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Stormwater Pollution

Stormwater is rainwater that does not soak into the ground but instead flows over roofs, roads, and open spaces. As this runoff travels, especially in urban and rural areas, it gathers pollutants along the way, which are then carried directly into stormwater drains and eventually into creeks, rivers, estuaries, and the ocean. Unlike wastewater, which is treated before it is released into the environment, stormwater is often untreated, posing a significant threat to water quality and ecosystems.

Hornsby Shire is fortunate to have an environmental levy called the Catchments Remediation Rate, which has funded the installation of over 400 stormwater quality improvement devices. These devices play a crucial role in filtering and reducing pollutants from stormwater before it enters local waterways, helping to protect the health of our creeks, rivers, and natural ecosystems.

How stormwater becomes polluted

Stormwater becomes polluted when rainwater picks up and transports various pollutants from human and natural activities. In urban areas, the presence of impervious surfaces like roads and buildings prevents water from being absorbed into the ground. As a result, rainwater flows rapidly over these surfaces, collecting contaminants such as litter, oil, and chemicals. In rural areas, pollutants from agriculture, land clearing, and livestock can similarly be swept into waterways. The speed and volume of stormwater runoff contribute to the scale of pollution, especially after heavy rainfall.

Sources of urban and rural stormwater pollution

Pollution sources vary significantly between urban and rural settings due to different land uses and activities:

  • Urban environments: In cities and towns, stormwater runoff carries pollutants from many sources, including:
    • Road surfaces: Oil, metals, and rubber particles from vehicles
    • Industrial and commercial premises: Chemical spills, waste materials, and hazardous substances.
    • Parks and gardens: Pesticides, herbicides, and excess fertilisers from lawn maintenance
    • Households: Detergents from car washing, paint residues, pet waste and home maintenance activities such as high-pressure roof cleaning
    • Degraded riparian areas: Eroded streambanks that contribute sediment to waterways
    • Construction and building sites: Inadequate erosion and sediment control measures contribute to significant sediment pollution, which can cloud waterways and smother aquatic habitats
    • Bush fires: Ash and sediment left behind after fires
    • Boats and marinas: Fuel spills and sewage discharge.
  • Rural areas: In rural areas, pollution sources are more dispersed and include:
    • Agricultural activities: Fertilisers, pesticides, and sediment from broadacre cropping and irrigation farming
    • Grazing and intensive livestock industries: Animal waste and soil compaction increasing runoff
    • Land clearing: Both historical and current clearing practices that lead to significant erosion and sediment deposition in waterways.

These sources highlight the diverse ways human activity impacts the health of our waterways, emphasising the need for behaviour change and pollution prevention.

Main types of stormwater pollutants

Stormwater pollution comes in many forms, each with its unique impacts on waterway health. The five main types include:

  1. Litter: Items like cigarette butts, cans, food wrappers, plastic bags, and drink bottles are often swept into storm drains. This debris can harm wildlife, block water flows, and degrade natural environments
  2. Chemical Pollution: Everyday chemicals such as car wash detergents, excess garden fertilisers, paint residues, oil, and grease contaminate stormwater. These substances can be toxic to aquatic life and disrupt ecosystems
  3. 'Natural' Pollution: Organic materials like leaves and lawn clippings might seem harmless but contribute to water pollution. Unnatural quantities are flushed into local waterways and as these materials decompose, they deplete oxygen levels, harming fish and other aquatic organisms
  4. Sediment Pollution: Poor erosion and sediment control practices on construction sites and in areas of cleared bushland lead to increased sediment in waterways. Excess sediment can smother aquatic habitats, reduce water quality, and disrupt aquatic life
  5. Pathogens: Bacteria and viruses from leaking septic tanks, animal faeces, and sewerage overflows pose health risks to humans and wildlife. These microorganisms can cause waterborne diseases and degrade recreational water quality.

Understanding these pollutants is the first step in taking action to minimise their impact and protect our valuable local waterways.

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