An American hydrologist has raised questions over the actions of Queensland dam engineers who made crucial decisions on water releases during the 2011 floods based not on forecast rain, but "water on the ground.''

Dr Ronald Christensen told a Sydney court yesterday that a forecast of heavy rain was a good enough reason to clean out water from a flood mitigation dam in the US.

When heavy rain was forecast he saw a reason to act, he said.

Releasing water from Wivenhoe Dam.
Releasing water from Wivenhoe Dam.


"What I see is a reason to take the levels down,'' he told the court.

"They (dam engineers) have a certain amount of storage available ... if they have not made their releases they will be in trouble.''

Dr Christensen was appearing as one of the key witnesses in a massive class action representing more than 6000 victims of the 2011 southeast Queensland floods.

The action, brought by Maurice Blackburn lawyers against the Queensland Government, Seqwater and SunWater, rests largely on a central argument that dam engineers held back too much water, and were then forced to release large volumes which contributed to flood damage. .

Dr Christensen has been brought in to argue the plaintiff's case that flood engineers working on Wivenhoe and Somerset dams should have noted the rainfall forecasts being broadcast in January 2011, and released water.

Releasing water from Wivenhoe Dam.
Releasing water from Wivenhoe Dam.

The State Government, Seqwater and SunWater appearing as defendants, have long argued that dam engineers followed their manual by basing dam releases on actual "water on the ground'' rather than forecast rainfalls during the crisis which gripped the south east in early January 2011.

Dr Christensen said the US Army Corp of Engineers who control around 700 hundred dams in the US do release water and retain water based on forecasts.

Dr Christensen said the US engineers followed a controlled schedule throughout the entire year largely based on historic average rainfall forecasts.

Seqwater lawyers questioned Dr Christensen's credentials yesterday, confirming with him that he had "never made a decision to release water from a dam.''

Asked if he had ever calculated releases based upon forecasts of rainfall in order to make a decision to release water from a dam Dr Christensen replied:

"I have done it in the computer world.

"But not in the real world?

"But not in real time, no.''

The hearing continues today.