Pevensey Bay Flashcards
Locational context
Located on the East Sussex coast,
> Over several
thousands of years of natural processes associated with sea level
rise, and subsequent wave and longshore drift action, from west
to the east, have created a natural shingle barrier.
> This shingle bank
extends for nine kilometers between Eastbourne and Bexhill, and
although the shape of the coastline has continually changed
through geomorphological processes over hundreds of years, and
continues to be modified today, it has remained a natural
defense against coastal flooding.
What do the natural and man-made sea defenses currently protect?
> against the risk of permanent flooding of a 50 km2 area – including communities in Pevensey Bay, Normans Bay,
Langley, Westham
● 10,000 properties
● A259 coast road and railway line from Hastings to Portsmouth
● two nature reserves and an SSSI wetland site
● numerous livestock and arable farms.
Coastal processes
> The prevailing winds from the SW move beach material toward the NE
> During storms the beaches become flatter, creating beach profiles that reduce wave energy and prevent waves
from reaching the top of the shingle bank, thus reducing the flood risk.
> In the past the shingle bank and beach have been maintained naturally, however, research showed that the
movement of sediment was increasingly irregular and there was a net loss of 25,000 m3 of beach every year.
> The natural supply of sediment has been exhausted so the coast is trying to return to its previous position before
the last ice age.
AO2:
> Soft man-made defenses constructed of sand and shingles are seen as most effective in absorbing and breaking up the power of the waves. The lack of sediment
means that the beach is no longer self-sustaining and therefore human intervention is required to maintain the
beach.
What are the current sea defenses and sustainable management at Pevensey bay?
> Organised and maintained by the country’s first public-private partnership
(PPP) coastal management scheme.
> The project began in 2000 after a realization in 1997 that a 1-in-20-year storm event could breach the shingle
beach.
> Pevensey Coastal Defence Ltd (PCDL), was to run for 25 years and had
an initial budget of £30 million. The defences centre on the need to manage and improve the existing shingle
beach.
> The management is environmentally and aesthetically acceptable and is an example of a development which
maximises opportunities for future recreational and environmental projects.
> The crest height of the defence is 6m and the shingle bank extends seawards an average of 45 m.
> maintained with the use of 150 ageing wooden timber groynes. Since 2000 the project has removed each groyne as it fails, with the aim of retaining about 10, and focuses on a more sustainable soft
management approach to work with the coast processes.
AO2:
> removing groynes demonstrates the strengths of the soft engineering approach over old hard engineering methods.
> Climate change will cause sea level rise and extreme winter storms, increasing risk despite
these defences.
Recharge (beach management strategy)
Lorries transport 5,000 m3 around the harbour each year, but the remaining 20,000 m3 of gravel and sand is dredged from
the sea floor just offshore by the boat called the Sospan Dau and delivered to the beach over high tide.
The dredger comes very close to the beach and discharges a mixture of sediment and water using a technique known as rainbowing; which creates a mound of material high on the foreshore.
In recent years, rather than using bulldozers to push it into place (causing noise and disruption), all 20,000 m3 have been left in situ and redistribution was left to the natural process of longshore drift. This provided more natural sorting of the beach material and
saved considerable amounts of time and money.
Recycling (Beach management strategy)
Dump trucks and bulldozers are used to redistribute sand and shingle from areas of gain.
If relatively small amounts of sediment need recycling a ‘box’ or earth scraper is attached to the bulldozer to limit the use of larger plant machinery.
A02;
> Use of the Sospan Dau boat rather than the lorries is more socially sustainable as it reduces noise and congestion on local roads. Also, a much faster process so the beach is not left vulnerable to erosion.
Bypassing-shingle transfer (Beach management strategy)
During the winter months (so as not to disrupt the tourist season) trucks are used to transfer between 5,000 and 15,000 m3 of surplus shingle to the west (bypassing the harbour). This is either added directly to the beach or stockpiled as an emergency source of beach material.
Reprofiling (beach management strategy)
Destructive waves in winter storms remove material from the crest of the shingle beach and deposit it lower down the beach.
To prevent the shingle from being transported away by longshore drift a bulldozer simply pushes the material back up the beach, re-instating the beach crest.
AO2:
> Although developing a larger, wider beach is effective in reducing the flood risk, it does need constant maintenance which creates an economic and logistical challenge.
Groynes(beach management strategy)
Restoring the 150 groynes along the bay would have cost 40 % of the 25-year budget, about £12 million.
Instead, as each groyne fails it is carefully removed, so that it does not become dangerous for beach users or break apart and float out to sea. The wood is reused to either repair the remaining groynes or made available to local residents, businesses and farmers to be recycled and reused.
AO2:
> Removal demonstrates that despite trapping sediment moved by LSD, groynes have not proved to be a successful strategy here.
Beach surveys (beach management strategy)
Twice a month a quad bike with a GPS receiver surveys the beach. The data is used to produce three-dimensional models of the shingle bank and beach.
The system works like a satellite navigation system in a car but is
accurate to between 15 and 30 mm.
Surveying the sandy foreshore can be particularly dangerous as soft spots, which mainly develop locally in the summer, are difficult to spot and can lead to the quad bike running into problems.
AO2:
> These surveys help to maintain the sustainability of the project as replenishment, reprofiling and recycling can be targeted only where needed.
