Case Study: Sediment cell 2A Flashcards
Holderness overview
- 50km stretch of coastline facing the North Sea, part of sediment cell 2a
- Stretches from Flamborough head in the North to Spurn spit in South
- Cliff line retreating faster than 1m / year, lost 29 villages lost over the last 1000 years.
- In light of climate change sustainable management of East Yorkshire coastline is of increasing concern
Problems in management of coastline due to physical factors
Geology:
- Flamborough Head resistant chalk but to the south, glacial till/boulder clay deposited at end of last ice age by glacial rivers which is extremely vulnerable to wave erosion (cliff foot processes) and cliff collapse (cliff face / subaerial process) - upto 10m/yr erosion which is 10x rate of chalk
Wind + wave direction:
- Strong north easterly prevailing winds which are driven by their maximum fetch from the NE create a drift aligned coastline with sediment transported south
- 1 million m3 of sediment is eroded from teh cliffs each year and transported south and a further 2million m3 is eroded from the foreshore.
- Winter storms driven by the northerly winds narrow beaches and leave clay cliffs exposed to landslides. This can generate a lot of sediment but because it is clay and can be carried in suspension, it is more easily carried offshore and even lost from the sediment cell - this means that there is less sediment to build up beaches as a first line of defence
Tides:
- Tides and rip currents which create ‘ords’ add to the removal and loss of sediment offshore - reduce beach size further so less absorption of wave energy which leaves cliff faces vulnerable to marine processes
Problems in management of coastline due to human factors
- There are a range of stakeholders involved in the management of the coastline with competing interests e.g. UK’s energy strategy and the need to protect the gas terminal at Easington.
- B1242 road along with the protection of jobs in agriculture and tourism which are important for the local economies and slow rural depopulation.
- Cost Benefit Analysis (CBA) underlies all the decisions regarding management - the Environment Agency work on the CBA basis that for every £1 spent the management strategy must save £8 in assets.
- Due to the high costs of carrying out such works (over £10,000 per metre), it is difficult for authorities to approve defence works outside the main settlements with developed frontages.
- Management - Prior to the mid 1990s, management of the coast took place without an appreciation of the effect these actions could have on other places up and down the coast (SMPS not until 1994) so much of what exists + issues in sediment cell 2a pre-dates this
- strategic decisions to manage key energy infrastructure as well as the local coastal road and sewer have led to inevitable consequences downdrift of such protected locations _ terminal groyne syndrome
· management has created a series of artificial protrusions / headlands in the coastline which are areas which are protected ‘‘hard points’ which don’t erode and which interrupt the smooth nature of a typical drift aligned coastline - these hard points are separated by a series of artificial ‘bays’ where erosion rates are high.
Groynes Holderness
· Wooden rock structures built at right angles to the shore, control longshore drift and removal of sediment by encouraging deposition. Creates wider beaches
· E.g. 1991 rock groynes used at Mappleton
· Prevailing wind along Holderness coastline coming from NE -> LSD, transporting and removing up to 1 million m3 of sediment per year
· Made the beach at the cliff line very narrow, leaving less resistant, un-lithified boulder clay susceptible to erosion at rates of 1.8m/y
· Put clifftop housing, hotels and B1242 road at risk
· Therefore, implementation of groynes helped the beach build up, absorbing the destructive energy of incoming waves. (Reduces the erosion of the cliff-face slows down coastal retreat)
· Relatively cheap - wooden groynes £10-15,000 per structure
· Wider beaches encourage tourism, multiplier effect benefitting local economy
- Financially unsustainable
- Only last 20 years. Need regular maintenance (rock needs less but arguably higher upfront costs > £10-15,000. Higher transportation and construction. In total cost £2million
- Particularly controversial as only protected 30 homes for this cost
- Visually unappealing, tourism has not increased since implementation of groynes, compounding financial cost of these groynes
Most significant may be problems caused downstream:
- Sediment accumulates on Northern side of the groyne, starving beaches to the Coast of sediment
- Hornsea and Withensea starved off sediment. Great Cowden farm disappeared into the sea 45 years earlier than expected…
Judgement:
- Effective management technique, however, almost too effective - costs further down the coast
Rock armour Holderness
- Large blocks or concrete tetrapods placed in front of a sea wall or cliff face
- E.g. rock armour used at Withernsea
- Necessary as a result of inflicted ‘Terminal Groyne Syndrome’, erosion rates increased from 1-3m p.a.
-Protected sea wall and buildings related to the coastal tourist industry - Also used at Easington
- Protect gas terminal at Easington
- Protected huge number of jobs, in industries such as tourism and energy
- Also, agriculture - much of rural coastal land between Bridlington and Withernsea used for agriculture, main employer
· Financial:
o £2,000 per metre, very high transport costs (material not sourced locally, e.g. granite boulders from Scandinavia)
o Restrict access to beach and are ugly, protects jobs in tourism may actually shrink demand
· Terminal Groyne Syndrome:
o Most Southern parts now receive hardly any sediment from LSD
o East Riding of Yorkshire council predict that Spurn head will turn into a peninsula,
o Destroy part of the salt-marsh and reduce the habitat of migrating birds…
o Ultimately, it’s survival will depend on aeolian deposition, river sediment from estuary and dune / plant succession
Judgement
· Like groynes it is effective, yet similarly unsustainable
Managed retreat
· Current sea defences are allowed to be breached, flooding low lying land. Leads to the formation of a salt-marsh, which may protect the higher land behind from erosion and flooding
· E.g. Medmerry, West Sussex (very little soft-engineering along Holderness coastline)
o Low lying coastline under threat from SW prevailing winds
o Shingle ridge that had previously protected the are was finally overtopped, flooding farmland and properties
o In 2014 land allowed to flood 2km inland, drainage ditches and ponds built to create new salt marsh habitats
o Protects over 350homes, main road and two holiday parks
· Financial sustainability
o Total cost was very high - 28 million pounds
· Feasibility:
o Not an effective solution along many coastlines
+ Need large amount of land and / or ability to relocate entire villages
· Success:
o Already working, defences held firm against the 2013/14 storms on South Coast which were the worst for 20 years
· Financial / env:
o Protected homes worth £60mil at 2015 prices, so cost benefit analysis shows that this project was certainly financially worthwhile
o 180 hectares of wetland has provided increased habitat for wading birds at Medmerry and mammals such as water vole, seals
o Increased tourism in the area, caravan parks rebranded as ‘ecotourism’ destinations (cost-benefit again…)
Judgement:
· No always an appropriate form of management
· However, when implemented, certainly more sustainable than methods of hard engineering
- Due to social, economic, environmental and environmental long-term (and widespread…!) benefits
