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Stormwater

StormwaterMost of our district’s stormwater goes into the Karamu Stream and then out to sea. That means the things we do above ground at home, at work and when we are out and about, can directly affect the stream.

Stormwater is not treated. What you put onto your driveway or throw onto the street gets washed into the stream and then out into Hawke Bay: Paint, grass clippings, car wash soap, engine oil and grease, construction debris, pesticides, cigarette butts, dog poo . . .

Those pollutants affect the health of the stream and sea water and that of the animals living in them, whether by increasing levels of nitrogen that encourages unnaturally high algae and plant growth, or by choking animals trying to eat bottle tops or cigarette butts.

We all want cleaner waterways, so we all need to care.

Stormwater drains are for rain – nothing else!

What is stormwater and how do we deal with it?

Stormwater is essentially in the name: rain; particularly heavy storm-related rain.

Stormwater systems are used in built-up areas to remove rain water from streets to prevent flooding. It is necessary because areas where towns are built lose large amounts of natural habitat that would normally soak up rain water.

The more hard surfaces we have – things like roofs, driveways and forecourts – the more rain runs into the stormwater system rather than seeping into soft areas like gardens and lawns.

In areas with a very high ratio of hard to soft surfaces, typically commercial/industrial areas and high-density housing subdivisions, on-site stormwater detention systems are required to help stop the system being overwhelmed during large rain events.

While it is principally about rain, in both commercial and home settings it also copes with water from other sources, such as from hoses used for cleaning.

In both instances, the water carries whatever is on the ground into the stormwater system. That’s where the problem is. All water in the stormwater system ends up, untreated, in the Karamū Stream.

With 331 kilometres of pipe coping with an average 8.6 cubic metres of water a second, our stormwater system certainly has a lot of work to do.

Much of the core pipe infrastructure dates back to 1950, when the district’s then councils decided that a system should be installed to direct stormwater away from built up areas to reduce the risks of flooding. Those same risks exist today; in fact, with increasing housing and business density, leaving less and less soft ground to soak up rain water, the risk has grown.

The sizes of the pipes vary considerably, with the largest of the modern pipes having a diameter of 2.3m – roomy enough for the world’s tallest NBA basketballer (2018) to stand up in with a couple of inches to spare.

There is about one kilometre of pipe for every 213 people living in the urban areas serviced by the stormwater system: Hastings, Flaxmere and Havelock North.

It is not just about pipes however; there are more than 5000 roadside stormwater drains, 6000 sumps, 21,000 connections and 12 pumping stations across the network.

In today’s money, the infrastructure has a replacement value of $250 million and costs in the vicinity of $700,000 a year to maintain.

In rural areas, stormwater is generally managed using open roadside drains which are maintained by the owner of the road. In the case of highways that is NZTA, while local rural roads and drains are maintained by Hastings District Council’s roading team.

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