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Office of the Commissioner for Sustainability and the Environment



Indicator: Surface Water Quality

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Summary of results

Water quality data in the ACT clearly demonstrate that water quality varied over time and across the ACT. This was a function of land use and climatic factors.

Further comparison of the quality of water flowing into the ACT (at Murrumbidgee at Angle Crossing) with that leaving the ACT (Murrumbidgee at Halls Crossing) showed that the ACT has had minimal impact on water quality in the Murrumbidgee, and land planning and management effectively controlled transport and delivery of urban-derived pollutants into the main drainage system during the reporting period.

Elevated salt loads did exist; however, this was a result of the salts excreted from the human population, and did not indicate additional salt loads derived from degraded catchment condition. Furthermore, there was a significant increase in values for chlorophyll ‘a’, indicative of eutrophication.

Over the current reporting period, it was evident that a number of events have occurred which compromised water quality at a site, subcatchment or whole catchment scale. These events include prolonged drought, the bushfires of 2001 and 2003, large storm events, and accidental discharge of sewage. A number of issues emerged as a result of these events.

Firstly, poor water quality of Lake Burley Griffin as a function of bacteriological contamination, inflow of stormwater and in-lake processes was a cause of major concern in relation to management of the lake and its catchment. All the urban lakes were sites of considerable bacteriological contamination, as were some of the recreational beaches of the Murrumbidgee. Contamination was the result of both point source pollution and eutrophic conditions generated by in-lake processes.

Secondly, urban activities, especially in the Gungahlin area, had a quantifiable impact on downstream water quality. The water flowing from Ginninderra Creek catchment was relatively poor as a result, although the trapping efficiency of retention ponds, Gungahlin Pond and Lake Ginninderra played a mitigating role.

Finally, the impacts imposed by prolonged drought and the 2003 bushfires were associated with catchment vulnerability. It was anticipated that water quality will continue to respond to mobilisation of sediments and nutrients from these vulnerable catchments until a new equilibrium is reached.

What the results tell us about the ACT

Water quality across the ACT reflects the impacts of landuse and condition under different climatic and developmental regimes.

Canberra’s overall impact on the Murrumbidgee River

Data indicate that the quality of water leaving the ACT (Murrumbidgee at Halls Crossing) was still well within acceptable limits and comparable to the quality of water entering the ACT (Murrumbidgee at Angle Crossing).

This result suggests that the intensive landuse associated with urbanisation and other human activities in the ACT has minimal impact on water quality in the Murrumbidgee, and that land planning and management effectively controls the transport and delivery of urban-derived pollutants into the main drainage system. Whilst elevated salt loads do exist, these are the result of excretion from the human population.

Values of total suspended solids, turbidity, conductivity, pH, ammonia and total phosphorus were averaged over three years (2000–03) for this analysis, and did not vary significantly (see ;list of sites, and Table 1). The changes in water quality that were observed could be traced to the Ginninderra Creek catchment, where higher sediment and nutrient loads occur.

A small number of sites exceeded water quality standards for turbidity and/or chlorophyll ‘a’ on a significant number of occasions throughout the reporting period.

Following the protocol set down in the Water Quality Guidelines (ANZECC, 2000), these sites were analysed in more detail and it was confirmed that they are vulnerable to low water quality. This means prioritisation for further investigation should be directed to:

  • Lake Tuggeranong at Dam (chlorophyll ‘a’,turbidity)
  • 270 Point Hut Pond at Dam Wall (turbidity)
  • 321 Lake Ginninderra at East Arm (turbidity)
  • 529 Lake Burley Griffin, East Basin off Bowen Park (chlorophyll ‘a’)

The trends in water quality during the reporting period suggest that:

  • extreme natural events may be high intensity and short duration (bushfires, flooding), or variable and prolonged (drought), with disparate recurrence intervals
  • vulnerability, persistence of poor catchment condition and recovery are functions of highly complex, interrelated factors.

Consequently, water resource management and planning needs to integrate potential impacts imposed by climatic variability and change, catchment condition and urban development.

Water quality analysed before and after the 2003 bushfires

To make assessment of the ACT’s water quality over the reporting period meaningful, a two-phase approach was taken:

  • Phase 1 encompassed drought conditions in association with El Niņo and the Southern Oscillation (2000–02). Over those three years, the efficacy of water resource management, impacts of land use and management, and the effects of climate (as both event-based storm events and continuing drought) were reflected in water quality responses at site-specific and catchment scales.
  • Phase 2 related to the reporting period after the January 2003 bushfires. During this time, catchments responded to the combined effects of prolonged drought, broadscale bushfires, and significant runoff generated by major storm events (particularly in February 2003). This phase represented extreme natural events that provided a unique opportunity for State of the Environment reporting.

