Shanklin Coastal Defence Scheme Information Page

Overview

Welcome to the Shanklin Coastal Defence Scheme Information Page.

Latest update: 28 March 2024

Members of the project team visited Yaverland and Shanklin this week to review the draft engineering designs and allow our estimator to update the project construction costs. Opportunities to improve the design and increase efficiency of the construction work were identified. 

Preferred option announcement: 18 March 2024

Our latest newsletter can be viewed below. 

A copy of the March 2024 newsletter can be downloaded here. 

Design work to progress on option chosen to refurbish the coastal defences

The coastal defences will continue to reduce the risk of coastal erosion and flooding to Shanklin for 50 years to come following a decision by Isle of Wight Council on the best way forward. The decision to refurbish the coastal defences was made following review of a series of ground investigative works, financial analysis and flood risk assessments. The public consultation told us that better protection from coastal erosion and flooding is important locally. The scheme will provide over £80 million worth of benefits to people, property and the environment. The project team will now work to draw up an initial design and establish a construction methodology for the refurbishment work.

A reminder of the short list of options

In November 2023 we were pleased to hold public exhibitions to showcase the short list of options for refurbishing the coastal defences.

We produced the following information for our public exhibitions to help explain what the scheme is about and how we arrived at our short list of options:

Exhibition banner 1 - Introduction

Exhibition Banner 2 - Scheme extent

Exhibition Poster 1 - Survey and Investigations

Exhibition Poster 2 - Constraints and Opportunities

Exhibition Poster 3 - Measures considered

Exhibition Poster 4 - Project objectives and criteria

Exhibition Poster 5 - Short List

The short list of options being considered were:

Option 1: Do Nothing

Option 2: Do Minimum

Option 3: Keep the existing defence level

Option 4: Raise the level of the defence in stages into the future

Option 5: Raise the defence level now

Preferred option: Option 3 (Keep the existing defence level).

Option 3 (Keep the existing defence level) has been chosen by Isle of Wight Council as the preferred way forward following a recommendation made by the Environment Agency.

Option 3 will involve construction works to refurbish the sea wall, timber groynes and concrete groynes. The methodology for refurbishment will be confirmed during the next stage as the team progress with drawing up an initial design. The current thinking is that works to the walls will be constructed using shutters and in-situ pour of concrete 200mm against the face of the existing sea wall. This option will provide a quality finish. Temporary works such as sheet piling will be required along the section of wall and groyne being worked on to provide a safe and dry working corridor.

The defence level will be kept at the existing level. No raising of the existing defence height will be made over the next 50 years. As part of the refurbishment project, we will include works which strengthen the foundations of the seawall with the foresight that a decision to raise the height of the sea wall may be a viable option in 50 years’ time.

How was the preferred option selected?

An overview of the options appraisal process at Outline Business Case stage is presented in the poster below:

Exhibition Banner 2 - Scheme extent

Summary of public consultation responses

We received 42 responses in total. Of the 42 responses, 36 people gave their permission for us to publish their response.

Summary of key findings from the consultation responses:

• No one favoured the do nothing or do minimal option (short list Option 1 and Option 2). Respondents told us that better protection from coastal erosion and flooding is a priority. 
• Option 5 was the most favourable option to raise the defences now to address future sea level rise. A total of 33 of the 36 respondents agreed or strongly agreed with taking option 5 forward. Respondents told us that there is an interest locally in raising the height of the coastal defences to reduce the risk to Shanklin from rising sea level both now and in the future.

The full report summarising the responses to the public consultation can be viewed here.

The flood risk assessments and financial analysis were being progressed at the same time as public consultation. This information is now available and presented below.

What did our investigation work show?

Updated flood risk assessment

Flood modelling uses predicted river flows, rainfall, and coastal levels combined with topographic data and flow equations to generate flood risk information (such as depth, velocity, flood levels, and hazards). Our team of specialists updated the coastal flood modelling for Shanklin to ensure it uses the latest information and software available.

The main coastal threat to Shanklin is erosion of the sea defences due to their current poor condition. Our latest modelling predicts that failure of the coastal defences would lead to the loss of the beach amenity and access to the esplanade. This which would have significant knock-on impacts to the area. We estimate that 76 residential and 55 non-residential properties are at risk of flooding from failure of the sea wall.  The below map shows the anticipated flood extent in the event of defences failing.

