Subsidence Zones

Zone 2A

Worst subsidence zone at this stage.
A region of soft soil deep below the surface is having the water drawn out of it and it is collapsing. This is the result of Winstone Aggregates pumping the water out of the aquifer so that they can continue mining down to sea level.

Zone 2B The “Black Hole”
Second worst subsidence zone at this stage. The sub-surface soils have yet to be investigated, but the problem is thought to be the same as Zone 2A

Zones 3A and 3B
The experts predict that subsidence will be worse than in the neighbouring zones but maybe not as bad as in Zones 2A and 2B. Winstone Aggregates decided not to monitor these Zones during the first 3 years of dewatering from the quarry. At present there is insufficient survey data to indicate the severity of the subsidence problem.

Land Subsidence - What Went Wrong

March 1999 Winstone Aggregates started pumping the water out of the Three Kings Aquifer.
July 1999 First indications from the monitoring data (bore holes 11A and 15) that the subsidence predictions were inaccurate. Dewatering continues.
November 1999    Second indication of problems (bore hole 18A). Dewatering continues.
February 2000    Third indication of problems (bore hole 13B). Dewatering continues.
September 2001    Land subsidence exceeds the Resource Consent limit in Hillsborough Road (survey mark SM1979). Dewatering continues.
December 2001    Land subsidence exceeds the Resource Consent limit in the St Andrews Road / Mt Albert Road area (survey mark AP8A). Dewatering continues.
April 2002    Land subsidence exceeds the Resource Consent limit in the area around Shackleton Rd, Mt Eden Rd, Landscape Rd, Rewa Rd and Fulljames St. Also in the area around Rowan Rd and Mt Albert Rd. (data from 7 survey marks) Dewatering continues.
October 2002    Land subsidence exceeds the Resource Consent limit at 18 more survey sites in the following areas;
    :- Three Kings Plaza
    :- Duke St, Hamon Ave, McCulloch Ave
    :- St Leonards Rd, Mt Eden Rd
    :- Landscape Rd, Rewa Rd, Duke St, Mt Eden Rd
    :- Quentin Ave, Gorrie Ave, St Andrews Rd, Rowan Rd
    The Auckland Regional Council finally takes action and requests a temporary halt to the dewatering.

Land Subsidence   -   Recent Events
February 2003    Winstone Aggregates issued a report from Pattle Delamore Partners Ltd which recommends that “Active dewatering of the quarry should be reinstated quickly to allow a simpler model for transient calibration of the groundwater analysis.”
February 2003    Winstone Aggregates issued a report from Tonkin & Taylor Ltd requesting that the Auckland Regional Council accept far greater levels of subsidence than were approved in the Resource Consent. For Zone 2B there is no limit stated for the amount of subsidence.
March 2003    The Three Kings community waits to see if the Auckland Regional Council has the will to stop this subsidence problem before it gets seriously worse.