LAKE COLAC WATER LEVELS ON TARGET FOR JULY

Corangamite Catchment Management Authority (CMA), the statutory manager of the Lough Calvert Drainage Scheme, says the water level at Lake Colac is on target for July. Currently sitting at 116.4 metres Australian Height Datum (AHD), which refers to the height above sea level, the water level is very similar to this time last year (116.9m AHD) and the long-term average for July.

“We’re happy with the current water levels, they’re looking great, and we want to keep it that way. We have water level data going back to 1942, and the July average over the last 82 years is 116.4m AHD,” said Corangamite CMA CEO Dr Amber Clarke.

Lake Colac has had low to very low water levels over the past two decades and dried up during the millennium drought, however in December 2022 and July 2023 it reached as high as 117m AHD – the highest it has been since the mid-1990s – due to high rainfall from three La Niña years in a row. Private land and public infrastructure starts to flood at 117.2m AHD.

Last winter, for the first time since 1996, high water levels triggered the operation of the Lough Calvert Drainage Scheme. Established in 1953, the Scheme was designed to mitigate flood damage by regulating the water level of Lake Colac and diverting water from the lake along a 30km long channel to Birregurra Creek and into the Barwon River. The current operating rules for the Scheme were adopted in 1993, and dictate that it can only operate between May and October in any year, within strict water level and salinity trigger points.

In 2023 the Corangamite CMA commenced releasing water from the Scheme on 21 July and ceased operations on 27 September once the risk of flooding was under control and because the climate forecast at the time predicted a dry El Niño summer.

The Lough Calvert Scheme is designed to prevent high water levels in the lake inundating private land and public infrastructure as well as potentially increasing erosion rates on the eastern shore. In addition, the Scheme can alleviate flooding to large areas of farmland to the east of Lake Colac.

“We’re happy with the way the Scheme was operated last year. It was operated at less than one third of the Scheme’s capacity and flexibly over the 70-day period to maintain lake levels and minimise downstream impacts on water users and the environment along Birregurra Creek and the Barwon River, whilst also mitigating the risk of flooding to private land and public infrastructure,” said Dr Clarke.

“Only 3.55% of the lake’s total volume was released – the lake holds 76,000ML when full. The current lake level is ultimately a product of the prevailing weather conditions and changing climate, and not a result of operating the Scheme last year.

“The Corangamite CMA undertook extensive stakeholder and community engagement activities with landholders, government bodies and the general public in the lead up to operating, during the operation, and after the operation of the Drainage Scheme,” she said.

The Corangamite CMA’s role at Lake Colac is to operate the Lough Calvert Drainage Scheme for flood and erosion mitigation; it is not responsible for managing the land or water activities at the lake. The Corangamite CMA can only release water from the lake within the confines of the Lough Calvert Drainage Scheme operating rules, which legally dictate when water can be released and how much water can be released to avoid downstream impacts. The Corangamite CMA regularly monitors lake levels, upstream and downstream flows, salinity, rainfall and erosion on the eastern shore and has a model that informs decision making.

“We don’t anticipate operating the Lough Calvert Drainage Scheme this year as the lake levels are not within Scheme operating limits and the current long-range forecast predicts dry conditions. This may change however, if we experience high rainfall over the remaining winter or spring months. We will continue to monitor the lake levels and weather forecast throughout winter and if they fall within the rules of the Scheme and we are required to commence operating the Scheme, we will keep the community and stakeholders informed,” said Dr Clarke.

To check the water and rainfall levels at Lake Colac, visit the 'What's Happening in my region' section of the Corangamite CMA website. The data is updated daily.