Preventing this scenario can be achieved through either Option 3, Option 4 or Option 5. Increasing the height of the coastal defences does not provide any additional erosion protection over Option 3, it only provides a greater level of protection against flooding associated with waves overtopping the sea wall.

Modelling results tell us that the risk of flooding from wave overtopping is low given the existing height of the defences and raised floor levels of properties. Modelling suggests that 5 non-residential properties and 0 residential properties in Shanklin would remain at risk of internal flooding from overtopping after completion of Option 3.

Financial analysis

Option 3 provides over £80 million worth of benefits to people, property and the environment. The additional benefits associated with Option 4 and Option 5 are not as great. The figure below shows the cost to construct Option 3 is significantly less compared with Option 4 and Option 5. Increasing the height of the sea wall almost doubles the cost of the scheme. The public consultation told us that there is interest locally in raising the height of the existing defences however the funding shortfall of £4.9million and £8.5million for Option 4 and Option 5 respectively makes these unviable options for Isle of Wight Council to take forward.

Information on how Flood and Coastal Erosion Risk Management schemes are funded can be found here: https://thefloodhub.co.uk/frms-funding-and-delivery/

How will the shortfall in funding for the preferred option be addressed?

Isle of Wight Council as the owner of the coastal defences will develop a funding strategy to address the shortfall in funding with support from the Environment Agency. The funding strategy will be produced during the Full Business Case stage in 2025. Project costs are expected to change following more detailed costings from our contractor.

Ground investigative work

Our contractors drilled boreholes at various points on the sea wall at Shanklin Esplanade using specialist equipment to retrieve a core which was sent to the laboratory for analysis. Machine excavated trenches located at intervals along the sea wall and next to the groynes were also dug.

This work helped to increase our understanding of the existing structures and will help us plan the refurbishment work. The key findings are:

• A total of four concrete cores were extracted at strategic locations along the concrete sea wall. Ferruginous Sands Formation (weathered bedrock) was encountered in all boreholes. This comprised a mixture of granular and cohesive soils described to range between very dense silty sand and firm sandy clay.
• The sea walls are much thinner than modern engineering standards. This tells us that works to the foundations will be needed as part of the refurbishment work.
• Borehole cores extracted from the ground have been donated to the British Geological Society. Their data sets provided useful information for our projects, and we hope our contribution will help others in the future.

The below image shows one of the borehole cores extracted from the ground and stored in its wooden container:

Coastal processes assessment

• The historic trends in beach profile from 2004 to 2020 were reviewed. The min/max envelope in the above image shows the beach level overall remains relatively stable across the survey period.
• Short term fluctuations are observed and indicate seasonal changes.
• The overall stable condition is attributed to the constant nourishment of sediment received from the south-north net sediment transport rate of 25,000m3/year on average. The assessment shows that the two concrete groynes known as Osbourne and Hope Groynes are important for the long-term stability of beach levels.
• Past storm events have caused beach levels to lower by up to 1metre in front of the sea walls.  
• One of the major physical impacts of a rise in sea level includes erosion of beaches. Our coastal processes assessment shows that beach levels are expected to lower by less than 5cm by 2040 and up to 2m by 2125.  It is expected that the toe of the sea wall will have sufficient beach cover to protect it from erosion for the next 50 years. After this point, works to prevent scour at the toe of the sea wall may be needed.

Why was the preferred option selected?

The financial assessment compared the benefits and costs to identify the impact of each option overall. The benefits to the community of progressing Option 3 (the preferred option) outweigh the costs. The work will bring over £80 million worth of benefits to the community, the local infrastructure and the local environment.

The figure below summarises the Short List appraisal for those options deemed to qualify for consideration as the Preferred Option (Options 3, 4 & 5).

The ranking of the options is based on:

• The criteria grouped by PESTLE (Political, Economic, Social, Technical, Legal, Environmental).
• The criteria grouped by Objectives.
• Economic, Financial, and Carbon ranking

A PESTLE analysis studies the key external factors (Political, Economic, Social, Technal, Legal and Environmental) that influence an organisation or environment. It can be used in a range of different scenarios, and can guide people and professionals in strategic decision-making.

