Ipswich
AN OBSERVATION OF THE CONFLUENCE OF STATISTICAL ABERRATIONS, DAM RATIOS, TIMING AND UNCOMMON RAINFALL EVENTS THAT COMBINED TO HAVE OUR LEADERS DRAW INCORRECT CONCLUSIONS. THEIR INFLUENCE ON ACTIONS TAKEN.

Author : J. V. Hodgkinson F. C. A. Chartered Accountant : Aug 2006 to November 2013    

The principal thrust of this website is
FLOOD PROOFING BRISBANE from damaging floods to the point of extinction. MITIGATING flooding in Ipswich and Gympie. Putting REAL MEANING into "Drought proofing SEQ" and ensuring our water supplies by natural means well into the future

This is my review based on official statistics and documents. It is done in conjunction with Ron McMah, grazier of Imbil and Trevor Herse, retired of the Gold Coast

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The following indicates that the Bremer River and local creeks that front the Brisbane River were impacted by the Wivenhoe/Somerset catchments. It relates specifically to the 2011 flood. My Ipswich correspondents assure me that 1974 was quite different.

The impact of the releases from the Wivenhoe Somerset are clearly seen from these Seqwater produced hydrographs. I have added a red line at the point where rain ceased.

Releases from Wivenhoe 6 hours.jpg (128681 bytes)Bremer Savages Cross Hydrographs.jpg (109453 bytes)Hydro Moggill Brisbane Port off.jpg (105248 bytes)2011 Major Minor 2011_0001.jpg (138740 bytes)

 

 

 

 

Photos left to right: Dam releases from the Wivenhoe; Hydrographs Savages Crossing and Bremer River; Hydrographs Moggill and Brisbane City; My overlay of Seqwater graph defining the minor and major floods.

First of all the later releases clearly held up the flood after the peak at all points. This has little relevance to the peak of the flood but is an indicator of the "barrier" created at the Bremer River mouth as mentioned in the Ipswich City Council submission.

The second point is that according to the three major hydrology firms engaged by the Insurance Council of Australia, the major release from the Wivenhoe created a rise of 7 metres at One Mile Bridge. The graph of the releases from the Wivenhoe was constructed by me from the Seqwater flood submission.

One Mile Bridge on the Bremer River is 47 Klm from the Bremer River mouth.

This, of course, would have a significant bearing on the flooding in Ipswich from the One Mile Bridge to the Bremer River mouth.

Those Hydrologists ignored altogether the minor flood which also occurred in the Bremer prior to the major flood. This supports my view that there were two floods being a minor flood closely followed by a major flood.

It also contradicts claims at the Flood Inquiry that early release of the minor flood would not have made any difference.

The combination would have resulted in a minor flood all-round. Instead, that volume being 400,000ML, based on Seqwater operational submission, was released at the peak creating creating the scenario outlined by the Insurance Council Hydrologists.

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On flooding in Ipswich the Ipswich City Council had this to say to the Flood Inquiry

The impact of a Brisbane River flood is twofold.

Firstly, it the direct cause of flooding in the southern areas of the City such as the suburbs of Redbank and Goodna.
 

Secondly, a Brisbane River flood can act as a "barrier" to the Bremer River (and other creeks such as Goodna Creek) entering the Brisbane River at the junction of those waterways with the Brisbane River.

As a result water from the Bremer River are then unable to enter the Brisbane River and are forced back up the the Bremer River.

This exacerbates the flood experience in that river and in the creeks, such as Bundamba Creek, that feed into the Bremer River near to its junction with the Brisbane River.

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While the containment of the Inflow from the Wivenhoe/Somerset is our goal, the question arises as to just how much water flows to the Brisbane River from the Bremer River and Lockyer Creek.

The Flood Inquiry has revealed so far that there is no modelling of the influence of the Wivenhoe/Somerset released water on the flows of the Bremer River and Lockyer Creek.

Bremer Rain stations.jpg (91814 bytes)Lockyer rain stations.jpg (121007 bytes)Fourteen rainfall stations were reviewed that were in operation in 1974 and 2011. They covered both catchments.

