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Pegasus Lake Aeration Trial Information

Updated: Jun 19, 2022

At our Templeton drop-in session in May, attendees had the opportunity to learn more about the upcoming Lake Trial.


Templeton Group have contracted WSP to carry out the lake trial to improve water quality of the lake. Dr Katie Coluccio, a Hydrogeologist, heads up the project and was available to meet on the night.


Below is a copy of the information from WSP which outlines the trial (which you can also download below).


Pegasus Lake Aeration Trial

Project Update June 2022


Water quality issues in Pegasus Lake

As many members of the public are aware, water quality in Pegasus Lake has declined since the lake first became operational. For the past several years, the lake has suffered from toxic blue-green algae blooms during summer. As a result, a health advisory has been issued the past several summers, which impacts activities at the lake such as boating, swimming and walking dogs near the water’s edge.


What are we doing about it?

Templeton Pegasus Limited (TPL) has contracted WSP to carry out a trial to improve water quality in the lake. Following consultation with scientists at NIWA and Environment Canterbury, bubble aeration was selected as the first option to trial in the lake.


What problems are we trying to address?

The aeration was selected primarily to disrupt seasonal stratification in the lake. This is a common issue in lakes, typical in summer months, where there are warmer temperatures at the surface of the water and colder, low-oxygen water near the bottom. These conditions promote nutrient release, which helps fuel algae blooms.


Will aeration address algae blooms?

Algae blooms are caused by several factors including high nutrient levels, warm temperatures and low rainfall. Unfortunately, they are often difficult to treat. The aeration has been selected to primarily address stratification in the water column, which contributes to algae blooms. The aeration addresses some of the underlying causes of the algae blooms, but it is not a direct treatment. More than one treatment option may be required to effectively reduce algae blooms in Pegasus Lake.


How does bubble aeration work?

The concept is simple. Air will be pumped into the lake through diffuser devices installed on the lakebed. This will produce a bubble curtain in the water column. As the bubbles float upwards, they increase oxygen levels in the bottom waters of the lake. An air compressor will be installed on land which will pump air into the diffusers. The air compressor will be installed under the footbridge on the eastern side of the lake and housed in a sound-dampening box. TPL has engaged Apex Water to provide and install the aeration system.


How will we monitor the effects of the trial?

  • Two buoys have been installed in the lake to continuously measure water temperature and oxygen levels

  • Monthly nutrient sampling and algae sampling at the lake buoy sites

  • Monthly water quality measurements by boat at sampling sites across lake

When is the aeration happening?

  • March to June 2022: Site preparations and monitoring equipment installed.

  • July to September 2022: Aeration switched ON when lake conditions are suitable.

  • July 2022 to April 2023: Ongoing water quality monitoring and aeration system maintenance.

  • April 2023: Aeration switched OFF.

  • May 2023: Assess trial outcomes and consider next steps.

Where is equipment being installed?

So that the effects of the aeration can be assessed, we are establishing a ‘trial area’ in the southern area of the lake where the aeration will be installed. Baffle curtains will be installed below both footbridges so that water flow is limited between the trial area and the rest of the lake.

Pegasus Aerator Trial Map for Stakeholders_Landscape
.pdf
Download PDF • 1.87MB

Will access to the lake be affected?

To avoid damage to the baffle curtains that separate the trial area from the rest of lake, we would appreciate if lake users could avoid crossing over the curtains.

Aeration Trial_Project Overview June 2022
.pdf
Download PDF • 316KB

Contact details for more information:

Chris Simpson, Templeton Pegasus Limited, chris.simpson@templetongroup.co.nz

Katie Coluccio, WSP, katie.coluccio@wsp.com





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