The armour

What the city bolted onto the hills when the rocks came down. 288 engineered rockfall defences sit in the council’s asset register: anchors drilled into cliff faces, cables lashing boulders to the slope, mesh draped over loose ground, catch fences between the rocks and the road. 288 of them still carry "temporary" in the name: emergency works from the quake years that became permanent by default.

Defences on file

288

Still "temporary"

288

emergency works, kept

Anchors & cables

236

holding the rock to the hill

Rated poor or worse

on the file’s own scale

The armour, drawn

Every defence in the register over the suburb outlines: dark pins are anchors drilled into the cliffs, accent pins the cables, green shapes the mesh drapes and the bund, red lines the catch fences. Hover for the kind, install year and the file’s condition.

By the kind of work

anchor installed 2010–2012 · 3 rated poor on the file 131

cable installed 2010–2012 · 3 rated poor on the file 105

mesh installed 2010–2012 36

barrier installed 2010–2011 · 6 rated poor on the file 15

bund installed 2011–2011 1

Where the armour stands, by suburb

By the count of defences the register files under each suburb.

Each defence files under the suburb that holds its pin: the count, the kinds, how many are still named temporary and how many the file rates poor. A record is the asset file’s word, not a current engineering assessment.

The latest works on file

Temporary Rockfall Meshinstalled 2012-07-30 · good · the ground →
Temporary Rockfall Meshinstalled 2012-07-30 · good · the ground →
Temporary Rockfall Meshinstalled 2012-07-30 · good · the ground →
Temporary Rockfall Meshinstalled 2012-07-30 · good · the ground →
Temporary Rockfall Meshinstalled 2012-07-30 · very good · the ground →
Temporary Rockfall Meshinstalled 2012-07-30 · good · the ground →
Temporary Rockfall Meshinstalled 2012-07-30 · good · the ground →
Temporary Rockfall Cableinstalled 2012-07-30 · good · the ground →

Questions, answered briefly

What are the defences?

The engineered armour on the Port Hills. After the earthquakes shook 20,000 rocks loose, the council bolted the slopes back together: 131 rock anchors, 105 rock cables, 36 mesh drapes, 15 catch fences, 1 bunds, 288 assets in the register, clustered where the rockfall survey found the houses exposed. An anchor is a steel bar drilled deep into a cliff; a cable lashes a boulder to the slope; mesh drapes the loose face; a catch fence stands between the rocks and the road.

Why does the register call them temporary?

Because that is what they were: emergency works, installed through the quake years while the hills kept dropping rock on the suburbs below. 288 of the 288 assets still carry "Temporary" in the asset name. Temporary stopped meaning soon a long time ago: the works are inspected and condition-rated like any other asset, and they are still the thing between the boulders and the houses.

How does this differ from the boulders page?

/boulders is the survey, every rock the geologists mapped after the quakes, fallen or still wobbling. This page is the response, the hardware the city installed to keep the wobblers where they are. Read together they are the whole rockfall story: what came down, what might still, and what is holding it.

What does the condition rating mean?

The asset file’s own grade, 1 is very good, 5 is very poor, recorded at the last inspection. It is the register’s word on the asset, not a fresh engineering assessment: steel corrodes on a marine cliff and the rating on file is only as fresh as the last look. A defence near a house is a maintenance record, not a guarantee.

The record behind this

Christchurch City Council’s open data, the Structure service’s rockfall-protection layers: RockAnchor, RockCable, RockMesh, RockBarrier and RockBund. A record is the asset file’s word on what was installed and its last condition rating, not a current engineering assessment. The rocks the survey mapped are /boulders; the houses below carry their own ground record at /before.

This page as markdown: /defences.md · the record as data: /defences.json · /defences.geojson · /suburb-defences.json · on the live map: /map?layer=defences.