Monday, 11 April 2011

Shoreline Management Plans (SMP's)

 A Shoreline Management Plan is designed to try and decide upon the most suitable scheme for each individual sediment cell. Although each sediment cell has its own SMP, often each sediment cell is split up into sub-sinks (normally beaches or other sedimentary features) which then often have a slightly altered SMP. DEFRA (Department for Environment, Food and Rural Affairs) oversee and partially fund coastal protection, amognst other things, and produce SMP's. They recognise that processes operating within the coastline occur within distinct lengths of coastline - hence why they split it up into sediment cells. They also recognise that the promotion of cooperation between all the other interested authorites is key and that they should all be involved with the development of an SMP. The development of a shoreline management plan is split into two stages.........

STAGE 1 - identify all those with an interest in the area and collate and analyse data on the key issues. Then, using this as the foundations, set management objectives and a plan for the area.
STAGE 2 - define the management units, decide on the objectives and then, before procuding the plan, consult on the preferred strategies of defence.

When considering coastal management, there are four options............
DO NOTHING - carry out no defence works except for those required for safety
HOLD THE LINE - maintain or upgrade the level of protection provided by the existing defences or build new defences along the coastline
ADVANCE THE LINE - build new defences seawards of the existing position
MANAGED RETREAT - adopt a more landward defence postion

There is one more option, that is only considered in areas where there has not been enough research and the processes at work have not yet be understood........
OBSERVE AND MONITOR - undertake a period of detailed examination of the shoreline and then decide on one of the previous options

When deciding on what option to take and what should be including on the SMP, it is often difficult to find a comprimise as, often, all the parties involved have conflicting interests. For example, property owners want protection, tourists want access and for the area to remain aesthetically pleasing, businiesses want to maintain their coastal industries whilst environmentalists want to protect rare natural habitats and environments. A lot of this often dictates whether or not hard or soft engineering is used or, in fact, a bit of both.

HARD ENGINEERING:

Groynes:
- Aim to build up sediment by preventing longshore drift from moving it along the coast. They are built at right angles to the coastline and are usually spaced between 50 - 100m apart. As they build up nice beaches they are popular with tourists and the way in which they divide the beach into sections is often welcomed by locals as well as it means that tourists can occupy one end whilst the locals the other. This is evident at Lyme Regis where the groynes seperate the shingle beach, which is quieter, from the sandy beach which is very popular with the tourists in the summer.
- They can be made from wood, concrete or blocks of stone and often need maintaince as, especially if made from wood, can be easily damaged by the marine processes
- In terms of cost they cost around £60 per metre but this can vary depending on the material used
- Although groynes help to build up the beach in the area they are implemented they can cause severe problems at stretches of the coastline downdrift (think about the impacts the groynes at Mappleton have had on Cowden and even the groynes at Lyme have impacted on Charmouth) like terminal groynes syndrome, also known as sediment starvation,  which results in increases in the rate of erosion

Sea Walls (curved):
- Aim is to reflect wave energy back out to sea and reduce the risk of flooding but, because they fail to reduce wave energy or cause waves to break early, scouring (excessive erosion causing removal of sediment at the base) often occurs. This means that, in conjunction with the construction of a sea wall, beach nourishment or, like at Lyme Regis, rip rap is placed at the base to reduce this and extend the life of the sea wall.
- This adds to the costs involved. ontop of the frequent maintainence that is required. Sea walls, alone, cost anything between £800 and £5000 per metre and are not expected to last any longer than 30 years.


Revetments:
- Aim to protect the shoreline behind them by provoking the waves to break early and so reducing the energy of the waves as they reach the beach and hit the base of the cliff.
- Like groynes, they can be made of blocks, wooden slats or concrete but ar positioned parallel to the coastline. They are often placed infront of a sea wall to increase the life of the sea wall by reducing scouring
- Average cost per metre is £1000 but constant maintainence is required
- The biggest issue is the fact that, because it reduces the erosion of the cliff, there is no fresh sediment entering the system and so it reduces the amount of sediment downdrift. This means that, in conjunction with the building of a revetment, beach nourishment is needed.



