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Our stormwater systemWai āwha

One of the core goals of the city’s stormwater system is to minimise the effects of flooding. Our system consists of open drains, large underground mains pipes and pump stations with about three quarters of the city now reliant on pumped systems for stormwater drainage.

Crossing State Highway 2, Cross Country Drain Project 2009.

Our goal is for the stormwater in Napier City to meet the 80% ANZECC guideline for water quality. This means that the urban waterways, one day, will be able to support healthy ecosystems with thriving aquatic and riparian life, becoming areas of pride for people of Napier.

What is stormwater?

Stormwater is the water that comes from rain which falls on our roofs and yards and doesn’t soak into the ground. Because most of Napier City is very low lying and flat, this water has to go somewhere or our homes and streets could flood.

That’s the job of the stormwater network; to move the water that hits the ground from roofs in order to prevent flooding. The network consists of a series of roadside channels, sumps, underground pipes, pumping stations and urban waterways (such as those that pass under Kennedy Road, heading towards Ahuriri Estuary).

Unfortunately, more and more development has meant that a large area of our city is covered with impervious surfaces like roads, roofs and pavements. Impervious means water can’t soak through it and replenish our groundwater supplies. As this stormwater runs across these surfaces, it picks up many things along the way. Anything left outside such as paint, oils, sediment (dirt), chemicals and litter can be carried by stormwater.

Vehicles can also play a big part, moving dirt, oils and chemicals. Anything that is left lying on the ground of a yard that a vehicle may drive over can be tracked onto the road where it also poses a threat to the health of our waterways.

When it rains, about 70% of the stormwater in Napier City is carried to the Ahuriri Estuary.  The rest is carried to the Pacific Ocean along Marine Parade, Hardinge Road, and Westshore.

This means that the estuary and the ocean can get dirty from everything we do around it. There are about 14,500 hectares of land that drain to the estuary, and when we leave contaminants (such as paint, oils, chemicals, litter, etc.) exposed to rain, the water that flows off our properties pollutes this precious environment.

Pollutants can be very toxic to aquatic life and often increase algae and microbes (bugs) in the water, negatively affecting ecosystems and people. The contaminants increase until they arrive at the estuary or coast. This affects our ability to collect kai moana and enjoy recreational activities.

The stormwater network – where does it all go?

The furthest areas of the stormwater network (Awatoto North, Meeanee, Jervoistown, Taradale, Poraiti, Bay View) are largely agricultural or lifestyle areas. Activities in these areas result in contaminated stormwater from run-off of agrichemicals, farm animals, septic tanks and sediment.

Downstream from here (Greenmeadows, Pirimai, Marewa, Onekawa, Maraenui, Te Awa, Parklands, Tamatea, Napier Hill, Westshore), residential activities result in litter, car washwater, lawn clippings, dog droppings, paints, oils, sediment, and brake dust.

Downstream from here (Napier South, Napier CBD, Carlyle/Thackeray Street, Corunna Bay), commercial premises introduce litter, rubber residue, oils and brake dust, more car washwater and spills.

Downstream from here and closest to the estuary, we have Onekawa and Pandora Industrial Areas, with heavy wet industries and heavy vehicles which can move contaminants with their tyres onto impervious surface areas.

What about wastewater?

Wastewater is different: The wastewater network is made up of underground sewer pipes that are designed to only take away ‘waste’ water from domestic uses such as washing dishes and clothes, showering, and toileting. It also takes away certain liquids from industrial processes. It is not designed to take rainfall. Sewer pipes take this wastewater to the Wastewater Treatment Plant at Awatoto.

What is the Napier City Council doing about stormwater?

Napier City Council has committed to spending $20.6 million on stormwater improvements in the next ten years. This, if combined with us all working together to look after our water, will improve the water quality of our estuary, so that it can remain one of the most significant cultural, environmental, ecological, and recreational sites on the East Coast of New Zealand.

The urban stormwater system is being continually upgraded. The current design standard requires the system to be designed to cater for the type of storm the city might expect to experience once in every 10 years in such a way that limits surface ponding. Increasing infill and greenfield developments have added more buildings, driveways, roads and sealed surfaces within the city boundaries, resulting in greater volumes of water running off the hard, impermeable surfaces and putting pressure on the existing stormwater and pumping systems. Up until 1996, the system was based upon a two year return period, meaning the city had a 50 per cent chance of stormwater ponding in the streets each year. There is now about a 10 per cent chance of similar ponding in any one year, known as a 10 year return standard.

It is a huge and very expensive task that will take decades to increase the stormwater system's capacity from the old design standard to the new design standard. The Council has been allocating funding for this purpose ever since the new standard was introduced.

During floods, priority is given to pump station operations, in particular cleaning the screens free of weed to allow the pumps to operate to their peak capacity.

How can we improve our stormwater and urban waterways to help our estuary and coast?

The most important message is that only rain should drain to the stormwater network, and you can help by ensuring you keep your yard clean of potential contaminants, limiting the chance of stormwater contamination.

Stormwater Cross Country Drain

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