Stormwater control critical to good health of our waterways

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Central Otago District Council executive manager infrastructure services Julie Muir outlines stormwater systems in this week’s Protecting our Water series.

Some stormwater and groundwater can get into wastewater networks. This is as a result of faulty pipes, and where private properties illegally attach stormwater drains to the public wastewater system.

During periods of rainfall, stormwater volume can increase and exceed the capacity of a wastewater network to convey it. When the network capacity is exceeded, heavily diluted wastewater is released into the environment.

There are a number of ways to reduce the frequency and volume of these “wet weather overflows”. Property owners should ensure downpipes are not connected to gully traps, and gully traps do not allow entry of stormwater run-off from surrounding areas.

Stormwater infiltration can also cause major problems in wastewater treatment plants by increasing the volume of effluent they have to deal with, reducing the effectiveness of treatment, and increasing the risk that treatment systems will flood and allow effluent to escape.

Central Otago District Council will be carrying out maintenance smoke testing on wastewater pipes in Alexandra and Cromwell throughout July and August.

The testing started last year in Alexandra. Smoke testing involves pumping smoke into the wastewater network to identify any cracks, breaks or faulty connections. It also pinpoints where stormwater is getting into the wastewater network through illegal connections, which costs our community.

Gully traps on the house will be checked at the same time to make sure they comply with regulations so that stormwater run-off from the property cannot run into the wastewater network.

Keeping the stormwater out of the wastewater network results in improved environmental outcomes for our community.

In Central Otago urban areas, approximately 40% of existing stormwater catchpits dispose water to the ground through soakpits. A soakpit is a porous-walled chamber that allows water to slowly soak into the ground. The remaining 60% feed into stormwater reticulation, which typically discharges directly to waterways.

To lessen the amount of stormwater going into waterways, new subdivisions usually install low-impact stormwater designs, which also discharge to ground rather than being fed into reticulation and ultimately waterways.

Council is reviewing the existing stormwater reticulation discharge points and considering options for reducing the impact this has on waterways.

Everyone in our community needs to work together with council in minimising the impact of stormwater on our environment. Wash your car on the grass to allow the dirty and soapy water to be absorbed into the ground, filtering the water and preventing it from washing into a stormwater drain. Be careful to clean up after any spills of paints (oil-based and water-based) and thinners, and avoid allowing any chemicals or cement to reach stormwater drains.

Safe, clean water is a precious resource we all value and council is committed to protecting it now and for future generations.