Low-flows for water ecosystem health
Water-dependent ecosystems in seasonally flowing streams, creeks and rivers across the Mount Lofty Ranges are mostly degraded because the timing, volume and duration of flows have been significantly altered.
Water which is set aside for environmental purposes doesn’t achieve its potential because flows are intercepted by one or more of the many thousands of farm dams and watercourse diversions in catchments. The flows which are most affected by catchment development are called ‘low-flows.’
What are low-flows?
Low-flows are naturally occurring, regular, small flow events that are a vital part of the annual water flow pattern in a catchment. They are a small but vital part of the annual flow pattern in a catchment which are needed to maintain natural processes and catchment health.
Low-flows maintain habitats through the driest part of the year, particularly through the Mount Lofty Ranges, where many watercourses are ephemeral, or only holding water for short periods of time.
How do low-flows benefit water-dependent ecosystems?
There are many species throughout the Mount Lofty Ranges that rely on low-flows. Low-flows provide and maintain aquatic refuges, support the life-cycle of water dependent plants and animals and allow survival throughout the drier summer months.
Some watercourses are permanent and some temporary but they all play a special role in sustaining water dependent species, and critically, they need to be maintained by low-flows.
Many watercourses in the Mount Lofty Ranges flow for only a small number of days each year. These flows supply pools within watercourses which are able to support water-dependent life for much longer than the channel itself.
Passing low-flows downstream results in a number of environmental benefits including longer periods of flow, a freshening of pools and reduction in stagnation, maintenance of permanent pools, re-colonisation of aquatic plants, improved condition of macroinvertebrate and native fish communities, and an improved stability of watercourses.
How are low-flows being impeded?
Rainfall collects in catchment areas and travels downstream in creeks, streams and rivers, supporting all living things as it goes.
The natural movement of water through these catchments has been disrupted by the construction of thousands of dams and watercourse diversions across the Mount Lofty Ranges, as well as modification to landscapes through agriculture. This has affected the timing and volume of flow reaching watercourses.
As a result, low-flows are impeded until dams fill and spill, shortening the flowing season, and delaying water flows until later in the season. This change to flow patterns is a major contributor to declining catchment health.
How are impeded low-flows affecting water-dependent ecosystems?
Despite catchments in the Mount Lofty Ranges receiving some of the highest annual rainfall in the state, our inability to reliably provide low-flows has serious implications for water-dependent ecosystems in most catchments.
Most aquatic flora and fauna in the region depend on a specific range of flow conditions to survive. According to the Hills and Fleurieu Landscape Board’s 2021 Water Trend and Condition Snapshot, results from 35 stream flows across the Hills and Fleurieu region indicate that flow conditions can be rated fair or poor in terms of their ecological value, and are on a downward trend. Considering low-flow frequency and volume is dependent on timely rainfall events, and climate-change projections are indicating that the region will become hotter and drier, with lower annual rainfall; managing these catchments and water-dependent ecosystems will become more of a challenge in the future.
The snapshot also references the condition of fish and macro-invertebrate communities, both of which are useful indicators of aquatic ecosystem condition.
It found that of 55 sites surveyed for fish in the Eastern Mount Lofty Ranges, only 4 (7%) are in good condition. Results show that conditions are better in the south of the region, which is consistent with the prolonged dry conditions experienced in northern areas. There has been a near total loss of fish in the northern part of the Hills and Fleurieu region.
Monitoring results also showed a higher prevalence of macro-invertebrates (waterbugs) in areas with fewer dams and diversions, higher rainfall and remnant vegetation – predominantly the southern Fleurieu Peninsula and higher parts of the Mount Lofty Ranges. Some sites have shown improvement since the Millenium Drought, giving evidence to the benefit of higher rainfall. Almost half of the sites surveyed however, have shown declining condition – typically in the drier Eastern Mount Lofty Ranges.
How can landholders help to provide low-flows?
Productive and sustainable businesses need healthy water catchments. By looking after the health of our catchments today, we can help ensure future landholders have the opportunity to farm viably and be surrounded by healthy ecosystems that are in the best position to survive in the years to come.
The Flows for the Future Program was established by the Australian and South Australian governments to ensure the long term viability of catchment health within the Eastern Mount Lofty Ranges. By funding the design and restoration of ‘low flows’ on dams and watercourse diversions, the program is restoring more natural stream flows to bring life to our catchments.
There are other cost-effective ways landholders can provide low-flows as well. Many dams already have pipes installed through walls which can be easily modified to provide trickle flows. Alternatively a small siphon pipe can be quickly installed over the top of the dam wall. A group of landholders in the Inman Valley catchment is using these approaches in a community-led project to provide additional flows in their catchment.
How is the Hills and Fleurieu Landscape Board addressing the issue?
The board recognises that water is vital to the health of the environment and ecosystems, as well as being a precious shared resource for landholders and farmers throughout the region. Getting the balance right between leaving enough water to sustain water-dependant ecosystems, while providing water to support agricultural productivity across the region, requires careful management.
In the Hills and Fleurieu Landscape Board Plan 2021-26, the board has made clear commitments to deliver water resource planning to meet ecological, economic, cultural and social needs; to protect and restore our freshwater ecosystems; and to recover our threatened species and ecological communities.
Under the Landscape South Australia Act 2019, the board develops and co-implements water allocation plans which set out the rules for the use of water in each prescribed water area. It also issues permits for water affecting activities to ensure that any work done to construct or modify a watercourse doesn’t negatively impact other water users or the natural environment.
The Hills and Fleurieu region is the most biologically diverse in the state, home to half of South Australia’s species of native plants and three-quarters of its native bird species. The board has strategies in place to conserve biodiversity by maintaining intact (viable) landscapes, by reversing existing declines, by recovering threatened species and ecological communities, and by controlling emerging threats (such as climate change or new pest incursions).
Read our sedge and rush planting guide for creeks and dams.
What is the cultural significance of restoring low-flows?
The Mount Lofty Ranges are the traditional lands of the Ngadjuri, Kaurna, Peramangk and Ngarrindjeri people. Freshwater is core to culture and identity of aboriginal people across the Murray-Darling Basin. The freshwater systems bring life to the region and inextricably link people and culture to Country and all living things. Restoring low-flows is essentially preserving an important aspect of First Nations culture.
Citizen Science in action to monitor water-dependent ecosystem health
The board, in partnership with the Murraylands and Riverland Landscape Board, Department for Environment and Water (DEW), Goolwa to Wellington Local Planning Association and Peramangk and Nganguraku First Nations people, supports volunteer citizen scientists to assess the health of waterways across the region as part of the community ‘Angas-Finniss Waterbug Bioblitz’ monitoring program.
Now in its seventh year, and run biannually at sites across the regions, the team joins forces with volunteers and aquatic ecologists to collect as much information as possible about the macroinvertebrates and water quality of a catchment. The data collected helps assess and identify long-term trends in overall catchment health and records the outcomes of increased flow achieved by the DEW Flows for the Future program.
During 2021 the Angus catchment received a high level of flow not seen since 2017. The improved flowing habitat lead to improved Bioblitz results, including an increase in recordings of sensitive waterbug and fish species, such as the Obscure galaxias fish (Obscure galaxias) which was found at several sites. Many of the species have not been recorded for a number of years.
The program is delivered under the Murray–Darling Basin Plan by DEW and jointly funded through the Australian Government Department of Agriculture, Water and the Environment and DEW.
The ultimate aim is to protect and conserve the environment and equitably share the available water between users to ensure its long term sustainability.
This is more important than ever, with forecasts showing we will have to learn to live with less water, of variable quality, in the future.