Coastal flooding, 1607 floods, recent

storm surges and weather events in

the Severn estuary

Dr Kevin Horsburgh

Head of Marine Physics, National Oceanography

Centre

23 September 2011

National Oceanography Centrefrom coast to deep ocean

Waterfront Campus, Southampton Joseph Proudman Building, Liverpool

Vision: The National Oceanography Centre will, by 2015,

be recognised as the world-leading Centre for integrated ocean sciences and technology".

Some key facts

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Mean Sea Level

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Independent scientific advice

Global mean sea level rise

Storm surge hypothesis for the 1607 flood

Storm surges

• Deviations from

predicted tidal heights

are mainly due to the

effect of the weather on

the sea surface

– Low atmospheric

pressure

– Strong winds

• Storm surges are

devastating, and cause

loss of life

The flooding of the Bristol Channel in 1607

• At about 0900Z, on 30 January 1607, the lowlands surrounding the

Bristol Channel suffered the worst coastal flooding on record

• The flood waters caused extensive damage in Bristol, the Somerset

levels, Barnstaple and places on the Gwent levels

• Its geometry, orientation with

respect to prevailing storms, and

exceptional tidal range make the

Bristol Channel and surrounding

regions susceptible to flooding

• About 44 square miles (120 km2)

of Somerset are at or below sea

level, a fact that inevitably gives

rise to inundation

• Similar topography on Welsh

side

• A flood risk management

document for the Environment

Agency refers to severe

historical flood events in 1672,

1770 and 1809

Taunton to

Glastonbury road

in flood (2000)

Bristol Channel tides• The Bristol Channel has the world’s second highest tidal

range:

– Bay of Fundy, Novascotia 15.4 m (Spring range)

– Bristol Channel 12.6 m

• Gulfs like the Bay of Fundy and the Bristol Channel are

known as quarter-wave resonators. They dimensions are

very favourable to amplification of any ocean wave (e.g.

tides)

ocean tide

head of gulf

amplification

l

Real time data span selector

• The tide of January 1607 was the largest in a century

• Tidal amplitude was 7.86 m which occurred at 0900h on 30 January 1607 (new style)

• Times of exceptional tidal forcing tend to recur every 4-5 years

• The largest tide at Avonmouth this century was 7.78 m on 20 March 2007

But the yeere 1606, the fourth of King James, the ryver of Severn rose upon a sodeyn

Tuesday mornyng the 20 of January beyng the full pryme day and hyghest tyde after

the change of the moone by reason of a myghty strong western wynde.

John Paul, Vicar of Almondsbury, 26 January 1606 (Old Style).

This storme begane at 3 of clock in the morning and continue tyll 12 of clock on the

same day.

Barnstaple Parish Register, 1607

Source/

Reported weather

Chap-book by Edward White Stormy

Puritan pamphlet by William Jones Vaguely implies fine weather

Anonymous pamphlet Stormy

Camden’s Brittania Stormy

Walter Yonge’s Diary (1848) Stormy

Barnstaple Parish Register Stormy (see text box)

Almondsbury Parish Register Stormy (see text box)

Arlingham (Glos) Parish Register Stormy

Stow (1631) Stormy

Historical sources of information

1 “A true report of certaine wondefulle

overflowings…”

Chap-book by Edward

White

The Mirror?

2 “God’s warning to his people of

England…..”

Puritan pamphlet by

William Jones

The Mail?

3 “Lamentable Newes out of

Monmouthshire in Wales….”

Anonmymous pamphlet The Sun?

4 Brittania William Camden The Telegraph?

5 Stow’s Chronicle The Times?

6 The diary of Walter Yonge Spectator?

Storm surges in the Bristol Channel

• Tidal curves for Avonmouth, Newport and Hinkley Point were calculated

• Surge (from 27 Oct 2002) of amplitude 2 m was added to the tidal curve over a cycle centred on high water, plus 0.3m for wave set-up

• The water level was input to a flood plain inundation computer model

• Even allowing for topographic changes, the inundation of 30 January 1607 could have been brought about by a more modest surge than that selected here

The Lisbon 1755 earthquake and tsunami

• The great earthquake

of 1 November 1755

(~8.5 Ms) destroyed

the city of Lisbon

• Waves of over 10 m

were reported in Cadiz

along North African

coastline

• Evidence of waves 2-3

m with correct periods

in Mounts Bay,

Cornwall Copper engraving of Lisbon harbour (J

Kozak collection)

Run 26 - Bristol Channel

0

0.5

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1.5

2

2.5

3

3.5

4

4.5

0 50 100 150 200 250 300 350 400 450 500

Node number along section

Ma

xim

um

tsu

na

mi

wa

ve h

eig

ht

(m)

Ten

by

Mil

ford

Hav

en

Car

dif

f

Lla

nel

li

Sw

anse

a

Av

on

mo

uth

Min

ehea

d

Ilfr

aco

mb

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Bu

de

Further flooding events of 1607

• According to the same

historical sources, regions

in East Anglia flooded on

the same day – (two

tsunamis would certainly be

a warning from God)

• The 1607 event reminds us

of the destructive power of

storm surges

• Scientific effort goes

constantly into the

improvement of surge (and

tsunami) forecasting

systems

Components of the UK coastal flood warning system

National tide

gauge network

15° real-time

data

Met Office

0.11°atmospheric

model

0.22°ensemble

atmosphere

3rd

generation

wave model

NOC

Tide-surge

models

Surge

ensemble

Flood

Forecasting

Centre

24/7/365

Environment Agency

Regional forecasters

(Wave transformation and

overtopping models)

EMERGENCY

RESPONSE

UK operational storm surge modelling system

What caused the flooding in 1607?

• The balance of evidence is that the event

was a storm surge on top on an

exceptionally high tide

• The majority of the historical writings imply

a time of great storminess and the same

conditions were reported widely across

Britain

• The villages affected correspond to those

that suffer during floods today

Meteotsunami

– 27 June 2011

Weather patterns for 1607• The 16th and 17th centuries appear to have been

windy. Lamb (1977) records 116 North Sea flood events between the years 1500-1599 and 128 events for the 17th century. This number then diminishes to 68 for the years 1700-1799

• One climatic reconstruction for 1596 suggests constant gales for western Britain as a result of enhanced variability of temperature

• One serious candidate for the windy conditions would be the displacement southwards of the atmospheric jetstream, causing a corresponding shift in depression tracks to lower latitudes than now (i.e. Britain would receive ‘Icelandic’ weather)

Sheerness

Lowestoft

Immingham