The Eastoke
Peninsula - A Study in Coastal Defence
To see a poster version of this
information with more images, follow these links (PDF - Adobe
Acrobat required):
- Page 1a -
Introduction (346kb)
- Page 1b
- Eastoke Facts (357kb)
- Page
2 - Beach Replenishment (275kb)
- Page 3 - The Future; Climate Change; CHIMET
live data service (203kb)
Since the early 1920's the Eastoke Peninsula has been
increasingly developed as a residential area. The building of beach
huts and bungalows commenced in the 1930's along the backshore of
the wide shingle beach. Natural erosion of the foreshore made it
necessary to build defences to protect these properties.
By 1939 it was necessary to build a concrete seawall in front
of the Beach Club, with a timber revetment (sloping surface) and
groynes adjacent to it.
By 1974 these defences had extended to the east and west, for
a total of 2.6 kilometres. It was this seawall which made the
natural erosion of the foreshore worse. Beach levels continued to
reduce and by 1978 repairs to the seawall were required.
Prior to the 1985 Beach Replenishment Scheme the southern
Eastoke Peninsula frontage regularly overtopped, causing flooding
damage. The ageing concrete seawall was also approaching the end of
its serviceable life and a failure could have led to erosion of up
to 3 metres per annum and subsequent loss of properties. The
frequency and severity of overtopping (water carried over the top
of a coastal defence) events was increasing annually. In an effort
to reduce the damage, a rear splash wall was constructed along the
entire length of the seawall. These measures did not adequately
prevent regular overtopping or storm damage to properties.
- FACT: Original 1920's beach was a mixtures of
sand and shingle.
- FACT: Residential development resulted in need
for defences.
- FACT: Defences caused erosion leading to a
loss of Sand and Shingle beach, which led to a need for
BIGGER not necessarily better
defences.
- FACT: Flood Damage = Structural damage, a
common occurrence.
| The Beach Replenishment Scheme (1985) has successfully
alleviated further incidents of this nature by removing the waves
energy before it is reflected by the concrete seawall. The scheme
involved importing half a million cubic metres of shingle from the
Owers Bank and placing it on the beach over a length of 2.2
kilometres. There is a requirement for ongoing maintenance to
provide the necessary level of protection. |
 |
|
Such a large amount of material being injected into the sediment
transport system, resulted in the rapid transport of material along
the frontage. In 1987 timber groynes were built in order to try and
control the transport rate along the replenished area and in 1990 a
rock groyne was constructed to further reduce loss of material
around Eastoke Point.
In 1992 it was necessary for emergency repairs to be carried
out at Eastoke Point, these works involved the construction of 150
metres of rock revetment and rock stub groynes. These works proved
to be successful and a stable beach was maintained.
|
 |
A Beach Management Plan was adopted in 1992, although now
expired, the objectives of this plan included:
- Continuous monitoring of the beach.
- Immediate reaction to any rapid drawdown (rate at which sea
removes material) in a groyne bay (beach compartment between two
groynes).
- Carry out annual beach recycling.
- Use of material accreting (accumulation of beach sediment) at
Central Beachlands as a source of material.
The success of the Beach Management Plan (1992), led the
Council to develop and approve recommendations contained within the
Beach Management Strategy Plan for the southern frontage of the
Eastoke Peninsula (1999). This Plan recommended defending the
frontage against a storm event with a return period (average period
of time between occurrences of a given event) of 1 in 200 years,
which is achieved by adopting the following:
Groynes and revetments are regularly monitored along the
beach, with the profile of the groynes being adjusted by adding or
reducing the number of planks to suit the changes in beach profile.
Unfortunately there is a net loss of some 5,000 cubic metres per
year of shingle from the Eastoke frontage, this is due to it not
being possible to recycle all the shingle that is moved out of the
area; the 5-yearly nourishment operations restore this
material.
The most suitable time for undertaking the annual shingle
recycling operation is around Easter; as this will avoid the
severest winter storms and the summer period will allow the
material to naturally sort and develop a resistance to storm
events.
Monitoring and research is an important part of Beach
Management. Surveys are carried out in order to identify sources of
suitable material available for extraction and recycling to the
Eastoke promenade area. The better our understanding of coastal
processes allows Engineers to design sustainable schemes. The
following are examples of the type of monitoring that the Council
undertakes:
- Surveys of beach profiles.
- Surveys of seabed bathymetry.
- Sediment Budget Analysis.
- Recording wave heights.
- Recording wind speed and direction.
- Recording tidal data.
- Measurements of current velocity and direction throughout tidal
cycle.
BEACH
NOURISHMENT OF THE EASTOKE FRONTAGE
Beach nourishment is the placing of material
from offshore onto the beach, in order to maintain the required
standard of protection along the frontage for the residents of
Eastoke, Hayling Island.
