Coastal Protection - Hard Engineering

Coastal protection measures have been put in place at various locations around Britain’s coasts for over a century in an attempt to slow down and arrest coastal erosion. Many of the Victorian defences are now deteriorating and even for more recent defences, maintenance and repair costs are escalating. As traditional coastal protection methods present issues, then the more recent perspective of analysing coasts as systems in which sediment is recycled between various stores is shifting coastal management strategy towards more sustainable techniques that operate in co-ordination with natural systems rather than attempting to impede them.

Hard engineering coastal protection (erosion)

These traditional strategies aim to slow down or prevent further erosion of the coastline taking place, usually by placing an artificial, more resistant barrier between wave action and the coast.

These strategies are summarised below.

Concrete sea wall

Solid facing to a coastal wall or cliff.

Benefits

Traditional, long used and with proven effectiveness. Absorbs and deflects wave energy back to sea. Recurved upper lip dampens down oncoming wave power

Issues

Requires regular repair Quarrying at base can undermine sea wall foundations. Expensive to construct Gives an artificial appearance to the coast

Revetment

Open slanted concrete or wooden facing/fence offering partial resistance but letting some seawater to pass through

Benefits

Cheaper to construct than a sea wall Along a beach they allow beach material to be deposited behind Reduce power of oncoming waves

Issues

Can restrict sea access from a beach Unattractive along a length of beach Can be damaged in high energy conditions Require regular maintenance & repair

Rip rap / rock armour

Massive blocks of natural rock placed in position and piled up at the base of a cliff

Benefits

Requires less maintenance than a sea wall Granite often used that is barely eroded even under highest energy conditions May look more natural than a concrete sea wall

Issues

Expensive to extract, transport and place in position Can impede access to a beach by visitors Can lead to injuries climbing over Rodents may inhabit spaces between rocks

Tetrapods

Moulded multi-angular concrete shapes formed on site and tipped onto beach to form interlocking components

Benefits

Cheaper than rock armour but doing the same role by being constructed on site from liquid concrete Effective along long stretches of coastline requiring protection

Issues

Less attractive than natural rock – look artificial May protrude into sea and endanger swimmers/small craft Almost impossible to climb over to get access to a beach

Gabions

Rock-filled wire cages placed along a vulnerable coast

Benefits

Cheaper than tetrapods but doing the same role May look more attractive than alternatives

Issues

Wire containers may rust and be broken under high energy conditions Require regular repair & replacement Rodents may inhabit spaces between rocks

Groynes

Wooden (or less often, boulder) ‘breakwaters’ at right angles to a beach extending into the sea designed to capture longshore drift sediments to build up beach width and height

Benefits

Effective at increasing a natural barrier of beach between sea and shore Tourism amenity as wider beaches attract more visitors Attractive Groynes can act as ‘wind breaks’ for visitors Calmer inshore water

Issues

Traditionally constructed of hardwood – which is increasingly environmentally unsustainable Require maintenance and repair Speed up downcoast erosion by robbing adjacent beaches of sand

Offshore reefs

Artificial sand/gravel offshore deposits designed to intercept destructive wave action

The most ‘natural’ of hard engineering techniques Create additional shore habitat Create calmer water conditions between them and shore – benefits tourist use

Issues

Vulnerable to storm conditions Less reliable than ‘concrete/rock’ strategies May be overwhelmed by rising sea levels

The concerns about using hard engineering techniques to protect the coast go beyond cost and extend to their interruption of natural systems at the coast. By slowing down or preventing coastal erosion the input of sediment into the system is reduced, which has implications for beach size, depositional features and transfers to neighbouring sub-systems. The protective benefit for some groups at a particular location on the coast is often at the expense of other groups further along the coast.

Hard engineering: protection from coastal flooding

Preventing periodic inundation of low-lying coastal land from the sea invariably involves constructing high continuous barriers that block penetration of the land by the sea:

• High concrete sea wall (Canvey Island)
• Barrier dams (Dutch constructions protecting low-lying polders of reclaimed land)
• Moveable estuary barriers (Thames barrier)

All are very expensive to construct and are vulnerable to

• Storm surges
• Tidal surges at spring tides with accompanying low pressure systems
• Rising sea levels