4.A - intentional activity on the west somerset coastline Flashcards
what is the purpose of intentional activity?
- coastal management is an INTENTIONAL CHANGE
- planned, deliberate
- aim to protect land behind from floods, retreat, mass movement, threshold events
- with groynes, sea walls etc
why are coastlines managed and how are they managed?
- the aim of coastal management is to protect people and the environment from the impacts of coastal erosion and flooding.
- however, tough decisions have to be made about where to spend the money and also to consider the impacts of management strategies to the coastal system.
- the next step is to come up with a Shoreline Management Plan (SMP)
what is a shoreline management plan?
- An SMP oversees a sediment sub-cell.
- it assesses the risk to people and the environment and devises a sustainable strategy for flood and coastal defences.
what are the 4 options for managing a coastline?
- Do nothing - take no further action
- Retreat the line - allow the shoreline to move inshore in a controlled manner (managed retreat/realignment). there is intention here to allow the land behind the coastline to be reclaimed by the sea (often forming a saltmarsh)
- hold the line - maintain or sustain the present shoreline using soft and/or hard engineering techniques.
- advance the line - use coastal defence works to move the shoreline into areas now covered by the sea. not common but it does happen in large port cities where space is at a premium.
what is the do nothing coastal management plan?
take no further action
what is the retreat the line coastal management plan?
Retreat the line - allow the shoreline to move inshore in a controlled manner (managed retreat/realignment). there is intention here to allow the land behind the coastline to be reclaimed by the sea (often forming a saltmarsh)
what is the hold the line coastal management plan?
maintain or sustain the present shoreline using soft and/or hard engineering techniques
what is the advance the line coastal management plan?
- use coastal defence works to move the shoreline into areas now covered by the sea.
- not common but it does happen in large port cities where space is at a premium.
how does a curved sea wall work in coastal management?
- this deflects waves and reduces overtopping.
- the recurved face rotates the wave backwards so that some of the energy is reflected back at sea.
- this impedes the next wave, reducing its energy, and thus its erosive power.
- the nature of the wall also prevents all but extreme coastal flooding
how does Rip Rap/rock armour work in coastal management?
- a permanent, erosion-resistant ground cover of large, loose, angular stone boulders.
- the boulders absorb wave energy and so reduce erosion and flooding
- some consideration needs to be given to the size of the boulders and the rock type to ensure resilience
how does (stepped) revetments work in coastal management?
- they can be made of wood or concrete (although concrete step now seem to be favoured)
- they allow the backwash to lose energy and so encourage deposition building up the beach profile
how do groynes work in coastal management?
- these are constructed from a variety of materials, including concrete and wood
- they are rarely used on their own and are placed in what is known as a groyne field.
- they interrupt LSD so that sand accumulates between the groynes and helps build up the beach profile.
how does managed retreat work in coastal management?
- this where the coastline is left undefended, so that the coastal processes may flood the land, often creating a salt marsh.
- this then creates a natural buffer to protect land further inland.
- it is inexpensive, sustainable and creates good habitat
how does beach nourishment work in coastal management?
- sometimes known as beach recharge, this strategy depends on a source of sediment nearby, which can then be dredged and placed on the depleted beach
- this builds up the beach and helps create a natural buffer against erosion and flooding.
- also helpful for the tourism industry by bolstering the local beach
what is the management strategy Gore point to Hurlstone Point and the justification for it?
MANAGED RETREAT in short and longer term.
- low value land
- already a salt marsh there
what is the management strategy Selworthy Cliffs and the justification for it?
DO NOTHING
- land has no settlements behind/hills behind cliff, therefore not important land to keep safe.
- cliffs act as a natural barrier
what is the management strategy Minehead and the justification for it?
HOLD THE LINE by maintaining and improving defences
- keep beach wide for tourism
- populated, high value land
- bay made of mudstones (vulnerable)
- 3x the amount of beach material on the updrift side of the groyne
- sediment provided to Minehead due to slow erosion = increased inputs
what is the management strategy The Warren (golf course) and the justification for it?
- Continuing to provide protection by HOLDING THE LINE.
- In the long term (as it becomes unsustainable) = managed retreat
- not important in ST, but if flooded, massive impact on Butlins
what is the geology of West Somerset?
- Porlock Bay = softer Permian Triassic marls
- Old Red Devonian Sandstone (quartzite)
- Minehead = mudstone
what was the cost of the management strategies in Minehead?
