Introduction

The tail-race has a long history of use as a slalom site.

The Whitewater Taranaki had working bees to install rock groynes by hand to create eddies in the early 1980's. They organized some slalom events, and we had some good events in the 90's

The tail-race has been used for slalom training camps.

The course has been recognized by good slalom paddlers to have potential.

However in recent years without long boats, the emphasis has been on play-boats, and now creek boats.

The following is a short history of tail-race development since 2001 when it was realized that there was a potential for a play-spot. The idea of the ledge came from Penrith white water course. The idea of the weir came from the fact that water backed up during a flood making the very rough play-spot in existence better.

BOTTOM PLAY WAVE

The initial step was to build a play wave below the bridge. Permissions were gained in 2002 from TRC ,Trustpower, and DOC. The ledge was built by trial and error using a digger. This used large boulders delivered from the quarry.

Then cement was used to create a level ledge.

A petrol motor hire concrete cutter was used to trim the rocks making up the ledge.

In 2010, a digger and then a working bee deepened the pool. This changed the characteristic of the hole in that the play-boaters right side was not so easy to spin on. However it was successful in cleaning out the frustrating rock obstruction to vertical moves.

A recent no flow inspection has revealed a couple of rocks that still need to be moved where there is the boil on the right hand side. These rocks cleared out in 2016 reducing the boil.

In 2013 the shoulder on the left was tweaked-made higher to get rid of annoying flush outs on that side.

In 2016 the shoulders were further modified to guide the flow. This has improved the hole at low flow i.e does not flush out at low flow anymore.

WEIR

The weir was built by digger in 2003 and cemented by a working bee. The weir is almost the same height as the play-hole ledge.

The weir provides control of water level for the play-hole. The gap on the right of the weir is used for fine tuning this level. The level is critical to how retentive or flushy the play-hole is.The optimum level at high flow seems to be slightly under 300mm on the gauge placed near the big tree. This means the pool level is 300mm above the ledge.

In 2010 a digger and then a working bee deepened the pool. 4 wheel drive was successful in dragging rocks out with a rope basket.

The weir was tidied up on upstream edge to prevent any possibility of foot entrapment at Topec's request during power station shutdown. The downstream edge is still jagged and undercut however. In retrospect I think the weir should have been another ledge. This could still be done by trimming the downstream side with a concrete cutter, and placing timber plank boxing, and filling gap with concrete. The rocks in pool below need cleaning out. This would make the weir safe for swimmers.

TOP WAVE

The top wave was built in 2010 during a power station shutdown. The purpose was to allow front surfing and spinning for intermediate level paddlers to develop their skills and for teaching.

The digger was used in 2011 to deepen the pool (but the power cable gets in the way to some extent). The wave would be improved at high flow by raising the shoulders by50mm or so. Unfortunately the power station does not like this at it can back up the water level on maximum flow causing erosion.

In 2016 a flat pad was created on the shoulder allowing blocks to be easily added - directing all the water through the wave, thus building up the pile. It is a perfect spin spot at high flow. Blocks need to be removed to keep power station happy.

MIDDLE WAVE

This wave was built in 2014 during another power station shutdown. It provides a wave cross between the two eddies on either side, and front surfing. The ledge has been raised slightly with a temporary wooden strip to make the wave pile higher and wider. Removed again. Need to build shoulders higher before raising the ledge.

TROLL WAVE

The troll wave under the bridge was built in 2012 during a power station maintenance period.This provides some interesting front surfing. It also backs up the eddies further up and deepens the channel. A bit flushy at high flow and could be tweaked by raising the ledge a little.

SLALOM EDDIES

The tail-race course is primarily for kayak play-boats, but is also designed for kayak slalom boats. The aim is to create eddies for upstream gates. And to deepen these eddies so that paddle does not

touch bottom. And to provide room between eddy line and gate to plant paddle to turn slalom boat.

PUBLIC USE

Sleds, lilos and boogie boards must also be considered.

Here the aim is to deepen and clean up the central channel so that these users do not bump into rocks

MAINTENANCE

Annual maintenance is needed to combat any flood erosion and to trim the vegetation.

A stock fence has been put in Feb 2015 by NPDC to keep cattle out of tail-race (at instigation of a resident living near TOPEC).

All work is carried out with rocks for natural look. Tyres, wire baskets, timber, etc are all avoided.

Cement is used to bind rocks to prevent collapse of features. However all work is reversible- the cement can be readily broken up using a sledge hammer. Hopefully this will never be necessary.

Photos from slalom practice day 10 November 2012