Overview for 2000–02

During 2000–02, the best water quality was associated with the forested catchments of the Gudgenby and Cotter Rivers, whilst the poorest was associated with the developing suburban catchments of Ginninderra and Tuggeranong Creeks.

Temporal variability of water quality before 2003 was due to extreme rainfall events, prolonged wetter than average periods (November 2000 and February 2002), accidental spillages, or to catchment activities such as suburban development and agriculture. In particular, during the reporting period, it was evident that poor water quality in the urban lakes was an ongoing issue due to spillages and inflow of stormwater, or to inlake eutrophication. Climate can play an important role in generating some of these problems due to impacts on algal concentrations and the lack of flushing flows during prolonged drought.

Bacteriological trends

Bacteriological data are incomplete for the urban lakes due to loss of records at the laboratories from fire damage. It should be noted, however, that where data exist, the compliance rate at Lake Tuggeranong ranged from 43% to 85% with the best water quality at Centre Reach and the poorest at the Recreational Area. By contrast, compliance rates at Lake Ginninderra were significantly lower, ranging from 23% (East Bridge Beach) to 73% (Police Jetty Beach).

Water quality in Lake Burley Griffin was an ongoing concern, and data indicate that the site where water quality was poorest was in East Basin, where not only bacteriological concentrations could be high, but also chlorophyll ‘a’, phosphorus, turbidity and total suspended solids. This indicates that catchment processes associated with Jerrabomberra Creek and the area immediately upstream of the Molonglo inflow (in the vicinity of Dairy Road) are important controlling factors.

Impacts of activities on water quality

Although some improvement in turbidity at a number of sites suzggested that the trapping efficiency of urban dams and lakes was increasing, development activities are nevertheless playing an important role in moving sediments and nutrients through the system. This not only has event-linked impacts on aquatic biota and river health, but also compromises recreational and amenity values.

The largest contribution to turbidity was derived from diffuse sources such as erosion from gullies, rills and streambanks. Some particulate solids are derived from point sources, such as sewage and industrial discharges, but this of much smaller significance.

In less developed areas the impact of prolonged drought and the associated effects on vegetation and land condition are expressed as increased vulnerability to rainfall events. In contrast, phases of development, which are dislocated from climatic events, are reflected in water quality responses in the Ginninderra Creek catchment and, to a lesser degree, in the Tuggeranong Creek catchment.

Overview – after the fires

Major impacts that overlay these general trends were evident after the January 2003 bushfires and the large rainfall event of February 2003. The bushfires burnt approximately 70% of the ACT (Philpot et al., 2003) including a significant proportion of the water supply catchments. These fires had a number of impacts on surface water quality due to an increased delivery of carbon (as burnt organic and mineral material), nutrients and sediments to streams.

Runoff generated by the February 2003 storm event polluted the ACT water supply dams (Bendora, Corin and Cotter) due to high sediment and solute loads which rendered drinking water unpotable.

This is of concern because bacterial decomposition of instream material can lead to depletion of dissolved oxygen in the water column and release of further nutrients. Populations of algae and chlorophyll ‘a’ can multiply opportunistically due to increased light penetration of surface waters, as a result of reduced vegetation, and the supply of available nutrients. As a consequence, eutrophication can occur.

While ACT water quality (and therefore water supply) has been affected throughout 2003, it should also be realised that these will be expressed for a number of years as vegetation reestablishes and surface condition stabilises. The length of recovery will be largely determined by climatic factors, such as frequency and intensity of rainfall events (Wasson et al., 2003).

About the data

Community participation in monitoring

A community response, the monitoring program Campfire, was initiated to document the temporal and spatial changes in key water quality indicators over time. The principal aim of the program was ‘to monitor the ecological affects of bushfires on our waterways’ and the objectives included:

  • an assessment of how rural and urban catchments have been affected by the fires
  • monitoring specific sites over time to establish how long it takes for systems to recover
  • an assessment of the implications for stream ecology, human uses, and stream rehabilitation.

The program was aimed at community groups, such as Landcare, Waterwatch, Bushcare, and at schools. However, it was expected that regional government agencies would also use the information derived. The measured water quality variables included:

  • physico-chemical – pH, electrical conductivity, turbidity, ortho-phosphates, temperature, rainfall, water level and flow (descriptive only)
  • biological – riparian vegetation, macroinvertebrates and frogs These variables are monitored regularly including, for example, monthly (physicochemical), quarterly (macroinvertebrates and riparian vegetation), and half-yearly (frogs). Results for 2003 are summarised in this report.

 

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