CSIRO water scientists have a long-standing active program building up an understanding of the complex chain of events that leads to an algal bloom, and the aftermath of toxins released into the water.

Remote sensing of inland water quality

Existing inland water quality data for Australia are scarce but what data we have show that Australia’s inland water quality is declining.

Fast and cost-effective assessments of water quality are needed to assess baseline conditions of our inland water quality so we can identify changes in water quality in response to influences such as land use changes, flooding, fires, and climate change.

Once developed, a monitoring approach based on a combination of near-surface and satellite approaches could improve knowledge of inland water quality conditions of interest to both the scientific community and management agencies alike.

Such conditions could include the occurrence, timing and persistence of algal blooms including cyanobacterial blooms, black water events, and general indicators of eutrophication status.

Traditional sampling approaches require repeated travel to often remote and harsh areas; they may also involve costly follow-up laboratory analyses. But we need assessments across a range of scales, from in-situ measurements through to large regional-scale investigations.

Over a 10-year investment strategy, CSIRO has developed a way of using remote sensing techniques to remotely detect ‘visually active’ water quality variables in marine coastal waters.

By measuring the colour of the water in detail, variables such as chlorophyll, cyanobacterial pigments, organic and inorganic sediments as well as dissolved organic matter can be quantitatively observed. The approach of measuring water colour works for instruments in close proximity to the water surface or for satellite sensors based hundreds of kilometres in space.

CSIRO has developed an algorithm based on physics-based adaptive linear matrix inversion (aLMI) which can simultaneously derive concentrations of a number of water quality variables over different water types. The Great Barrier Reef Marine Park Authority now uses this technique for systematic and cost-effective assessment of water quality variables in the Great Barrier Reef lagoon using satellite data.

The current one-year project will investigate the application of the aLMI to develop this same capability for Australia’s inland waters.  The algorithm will require different optical datasets to cope with the greater range of water quality that exists in inland waters. One of the project objectives is to collate and evaluate existing datasets and develop new datasets for variables relevant to Australian inland waters.

As well as testing the method on satellite data, the project will also test novel, ‘near-surface sensing’ approaches to provide continuous water quality monitoring. These methods will be validated against traditional sampling methods.

Initial demonstration projects for near-surface sensors and satellite retrievals are proposed in the Murray-Darling Basin and in Queensland where a range of water types provide opportunities to investigate the robustness of the approach, covering a range of hydrological conditions, sediment events, algal blooms and black water events.

Adoption of the method by relevant inland water management agencies is a key aim of this project.

Shedding light on Australia's lakes and reservoirs

The measurements are part of a project that CSIRO postdoctoral fellow, Erin Hestir, hopes will lead to the development of a continental scale product for assessing Australia’s inland waters from space.

Dr Hestir and her team are measuring the optical properties of Australian lakes and reservoirs in order to build tools that can be used to identify trends in inland surface water quality and the response of inland water systems to extreme events (such as fire, floods and drought), land use and climate changes.

Remote sensing studies of inland water quality to date have been limited to local or regional assessments.

Dr Hestir’s project aims to develop continental scale earth observation products of inland water quality from satellite imagery over Australia. This involves measuring the optical properties of inland water systems and comparing them to remote sensing signals from space.

The project team will measure the absorption, attenuation and backscattering of light in reservoirs and lakes in Queensland and the Murray Darling Basin in NSW. These measurements will be used to model the remote sensing signal (the colour of the water surface determined by the amount of reflected light at different wavelengths) that can be

By measuring the light absorption and backscattering properties of reservoirs such as Lake Wivenhoe in Queensland, we can understand the complexity of conditions that give the lake its colour,” says Dr Hestir. “This understanding will help us build the tools needed to estimate suspended matter and algal concentrations from space.”

In addition to the below surface water measurements, a handheld radiometer will be used to measure the remote sensing reflectance above the water. This provides a bridge between the measurements in the water and those received from the satellite.

The team will also be collecting water samples and analysing them for chlorophyll, suspended sediment and coloured dissolved organic matter back in the laboratory. By relating the water samples with the remote sensing signals, the team will be able estimate water quality from space at regional to continental scales.

The intention of this project is to provide a cost-efficient tool that can be used by water managers to monitor the condition of Australia’s inland water systems and reduce the requirement for repeat travel, often to remote areas, and the need for costly laboratory analyses.

The products developed from this project will also be used to demonstrate the capability of the upcoming European Space Agency Sentinel satellite mission to be launched in 2013.

Shade-cloth keeps water storages cleaner

Algal bloom problems in water basins

Many townships get their drinking water from specially constructed small water basins that are topped up from local rivers during times of clear water flow.

Algal blooms within the basins are a major problem. Controlling algal growth often requires attention from maintenance staff and additional chemical usage.

How CSIRO helped

As part of a research program on technical textiles, a team from CSIRO monitored water properties in water supply basins covered with heavy duty shade-cloth.

The project was set up after promising results from the covering of a single basin in East Gippsland, Victoria, Australia, in 2001. The covering blocked the light and reduced algal growth, so a more comprehensive trial was set up in 2004.

Its aims are to improve water quality by:

  • reducing light levels to minimise algal and plant growth
  • reducing entry of wind-borne debris
  • keeping birds out, especially water birds
  • reduce evaporation
  • improve security of supply
  • reduce chemical use
  • improve security against wilful contamination.

Six basins studied

CSIRO partnered with the manufacturer Gale Pacific and East Gippsland Water on the project, which ran for two years.

Four basins were monitored for one year uncovered and one year covered. Two of these are treated-water storages (Mallacoota and Omeo) and two are raw-water storages (Swifts Creek and Cann River). Two uncovered basins (Sarsfield and Orbost) were monitored for two years.

Observations are in the final stages of analysis.

Tough fabric

Shade-cloth covers were specifically designed by Gale Pacific Limited to block about 95 per cent of the light. They had to be strong, durable, UV stable, abrasion-, flex-, and heat-resistant, and be able to sustain tensions for long periods in extremes of heat, cold, and windy conditions.

The Omeo basin was usable throughout the summer, especially over weekends, significantly reducing the hours required to tend the treatment plant.

— Mr Scott Barnes, Experimental Scientist, CSIRO

The fabrics are knitted from high density polyethylene monofilament yarns and tapes, supported externally by steel cables and poles situated outside the basin banks. The covers and their support structures were designed, fabricated and installed by Superspan Pty Ltd.

The support structures had to withstand high winds and snow loadings. The covers were tensioned with about 1500 kg force at each mounting point.

No blooms

The Omeo basin was usable throughout the summer, especially over weekends, significantly reducing the hours required to tend the treatment plant. In previous summers, algal blooms made the basin unusable for periods.

The Omeo cover also withstood high winds and heavy snow falls in 2005.

Adverse bacterial events became rare in the treated-water storages but were much the same in the raw-water storages, which are fed directly from rivers.

Water birds and wind-borne debris were kept out by the covers.

Plants no longer grew at the bottom of the basins because of the lack of light, and this reduced maintenance costs.

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