• hydrologic disturbance – eg changing surface and sub-surface flows, altering the volume or timing of water flows
  
• physical disturbance – eg by altering landforms, realigning or altering creek lines, lining of channels, changing water temperature
  
• contributing pollutants.
  
  

Vehicles and roadways contribute pollutants from:

• construction (sediments)

• fuel emissions
  
• wear and tear from vehicle tyres, brakes and other mechanical components
  
• accidental spills
  
• wear of the road surface, shoulder and verge
  
• maintenance practices such as herbicide use, mowing, road surface cleaning or reparation.

In addition, roads collect pollutants from the atmosphere and adjacent land use that are also washed off into the stormwater system.

Some of the impacts include:

• reduction of light penetration by increased sediments. This may clog the gills of fish and can hinder the ability of some fish species to see their prey. Sediments may also affect photosynthesis – the process that allows plants to use light as their source of energy
  

• when green waste decays in water it uses up oxygen
  
• litter clogs waterways and may be toxic to plant and animal life
  
• decay of some hydrocarbons can decrease dissolved oxygen levels
  
• nitrogen and phosphorus stimulate the growth of algae and aquatic plants
  
• changing the pH of water
  
• heavy metals from vehicle wear and chemicals from spills may be toxic to fish and invertebrates, or accumulate in the food chain.

Transport SA Management Measures

Transport SA minimises the impact of transport on water quality by including treatment measures in the design of infrastructure projects. This includes measures to treat pollutants in runoff from operational use of the road where feasible and practicable. For example, road runoff from the new bridge over the River Murray at Blanchetown is contained and directed to detention basins to remove pollutants

.

In addition, management measures are incorporated into contract requirements during construction. This includes documenting key project issues in an Environmental Management Plan and the contractor’s Environmental Management Implementation Plan and Soil Erosion and Drainage Management Plan. Treatment measures used during construction include silt fences, temporary cut off drains which drain to detention basins, stabilisation of slopes through mulching or revegetation.

Further information on how Transport SA protects waterways is provided in the following documents:

• Environmental Code of Practice for Construction This Code provides a guide to best practice for a range of environmental issues for those involved in construction of infrastructure projects.
  
• Environmental Code of Practice for Road Maintenance Workers This Code provides a guide to best practice for a range of environmental issues for those undertaking road maintenance.
  
• Water Quality Monitoring Manual for Construction Sites This manual provides a guide to planners and construction managers on water quality monitoring on construction sites.
  
• Protecting Waterways Manual This manual provides a guide to planners, designers and managers of transport assets on ways to minimise impacts on water quality and aquatic environments.

For more information see the case study or the "Water, wetlands and wildlife" fact sheet.

Understanding the impact of roads and traffic on road runoff and designing protective measures to minimise this impact is becoming more important. Transport SA is continually working towards a better understanding of the environmental effects of road and vehicle runoff. For further information see Transport SA – Water Quality Responsibilities .

Studies undertaken by Transport SA include:

Uni SA (1999) Arterial Road Runoff – Literature Review which summarises studies undertaken on the contribution of road runoff to stormwater pollution and includes strategic directions for further investigation from a workshop by key stakeholders.

Uni SA (2000) An Environmental Investigation to Assess the Effectiveness of Stormwater Detention Basins in Improving Road Runoff for Transport SA in which water quality monitoring of a detention basin on the Southern Expressway was undertaken to determine the effectiveness of the basin in removing pollutants.

Transport SA June 2002. Stormwater Detention Basins Sediment Assessment Report. Tonkin Engineering . This study undertook a chemical analysis of the sediments in a number of detention basins established to treat stormwater from sections of Transport SA roads.

University of SA (2002) - The toxicity of arterial road runoff in Metropolitan Adelaide - Stage 2