As part of a three-year trial, logs have been reintroduced to a channelised section of the Harvey River to mimic fallen trees, and the riverbanks replanted with native species to combat weeds and prevent soil erosion.
These interventions are designed to create pockets of cooler water and diverse underwater habitat, enabling aquatic life to survive during the hot, dry summer months.
Members of the Harvey Aboriginal Corporation were invited to join the first monitoring survey following installation of the instream habitat, bringing their unique knowledge about the river and its importance to Binjareb Noongar culture.
They joined in the excitement of some significant finds by the monitoring team from Murdoch University’s Harry Butler Institute.
A major find at the restored sites were the Smooth Marron, a freshwater crayfish species endemic to south-west WA. They had not been detected in this part of the river in any of the previous surveys (in 2009, 2018/19 and 2021).
A significant greater abundance of large Nightfish at the restored sites, compared to the unrestored sites, suggests the species is favouring the new habitats.
These are really positive signs that the restoration is beginning to have an impact by providing more complex habitat and refuges to support a greater range of aquatic species in the waterway.
“We modelled the effect of securing these large logs to the riverbed and banks on water level and flow, to ensure there would be negligible risk of flooding or erosion. By carefully positioning the logs, we can control areas of instream erosion and scouring from water flow, creating different flows and depth habitats for aquatic life. A key objective was to create deeper pools as shelter for temperature-sensitive species during the increasing periods and severity of low flows.” – Dr Tim Storer, WA Department of Water and Environmental Regulation
Further aquatic monitoring, planned for Autumn of this year and also in 2023, will provide more data to determine longer term impacts of the restoration.
It will be particularly interesting to explore whether the instream habitat project helps provide sanctuary for different species during the more extreme conditions that occur during the dry season.
The coming months will also see flora monitoring of the riverbank plantings, which inevitably will need longer to take shape.
“It’s so encouraging to see the results from installing logs for aquatic habitat in such a short space of time. It’s important to consider the long term as well, which is where revegetating the riverbanks comes in.”
“As these trees and shrubs get established, they can also help shade the waterway, prevent erosion and outcompete weeds. And we can create a habitat corridor for other biodiversity such as our cockatoos and other bird species to move safely through the landscape.” – Ruth Cripps, Greening Australia
The overall results of the trial will be an important reference for future efforts to restore channelised river systems in Western Australia’s South West.
Helping the Harvey is part of Greening Australia’s Great Southern Landscapes program, an Alcoa Foundation funded project through the Three Rivers, One Estuary initiative, and forms part of the wider collaborative partnership between Harvey River Restoration Taskforce, Water Corporation, and Greening Australia under the ‘Marron More Than a Meal-Revive our Rivers Program’ funded by the Peel-Harvey Catchment Council, State Natural Resource Management Program, and Water Corporation.