mount barker floodplain mapping project 28 june 2011 · floodplain mapping project 28 june 2011...

Professional, independent

land and water

solutions benefiting

people and the environment.

Mount Barker

Floodplain Mapping

Project

28 June 2011


land and water



Evening Outline1. Welcome and Introductions (10 mins)

– Background to the Project

2. Introduction to Floodplain Mapping (5 mins)

– What the maps represent

– How they are used

3. Presentation on the development of the maps (30 mins)

– Steering Committee

– Historic information

– DTM/Survey

– Hydrology

– Hydraulic modelling

4. Explanation of the maps (10 mins)

– Flood inundation

– Flood Hazard

5. Some thoughts on flood preparedness (10 mins)

6. Some Words from Emergency Services (5 mins)

7. Where to from here (5 mins)

8. Questions and Comments (15 mins)

A u s t r a l i a n

WATEREnvironments


land and water solutions

benefiting people and the environment.


land and water



Introduction

Project Background

• Flood plain maps

– Inundation maps - the maximum depth in a flood

– Flood hazard maps – combines depth with the speed of water

• How they are used

– Identifying need for works and actions

– Town planning

– Assess damage costs

– Raising awareness

– Help SES to respond


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• Flood risk can be considered in terms of the average recurrence interval (ARI).

• This is the number of years on average within which a given flood will be equalled or exceeded

• 1 in 100 ARI means there is a 1% chance of a 100 year flood in any year

• The occurrence of floods is largely random– a 1 in 100 year flood may not occur in every 100 years and conversely,

several floods which exceed the 1 in 100 could occur within any period of 100 years

– (e.g. Rural City of Murray Bridge had two 1 in 100 ARI floods within a few months)

ARI

(average recurrence interval)


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Study Approach

• Define mapping area

• Collect ground elevation data in area to be mapped (Digital Terrain Model (DTM))

• Collect ground survey to fill in gaps and verify structures

• Collate hydrological data across catchment Rainfall Data and streamflow data

A4260557 – located near Mt Barker Springs

• Collate relevant reports and historical

information


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Big Floods

• Mount Barker Creek has experienced minor flooding over the last 30 years with significant flows in 1987, 1992 and 1996 resulting in minimal damage

• Last significant flooding event April 1970 (prior to installation of stream gauging for Mt Barker Creek)


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Catchment

85.8 km2

30 year growth area


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Bridge and Culvert Locations

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!South

Eastern Freeway

Mount

Barker

Creek

Wes

tern

Fla

t

Cre

ek

Mount BarkerRoad

Adela

ide R

oad

Wellington

Roa

d

Road

Mount Barker

Littlehampton

Fla

xley

Cre

ek

Fla

t

Wes

tern

Cre

ek

Rail

way

35

36

X2

X4

37

X9

X8 X7

X6

X5

X3

X1

X20

X32

X31X30

X29

X28

X27

X26 X25

X24

X23

X22

X21

X19

X17

X16

X14

X13X12

X11

X10

X34

X33

Bridge railway

X18

X15


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Predicting flood flows

• Develop numerical model of flood hydrology

(RORB /Drains used to estimate the volumes and rates of runoff generated from rainfall

Mike 21 used to predict how the runoff will flow across the landscape)

• Calibrate model against recorded and

observed information

• Establish floodplain hydraulic model

• Test model and prepare maps


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Sub - catchments


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Calibration Challenges• Mount Barker has being growing rapidly

• Other changes in the catchment over time

• Limited number of “extreme” events to calibrate against

• June 1987

• August 1992

• September 1996

• Calibration Results


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Design Floods

• Based on design rainfalls from BoM research.

• Rainfall of xx ARI causes flood of same likelihood.

• Rainfall occurs across whole catchment.

• Catchment conditions do not change.

• Fully developed catchment.

• Allowance made for farm dams.


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Design Floods

ARIPeak Flow

(m3/s)

Rainfall

(mm)

Duration

(hrs)

20 58.6 65 9

50 77.6 80 9

100 117.8 92 9


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100 Year ARI

Calculated hydrograph, OUTFALL

0

10

20

30

40

50

60

70

80

90

100

110

120

Dis

cha

rge

(m

³/s)

0 5 10 15 20 25 30 35 40 45 50

Time (hr)

Calculated02468

10121416182022

Ra

infa

ll (m

m)

Gross rainfall

Rainfall excess


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Explanation of the Maps

Flood Inundation


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Explanation of the Maps

Flood Hazard


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1 in 100

ARI Event


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Flood Preparedness

• Damages reduced if people are forewarned and have a plan of action in place. The longer the better!

• Flood warning – rainfall and stream gauges and a

communication system.

• Flood response plan for individual landholders. Minor improvements can reduce damages. (Flood proofing).

• Planning to manage new development so that the

potential damages don’t get any worse


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Flood Preparedness

• Key is to be prepared ahead of time

• Prepare a Flood Management Plan

– What parts of your property are at risk ?

