Coastal erosion and the threat of flooding will only increase as sea levels rise over time. As our shores and landscapes change naturally, without intervention more water will reach further inland putting more homes and communities at risk of flooding.
Government funding for Flood and Coastal Erosion Risk Management in England will exceed £690m in 2017/18 in order to try to alleviate constant erosion of the coastline by the forces of the wind and sea.
The 4 main processes through which coastal erosion occurs are;-
Attrition – Stones and rocks smash against each other breaking them up
Hydraulic action – Waves force pressurized water into voids or weaknesses in the rock eventually cracking and splitting it
Abrasion – The continuous effect of sand and gravel suspended in waves wearing away at the land
Corrosion – The acidity of seawater eats away at certain types of rock such as limestone
Various techniques can be used to slow down the effects of coastal erosion and are generally separated into either soft or hard engineered options. Site specific risk will be taken into consideration when choosing which option will be used.
Beach nourishment is the replenishment of a beach where there has been significant shoreline erosion. The material used may be dredged from the area or transported from inland quarries. Beach nourishment may be an effective short term solution to erosion, but the process would need to be managed over time and would have ongoing costs.
A longer lasting method, which was piloted in the Netherlands in 2011 uses a ‘Sand Motor’ and involves the placement of 21.5million m³ of material to form an artificial sand bar which is designed to erode over time and allow wind and waves to replenish the beach where needed.
The natural salt marshes on our coastline act as buffers against the sea and can dissipate the wave energy of storm surges. Salt marshes also have the added benefit of creating natural habitat for wildlife. Marsh regeneration is currently being introduced through schemes such as the Hesketh Out Marsh, see more information on the Newground blog here.
Managed Retreat or Realignment
In areas where land is considered to be of low value, coastal defences may be removed or relocated inland promoting the natural reinstatement of intertidal habitats. The introduction of these natural marshlands could save money in the long term due to the maintenance costs associated with hard engineered coastal flood defences.
Wood or concrete structures built out from the shore which are designed to trap sand and dissipate wave energy limiting the transfer of material along and away from the beach as a result of long shore drift. Long shore drift occurs when prevailing winds blow waves across the shore at an angle resulting in material being carried and deposited further along the beach.
Large rocks or pre cast concrete blocks interlock creating a mass which can deflect wave energy, also has gaps which help to absorb the forces of waves. Rock armour is placed around structures or parts of the coastline which may be susceptible to erosion, acting as a buffer.
Steel mesh baskets filled with stone/rock that can stabilize loose ground and also absorb the force of waves by allowing water to move through them. Gabion baskets have a relatively short lifespan in comparison to other protection measures such as rock armour as the mesh holding them together deteriorates or waves destroy them.
A solid barrier designed to stop high tides and storm surges reaching inland. As the tidal forces are not absorbed and dissipated sea walls can cause scour and further erosion of the beach/salt marshes that may be in front of them. The constant impact from the sea means that sea walls may require continual maintenance costs.
These are either concrete or wood constructed gradients which may be built in front of sea walls. Revetments help to dissipate the force of waves and may have surfaces which are textured to lessen wave energy further.
For many years there has been a “hold the line” hard engineered approach to coastal management which is costly to maintain, in more recent times, and where conditions are suitable there has been a shift toward letting the water in and creating a more natural habitats.