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Gorge Update from David McGonigal

by | Dec 19, 2011

This week has seen a second crew swing into action at the bottom of the slip, so we now have two teams ready to work seven days a week to clear the slip and get the road re-opened. Although wet weather has prevented work at the top of the slip for the past couple of days, work to clear debris at the bottom is continuing.

The slip

The benching team made fantastic progress this week (in spite of the weather) and we are close to finishing the first bench.

You can see from this photograph just how deep they’ve had to cut down into the hillside.gorge 1

Finishing off the first bench

Our engineers have developed an easy to understand series of diagrams to help explain the technical side of the earthworks operation going on at the top of the slip. We are currently finishing Stage 4 and, as soon as the weather clears, we’ll embark on Stage 5: cutting the second bench. A second crew started down at the bottom of the slip this week, including spotters to keep watch at the slipface. Using a 20-tonne digger and a large loader, they’re shifting significant amounts of slip material away from the river—up to 250 truck movements a day, with 10-14 trucks being filled in a rotating convoy, rather like a conveyor belt. It takes two bucket-loads of the large loader to fill each truck. This has created a ‘hole’ and the benching crew up top can send their material down towards it. This means that a good proportion of debris can now be cleared away by the road crew rather than falling down into the river.

 gorge 2The road crew creating the hole to collect debris from the top of the slip

The river

As you’ll know from last week’s update, rocks and dirt have slumped down the slip face into the river, and the Horizons Regional Council decided to close the section of river 200m either side of the slip in late November. You can see from the photo below that the sediment entering the river has formed a “delta” that has narrowed it at the base of the slip. This is having a small impact on the flow of the river. But with the road crew now onsite, the amount of sediment going into the river will be greatly reduced, and we expect that rain will allow the river to naturally wash away the bulk of the sandy debris forming the delta.

gorge 3The delta of debris pushing out into the river

Horizons experts have been monitoring the river and we are working collaboratively with them, MWH and Higgins to minimise any risks associated with the slip. Work is being carried out under the emergency provisions of the RMA, and while we don’t anticipate the river will become blocked, a protocol has been developed in case it does. Work will stop immediately, Horizons Emergency Management team will be alerted and the river will be cleared of recreational activity down as far as Ashhurst Bridge.

Alternative routes and Woodlands Road

We continue to monitor conditions on the alternate routes and are making repairs quickly and efficiently wherever necessary. Now that the council has closed Oxford Road, maintaining Woodlands Road is even more important. We’re tackling it in two sections. The first is between Oxford Road and Sowry Rd. We’ve stabilised this section and will seal it at the weekend (weather permitting). The second section is between Sowry Rd and SH3. Our focus is on keeping this section of pavement intact, so we are patching any damage as necessary during the holiday season and will begin a full restoration job in early January. By holding off until then, motorists won’t have to deal with this section of road being unsealed during the busy holiday time.

Something to look for on Saturday NZTA Regional Director Central Jenny Chetwynd has written an opinion piece for Saturday’s Manawatu Standard. It reiterates that sorting the Gorge out is our top priority, and outlines our approach to getting the Gorge re-opened and ensuring a sustainable future for the alternative routes. Please be sure to have a look for it at the weekend.

In the meantime, remember to look at our dedicated gorge web page: http://www.nzta.govt.nz/manawatu-gorge.