The combined rainfall for the 1974 and 2011 floods was constant with only a minor variation.

There was fluctuation in the contributions with the Bremer, lower in 2011 than 1974 and the Lockyer higher in 2011 and with a larger catchment. 

Impact on flooding in Ipswich

2011 : This has been dealt with above. It seems that it could have been avoided or largely minimised.

1974 : My correspondents in Ipswich point out that all historical buildings are all above 1893 flood levels.

There is evidence that the 1974 flood was higher than 1893. 

The David Trumpy Bridge gauge shows 1893 at 24.50 metres and 1974 at 20.70 metres. However that gauge is markedly affected by the Brisbane River "barrier". 

Further examination shows that 1893 is indeed less than 1974 and 2011 at least in some areas. For example, Ipswich in 1893 had rainfall volumes of 236mm for major 1893(1), 104mm for minor flood in between and 355mm for major 1893(2). The 1974 volume was 662mm which far exceeded any flood in 1893. 

In the Lockyer Creek, Helidon was the only available Rainfall station covering 1893, 1974 an 2011. The individual rainfall days were not available but the monthly totals read 1893 (for 2 floods) 797mm, 1974 448mm and 2011 395mm.

The requirement to mitigate flooding in Ipswich for a 1974/1893 type flood is still inclusive. My correspondents tell me that it is not possible. They agree that the creeks that join the Bremer near the mouth and those that front the Brisbane River will benefit from the exclusion of the Wivenhoe/Somerset but are doubtful about Ipswich City benefit.

The requirement to eliminate flooding in Brisbane:

The Bremer River and the Lockyer Creek are the main catchment areas that would influence flooding in Brisbane.

With the Wivenhoe/Somerset fully contained they are allowed to run free.

The volumes of flow from the Bremer and Lockyer Creek, on the basis I have adopted to 1,530,000ML or 131% Bremer Lockyer summary 1974 2011.jpg (133671 bytes) of the Wivenhoe Capacity. The 1974 flood period was a little over three days requiring 38% of the capacity of the Wivenhoe dam to be dealt with for each of the three and one half days. The 2011 flood was over a longer period.

If the assessments of 1893 are correct, then the additional volume should be minimal if any. 

 

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The impact of the releases from the Wivenhoe Somerset are clearly seen from these Seqwater produced hydrographs. I have added a red line at the point where rain ceased.

Releases from Wivenhoe 6 hours.jpg (128681 bytes)Bremer Savages Cross Hydrographs.jpg (109453 bytes)Hydro Moggill Brisbane Port off.jpg (105248 bytes)2011 Major Minor 2011_0001.jpg (138740 bytes)Flow Wiv Brem Lock 2011.jpg (83033 bytes)

 

 

 

 

Photos left to right: Dam releases from the Wivenhoe; Hydrographs Savages Crossing and Bremer River; Hydrographs Moggill and Brisbane City; My overlay of Seqwater graph defining the minor and major floods.
Combination of the Bremer/Lockyer/major releases Wivenhoe on the right. Wivenhoe in red and Lockyer/Bremer in blue. Timing every 6 hours from 5th January 2011

First of all the later releases clearly held up the flood after the peak at all points. This has little relevance to the peak of the flood but is an indicator of the " barrier" created at the Bremer River mouth as mentioned in the Ipswich City Council submission.

The second point is that according to the three major hydrology firms engaged by the Insurance Council of Australia, the major release from the Wivenhoe created a rise of 7 metres at One Mile Bridge. The graph of the releases from the Wivenhoe was constructed by me from the Seqwater flood submission.

One Mile Bridge on the Bremer River is 47 Klm from the Bremer River mouth.

This, of course, would have a significant bearing on the flooding in Ipswich from the One Mile Bridge to the Bremer River mouth.

Those Hydrologists ignored altogether the minor flood which also occurred in the Bremer prior to the major flood. This supports my observation that a minor and major flood occurred.

The above is all related to the flood of 2011. My correspondents from Ipswich assure me that the flood of 1974 had a very different result.