The contemporary engineering approach to drainage is to recognise stormwater is part of the total water cycle.
Consideration needs to be given to the impact on the receiving environment, its integration into the built environment, and to recognise water supply is a limited resource and the urban drainage system provides opportunities to reduce the consumption of potable water. The overall goal is to manage the quantity and quality of water effectively in regard to the amenity of development and the environment.
The following information outlines the key objectives to be considered in designing our drainage system. Further objectives specifically related to development services schemes can be found in our Principles for Provision of Waterway & Drainage Services for Urban Growth.
Increased area of impervious surfaces
Commercial, industrial and residential development increases the amount of impervious areas, which in turn increases the frequency and volume of runoff generated from rainfall.
This can adversely impact on the natural environment, resulting in increased flooding of land, increased waterway erosion, transport of sediment and pollutants, and detrimental impacts on aquatic and riparian life. Furthermore, in relation to the built environment, any increase in the frequency and intensity of flooding may impact on property and recreational uses.
To minimise the impact on Melbourne's waterways from changes to natural flow regimes, including flood frequency, runoff volume, runoff frequency and flow velocity resulting from urban development.
To ensure new urban developments don't have an adverse impact on downstream properties.
Decreased water quality
Urban development impacts on the quality of stormwater and can result in increased levels of nutrients, toxicants, sediment and litter entering the receiving waterways and ultimately Port Phillip and Western Port. This in turn has a detrimental impact on all life forms in both the aquatic and riparian environments.
To protect Melbourne's waterways from pollution, including, nutrients, toxicants, sediment, litter and changes to water chemistry.
Integrating drainage into the urban environment
Successful integration of elements of drainage systems into the urban landscape can provide benefits to all stakeholders. These resources can enhance visual amenity, provide recreational opportunities and can help to engender a sense of 'ownership' and focus for the local community.
Preserving, and in some cases restoring, natural features of drainage lines and waterways, such as natural channels, wetlands and riparian vegetation can often be advantageous to both the environment as well as enhancing visual amenity.
To encourage integration of drainage systems into the urban landscape to maximise the visual and recreational amenity of developments.
Flood impacts on property and life
Flood flows can damage built assets and impact on human safety. Drainage design needs to consider the extent, velocity and duration of flood on the built environment and issues associated with human access, isolation and protection.
To ensure new habitable buildings are protected from flooding in major storms and new subdivisions provide overland flow paths for all surface flows.
To ensure that flood waters don't present an unacceptable risk to the community.
Management of flows
Urban drainage systems are commonly designed to ensure minor flows don't collect in ways that cause inconvenience or hazard.
To ensure piped drains have sufficient capacity to convey minor storm events and guarantee flooding isn't a regular nuisance.
Water isn't an infinite resource and stormwater harvesting must be considered to reduce the consumption of potable water.
To encourage measures to reuse stormwater as part of urban development.
Culture and heritage
Protection of cultural and heritage assets helps to maintain a sense of continuity with the past and provides a sense of connection to the community and landscape to lived experiences.
To ensure the protection and preservation of cultural and heritage assets (wherever possible) in accordance with legislative requirements.
To ensure all new drainage assets being delivered through the land development process are constructed in a safe manner and don't present the community and our stakeholders with on-going safety issues.