Council flushing salt water from weir
22 August 2017
Precautionary water restrictions remain in place
Council has released water from Clarrie Hall Dam to flush salt water out of Bray Park Weir after high tides overtopped the weir wall on Monday night.
The flush of water from the dam should reach the weir by 5pm today.
More water tests will be conducted about 10 o’clock tonight and if the release has sufficiently reduced the salt content in the weir, the reticulated water supply will be switched back on and should be recharged by tomorrow morning allowing water restrictions to be lifted.
If the release from the dam does not sufficiently flush the weir pool, a second release will occur tomorrow morning, meaning restrictions will remain in place longer.
Council also has drained the salt-charged water from the Bray Park Water Treatment Plant and water mains. It has not drained the affected Hospital Hill reservoir in Murwillumbah as any residual salty water will dilute once fresh water enters the system.
“This morning’s release from the dam also should be sufficient to hold back any salt water from tonight’s high tide, which is expected to be 200mm above predictions,” Manager Water and Wastewater Anthony Burnham said.
Tidal data recorded at the entrance to the Tweed River confirms that since Saturday actual tides have been up to 380mm higher than the predicted tides. The predicted tides at Bray Park were to be 1.79 (Monday pm) and 1.81m (Tuesday am) respectively. The actual tides were 2.17m (Monday pm) and 2.11m (Tuesday am).
“Council uses tide prediction information available through the Bureau of Meteorology to manage the risk of the weir wall being overtopped by salty water. Plus, the natural flow of the Tweed River also helps to hold back a king tide.
“Last night’s incident occurred because the predicted tides, together with the fact that the natural water flow from the Tweed River was still going downstream over the weir wall, informed Council’s decision that sandbagging to raise the height of the weir wall was not warranted.
“In the past, we have had no issues with tides of 1.87m but, this time, the downstream river flows were not strong enough to hold back the salt water.”
The amount of salt water in the weir is significant but not unacceptably high. The Australian Drinking Water Guidelines rule <600mg/litre as being of ‘good’ quality; 600-900mg/litre as being of ‘fair quality; and, >1200mg/litre as being of ‘unacceptable’ quality. The water in the weir was tested this morning and the confirmed total dissolved solids were 620mg/litre.
Council has advised the North Coast Public Health Unit of the situation.
People with medical conditions, such as those using dialysis, are advised to contact their usual medical provider for advice.
Residents are asked NOT to use any water for outdoor uses, such as gardening, washing cars etc.
Residents should also be alert not to use the water on salt-sensitive plants, such as avocadoes, or in fresh-water fish tanks.
At this stage, indoor water use and commercial operations are not restricted. The drinking water supplies of Uki and Tyalgum are not affected.