Bray Park Weir Tidal Protection Project

Share on Facebook Share on Twitter Share on Linkedin Email this link

Alert for deployment of barrier to protect weir

There is a continuing risk that Bray Park Weir, which supplies raw water for the Tweed Shire, may be overtopped by tidal salt water during high tide and sea level anomaly events for the foreseeable future. Council monitors this risk and acts to protect the weir when necessary by installing concrete blocks to narrow the weir and temporarily raise the water level in the weir pool. The blocks are removed when the risk has passed. Residents who want to receive an email alert ahead of Council installing concrete blocks to temporarily protect the weir should register their name and email address by emailing wateradmin@tweed.nsw.gov.au (Subject: Weir Alert). Worst-case, Council will provide three hours’ notice of a temporary raising of the weir wall.

About

A combination of high tides plus an unforeseen sea level anomaly caused Bray Park Weir to be overtopped on the nights of the 21 and 22 August 2017.

The overtopping occurred at a time of low flow in the Tweed River and the consequence was salt water ingress into the Bray Park Weir pool.

The salt water ingress caused the raw water provided to the Bray Park Water Treatment Plant to be contaminated. Consequently, the contaminated salt water went into the Tweed drinking water supply.

At no time was it a risk to human health.

This issue will become worse over time with the impact of climate change and subsequent increases in sea levels.

This project seeks to identify and assess a range of options to reduce the risk of salt water ingress into Bray Park Weir both now and into the future and to identify a preferred option for Council’s consideration.

The preferred option may be a engineered or non-engineered solution or mix of solutions.

Alert for deployment of barrier to protect weir

There is a continuing risk that Bray Park Weir, which supplies raw water for the Tweed Shire, may be overtopped by tidal salt water during high tide and sea level anomaly events for the foreseeable future. Council monitors this risk and acts to protect the weir when necessary by installing concrete blocks to narrow the weir and temporarily raise the water level in the weir pool. The blocks are removed when the risk has passed. Residents who want to receive an email alert ahead of Council installing concrete blocks to temporarily protect the weir should register their name and email address by emailing wateradmin@tweed.nsw.gov.au (Subject: Weir Alert). Worst-case, Council will provide three hours’ notice of a temporary raising of the weir wall.

About

A combination of high tides plus an unforeseen sea level anomaly caused Bray Park Weir to be overtopped on the nights of the 21 and 22 August 2017.

The overtopping occurred at a time of low flow in the Tweed River and the consequence was salt water ingress into the Bray Park Weir pool.

The salt water ingress caused the raw water provided to the Bray Park Water Treatment Plant to be contaminated. Consequently, the contaminated salt water went into the Tweed drinking water supply.

At no time was it a risk to human health.

This issue will become worse over time with the impact of climate change and subsequent increases in sea levels.

This project seeks to identify and assess a range of options to reduce the risk of salt water ingress into Bray Park Weir both now and into the future and to identify a preferred option for Council’s consideration.

The preferred option may be a engineered or non-engineered solution or mix of solutions.

Q&A

loader image
Didn't receive confirmation?
Seems like you are already registered, please provide the password. Forgot your password? Create a new one now.
  • Share on Facebook Share on Twitter Share on Linkedin Email this link

    Has the level water downstream of the weir ever been above the prediction plus 20%? - PRG

    over 1 year ago

    Up until June 2019, there were 25 occasions when actual levels were greater than predicted plus 20%.  Since June 2019, there has been none.

  • Share on Facebook Share on Twitter Share on Linkedin Email this link

    On how many occasions since our last meeting have the blocks been deployed? - PRG

    over 1 year ago

    Ten.  In some cases, blocks have been deployed to cover a number of events.

  • Share on Facebook Share on Twitter Share on Linkedin Email this link

    What was the maximum height of the tides during each event? - PRG

    over 1 year ago

    Maximum heights ranged from 0.91 to 1.14 AHD.  There were eight results over 1.00m AHD.

  • Share on Facebook Share on Twitter Share on Linkedin Email this link

    What has been the total cost of the deployments and removals of barrier since 19 Sept 2018? - PRG

    over 1 year ago

    $47,900

  • Share on Facebook Share on Twitter Share on Linkedin Email this link

    Has there been any improvements / variations to either methodology or investigation towards public tender? - PRG

    over 1 year ago

    Yes, there have been improvements in the methodology for the deployment of the blocks bringing the cost of each deployment down.  Council’s management has determined that the current processes are the most effective way to manage these risks while still being able to respond at short notice and make adjustments on a daily basis if and as required.

  • Share on Facebook Share on Twitter Share on Linkedin Email this link

    During low flow periods, can the temporary blocks be either left on the weir wall or left partially in place on the weir wall to reduce costs? - PRG

    over 1 year ago

    Previously concerns had been raised about artificially increasing water levels for longer than required to prevent salt water intrusion.  Council can leave the blocks out longer if upstream flows do not necessitate their removal.  Any decision to leave the blocks out (prior to the implementation of a permanent solution) needs to consider issues such as aquatic weeds, fish ladder flows and minimising releases from Clarrie Hall Dam.

  • Share on Facebook Share on Twitter Share on Linkedin Email this link

    What is the present raw water salinity?

    over 1 year ago

    Results from 1 Jan 2018 – 8 Sept 2019 were: 

    Median conductivity – 182.0 us/cm2

    Mean conductivity – 182.3 us/cm2

    Standard Deviation – 29.4 us/cm2.

    5%ile on single tailed standard distribution = mean + 1.65 sd

    182.3 + 1.65*29.4 = 230.8 us/cm2

    230.8 us/cm2   = 152.3 mg/L

    1%ile on single tailed standard distribution = mean + 2.33 sd

    182.3 + 2.33*29.4 = 250.8 us/cm2

    251.5 us/cm2  = 165.5 mg/L


  • Share on Facebook Share on Twitter Share on Linkedin Email this link

    Has Council investigated the PRG proposal to enable the most efficient and cost effective method of installing the current temporary barriers, ie via a tender process or contract, until a longer term solution /s are determined?

    about 2 years ago

    As Council gains more experience it will continue to assess the viability of alternate methods of deploying the temporary barriers, such as going out to tender. 


  • Share on Facebook Share on Twitter Share on Linkedin Email this link

    Does the fish ladder remain closed for the duration of the period the blocks are installed, including low tides ?

    about 2 years ago

    Yes. When blocks are deployed, there are limited windows of opportunity where there would be appropriate flow through the fish ladder to allow fish passage. Because the fish ladder is opened and closed manually, to access every fish passage opportunity would require staff to be on call at all hours. This is neither practical nor cost effective.


  • Share on Facebook Share on Twitter Share on Linkedin Email this link

    For what period has NSW Fisheries and the relevant Water authorities approved the closure of the fish ladder?

    about 2 years ago

    The relevant authorities are aware of Council’s present practice with the deployment of blocks and closing and opening the fish ladder.  Council has sought advice from those authorities as to what approvals are required.  At this time, Council has not been advised of any approvals required.  Those authorities have indicated they will address the matter of the fish ladder when Council has determined a way forward.