Rip Rap:
- Aim is to dissipate wave energy NOT to provide defence against coastal flooding. They are large boulders that are placed towards the back of the beach, often at the base of a sea wall. They can be made from native rocks but, in areas like Lyme Regis, this is not possible as the rocks are not resistant enough. Instead a hard crystalline, igneous rock named labradorite ( I think that is how it is spelt???) is imported from Norway
- They cost around £300 per metre but don't have a very long life span (10-15 years)
- Not ideal in honeyspot sites as they are unsightly and tourists seem to like to clamber on them, despite the number of health risks they pose
Gabions: - Aim to absorb wave energy and encourage sediment deposition by reducing the strength of the backwash.
- They are wire cages filled with stones that are either placed in front of areas prone to erosion or underneath sand dunes
- They are a cheap solution (with an average cost of £ll per metre) but they are unsightly and so are often not a popular choice in honeypot sites
Offshore Breakwaters: - Aim to reduce the power of the waves before they hit the coastline, by provoking them to break earlier, and thereby widen the beach, due to the fact it blocks longshore drift
- They are unsighly and can be obstruct as by reducing wave energy and causing them to break early it restricts what water sports, imparticular, can take place in that area
- They can be quite costly at around £1950 per metre but can cost a lot more if constructed in deep water

SOFT ENGINEERING: 
Soft engineering is a more sustainable form of engineering as it uses the natural environment and processes to protect the area. It often involves one of the following:
                       - Beach nourishment (???is neither really hard or soft engineering)
                       - Salt marsh growth
                       - Sand dune stabilization
                       - Planting of sea grass
                       - Reef building

Beach nourishment:
- This is the placing of sand, similar to that naturally found in the area, on the beach to build up the beach and protect the coastline. This is often done in conjunction with the construction of groynes or a sea wall.
- Sourcing the sand can be an issue as it needs to be taken from a source which will not damage the coastline. Unchecked dredging has increased the erosion rates in the Bahamas and the effects that dredging has had on Hallsands has been disastrous. I don't know if any of you have visited Hallsands, but I have, and you can now only view it from a platform and the pictures really show the extent of the damage......
This is the village before the impacts of the dredging could really be seen, apart from the shrinking of the beach.
And this is what it presently looks like....... if I can find the time I will write a post about what caused this, in more detail, why dredging was taking place and how this has effected the approach to coastal manangement at Beesands, a beach just down the coast from Hallsands.

- Beach nourishment needs constant replacement if it is to have the desired effect as it only lasts from 1 - 10 years before major recharge is required. This means that it can often become costly (anything from £5000 to £200 000 per metre).

Sand Dune Stabilisation:
- Sand dunes provide a natural sea defence and so vegetation is often encouraged to grow on them to stabilise them. Marram grass is often chosen as it is long roots bind the soil and it is tolerant of the salty conditions.
- There are a few disadvantages of this method though. The sand dunes take a long time to build up and they require constant maintainence and monitoring. To tourists they provide a perfect slope to slide down but this kills the vegetation and thereby destroys the sand dunes and so keeping people off of the sand dunes is a crucial part of their management.
- On average, the vegetation costs around £2o per metre to plant but this does not include the monitoring and maintainence costs.

Managed Retreat:
- Managed retreat can involve allowing the area to turn back to salt marshes. In 2008, in the first move of its kind in the UK, the Environment Agency decided to turn the Cuckmere Valley in East Sussex into a salt marsh nature reserve rather than continually building ever bigger flood defences.
- There are not really any fixed costs with this option and the main costs are those spent on purchasing the land from residents and paying for the dismantling expenses. This means that, sometimes, this is a costly option.

As we have learnt in previous lessons, sub-aerial weathering is also a problem from coastlines, especially those consisting of unconsolidated and unresistant rocks. This means that there are some sub-defence methods that can be implemented, most of which aim to reduce the water in the cliffs to reduce teh risk of mass movement
- Drainage of the cliff
- Stabilisation through the planting of vegetation
- Run off channels
- Grouting
- Rock bolts
- Planning constraints on land use

Okay, so this is the bare bones of our lesson on shoreline management plans and so there is more detail for each point but hopefully it will be useful to some........

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