But in its executive summary the report finds that lowering Wivenhoe Dam's full supply volume (FSV) to 75 per cent would have reduced the overall flood height in Brisbane, measured at the Brisbane Port Office gauge.

It finds: “reducing the FSV to 75 per cent and using the [updated dam management manual] shows a decrease of the flood peak at the Port Office for the three events [floods in 1893, 1974 and 2011].

“Two out of three of the flood events modelled [1893 and 2011] showed that alternative operation of the Wivenhoe and Somerset Dam may have the potential to reduce peak levels at the Port Office gauge.”

Queensland Natural Resources Minister Rachel Nolan has today submitted this state government-commissioned report to the Queensland Floods Commission of Inquiry.

The report, by engineering consultants GHD Pty Ltd, includes a range of options to control flooding downstream of Wivenhoe Dam.

The report states a two-metre higher dam wall at a cost of more than $800 million would have made a "minimal difference" to flooding in the 2011 and 1974 floods, according to Ms Nolan said.

"It shows that raising Wivenhoe would be an expensive exercise and would not give Brisbane extra flood protection in all cases," Ms Nolan said.

The report models Brisbane's major floods in 1893, 1974 and 2011 and compares the difference between the approach of raising the dam wall and lowering the full supply level of the dam.

"Most significantly, the report finds that a higher dam would have made minimal difference in the 2011 flood and practically no difference in 1974," Ms Nolan said.

" This is because in 1974 most of the water came down tributaries downstream from Wivenhoe Dam."

In April and August this year, LNP leader Campbell Newman suggested raising the Wivenhoe Dam wall.

In March last year, LNP parliamentary leader Jeff Seeney said a “review” was needed for Wivenhoe Dam's “flood buffer” and how much for drinking water.”

The GHD study estimates the cost of raising the Wivenhoe Dam wall by two metres would be about $830 million and take four years to build.

The GHD Pty Ltd study investigates these options:

The study also finds flood damage would be reduced in the Moggill and surrounding areas if alternative water storage spaces could be found on the Bremer River and on Lockyer Creek.

“Additional storage on the Bremer and Lockyer Rivers would have a significant impact on Flood levels at Moggill during the 1974 and 2011 events, reducing damage to low levels,” it finds.

“However it would have limited effect on the 1893 event due to the variability in the geographic rainfall patterns.”

It says the biggest problem will be finding locations for water storage basins.

“The identification of suitable storage sites and likely significant costs of such storages may be problematic,” according to the report.

Experienced flood expert Professor Colin Apelt, then chairman of Brisbane City Council’s Flood Taskforce, identified this problem when he spoke with brisbanetimes.com.au in March this year.

Ms Nolan said the report recognised that all floods were different.

“And that raising the dam wall should be considered alongside other flood mitigation strategies such as lowering the full supply level and changing the dam's operating manual,” she said.

The report will now be considered by Queensland's Flood Commission of Inquiry, which will hand down their final report in February 2012.

The GHD report will be considered in more detail in the Wivenhoe and Somerset Dam Optimisation Study, which will be finalised by the end of 2012.

The optimisation study includes information from Seqwater, the Department of Environment and Resource Management, plus Brisbane, Ipswich and Somerset councils.

The GHD report is now publicly available the DERM website.