Seqwater’s Source Protection Team is undertaking a five-year catchment modelling program to better understand how risks and catchment scale interventions can impact South East Queensland’s drinking water supply at the source.
The program, a first for South East Queensland waterways, allows users to interact with modelled data to improve understanding of the relationship between sediment loads and riparian vegetation cover.
Seqwater Chief Executive Officer Peter Dennis said the model would ultimately be used to support long-term source water protection plans by providing a greater understanding of catchment behaviour.
“Previous investigations in South East Queensland have shown that riparian vegetation is the dominant factor in stabilising and protecting the banks of a river,” Mr Dennis said.
An investigation into the relationship between sediment loads and catchment characteristics, including runoff, land use, slope and remnant riparian vegetation, found that sediment yields from catchments containing no remnant riparian vegetation were between 50 and 200 times that of a fully vegetated catchment (Olley et al., 2012).
Mr Dennis said the modelling project would enable Seqwater to assess the effectiveness of investment in the region’s drinking water supply catchments at a broad scale.
“The model enables us to trial different scenarios within a catchment to target sources of high pollutant loads. For example, what is the sediment load reduction to waterways when all buffers are vegetated? Or what are the risks to water supply if vegetation clearing was to increase?” Mr Dennis said.
“Our modelling simulates water flows in the catchment. By observing how runoff from the land flows into streams and rivers, we can identify critical pollutant transport mechanisms.
“The various scenarios trialled within the tool are attempting to quantify the impacts to the source drinking water supply.”
Mr Dennis said the tool contained the current stream length in remnant riparian vegetation cover, which could be adjusted to inform an investment scenario.
“The riparian vegetation cover, calculated for each sub-catchment, can indicate where the highest risks are for sediment loads, so we can target investment accordingly,” he said.
“The land use summary tells us what the high level activities are in the catchment so that we can develop suitable projects and management actions. This provides an indication of what pollutants are typically coming off the land during rainfall events, which could help us identify where the water quality issues downstream are coming from.”
Mr Dennis said models were initially completed for the Mid-Brisbane and Lockyer Valley catchments, which deliver water to the Mt Crosby East Bank and West Bank water treatment plants.
The Mt Crosby water treatment plants are the primary source of drinking water for the greater Brisbane and Ipswich areas, and can contribute up to 40 per cent of the total drinking water supply for South East Queensland via the Water Grid.
“Research shows channel stabilisation is the best way to reduce adverse impacts to water quality in these downstream creeks and rivers. Therefore, a coordinated approach is recommended to target riparian bank stability and vegetation health.”
Mr Dennis said this type of catchment modelling is intended to only provide a high-level estimate of likely sediment loads from different areas of a catchment based on expected run-off, land use and riparian vegetation cover.
“The modelling allows us to identify hotspots in the catchment for likely sediment loads, which we can then examine in more detail for project development,” he said.
Seqwater now has catchment models developed for the Baroon, Upper Brisbane, Logan River and Nerang River catchments.
Further assessments will be assessing yield, future land use change, climate change impacts and different pollutants (such as pathogens and salinity) to better understand the risks to the drinking water supply at the source and where management interventions are best targeted.
For more information about Seqwater and its services, visit www.seqwater.com.au.
