Key dam strategies for Brisbane among censored data

SEQ Water has denied any deviation from the guidelines in the dam operation manual

PARTS of the recently released Queensland flood mitigation manual censored by the Queensland government for "security reasons" happen to contain nearly all the key strategies for Wivenhoe dam, such as the gate settings and water release levels for the days before and during the deluge.

An uncensored version of the 85-page manual, obtained by The Australian, also highlights the importance of another Brisbane Valley dam, Somerset, which is known to have cracking and stability problems.

Issues such as how the dam was managed and the flood warnings to Lockyer Valley residents will be the subject of an official flood inquiry starting this week. It will be headed by Queensland judge Cate Holmes with Jim O'Sullivan, a former Queensland police commissioner, and Phil Cummins, an international expert on dams, as her deputies.

Among information already provided to the inquiry is the Queensland Flood Mitigation Manual for the Wivenhoe and Somerset dams. The inquiry is expected to examine how closely authorities followed instructions in the document in managing dam water releases.

A heavily censored version of the manual was released publicly last month, with Premier Anna Bligh saying "design data" had been blacked out from the report for "security reasons".

Among the obscured pages in the manual were several significant operations strategies such as one known as W4B, which comes into play when the Wivenhoe dam's emergency spillway is close to being triggered -- the situation authorities encountered on January 11 and 12.

The blacked-out table says Wivenhoe Dam needs to be kept at a level below 75.5m, the level at which the emergency spillway is triggered.

The proposed action is to "retain water in Somerset Dam" and bring the gate open sequence forward to increase discharge from the dam. Somerset, which was finished in 1959 and holds back the Stanley River, was identified in an unrelated 2007 state government report as having cracking and stability issues associated with its main wall.

On January 11 and 12, Wivenhoe rose to at least 74.7m, 80cm below the fuse plug or the emergency spillway -- a scenario that would have seen an uncontrolled release of thousands of megalitres of water in order to ensure the safety of the dam wall.

Should one of the fuse plugs be triggered, the dam should be drained as fast as possible, the manual says -- a situation that would have resulted in significant impact on flood levels.

Another blacked-out strategy was S2 for Somerset, which is supposed to work closely in unison with Wivenhoe to mitigate the flood.

According to a graph, when Somerset is at 105.11m -- which it was on January 12 -- Wivenhoe should be at about 75m. Water level figures for Wivenhoe at that point were not available last night.

An engineer associated with the construction of Wivenhoe, who examined the figures yesterday, said Wivenhoe's gate settings for the weekend before the major flood should be closely examined to ensure the high levels of water in the dam on early Monday morning were consistent with the manual's operations.

SEQWater declined to go into detail about the issues, saying they would be dealt with by the commission of inquiry into the floods.

SEQWater has denied any deviation from the manual or that stability issues with Somerset Dam had any bearing on its operations.