£13.5 mill
what does the socio-economic profile of Minehead rely on?
Butlins
how does Butlins impact Minehead?
- main input of income
- popular all year round
- minehead beach = key attraction for tourists
- positive multiplier effect as tourists spend money = creates jobs
what are the advantages of using OS maps?
- easy to read/interpret
- gives scale = can compare differences and measure
- spatially/proportionally accurate
- layers of info -physical/human/land uses -rich source of data
how are the groynes impacting the beach profile?
- intentionally trapping beach material
- 3x the amount of sediment on the updrift side of the groynes
- building up the beach which acts as a coastal buffer and is also an attraction for tourists
what are the inputs to the West Somerset coastline?
- no fluvial inputs
- erosion from cliffs (hard rock, not very significant)
- marine inputs - LSD = sediment from the WEST
- historic input due to sea level rise
what are the outputs of the West Somerset coastline?
- backwash from sea wall
- LSD
- destructive/storm waves
what are the flows of the West Somerset coastline?
- LSD (from W to E)
- constructive waves.
pros of aerial photos
- easy to see land uses
- easier to update with changes
- can see time of year
- visually easy to see human vs physical
- allows for more visual comprehension
- vulnerable land clear to see
cons of aerial photos
- can’t tell height of land/scale
- lack of detailed info, can’t tell what things are
- no contours
- no tidal change
- North/South
what is phase 1 of the scheme in Minehead?
- launched in Jan 1997
- the following elements will be constructed during the first phase:
- sea wall
- drainage works
- raised areas along the promenade, including new shelters and seats
- rocks groynes
- rock armouring in front of the new sea wall
- new access ramps onto the beach
- landscaping
what is phase 2 of the scheme in Minehead?
- the second phase will involve the replenishment of the beach using sand and shingle dredged from the Bristol Channel
- all the material for this will be brought in by barge and pumped onshore between the new rock groynes
- bulldozers will be used to move the material into place and form the new beach
how has the defended coastline at Minehead impacted coastal retreat over the next 50-100 yrs?
- holding the line at minehead = very little/no retreat
- unprotected cliffline in front of coastline = flanking will occur as well as coastal flooding
- about 200m predicted in this area
- 3-4m per year. eroding cliffs fast now there is no beach protection.
- golf course will flood which creates huge problems for Butlins
how do hard engineering strategies in Minehead alter sediment budgets?
- the construction of hard engineering strategies will cause a large amount of damage to the beach by removing sediment for them to be put in place
- material removed from the system has to be added back to build it back up again
- infers that the beach is retreating -> NEGATIVE SEDIMENT BUDGET
- resistant rock in cliffs to west therefore little input of sediment
-> most sediment is relict, from last SL rise (Flandrian Transgression) - sea wall = large backwash means that in a storm there is an increase in outputs
what is the effect on the golf course at Minehead?
- retreat of 100m in next 80 yrs
- risk of flooding increased significantly - unlikely to protect for much longer (allow managed retreat)
- leads to risk of flooding (sea eroding and flooding from unprotected East)
how will the sea wall impact the system at Minehead?
- 0.6m high sea wall
- effective at preventing erosion, even if its expensive
- curved front deflects the waves
- curved top deters people from walking on it
- landward side is faced w/ attractive local red sandstone
- wide walkway with seating areas built alongside the sea wall (tourists and locals)
how will the rock armour impact the system at Minehead?
- dissipates some of the wave energy
- therefore effective at preventing erosion from waves
- 90,000 tonnes
- expensive but low maintainence
- rocks chosen blended w/ landscape
- can have a short life span but can be effective at preventing erosion.
- fishing and wildlife can also benefit
how will the groynes impact the system at Minehead?
- 4 rock groynes
- traps sediment moved by LSD to build up shoreline
- this absorbs wave energy and reduces flood risk in Minehead
- this has caused the beach to grow by up to 80m width
- the terminal groyne at E starves the area infront of the golf course therefore is more vulnerable to erosion/flooding
- in the next 50-100yrs, coastal retreat of up to 100m predicted
- good for tourists as provide shelter from wind and creates a bigger beach
- however can increase rates of erosion further down the coast
how will beach nourishment impact the system at Minehead?
- building up beach 2m in height, therefore waves break further out to sea = decreased chance of flooding
- v.expensive and has to be maintained
- 300,000 tonnes of sediment
- provides excellent sandy beach for tourists
how much did the defences at Minehead cost?
- £13 million
