Dam strong as ever: SunWater
SUNWATER has quashed local rumours the Leslie Dam wall is buckling under the pressure as floodwaters pushed it to 91 per cent of capacity this week.
Water spurting from its wall has caused raised eyebrows but is “not a cause of concern”.
Small crowds gathered at Leslie Dam watching water gushing from piping, flowing down the curvature of the wall and pooling at a catchment point at the base.
“Is that normal?” a concerned resident asked.
Very normal “seepage”, a SunWater spokeswoman assured.
“The water is just seepage from seals – people haven’t seen the dam so full in a while so they haven’t seen it like that before. It’s not a cause of concern,” the spokeswoman said yesterday.
She said the dam was able to handle the recent sharp increase in water – the dam has gone from 64 per cent to 91.4 per cent in one month – with no structural damage.
“Leslie Dam is now receiving only minor inflow and has been designed to fill and safely pass floodwaters through its spillway. There is no damage to the dam,” she said.
Leslie Dam came under scrutiny in October when a report for the Queensland Competition Authority urged the government to carry out dam safety upgrades prompted by a review of 100 years of rainfall data by the Bureau of Meteorology (BOM).
BOM projections of “extreme rainfall events” in Queensland show that “much larger (events) may be possible than previously believed”, meaning dams including Leslie may not be strong enough to contain a maximum flood.
In view of this week’s rain and flooding in the region, the spokeswoman said scheduled upgrades for Leslie Dam had not been brought forward.
SunWater has until 2035 to strengthen the dam wall in order to meet the extreme rainfall predictions.
“New extreme rainfall projections for Queensland announced by BOM have led to an increase in the standards applied to dam safety and the ability of dams to safely pass flood waters,” the spokeswoman said.
“Following this announcement SunWater has prioritised which of its dams will require safety upgrades based on Queensland and Australian dam safety guidelines.
“Leslie Dam is designed to safely pass extremely rare rainfall events in the vicinity of a one in 60,000-year occurrence.
“However, this only equates to approximately 90 per cent of the acceptable flood capacity defined by the Queensland Dam Safety Regulator and therefore the dam will require an upgrade to 100 per cent by 2035.”
Stringent contemporary safety regulations have improved somewhat since the mid-1980s.
The Department of Environment and Resource Management Dam Safety director Peter Allen recalled an incident at Leslie Dam some years ago in his paper Operation of spillway gates – How to avoid the problems and pitfalls.
“There was an incident at Leslie Dam near Warwick in the 1980s when, during a heavy mist, a water level sensor misread the reservoir level and the automatic gate operating system thought there was a flood in progress and it opened a gate prematurely,” the report said.
“Fortunately the reservoir level was below the gates and no water was lost but it caused a lot of rethinking on level sensors and the way the automatic operating system was employed.”