European Climate Adaptation Platform - Cliff Stabilisation
Coastal cliffs can be differentiated according to their morphology and structure: cliffs can be loose – sand, silt, clay, marl and chalk – or hard, made of limestone, sandstone, granite or other rocks. Loose cliffs are more prone to erosion and landslide than rocky cliffs, more characterised by rockslides or block fall. Cliff erosion in coastal areas is almost always the result of structural erosion, resulting in a gradual retreat of the coastline because the amount of sediment that eroded (rocks, cobbles or sand) exceeds the amount deposited.
Coastal cliff stabilisation techniques are ‘green’ measures to reduce cliff erosion and its consequences – landslide, collapse, falling of rocks – compared to cliff strengthening techniques that are ‘grey’ measures (these are described in a separate fact sheet). In practice, the two approaches are often combined. Stabilisation techniques include methods to increase the stability of the slope and measures to reduce marine erosion at the foot of the cliffs:
- Littoral strip reloading: compensate littoral imbalance caused by marine erosion by placing sand or pebbles at the foot of the cliff. Littoral strip reloading is similar to beach nourishment (see the separate fact sheet). It is generally suited for areas with insufficient littoral transit.
- Re-vegetation: managing existing vegetation to regain damaged areas or establishing a vegetation cover on the slope to limit the risk of instabilities. This can be applied by creating forested berms or water draining ditches. The nature of the vegetation planted varies according to the level of instability of the slope. On very mobile slopes, fast growing and deep rooted species are preferred as they grasp the soil and prevent movement. On more stable slopes, a plant ground-cover can be effective as it acts like a protective skin. This technique is particularly suitable to loose rocky cliffs and sandy cliffs.
These techniques are usually combined as revegetation alone is only a short term solution, which does not stop the erosion of the coastline. If structural erosion is not countered it will eventually lead to the steepening of the cliff and negate the effects of stabilisation measures.