Transcript Case Study: Christchurch Bay

Case Study:
Christchurch Bay
An extended stretch of coast.
Overview to Christchurch Bay
Christchurch bay is located
on the South Coast of
England. It is formed
between the headlandHegistbury Head near
Christchurch, Dorset and a
spit at Hurst, Keyhaven close
to the town of Lymington in
Hampshire.
Christchurch bay is located within cell 5
of the England and wales sediment
cells however this stretch of coast acts
as a sub cell on its own with little
sediment leaving this area and coming
into the area.
Christchurch Bay comprises a 16km section of
open coastline exposed to dominant waves
from the south-west.
This area of coast erodes at
between 1-3m/ year
Geology
• The rocks and clays forming the Christchurch Bay and Solent coasts include
• materials laid down when the Solent was an estuarine river that drained the
• Hampshire Basin. These were never subjected to the great pressures that
formed
• the harder rocks to the west. With rising sea levels after the last Ice Age, the
• chalk ridge that formerly linked the Purbecks with the Isle of Wight was
• breached, and the former river valley became the new coast, and started to
• erode. This led to the formation of Poole Bay. The land to the east was protected
• initially by the ironstone outcrop at Hengistbury Head, but in due course this too
• eroded and, as sea levels continued to rise, Christchurch Bay began to develop.
• The dominant south-westerly wind and waves created a littoral drift of shingle
• and sand along the coast in an easterly direction, initially forming the Shingles
• Bank which lies between the mainland and the Isle of Wight, and subsequently
• forming Hurst Spit.
Fetch
• Wind action generates waves that impinge on the shore from
various directions.
• The longer its ‘fetch’ (the distance the wind travels without
interruption),
• The more powerful are the waves that it generates. Around
the District’s coast, winds are strongest in Christchurch Bay,
where the fetch varies from 10 km for winds from the north to
many thousands of kilometres for those from the south-west,
extending across the Atlantic Ocean to the coast of South
America.
Sediment Cell 5
WEST TO EAST
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Hegistbury Head
Mudeford Quay
Mudeford/Avon Beach Site 1
Highcliffe Cliffs site 2
Barton on sea site 3
Milford on sea Site 4
Hurst spit site 5
Hegistbury Head
• Hegistbury Head is a sandstone headland located in Dorset on
the south coast close to Christchurch between Southampton
and Bournemouth.
The headland on the west
side of the bay.
• HH is a SSSI
The groyne that sticks out
into the sea makes sure that
sediment from
Bournemouth bay doesn’t
spread into that of
Christchurch bay.
Mudeford Quay
• Mudeford is where the Avon and Stour flow out of
Christchurch harbour into the sea this flow stops Hegistbury
head connecting with Mudeford spit.
Hegistbury Head
Christchurch
Harbour
Mudeford Spit
Mudeford
Mudeford/ Avon Beach Site 1
Avon beach
groyne
Mudeford
quay
Mudeford spit
Avon beach is located to the east of the
quay. This is one of the sandiest beaches in
the bay . This is due to the coastal defences
in the area but also due to artificial
dredging.
embankment
Sea wall
Highcliffe site 2
Friars cliff
Site 2
Highcliffe castle beach
LSD takes away material from
these beaches. And takes it to
Hurst
The HH long groyne stops these
beaches looking like those at
Bournemouth. As less sediment
is transferred to this bay.
Highcliffe site 2A
To Barton
TO HH
In this picture you
can make out the
coastal slump due
to the recent bad
weather. Naish
holiday village sits
on top of this cliff.
The cliff is
retreating at
roughly 1m per
year.
Barton-on-sea Site 3
Barton beach
-Coastal management: Groynes, Rock armour,
Each stone costs roughly £5000
- Erosion toward the middle of this picture you can see mass movement at Bartonrotational slip - this is due to cliff collapse due to a permeable rock sitting on an
impermeable rock
Milford On Sea Site 4
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Milford - sea wall rock armour
Cliff is very close to sea
this is eroding very quickly
up to 3m per year
rocks have been moved by current storms
The fetch here comes all the way from Brazil, this coast gets
battered by storms.
Hurst Spit site 5
• Currently there is Less material than usual at the spit is due to the recent
storms.
• Therefore emergency work is in place to rebuild the spit
• without this spit Lymington and surrounding area would be under water!
• Hurst spit it the headland at the most eastern part of the bay. Hurst spit is
formed due to a change in direction on the coast and a river mouth, this
creates the spit with Hurst castle on the end of it and Keyhaven salt
marshes.
Case study – Erosion and Destruction
JAN/FEB storm 2014
Barton
Hurst Spit
Sources
• Ian West - Southampton University
• New Milton Advertiser
• Google Maps