M2PP Expressway -The Big Flood –Is Kapiti flood management at risk? Part 1 the Setup.

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Actively supporting NZ’s endangered wetland birds

Wharemauku creek Bridge - from the West looking East

Last weekend (17-18 Sept) we had another large flood. This  followed the major storm event of last May when houses were evacuated around the lower reaches of the Wharemauku. This overnight storm dumped 150mm onto this coastal plain and then just kept going. The latest storm brought a lesser amount. around 125mm over a longer period -60 hours so the Wharemauku didn’t top its banks this time, but it stayed at banktopping level over this time while the flooding around the expressway was immediate and spectacular.

There has been no coverage of this in the local press so we are going to go through from the beginning. This will take a couple of posts so bear with us.

Aerial shot of dune lake before destruction

This is an orientation picture of the swamp as it used to be (2012). The Wharemauku creek weaves from lower right (east) through the settlement, then out top left (west). The Expressway has bisected this dune lake, cutting along the bent white line at top right of this Council foto. The original dunelake (dark spot in the middle of the orange) had been used as a holding pond, but has now been drained; while contractors are currently digging out and landscaping an  area on the Eastern side of the expressway.

Eastern excavations in progress

This area was being pumped out the day before the storm, over to the western side of the expressway and was pretty much empty.

Pumping water to west

The leaking hose

We reported previously that this area had been drained out into Drain 7, below the pollution monitors. Following our report this drain has been closed off. We are not sure whether we should take credit for this, but the effect was immediate in showing in clearer (though still dirty) water in the lower Wharemauku. This western side of the expressway however, now began to fill with dirty water being pumped from the east.

Western side before storm and draining - with new plantings under water

Dirty water pumped through e/way to west.

A new drain has been opened to drain the dune lake, into the Wharemauku but this was blocked by a large steel plate.

steel plate blocking drain

As the Wharemauku began to flood however, the force of water pushed aside the plate and began to backfill the whole area. 

Wharemauku Saturday morning -17th sept plate askew and backfilling underway

A farmed area above the bridge and nearer town usually acts as a flood plain for the creek, releasing water to help protect the residential area below from major floods.  But the Wharemauku wasn't bursting its banks and this area remained clear as the creek began to rise through Friday night. But with the bridge drain set low in the creek by the Saturday morning, both sides of the Wharemauku area had been engulfed. Come lunchtime the NZTA had sent a lone worker with a shovel down to sort it all out. 

A finger in the dyke? Shovelling in the storm lunchtime Saturday - 

This looks rather like the NZTA hasn't really much of a clue about what was happening down here. So did they?

In the next post we track the rising water…meanwhile  the track we are listening to while posting this is Leadbelly –Aint gonna study war no more. 

Gonna lay down my sword and shield

Down by the riverside

Down by the riverside

Down by the riverside

Gonna lay down my sword and shield

Down by the riverside

Ain't gonna study war no more.

He put that out 50 years ago and has it made a difference? We’re thinking of all those caught in Aleppo at the moment so that question answers itself.

Environmental artist Jill Studd’s blog

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