What is inflow?
Stormwater that enters directly into the sewer system.
Causes of inflow
Runoff from hard surfaces, such as roofs and driveways, which enters the sewer system through incorrectly installed downpipes, drains or low lying gully traps that overflow when it rains.
A gully trap prevents smells and overflows from entering buildings. They are usually located outside your house, generally in the area outside your kitchen, and should be above ground level to ensure that stormwater does not enter the sewer system.
What is infiltration?
Groundwater, or stormwater that seeps into the ground, then incorrectly enters the sewer system through defects in sewer pipes or joints.
Causes of Infiltration
Cracked sewer pipes that have deteriorated from:
- being placed under pressure from local development and heavy traffic
- damage from tree roots
- poor installation or maintenance.
Groundwater can then infiltrate through the cracks in the sewer pipes.
Infiltration usually occurs where the groundwater is higher than the sewer pipe or where soil above the sewer system becomes saturated from rain events.
Problems caused by inflow and infiltration
During heavy rain, excess stormwater that incorrectly enters the sewerage system can cause it to back up and overflow sewage into homes and the environment.
When stormwater or groundwater incorrectly enters the sewer system it can cause problems and increase costs for the community through:
- Property damage: Flooding on private residences and businesses can occur as sewage pipes become overloaded with stormwater and groundwater and this does not drain away fast enough;
- Environmental damage: The health of our waterways and its users can be compromised by overflow from the sewerage system when it enters our rivers and creeks;
- Infrastructure damage: Roads and surfaces deteriorate with surface flooding and poor drainage, increasing maintenance costs for Council and ratepayers; and
- Electricity and treatment costs at the sewage treatment plant increase to process the extra water in the sewerage system.