South Devon and Dorset

The role of sediment cells, Environment Impact Assessment and Cost Benefit Analysis in coastal management

What is a Cost-Benefit Analysis?

A CBA is an assessment used to establish the economic effectiveness of a proposed project. The cost of building and maintaining a strategy, such as a sea wall, is calculated. This is then compared to the cost of the land it is protecting to ensure it is a worthwhile cause to protect those areas.

Why are CBAs important?

They ensure limited funding is allocated to areas where the economic value of land, infrastructure and businesses justifies the investment, supporting the long-term financial sustainability of the SMP.

What is an Environmental Impact Assessment?

An EIA is a formal process used to evaluate the environmental consequences of any development project proposed along a stretch of the coastline. The environment is considered as the natural environment, such as habitats and built environments, such as heritage sites. EIAs evaluate both the positive and negative impacts to ensure any action taken is sustainable.

Why are EIAs important?

They prevent inappropriate or damaging schemes from being implemented, ensure that designated sites such as SSSIs are not harmed, and help managers choose strategies that minimise ecological disruption while still protecting people and property.

What are sediment cells?

A sediment cell is a self-contained system of sediment sources, transfers and sinks, usually driven by longshore drift.

Why is understanding sediment cells important?

Within a cell, sediment budgets must be balanced: Interrupting sediment supply in one location can starve beaches downdrift and increase erosion risk. Understanding these patterns is essential for sustainable management because coastal management strategies must not disrupt the natural sediment system or create negative impacts elsewhere.

South Devon and Dorset background

1. Sediment Cell 5 - Newly designated SMP2

2. The coastline is highly valued for its distinctive composition of erosional and depositional landforms.

3. UNESCO World Heritage Site - Jurassic Coast

4. The area is experiencing long-term coastal retreat - 1mm annually.

5. Climate change and rising sea levels are accelerating erosion.

6. Management plan combining hard and soft engineering has been developed.

How are CBAs, EIAs and understanding of sediment cells used to protect the coastline at Chiswell village and Chiswell beach?

1. A sediment cell analysis identified this area as an area vulnerable to erosion and flooding due to exposure to south-westerly storm waves.

2. EIAs raised concerns about the visual impact, but this was considered feasible to protect the valuable land of the beach and village.

3. A CBA justified the cost of the defences due to the large number of properties that would be protected.

The defences were proven feasible when, between December 2013 and March 2014, a series of storms removed 150,000m3 of beach sediment and in places the steel gabions burst open. However, only 6 out of 110 properties were damaged by flooding.

What Coastal management was used in Chiswell and Chesil Beach?

(Low lying fishing village)

1. A 300m long sea wall with a recurved edge constructed in 1959, which was later reinforced by driving steel pipes into its foundation.

2. Steel gabions were placed underneath the beach, forming a 550m mattress.

3. A 900 m long drainage channel was constructed to remove excess water from the beach from breaking storm waves.

How are CBAs, EIAs and understanding of sediment cells used to protect the coastline at West Bay Town and its Harbour?

1. A sediment cell understanding highlighted the vulnerability of the area as a low-lying area with erosion rates of 0.5 per year.

2. An EIA identified the harbour as an important element of this environment due to its use for fishing and recreational craft, as well as having protected land and marine habitats.

3. A CBA justified the cost of the defences due to West Bays economies reliance on fishing and tourism (60 businesses depend on tourism). (15 million pounds invested)

What Coastal management was used in West Bay and its Harbour?

1. East pier was strengthened with concrete rock armour and boulders to allow boat access.

2. West pier was lengthened by 230m and realigned to shelter the entrance.

3. A steel flood barrier was installed across the river near the harbour to be closed when there was a risk of flooding or high tide.

4. Small West Beach was backed with a sea wall and promenade.

How are CBAs, EIAs and understanding of sediment cells used to protect the coastline at West Bay Beach.

1. A sediment cell understanding identified this as an area vulnerable to erosion.

2. An EIA ensured that this protected environment is not damaged by inappropriate hard engineering

3. A CBA - N/A

What Coastal management was used in West Bay East Beach?

1. Since 1986, the area has been protected by a 7.5m shingle ridge built with material recycled from Burton Bradstock.

2. The beach has been reprofiled to improve its resistance to storm events.

3. In the long term, a managed realignment strategy will be implemented where a new inland flood defence will be deployed.

How are CBAs, EIAs and understanding of sediment cells used to protect the coastline at Chesil Beach?

1. Both EIA and CBA do not justify the use of any coastal management strategies in this area.

What Coastal management was used in Chesil Beach?

1. No active intervention