Island reservoir reserve regenerating

SA Water’s Middle River Reservoir is among several areas on Kangaroo Island experiencing vegetation regrowth and recovery, signalling regeneration post January’s Ravine bushfire.

This is not only improving the way the local landscape looks, but a naturally vegetated catchment also helps to manage the quality of runoff water entering the reservoir, which ultimately supports drinking water quality.

SA Water’s Senior Manager of Wastewater Expertise and Environment James Crocker said several species of plants and trees are becoming increasingly more visible across the reservoir reserve.

“One of the most noticeable is the Yaccas, with its green sword-shaped leaves seen emerging from the tops of rows and rows of blackened, but still alive, tree trunks,” James said.

“The Yaccas are a usually slow-growing, ancient native grass tree, with some at Middle River thought to be more than 200 years old.

“They’re very resistant to harsh conditions like fire or drought, as they can grow even in low nutrient soils, and their roots connect with underground fungi that takes nutrients from fallen timber and gives it to the Yaccas.

“Small shoots are also sprouting from the sides of many Eucalypts, which is the plant’s natural response to damage or stress, known as epicormic growth. The new shoots come from dormant buds beneath the tree’s bark, which provided shelter to the buds during the fire.

“The reservoir team also continues to see Acacia – or Wattle – and native grass regrowth, particularly along the edge of the reservoir.

“The bushfire in January burnt through the entirety of the Middle River catchment, so it’s promising to see even small parts of recovery now, before a further expected increase in regrowth during the winter months.”

This natural regeneration process was boosted by heavy rainfall in late January, as well as through SA Water’s proactive installation of sediment barriers around the edge of the reservoir prior to the rain event.

“Ten sediment control structures placed in targeted locations around the reservoir, helped to capture around 190 tonnes of sediment and debris, which rain washed into the catchment,” James said.

“The majority of these barriers are made of jute (jute plant fibre) matting, coir (coconut fibre) logs and metal posts secured with wiring. Large rocks placed on the up and downstream side of each structure also provided extra reinforcement.

“The barriers help to enhance the natural sedimentation process within drainage lines in the catchment, with the structures preventing sediment from entering the reservoir but also keeping seeds in the areas along the edge of the water and helping minimise erosion of gully vegetation.

“The flat nature of the reserve and the existing prevalence of rocks and trees also helped to slow the flow of sediment after the rainfall.”

Tap water quality has also well and truly returned to normal, with residents supplied by the Middle River Water Treatment Plant – which sources water from the nearby reservoir – seeing improvements in water taste and smell since mid to late February, as the remainder of the fire-affected water moved through the system.

“This follows the success of sediment barriers stopping some debris from entering the catchment, along with adjustments to treatment processes and the use of aerators in the reservoir,” James said.

“Throughout the fire event and our recovery process, water from Middle River has remained safe to drink, but people will have noticed a slightly smoky odour and earthy taste, as well as some discolouration.”

SA Water has also repaired fire-damaged fencing around the reservoir reserve, re-established access tracks and cleared fallen trees to ensure the site remains safe for its local team.

Remaining repairs at the Middle River Water Treatment Plant site will be undertaken over the next few months. This includes the installation of a permanent control room hut to replace the temporary structure put in place after the fire, and the replacement of a damaged electrical switchboard and building cladding.

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