Slips Bite into Council Roading Funds

Slips are creating a multi-million dollar headache for Kaipara roading engineers with approximately 300 active examples currently recorded around the District.

Council’s Roading Portfolio holder, Tom Smith, says storms in July 2008 were responsible for 74 slips across Kaipara with an estimated repair cost of at least $4.5million. Recent wet weather has added new ones and caused some existing slips to move further, adding another $1.5million in repairs.

Council has already received NZ Transport Agency (NZTA) funding for the 74 with most attracting a subsidy of 85% or better and applications for the recent ones are currently being prepared. So far 34 slips have been repaired this year although some current works are now on hold until drier weather.

“However, even at these subsidy rates the local share still leaves a big bill for ratepayers to pick up” says Councillor Smith. “It is a big and costly problem.”

He explains that all slips are inspected and prioritised for repair, taking into account a number of factors including the seriousness of the slip, urgency, the risk it constitutes, the effect on the community and the cost of repair. “For example, a low cost but high risk will put a slip to the top of the list, while if the cost is high and there isn’t a high risk it gets a low priority. Community impacts are very important so we take into account factors like the number of vehicles using the road, whether community facilities are being served or bus routes are involved.”

The repairs are grouped into special contracts or, where possible, included in maintenance contracts. Frequently a road can be kept open by just clearing minor falls as they happen. Making a site safe and re-opening to traffic is a top priority.

Working on the principal that spending a little early is better than a lot later, Council has persuaded NZTA to provide $660,000 to repair potential slips before they become major and costly. “This involves identifying areas where there is a risk of slips occurring and funding the highest risks. typically the cost is half that of waiting until damage occurs,” says Councillor Smith who adds that the current wet winter has shown the approach to be working well and Council is likely to continue it in future.

Meanwhile Kaipara District Council has begun using a new environmentally friendly “living” technique to repair some slips. This involves alternating layers of willow brush between layers of fill, allowing the brush to sprout, with the roots forming a reinforcing mat which is supplemented by “socks” of mulch and grass seed to cover and help stabilise the fill wall. This method is being used in Kaipara for the first time repairing a slip on Omamari Road and is planned for ten other suitable sites.