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GEOG309 Flood and Hazard Management in the Avon Corridor THE CHRISTCHURCH EARTHQUAKES 2010 - 2011

The earthquakes have caused subsidence along the Avon Corridor of around half a metre and in some places even more.

It is obvious when comparing LiDAR images before and after the earthquakes that some areas are actually lower

than the Red Zoned Bexley

Some areas are well below the High Tide.Ground levels at the end of Kibblewhite St. are 10.1m

The area inundates on every high tide.

Flood banks are stated to be 11.2mErosion is only about 30-40 cm below the

top of the flood banks.

The land is still subsiding

Lateral displacement of the area is significant.There are about 700 meters down to bedrock.

Current plans for Sea Level changes till 2100 = 50cm

Current plans and predictions from Council

estimate that the current flood banks are

sufficient to prevent flooding in the area

despite 50 cm sea level rise.

The fact with water and sand is that water will find

its way to it natural level. When sea level rises

the ground water rises and land bearing decreases.

Houses might sink.

This area has been dewatered

extensively after the earthquakes.

This is a very short term solution.M

arine ParadePine Avenue

Estuary Road

Pages Road Anzac Drive

Dyers Road

Union Street

Bexley Road

Bridge StreetBreezes Road

Keyes Road

New Brighton Road

Bak

er S

treet

Waitaki Street

Hawke Street

Oram

Avenue

Wairoa Street

Lons

dale

Street

Pal

mer

s R

oad

Beresford Street

Car

isbr

ooke

Stre

et

Owles Terrace

Birch Street

Bow

er A

venu

e

Eure

ka S

treet

Blake Street

Rowan Avenue

Rowse

s Road

Orari Street

Seaview Road

Marlow Road

Tovey Street

Wattle D

rive

Sin

clai

r Stre

et

Kibblewhite Street

Jervois Street

Jellicoe Street

Keppel Street

Falcon Street

Meo

n St

reet

Hood Street

Rodney Street

Sandra Street

Shackleton Street

Guernsey Street

Wetlands Grove

Cor

ham

pton

Stre

et

Morganwood Street

Rawson Street

Bellamy Avenue

Mountbatten Street

War

bling

ton

Stre

etFa

rnbo

roug

h St

reet

Cradock Street

Portchester Street

Admirals Way

Caithness Street

Brighton Mall

Woodlands Place

Mattingley Street

Drake Street

Parenga Place

Seabreeze Close

Waik

are

Lane

Rawhiti Avenue

Mitcha

m P

lace

Otakaro Place

Bexley Road

¯

LIDAR Data August 2011for CCC use only Scale: (A4)

Drawn: IBDate: 29 April 2013

Avon River Modelled Flood Depth: Map 6

LegendCity Plan Flood Management Area

Flood Depth0.0 - 0.2 m

0.2 - 0.4 m

0.4 - 0.6 m

0.6 - 0.8 m

0.8 - 1.0 m

1.0 - 1.2 m

1.2 - 1.4 m

1.4 - 1.6 m

1.6 - 1.8 m

1.8 - 2.0 m

2.0 - 2.2 m

2.2 - 2.4 m

2.4 - 2.6 m

2.6 - 2.8 m

2.8 - 3.0 m

0 500250Meters

Background: World Street MapESRI, ArcGIS Online Name: Avon_D13_50yr_pt5mSLR_PostDecEQ_SB11pt2_v5_Depth

1:15,000Model Version: D13Rainfall: 50 yearBathymetry: Post December EarthquakeSea Level Rise: 0.5 mStopbanks: 11.2 m RL

What you have seen so far is the area that has flood banks

Most of the area South of Bridge St. does not have any floodbanks in place.

Christchurch land is the best investigated land in the world

Should the communities be made aware of known hazards?

Should a managed retreat be considered?

What is the responsible approach?

Many Scientists have different

opinion on probable sea level rise.

The big question is.

WHAT DOES THE

FUTURE HOLD FOR THIS AREA?

200 Year flood plainCCC Plan

200 Year flood plainCCC Plan

Floor levels Before Earthquakes.

Damage after Earthquakes - Floor levels and Land drop.

BEFORE

NOW

Floor Level 11. 35m

Floor Level 11. 25m

Floor Level 11. 15m

Floor Level 11. 05m

Floor Level 10. 95m

Floor Level 10. 85m

Floor Drop , 15 cm

Floor Drop, 35 cm

Floor Drop, 45 cm

Floor Drop, 55 cm

Floor Drop, 65 cm

Floor Drop , 25 cm

Floor-levels now from 11.5 - 10.8 metersLowest properties, uninsurable, not a valid mortgage security. Hazard potential from building authorities.

These houses can be refused insurance. Consequences; EQC is not liable in case of future events.

50 Year flood plain

50 Year flood plain

200 Year flood plainCCC Plan

Using “Existing Use Rights” these repairs are allowed by CCC.

50 Year flood plain

CCC South New Brighton Reserves Management PlanPlan for Sea Level Rise of 50cm and consider a rise of at least 80cm by 2100.

Questions from The South Brighton Residents’ Association

Illustrations modified from EQC land report

AFTER REPAIRS

All houses built to then current floor-levels of 11.5 meters, 50 year flood plainValuable properties, insurable, valid mortgage security.

We would like to know why CCC has enabled the use of “Existing Use Rights” to by pass the Christchurch City Plan Regulations

1. What are the lowest floor levels CCC will consent based on "Existing Use Rights"? 2. Will CCC be liable for to low floor levels consented when flooding occurs in this area as per the leaking house syndrome?

3. Has CCC looked into legal implications of using "Existing Use Rights" in Flood management area considering the Land Drop? 4. What are the conditions that would trigger a Hazard Notice issued on the LIM/PIM? (No use in stating “we will not do that”) (Insurance question)5. What certainty can be given by the insurance companies that they will continue to provide insurance after flooding occurs in this area?

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