Stormwater discharges

'Stormwater runoff' comprises all forms of runoff from urban areas. It is enhanced by the web of impervious surfaces, including roads, roofs, footpaths, car parks and other structures, and is conveyed to coastal waterways by natural and man-made conduits and drains. The volume of stormwater discharged and the types of contaminants in stormwater are suggested indicators for State of the Environment reporting (e.g. Indicator 2.7 and 2.8 respectively in the Human Settlements Theme) [1].

The relative abundances of striped-leg and yellow-footed hermit crabs are also good indicators of unnatural freshwater flows caused by stormwater runoff to coastal waterways [2,3].

Black-winged stilts (Himantopus himantopus) feeding amongst rubbish delivered by stormwater drains at Tuggerah Lake, NSW. (photo by David Balean)

Photo 1. Black-winged stilts (Himantopus himantopus) feeding amongst rubbish delivered by stormwater drains at Tuggerah Lake, NSW. (photo by David Balean)

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Coastal issues arising from stormwater discharge

The impacts of stormwater on the coastal environment are many and varied, and are related to the extent, nature and intensity of urban and industrial development [1]. Further, stormwater discharges to coastal environments should increase with size of the coastal population.

Stormwater can locally increase freshwater flow to coastal waterways. Moreover, as stormwater runs over urban surfaces, it may collect a variety of contaminants, and therefore is a diffuse source of pollutants. These contaminants can be divided into five main classes [1]:

  • toxicants derived from household chemicals, petroleum products, garden pesticides & herbicides, and industrial by-products amongst others;
  • nutrients from fertilisers, detergents, eroding soils, decomposing lawn clippings, pet faeces and sewage overflows;
  • pathogenic organisms from pet faeces, manures and sewage overflows;
  • litter (plastic containers, junk mail, glass and cans); and
  • suspended solids from atmospheric fallout, organic matter (including sewage), and soils eroded from construction sites, roads, market gardens, mining sites and other sources.

Contaminants in stormwater can give rise to fish kills, shellfish closures, eutrophication and related problems (e.g. harmful algal blooms, anoxic & hypoxic events), and can contribute to an overall reduction in biodiversity.

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Existing information and data

More information on stormwater indicators (e.g. monitoring and design strategies, guidelines for analysis and interpretation, reporting scales etc.) can be found in the Human Settlements volume of Environmental Indicators for National State of the Environment Reporting [1]. The coastal discharges indicator includes wastewater discharges. See also the fact sheet on hermit crabs.

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References

  1. Newton, P., Flood, J., Berry, M., Bhatia, K., Brown, S., Cabelli, A., Gomboso, J., Higgins, J., Richardson, T., and Ritchie, V. 1998. Environmental Indicators for National State of the Environment Reporting: Human Settlements, Commonwealth of Australia, pp. 184.www.ea.gov.au/soe/
  2. Dunbar, S. G. 2002. Respiratory, Osmoregulatory and Behavioural Determinants of Distribution of Two Tropical Marine Hermit Crabs. PhD Thesis. School of Biological and Environmental Sciences, Central Queensland University. Pp. 322
  3. Dunbar, S. G., Coates, M., and Kay, A. 2003. Marine hermit crabs as indicators of freshwater inundation on tropical shores. Memoirs of Museum Victoria. 60 (1): 27 - 34.

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