Understanding the Pipe Network

An entry point to the pipe system near the school

What do we know about the pipe network and how it works? Answer: not everything. But over the last decade we have certainly increased our understanding of how it works. We know that the pipe under the landfill takes water from the springs, overland water from the hills and stormwater from the road. The water is contaminated by leachate from the tip, but we don’t know if that is intentionally or only through cracks in the ageing pipe structure.

The following are three parts of the system that have posed much head scratching and thought for quite some time, although the last (possibly) shows a welcome development.

Piping the Creek

The main (green) pipes come to and end, what does that signify?

When they first started the landfill, they had to put the small creek they were covering into a pipe. The largest nearby spring was also directed into the pipe, the other springs must have been deemed not sufficiently large to bother with. And that is the interesting point: as you work up the valley putting the water in the pipe, the quantity of water gradually gets smaller, because that is what streams do. So at what point do you stop the pipe, because if you go too far the water can’t get in! Looking at the maps there is a point just above the school where the main pipes stop, and a stormwater pipe enters from the side.

What too are the little propellor shapes, are they vents? (No surface evidence of that.) Are they there to let spring water in or leachate? Maybe one day someone might have the answer for us.

The Jumping Weir

Low water flow is diverted to the sewer, high water flow goes to the beach

The jumping weir is a system designed to divert leachate from the landfill into the sewer during low water flow, but to allow it to overflow into the stormwater system (and hence onto the beach) during heavy rainfall events (anything over 30 mm). The jumping weir consists of the three green close together manhole lids shown in the photo.

Given the increasing number of heavy rainfall events now, this means that the frequency of contaminated water entering the marine reserve is much higher. But the system has never worked completely effectively.

Connecting the Lowest Wetland into a Dedicated Stormwater Network

Getting water from the reserve to the (green) stormwater pipe at the bottom of Ara Haewai is not difficult at all

Much as many locals didn’t like the idea of the new housing developments down at the bottom of Houghton Bay Rd, one thing they have done is provide stormwater drainage along much of the lower part of the road.

Getting a new overland stormwater system down to the beach once the fields ran out was always a costly stumbling block to the idea of separating the leachate and the fresh water flows. A few years ago we could only imagine the cost of digging up Houghton Bay Rd to put a pipe from the lowest field right down to the roundabout, now from the maps it looks like we don’t have to do much more than cross the road to connect the lowest wetland into the stormwater network and avoid the jumping weir. This will save an enormous amount and really help the planning of the new system.

Of course, the million dollar question is: is that new pipe big enough to take all the water from the rest of the valley? Even if is isn’t, it may be enough to connect in the spring water and maybe even the overland water from the western hillsides, leaving the house and road stormwater for another stage. It wouldn’t allow for fish passage though.