Rivers have naturally-variable water flow patterns. On the Gold Coast, there are long periods of drought punctuated with substantial floods. Over thousands of years, native flora and fauna have adapted to these dry periods and natural flow events. Periods of low and high flows support a rich diversity of organisms and their habitat.
Water flow in our rivers comes from rainfall as well as from the release of water in storage reserves such as groundwater, lakes, and wetlands. This flow helps maintain natural processes and catchment health.
Natural water flows may be impacted by:
- intensive water abstraction (for example, irrigation or bottling water)
- flow diversion
- narrowing of channels
- flow regulation
- changing climate.
Interruption to natural water flows can impact on water quality, habitat availability, food production and amenity.
Our current challenges
Current dry conditions have resulted in the decline of water quality with a range of impacts including:
- higher nutrient levels
- blue-green algae outbreaks (also known as cyanobacteria)
- low-dissolved oxygen levels and subsequent fish kill events throughout our city.
Low water flows
Low water flows play a key role in maintaining the health of aquatic habitats during dry periods. Although small in volume, low flows provide a continuous or intermittent flow over the bottom of channels, connecting aquatic refuges and refreshing in-channel pools.
Low flows help:
- maintain water quality by flushing nutrients and pollutants that mount up
- provide and maintain aquatic refuges during dry periods
- support the life cycle of water dependent plants and animals
- maintain water critical to wildlife during drought
- maintain riparian vegetation alongside riverbanks. This protects the banks from erosion.
Changes to flow patterns impact the whole river system including:
- aquatic and land-based wildlife dependent on drought refuges
- placing pressure on riparian vegetation, wetlands and estuaries.
What impacts low flows in our city?
River flows are naturally unpredictable. The flow in a river at any moment in time is determined by a range of natural factors including:
- weather causes – rain, insolation and winds
- catchment attributes – size, topography, geology, soils, vegetation, and stream network features.
River flows are also influenced by human activities including:
- the removal of surface and groundwater for domestic, agriculture and commercial uses
- land use which changes to surface absorption and narrows water channels
- the construction of waterway barriers and flow regulation such as dams and weirs
- discharges from industry into the water.
During dry periods river flows generally decrease, with much or all the flow in a river derived from groundwater. During prolonged dry weather, the flow of water in a stream may drop to a level known as a low flow. This is different to a drought, which is more common than low flow.
The amount of flow in a river has major impacts on its aquatic life as well as water quality, fluvial geomorphology (the interaction between the physical shapes of rivers, their water and sediment transport systems and the landforms they create) and riparian vegetation.
Impacts to our natural flows can cause:
- a decline in dissolved oxygen levels and higher pollutant levels resulting in fish kill events
- aquatic wildlife and land wildlife that depend on them to become stressed and ultimately starve
- a decline in water quality, leading to great outbreaks of blue-green algae.
Aquatic wildlife generally adapt to the natural patterns of their waterway homes, including low flows. However, changes caused by human activity to river flow can severely impact on aquatic life. While some impacts are relatively permanent such as dams, other human activities are more changeable. Abstraction of groundwater also impacts on river flows, due to the connection between groundwater and surface water.
Permanent human impacts such as dams are important because they provide security of water supply. This said, the impact of dam development still impedes flow. Parts of the catchments go without flowing water for longer periods of time. With dam interceptions lengthening the time that catchments go without water, the no-flow period is getting longer and catchment health is declining. We know this because:
- water quality is decreasing
- watercourse pools are also drier for longer
- water-dependent vegetation and fish are disappearing
- plants and animals are struggling to reproduce and survive.
What we are doing to address issues
Our Catchment Management Unit is committed to making our waterways and environments healthy and resilient. They have taken actions to assist with the management of low flows. This includes the establishment of the pilot City Flows Project. This project installs continuous discharge and water quality gauges at key locations.
The Springbrook Groundwater Investigation is piloting a groundwater monitoring program that will contribute to our understanding of our city's water balance.
How can we all help?
Restoring low flows is a critical step towards improving our catchments' health. We are all water users and some of us are landholders. Securing the environmental benefits of our low flows will require all water users to work together. We can help by:
- using recycled water instead of river and groundwater
- retaining native vegetation around waterways
- stopping, delaying or limiting surface water and groundwater abstraction
- stopping, delaying, or limiting diversion of water from a natural source
- preventing the discharge of pollutants to waterways.
Improving the health of our waterways will achieve a range of short- and long-term outcomes including:
- a longer flowing period and maintenance of permanent pools
- improved diversity of macroinvertebrates (i.e. water bugs)
- recolonisation of water-dependent plants
- improved stability of watercourses and healthier native fish populations.
For more information, contact our Catchment Management Unit: