Drainage systems and design
Greater Bendigo's stormwater drainage network includes drainage pits, pipes, culverts, dams, basins and open channels that provide an important service to the community by removing surface water from our roads and parks, and provides a facility for buildings to connect their drainage to. The network is managed by the City of Greater Bendigo.
The City’s drainage assets are worth more than $300M and includes more than 42,000 drainage pits and 940kms of pipes and culverts. The City spends $1.5M per annum maintaining the system so that it remains serviceable. It also invests annually in the renewal and upgrade of existing stormwater systems to benefit the community.
Use the North Central CMA Flood Eye tool to check property flood levels and drainage information before buying.
- Keep flow paths clear of obstructions.
- Don’t build any structure or obstruction in stormwater easements.
- Don’t divert stormwater to your neighbour’s property.
- Keep gutters and downpipes clean.
- Keep paved areas to a minimum as they prevent water being absorbed into the ground.
- If there is an easement in your property it must be well-maintained by the property owner to allow stormwater to run freely.
In urban areas, the increase of impervious areas has reduced the amount of rain that infiltrates the ground or is retained by vegetation. Consequently, more stormwater run-off enters the drains system.
Prior to 2000, urban drainage in Bendigo was designed for the minor, frequent rain event and there wasn’t always consideration of what happens to flows in larger events. When Bendigo receives rainfall more intense than a minor event, pipes fill up, pits overflow and roads flood as the flow tries to make its way to the nearest creek or waterway.
The City of Greater Bendigo now has the challenging task of upgrading its network to modern day standards, to ensure major events do not impact people and property. The City is prioritising these works and at this stage there is in the order of $40M of work required to bring the network up to modern day standards. Due to the large amount of works required, these are being prioritised and some time will be required to work through these issues. The Urban Stormwater Management Plan review is being undertaken currently which will update the planed drainage upgrades.
An OSD system is designed to restrict the flow of stormwater from a development site to a rate equal or less than the pre-developed site conditions.
All new developments, particularly unit developments, create an increase in hard surface area resulting in a higher volume of runoff being discharged into City's existing drainage system. The existing drainage system was not designed to cope with the increased volume of runoff.
An OSD system is required as part of all new developments across the greater City of Bendigo to limit stormwater flow rates to pre-development levels. Stored flows are released slowly thus not increasing the overall rate of discharge.
An OSD system located within a development site is a private asset that is owned and maintained by the owner/s or owners corporation. The City is not responsible for these systems.
Ensure your building designer gives appropriate consideration to how your site drains. Ensure earthworks cuttings do not attract surface flow towards the dwelling and surfaces are graded away from the house.
Roof water must be connected to a legal point of discharge and it is a breach of the Water Act if stormwater causes a nuisance to downstream properties. City has no legislative powers to enforce the Water Act.
The road reserve in a subdivision has been designed to carry a large storm (1% Annual Exceedance Probability (AEP) event. At some point kerbs will overflow. Ensure flows are not encouraged into your new dwelling by setting of low house level or driveway design. Also ensure driveways are not located in line with the City’s drainage pits in the street.
Flood risks and drainage are key considerations when planning all new suburbs.
Today, underground drainage systems are generally designed to cope with frequent storms – those with a 20% chance of occurring in a year. Any excess water travels along planned overland flow paths that carry water away from properties. This prevents them from flooding in the majority of storms – up to those with a 1% chance of occurring in a year.
We also look at other benefits when designing drainage systems, including the impact on rivers and creeks. For example, including gross pollutant traps, which capture large litter items like plastic bags, bottles, newspapers to prevent them being washed into rivers and creeks. Including a wetland to improve stormwater quality, provide greater flood protection and other Water Sensitive Urban Design methods (WSUD).
Find more information at: http://www.bendigo.vic.gov.au/About/Document-Library/water-sensitive-urban-design-resource-kit
More technical information about stormwater drainage design is available here: http://www.designmanual.com.au/
For more information about drainage systems and design, please contact our Engineering unit on 1300 002 642 or [email protected]