– What depth will the water be ?

– What is the flood hazard rating ?

– Identify what is at risk.

– Identify who will do what.


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What is at Risk?

• – eg important documents, electrical goods, floor coverings, valuable furniture, photographs, gas bottles

• relocate permanently; relocate upon flood warning;

take upon evacuation; affix safely, building bunding to protect.


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Emergency Response Kit

• Portable radio• Torch

• Spare batteries• First aid kit and manual

• Waterproof bags

• Waterproof footwear with non-slip soles• Waterproof gloves

• Candles • Waterproof matches

• Spare clothing• Medicines

• Emergency contact names and numbers


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Special Needs Issues to Consider

• Personal Care Equipment

• Electricity-Dependent Equipment

• Water Service

• Mobility

• Debris

• Transport

• Routes to nearest high ground


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Reducing Flood Risks

• Keep a list of items to relocate if water threatens your home, including:

– dangerous items (eg chemicals), waste containers, electrical goods as well as valuables.

• Measures to take to protect your home –– turning off electricity and/or gas

– seal all openings to your home such as doors, gully traps and wall vents;

– identify items that will need to be secured to prevent floating away (eg gas bottles)


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Reducing Flood Risks

• Place important documents, personal effects and vital medical supplies in a waterproof case and move to a safe and easily accessible place in case you need to evacuate.

• Place furniture on beds / tables and personal items on the furniture.

• Secure items that may become buoyant in your yard (gas bottles, drums, timber etc).

• Block toilet bowl with a strong plastic bag filled with earth or sand to prevent a backflow of sewage into your home.

• Cover drains in showers, baths, laundries etc with a strong plastic bag filled with earth or sand to prevent a back flow of sewage into your home. Can also use rubber lined brick.

• Make arrangements for your pets.


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During a Flood

• Avoid driving or walking through floodwater - these are the main causes of death during floods.

• Floodwater may be deeper or faster flowing than you think and may contain hidden snags and debris.

• Crossing flooded bridges and causeways is dangerous and should not be attempted.

• Keep listening to a local radio station for further information and advice.

• Keep in contact with your neighbours.

• Be prepared to evacuate if advised.


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Emergency Services


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Where to from here


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1986 Floodplain Mapping

Freeway

Hawthorn Road

Adela

ide R

oad

Alexandrina Road

Flax

ley

Roa

d

Wellington R

oad

Bollen

Road


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Other Council Studies

• Nairne Creek Flood Study June 1995

Detention basin upstream of Parr Street

Current study for North Railway Terrace

• Meadows Township Stormwater Management Report 1992

Mawson Road Levee, channel widening, new culverts


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• Kanmantoo Township Stormwater Management Study 1992Flood control dam, channel widening, culverts (Kanmantoo Township Floodplain Mapping Report 2004 verifying effect of construction works)

• Littlehampton Flood Study Junction Road Catchment 2005Impacts of new developments “Spring Park Farm”


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• Callington Township, Kanmantoo Creek Flood Study 1992

Floodway and levee, Callington Drainage Plan, Drainage along South Terrace

• Macclesfield Flood Study 1995

Drainage works Luck, Lutterworth & Nunnely Streets


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Study Results

• The areas of greatest concern from a 1 in 100 ARI flood perspective are (in no particular order) at:-

– Railway Creek immediately downstream of Hurling

Drive and downstream of Fletcher Road;

– Surcharge from the Morphett Street drainage

system;

– Western Flat Creek between Adelaide Road

through to the junction with Littlehampton Creek;

– Littlehampton Creek just upstream and

downstream of Gawler Street


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Proposals under consideration within the 2011/2012 budget:

– Stormwater Drainage Network Analysis Mt Barker Township (including Min DPA)

– Upgrade the culverts at Hurling Drive to accommodate the 1 in 100 year ARI flows and widen the creek between the Hurling Drive and Faehrmann Avenue culverts.

– Bald Hills Road culverts upgraded to accommodate 1 in 100 ARI flows

– Council has made application funding from the Stormwater Management Authority for the above culvert upgrades

2011/2012 Budget Proposals


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• Following completion of the Stormwater Network Analysis, prepare and implement a Stormwater

Management Plan for Mount Barker township

• Seek grant funding from the Stormwater Management Authority for the preparation and

implementation of the plan

2012/13 and Beyond


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Key Messages

• The results of the Flood Plain Mapping will allow Council to better plan for any future development

within these areas

• Notify affected residents of the results of the study and

2011/12 budget proposals and beyond

• Reducing the risk of flooding is a shared responsibility

between Ratepayers and Council

• Whilst the proposed overall level of impact is considered relatively low, the issue is identified as a

high priority for Council to address


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Questions

mount barker floodplain mapping project 28 june 2011 · floodplain mapping project 28 june 2011...

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