoe Dam engineering officer Graham Keegan�s ... 20-odd emails - from January 5 until the crisis at the dam had passed late the following week - become urgent in tone early on Tuesday, January 11, with notification that �we are entering conditions where dam safety overrides other concerns - although minimisation of urban flooding remains very important�.

A few hours later at 9.50am he reported �the flood situation has moved into a critical phase�.

Communications with the FOC were difficult, river levels were rising rapidly, and the dam�s flood storage capacity was diminishing.

By that evening, Keegan ...warned that the dam was expected to reach �a maximum level of 75.5m provided no further significant rainfall occurs�.

�This is 0.1m below the trigger level for (an uncontrolled discharge) - this is the major focus of the current release strategy,� Keegan said....

A collapse of Wivenhoe, which would occur from over-topping because of the inflow from the catchment exceeding outflow from the dam�s gates, would be catastrophic. An engineering paper by the dam�s operators a decade ago found that �the population at risk within a distance that would result in less than three hours� warnings of a dam failure is between 57,000 and 244,000, depending on the time of day and nature of the breach�.

Since a safety upgrade a few years ago, keeping water below three collapsible engineered levee banks, known as �fuse plugs�, is the key to maintaining control of the dam. Should the levels rise to 75.7m and trigger a fuse plug, a very large release occurs to ease pressure, but the outpouring is not controlled by any gate - only by the speed at which the levee or bank is eroded by the water.
The link above: the operators were gravely concerned late on January 11 that the dam�s rising levels could trigger a collapse of the system goes to a damning article at The Australian:
The great avoidable flood: an inquiry's challenge
At 12.26pm on Wednesday, January 5, those in the loop for receiving advice on the operations at Wivenhoe Dam received a timely alert.

It was headed "Bureau of Meteorology (BOM) Severe Weather Warning - Dam Flood Operations". Its author, Wivenhoe Dam engineering officer Graham Keegan, wanted to ensure that those authorised to receive his emails understood that significant rainfall of 100mm to 200mm "may occur during the next few days".

Relaying information from his colleagues at the dam's Flood Operations Centre (FOC), he added: "Somerset and Wivenhoe Dams are still above (full supply level) and rising slowly due to continuing base-flows from their catchments. As the catchments are still wet it is likely that we will be releasing floodwaters in the near future if BOM's forecasts are accurate. Please be prepared. We will keep you up to date with our plans as this event develops."
It will be interesting to see if the people responsible for the waffling will be sacked. A tragic story...

Leave a comment

January 2021

Sun Mon Tue Wed Thu Fri Sat
          1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
31            

Environment and Climate
AccuWeather
Cliff Mass Weather Blog
Climate Depot
Ice Age Now
ICECAP
Jennifer Marohasy
Solar Cycle 24
Space Weather
Watts Up With That?


Science and Medicine
Junk Science
Life in the Fast Lane
Luboš Motl
Medgadget
Next Big Future
PhysOrg.com


Geek Stuff
Ars Technica
Boing Boing
Don Lancaster's Guru's Lair
Evil Mad Scientist Laboratories
FAIL Blog
Hack a Day
Kevin Kelly - Cool Tools
Neatorama
Slashdot: News for nerds
The Register
The Daily WTF


Comics
Achewood
The Argyle Sweater
Chip Bok
Broadside Cartoons
Day by Day
Dilbert
Medium Large
Michael Ramirez
Prickly City
Tundra
User Friendly
Vexarr
What The Duck
Wondermark
xkcd


NO WAI! WTF?¿?¿
Awkward Family Photos
Cake Wrecks
Not Always Right
Sober in a Nightclub
You Drive What?


Business and Economics
The Austrian Economists
Carpe Diem
Coyote Blog


Photography and Art
Digital Photography Review
DIYPhotography
James Gurney
Joe McNally's Blog
PetaPixel
photo.net
Shorpy
Strobist
The Online Photographer


Blogrolling
A Western Heart
AMCGLTD.COM
American Digest
The AnarchAngel
Anti-Idiotarian Rottweiler
Babalu Blog
Belmont Club
Bayou Renaissance Man
Classical Values
Cobb
Cold Fury
David Limbaugh
Defense Technology
Doug Ross @ Journal
Grouchy Old Cripple
Instapundit
iowahawk
Irons in the Fire
James Lileks
Lowering the Bar
Maggie's Farm
Marginal Revolution
Michael J. Totten
Mostly Cajun
Neanderpundit
neo-neocon
Power Line
ProfessorBainbridge.com
Questions and Observations
Rachel Lucas
Roger L. Simon
Samizdata.net
Sense of Events
Sound Politics
The Strata-Sphere
The Smallest Minority
The Volokh Conspiracy
Tim Blair
Velociworld
Weasel Zippers
WILLisms.com
Wizbang


Gone but not Forgotten...
A Coyote at the Dog Show
Bad Eagle
Steven DenBeste
democrats give conservatives indigestion
Allah
BigPictureSmallOffice
Cox and Forkum
The Diplomad
Priorities & Frivolities
Gut Rumbles
Mean Mr. Mustard 2.0
MegaPundit
Masamune
Neptunus Lex
Other Side of Kim
Publicola
Ramblings' Journal
Sgt. Stryker
shining full plate and a good broadsword
A Physicist's Perspective
The Daily Demarche
Wayne's Online Newsletter

About this Entry

This page contains a single entry by DaveH published on February 6, 2011 2:43 PM.

Luddites on parade was the previous entry in this blog.

A great demonstration of Nuclear Power is the next entry in this blog.

Find recent content on the main index or look in the archives to find all content.

Monthly Archives

Pages

OpenID accepted here Learn more about OpenID
Powered by Movable Type 5.2.9