Transcript
Page 1: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Coastal flooding risk on the Somerset coastline and

management responses

Dr. Chris Spencer

UWE, Bristol

Page 2: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Lecture :• Introduction to the location and environment

• History of flooding in the region

• Vulnerability to flooding and current protection

• Future problems

• Coastal management responses

Page 3: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

The roles of the coast :

• Defence

• Habitat

• Resource

Page 4: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Introduction to the location and environment

Page 5: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –
Page 6: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Introduction to the location and environment – coastal geomorphology

What are the key coastal influences in this area?

Remember your systems approach…..

Waves TidesWind RiverStorms Sea levelSediment supply VegetationGeology BeachesDunes SaltmarshesMudflats

Page 7: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Introduction to the location and environment – coastal geomorphology

What are the key coastal influences in this area?

Remember your systems approach…..

beach

waves sediment

sand dune

Page 8: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Introduction to the location and environment – coastal geomorphology

What are the key coastal influences in this area?

Remember your systems approach…..

Page 9: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Introduction to the location and environment – human environment

What are the characteristics of the human environment in this area?

Residential (Weston-super-Mare ~76,000, Burnham-on-Sea ~20,000)

Agriculture Somerset Levels

Industry Various

Energy Nuclear / Renewables

Tourism Various

Transport M5 / Railways

Page 10: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

A History of Flooding in Somerset?There is a long history of flooding along the Somerset coast13th December 1981

11km of coastal defences overtopped / damaged Flood water reached M5

Cooling pump at Hinkley power station affected 1000 properties flooded

50km2 agricultural land inundated 2500 cows/pigs/sheep killed

~£25M damage

Page 11: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

A History of Flooding in Somerset?

There is a long history of flooding along the Somerset coast

30th January 1607

~2000 people drowned 520km2 land flooded

Water depths of greater than 3m

Page 12: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

What makes this coastline so vulnerable to flooding?

1040 mb

1030 mb

1020 mb

1010 mb

1000 mb

990 mb

980 mb

970 mb

960 mb

Thursday 10th Friday 11th Saturday 12th Sunday 13th00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00

1040 mb

1030 mb

1020 mb

1010 mb

1000 mb

990 mb

980 mb

970 mb

960 mb

P.B.A AvonmouthBarograph13th Dec 1981With Hartland Pointsuperimposed

Vulnerability to flooding

Low lying land storm surges

Low and narrow natural barriers tsunamis???

Page 13: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Tide Gauge Plots forRiver Parrett, Bridgwater

15 16 17 18 19 20 21 22 23 24 01 02 03 04 05

m A.O.D.8

7

6

5

4

3

Normal tide

1.45 m surge

Actual tide

Storm surge• onshore winds• increased runoff• low pressure

• raised predicted tide level 1.45m

• Elsewhere in the area it was raised by 2m

Vulnerability to flooding

Page 14: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Areas Inundated by Sea Water

Parret EstuaryBanks

Portbury Wharf

West Leaze

ClevedonHurdick’s Blake’s

Wick St Lawrence

Sand Bay

Uphill

Brean

BurnhamHuntspill

SteartMinehead

Blue AnchorLilstock

PorlockHam Wall

Weston-S-Mare

STORM TIDE SURGE ON THE SOMERSETCOAST 20.25 GMT 13th Dec. 1981

Overtopped Sea Defences

BRISTOL CHANNELM5

Vulnerability to flooding

Page 15: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Just how close to flooding is this coastline?

Vulnerability to flooding

Completely reliant on the very narrow coastline?

Page 16: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Current defences

Coastal defence is currently provided by a combination of natural and man-made features

• Beaches and dunes• Mudflats and saltmarshes• Engineered defences

…..the 3 roles of the coast??

Page 17: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Current defences

The beaches and dunes absorb and dissipate wave energy by changing shape in response to high energy events.

beach

waves sediment

sand dune

This is a very delicate balance

Page 18: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Future problems….

What future coastal problems can you foresee?

Sea-level rise

Coastal squeeze

Increased storminess

Sediment starvation

Sand dune erosion

Compacted beaches

Page 19: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Future problems….sea level rise

Future global warming

Accelerated sea level rise

Page 20: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Future problems….sea level riseFuture global warming

Accelerated sea level rise

Page 21: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Future problems….sea level rise

Page 22: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –
Page 23: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Future problems….coastal squeeze

Natural coastal landforms migrate inland to cope with sea level rise

Can happen if no development/defence exists but all of our coast has defence and development

Thus the protective natural defence is narrowing….

Page 24: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Future problems….increased storminess

Increased storminess

Increased sea surface temperatures

Increased power of storms

Deeper low pressure and increased winds

More powerful storm surges

Page 25: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Future problems….

Sediment starvation

The Severn Estuary is sand starved

Beaches are becoming more muddy

Wet sticky beaches

Impact on sand supply to the dunes?

Page 26: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Future problems….

Sediment starvation

Reduced sand deposition

Increased silt/clay deposition

Coastal system responding to changes

Page 27: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Future problems….Sand dune erosion

Defence relies upon narrow dune ridge

Coastal system…..??

Sand being lost from dunes

Ridge narrowing, protection reducing

Risk of flood increasing

Page 28: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Future problems….compacted beach

Defence relies upon narrow dune ridge

Dunes rely on sediment from the beach

Becoming more muddy

Compaction reduces sand transport

Ridge narrowing, protection reducing

Risk of flood increasing

Page 29: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Summary:

Important area – defence / habitat / resource

Vulnerable to flooding in the past

Risk of flooding will increase with climate change

The protective coastal barrier narrowing and will continue to do so

What options exist to manage this situation?

Page 30: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Coastal management responses :

We will need some hard engineering

Few alternatives possible now

Land too valuable / too polluted

Good for defence/habitat/resource?

Page 31: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Coastal management responses :

Soft engineering solutions - beaches

Our systems approach to understanding coasts helps here

Wave energy will increase

We need to reduce wave energy

Can build beaches higher

Can build offshore barriers

beach

waves sediment

sand dune

Page 32: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Good for defence/habitat/resource?

Page 33: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Good for defence/habitat/resource?

Page 34: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Good for defence/habitat/resource?

Page 35: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Good for defence/habitat/resource?

Page 36: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Coastal management responses :

Soft engineering solutions - dunes

Our systems approach to understanding coasts helps here too beach

waves sediment

sand dune

Healthy beach – healthy dunes

Will increase sediment supply to the dunes

Manage footpath access

Restore ‘natural’ dune – maintain or increase the barrier protecting the low lying land

Page 37: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Work with the processes and a systems understanding of how dunes work

Restore dune vegetationManage tourist access

Repair eroded areas to maintain the natural barrier

Good for defence/habitat/resource?

Page 38: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

http://www.mass.gov/eea/docs/czm/stormsmart/properties/cost-comparison-chart.pdf

Coastal management responses cost

Page 39: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

Summary :

• The location is important locally and nationally in its human and physical environment

• The area has a history of flooding and is very vulnerable to high energy events

• This situation will worsen with climate change

• Some areas are already so developed that hard engineering approaches are the only solution

• Where possible we can use our systems approach to manage the coast to be resilient to future pressures

• Better able to provide defence / habitat / resource

Thank you….any questions?

Page 40: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –
Page 41: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –
Page 42: Coastal flooding risk on the Somerset coastline and ... · Remember your systems approach….. beach. waves. sediment. sand dune. Introduction to the location and environment –

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