In 1985 the beach nourishment
scheme was implemented, creating a man made beach in front of the
now redundant sea wall. Coastal processes are constantly eroding
this frontage and without intervention the redundant concrete
seawall would again be exposed. The result of this would be a
return to regular serious flooding of Eastoke, through continuing
erosion of the coastline.
The wave energy dissipation diagram shows how the beach
profile created through nourishment will absorb the wave energy and
help to prevent overtopping.
The shingle beach along the
southern frontage of the Eastoke peninsula is the first line of
defence against the threat of coastal erosion and flooding. The
Council is the Coast Protection Authority that enables the use of
permissive powers to manage these risks when it is considered in
the Public interest. The Council developed and approved a Beach
Management Strategy Plan that identified the most effective
approach to managing this frontage; this decision was made after
considering all economic, environmental and technical criteria. The
beach nourishment works are one element of this preferred approach
to managing this frontage and will restore beach material that is
moved out of the area by natural coastal processes.
Council Officers have been monitoring the coastal processes
around the Eastoke area over many years and have determined that
wave and tidal action moves shingle in both directions along
the beach from a drift divide around the middle of the
frontage. Part of this material therefore moves eastwards along the
frontage and into the entrance to Chichester Harbour. This material
is then moved by strong ebb tidal currents at the entrance to the
Harbour and comes to rest approximately a kilometre offshore.
The above diagram shows how the natural coastal processes move
beach material around the Eastoke area.
(To view the images click on the thumbnails above. To return
to this page use your browser's "Back" button or equivalent.
)
The above diagram shows the areas of accretion within the
safe passage of navigation that can be a hazard to mariners
navigating the approach channel to Chichester Harbour. Havant
Borough Council work in partnership with Chichester Harbour
Conservancy to reduce the hazards identified, where possible,
through the beneficial use of arisings for Beach Nourishment
operations. This ensures the material is not removed from the
local sediment transport system.
Nourishment Works Summer 2009
In September 2008, Havant Borough Council
successfully completed phase one of the Beach Nourishment scheme
placing 25,000m³ of material on the frontage of Eastoke.
After securing funding from the Environment Agency, Havant Borough
Council now intends to carry out the second phase of the operation
this summer. This involves placing a further 65,000m³ of
material on the frontage to raise the beach to the recommended 1 in
200 year Standard of Protection. The works will take
approximately 2 months to complete, dependant on weather and the
dredger commitments.
The estimated arrival date of the Dredger is
between 10th June - 17th June 2009. This start date is
subject to change dependant on weather and the dredger
commitments.
For further information on the 2009 Beach Nourishment
scheme please follow the link below:
In an attempt to further improve the management of the Eastoke
coastline, the Council is working with the Environment Agency to
develop an Eastoke Peninsula Strategy Plan. This will identify the
preferred coastal management approach for both the southern and the
northern frontage. It is hoped that this document will enable the
necessary funding to be acquired from central government to
continue to protect the Eastoke residents.
Adequate protection at Eastoke Point, around the Nature
Reserve, is of crucial importance to the prevention of flooding.
Upon approval of the Eastoke Strategy, Council Officers will be
carefully considering all options available to improve the present
standard of protection.
Advances in technology will enable improvements in the
delivery of the coastal defence service, the following are some of
these opportunities:
- Use of Global Positioning Systems ('GPS') satellites to monitor
changes in beach levels.
- Use of the Internet to make information available.
The Council has published the East Solent Shoreline Management
Plan 1997. This document contains a wealth of information on our
existing knowledge of the coastline from Pagham Harbour through to
the River Hamble and also recommends the preferred approach to
future coastal management.
Another popular web site is
CHIMET, which provides actual
measurements of:
- Tidal Heights.
- Wind Speed.
- Wave Heights.
- Temperature.
- Barometric Pressure.
The provision of this service has been undertaken in
partnership with Havant Borough Council, the Chichester Harbour
Conservancy, the
RNLI and the
Chichester Harbour Federation.
The predicted effects of climate change and sea level rise
present a significant challenge for future coastal management. It
is anticipated that there will be increased risk to many coastal
assets. Key pressures are identified as follows:
- Increased problems of overtopping of existing defence
structures due to sea level rise.
- Increased beach volatility and increasing sea levels will mean
beach recharge schemes may require increased material volumes.
- Diminishing beaches and marshes in front of defences reducing
both support and protection of structures.
- Higher sea levels will result in greater wave heights at the
shoreline, resulting in increased wave forces on structures.
- Potential changes in patterns of longshore drift could result
in altered patterns of erosion and deposition.
- Increased potential for 'flash flooding' of low-lying areas by
intense rainfall events.
- Erosion and 'squeeze' of inter tidal habitats between rising
sea levels and existing or new coastal defences.