Soft engineering strategies

Overview

Soft engineering at the coast, beach nourishment and managed retreat.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is soft engineering at the coast?

   Model answer

   An approach that manages the coast by working with natural processes rather than against them, using natural materials and natural systems to absorb wave energy and to accommodate change, instead of building fixed structures to resist it. It generally aims to maintain or restore a beach, a dune system or a salt marsh so that these absorb the energy, and it accepts that the shoreline will move rather than trying to hold it in one place. It is usually cheaper to establish, less visually intrusive and more sustainable, but it requires continuing attention and does not give the immediate, visible reassurance a wall does.

2. 2

   What is beach nourishment, and how does it protect the coast?

   Model answer

   Beach nourishment is the addition of sand or shingle to a beach to make it wider and higher, the material usually being dredged from offshore or brought from elsewhere and then shaped into the desired profile. It protects the coast because the beach is itself the most effective natural defence: a wider, higher beach makes waves break further out and dissipates their energy through friction and percolation across its surface, so much less energy reaches the cliff, dune or wall behind. It is often combined with groynes or with periodic reprofiling, in which material combed down the beach by storms is pushed back up to restore the profile.

3. 3

   What are the advantages and disadvantages of beach nourishment?

   Model answer

   Its advantages are that it looks entirely natural and preserves the appearance of the coast, it maintains the beach as an amenity for tourism and recreation as well as a defence, it does not cause the scour or the downdrift starvation that hard structures do, and it can be adjusted in scale as conditions change. Its disadvantages are that it is not permanent: the added sediment is subject to the same drift and storm losses as any other, so it has to be repeated at intervals, often every few years, which makes it a recurring cost rather than a one-off. Dredging the source material damages the offshore sea bed habitat and may, if taken from too close inshore, alter wave patterns and simply move the erosion problem. The imported material must match the native sediment in grain size, or the beach profile and its ecology will change, and the works themselves disturb the beach while in progress.

4. 4

   What does dune regeneration involve?

   Model answer

   Restoring and stabilising a damaged dune system so that it functions again as a natural sea defence. Typical measures are planting marram grass and other binding species to trap sand and hold it with their roots; erecting brushwood, chestnut paling or sand fences to slow the wind and encourage deposition, and to protect young plants; laying boardwalks and fencing off vulnerable areas to channel visitors away from the fragile ridge and prevent trampling; controlling vehicles and grazing; and filling and replanting blowouts before they enlarge. Signage and education are part of it, since most of the damage is caused by people who do not realise the dune is a defence.

5. 5

   Why is a dune system worth protecting as a coastal defence?

   Model answer

   Because a well-vegetated dune ridge is a substantial and self-repairing barrier. It absorbs the energy of storm waves and surges, and it holds a large reserve of sand which can be eroded during a storm and then rebuilt naturally by wind and constructive waves afterwards, so unlike a wall it recovers rather than degrades. It provides a flexible defence that can migrate landwards as sea level rises, provided there is space behind it. It costs a fraction of a hard structure to maintain, it is a valuable and often legally protected habitat in its own right, and it supports recreation and tourism. Its limitations are that it is easily damaged by trampling and by vehicles, that it can be breached by an exceptional storm, and that it needs space and a continuing sand supply.

6. 6

   What is managed retreat, and how is it carried out?

   Model answer

   Managed retreat, also called managed realignment, is the deliberate decision to allow the shoreline to move landwards in a controlled way rather than holding it in place. In practice an existing defence such as a sea wall or an embankment is deliberately breached or removed, and a new, lower and cheaper defence is constructed further inland to protect what still needs protecting. The land between the old and new lines is allowed to flood on the tide and to develop into intertidal mudflat and salt marsh. Landowners are compensated for the land given up, and the process is planned in advance with those affected rather than being an abandonment of the coast.

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