Little Stringybark Creek

Testing that we make a difference

We know from studies conducted over the last 6 years that stormwater runoff is the primary degrading influence on stream ecosystems in the eastern suburbs and fringes of Melbourne. In a series of scientific papers (see below), we found that Little Stringybark Creek is degraded by urban stormwater runoff delivered to the stream through the stormwater drainage system.

We modelled the response of a range of ecological indicators to piped stormwater drainage (see Walsh et al. 2005). We found that impervious areas like roofs and roads have much less effect on streams if they don't drain directly to a stream through stormwater pipes. We found that if we could reduce the area of directly connected impervious surfaces from the existing 5.5% of the catchment area to around 2% of the catchment area, we could reduce stormwater impacts to Little Stringybark Creek to about the same level experienced by streams of the region that are in very good condition. We predicted that this level of treatment would be necessary if we were to see any improvement in the ecological condition of the creek.

Little Stringybark Creek (red in the figure opposite) is in poor condition compared to streams with minimal urban (or other) impact (blue) and is in similar condition to other streams that suffer from catchment urban impacts (yellow). These differences in condition are consistent across a range of indicators that measure different parts of the stream ecosystem, and the differences have been stable over the period that we have been measuring them.

A selection of some of the variables that we have monitored in seven study streams in eastern Melbourne since Sep 2001. Data to 2003 are from a) Hatt et al. 2005 (filterable reactive phosphorus, a nutrient vital for life, but, which in excess, can cause algal blooms), b) Walsh 2004 (SIGNAL, an index based on the sensitivity of macroinvertebrate families found in a creek: 6-7 indicates a healthy stream, less than 5 indicates problems), c) Taylor et al. 2005 (algal biomass: healthy streams tend to have less algae), and d) Newall and Walsh 2005 (IBD, an index like SIGNAL, but based on the species of diatom algae that are found in the stream: above 13 is good). Data after 2003 are unpublished.
Red: L. Stringybark Ck
Blue: reference streams in good condition
Yellow: control, degraded urban streams

This stable pattern suggests that we will be in a strong position to assess any changes that might occur in Little Stringybark Creek following Stormwater Tender and installation of raingardens on the streets. Our aim is that Little Stringybark should become less like the yellow control sites and more like the blue reference sites following our work in the catchment.

We have continued to sample macroinvertebrates each year since these data were collected, and Melbourne Water have agreed to continue monitoring macroinvertebrates at these sites as part of their long-term monitoring program. We have applied for funding to restart monitoring of other ecological indicators in the streams this year, and for at least 2 or 3 years after the works in the Little Stringybark catchment have been completed.

Further reading

Hatt, B. E., Fletcher, T. D., Walsh, C. J., and Taylor, S. L. (2004). The influence of urban density and drainage infrastructure on the concentrations and loads of pollutants in small streams. Environmental Management 34,112–124.

Newall, P., and Walsh, C. J. (2005). Response of epilithic diatom assemblages to urbanization influences. Hydrobiologia 532, 53–67.

Taylor, S. L., Roberts, S. C., Walsh, C. J., and Hatt, B. E. (2004). Catchment urbanization and increased benthic algal biomass in streams: linking mechanisms to management. Freshwater Biology 49, 835–851.

Walsh, C. J. (2004). Protection of in-stream biota from urban impacts: to minimize catchment imperviousness or to improve drainage design? Marine and Freshwater Research 55, 317–326.

Walsh, C. J., Fletcher, T. D., and Ladson, A. R. (2005). Stream restoration in urban catchments through re-designing stormwater systems: looking to the catchment to save the stream. Journal of the North American Benthological Society 24 690–705.