In terms of appraisal against the criteria, Option 3 at Shanklin was ranked first overall. Option 3 ranked second for PESTLE. Option 3 ranked second for scheme objectives but still meets all scheme objectives. Option 3 ranked highest of all options for economic, financial and carbon ranking. Option 3 has the longest duration of benefits (50 years) when compared to the other options (20-40 years). Other than the usual maintenance for Isle of Wight Council, no interim works are expected in the 50 years of the scheme.

Why is the height of the sea wall not being increased?

The flood risk assessment shows that the risk of internal property flooding from waves overtopping the existing sea wall is low given the height of the existing wall and raised floor levels of properties. Only a small number of properties would remain at risk of internal flooding from waves overtopping the sea wall after the refurbishment work is complete. Our modelling estimates that no homes and only 5 businesses would remain at risk of internal property flooding from a tidal flooding event with a 0.5% annual probability (1 in 200 chance each year).

The financial analysis has indicated that other measures such as Property Flood Resilience (PFR) measures are a more cost-effective method of reducing the risk of internal flooding to these properties. This opportunity will be explored as part of the next phase of work on the scheme. PFR measures can include flood boards, air brick covers, non-return valves and pumps, as well as work to ensure that the fabric of the property is sound. More information about PFR can be found here: https://bluepages.org.uk/

We can never remove the risk of flooding entirely. Our flood risk assessment shows that if the height of the sea wall was to be increased, there would still be a risk of wave overtopping and associated internal property flooding. The same 5 businesses would remain at risk of internal flooding even if Option 4 and Option 5 were to be implemented.

The results of the financial analysis have shown that the additional scheme benefits from raising the height of the sea wall do not outweigh the additional scheme costs. Increasing the height of the sea wall almost doubles the cost of the scheme. The shortfall in funding makes the option to raise the height of the sea wall an unviable option for Isle of Wight Council to take forward.

Where does this leave us in the future with sea level rise?

The risk of flooding from the sea over the next 100 years with 1 metre of sea level rise was modelled to improve our understanding of how the risk of flooding in the area may change in the future. It is estimated that without increasing the height of the sea wall, 11 homes and 30 businesses would be at risk of internal flooding from the sea by the year 2121. Raising the height of the sea wall would still leave 5 homes and 18 businesses at risk of internal property flooding from the sea by the year 2121.

As part of the refurbishment project, we will include works which strengthen the foundations of the seawall with the foresight that a decision to raise the height of the seawall may be a viable option in 50 years’ time.

Previous updates:

Background

The Environment Agency in partnership with the Isle of Wight Council, with expert support from JBA Consulting and VolkerStevin, are exploring a sustainable future for the coastal frontage at Shanklin Esplanade, located on the eastern coast of the Isle of Wight.

The Shanklin frontage is identified as defence unit IW27 in the 2010 Isle of Wight Shoreline Management Plan 2 (SMP2). The policy for this unit is hold the line.

The scheme will cover approximately 900 metres of coastal frontage from the large concrete Hope Groyne at the northern end of the Shanklin Esplanade to Shanklin Chine wooded coastal ravine and nature reserve in the south. Area denoted by red line in Figure 1 below.

Figure 1

The Shanklin project aims to investigate how best to respond to the challenges facing the Shanklin Esplanade coastal frontage, thereby protecting the community and preserving the area’s tourism and heritage value. Options being considered involve capital works, which may include refurbishment and repair of the existing defences. Additionally, the project will explore longer term flood and erosion management solutions which protect and enhance the seafront for future generations and provide a platform for regeneration.

What if we do nothing More Information

The condition of the existing seawall, which is over 100 years old, and groyne structures protecting the Esplanade varies. Some sections are expected to offer sufficient protection for many years to come, whilst other sections are in need of immediate repair.

Northern (left) and Southern (right) seawall showing historic deterioration

If no action is taken to prevent further deterioration, the risk of asset failure increases. In the short term, this will result in damage to the Esplanade highway (including services). Vehicular access to the seafront would become impossible if the only access road is lost, preventing access to the majority of properties on the frontage and resulting in the closure of Hope Car Park and others in the area. The Environment Agency anciptates that an initial scheme would benefit 121 properties by reducing the risk that access to these properties would be lost through coastal erosion. In the longer term, there could be direct property loss and an acceleration of coastal erosion towards the town. The risk of future wave overtopping also requires further consideration.

Frequently asked questions can be viewed here.

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