Weymouth Harbour and Esplanade Flood and Coastal Risk Management Strategy 2020

This document aims to bring together the findings and recommendations from a number of recent studies undertaken by Weymouth & Portland Borough Council (now Dorset Council) and the Environment Agency, namely:

• Weymouth Bay Coastal Processes Study (Jackson-Hyder, 2015 to March 2018).
• Weymouth Model Updates (JBA, August 2016)
• Weymouth Inundation Modelling Study (JBA, February 2019)
• Weymouth Harbour & Esplanade Flood & Coastal Risk Management Strategy Update (WSP, March 2019)
• Masonry Harbour Walls Condition Assessment (JBA, June 2019)
• Sheet Pile Harbour Walls Condition Assessment (JBA, June 2019)
• Weymouth Beach Management Plan (Jacobs, July 2019)

The above studies have all built upon the original Weymouth Flood Risk Management Strategy (Royal Haskoning, 2010) which itself aligns to the long-term policy to continue to defend Weymouth Harbour and seafront through ‘Hold the Line’ policy adoption defined in the South Devon & Dorset Shoreline Management Plan (Halcrow, 2011).

The section on flood and erosion risk sets out the risks faced in Weymouth from coastal flooding and erosion if no action is taken to maintain or improve the current harbour and esplanade defences and assets.

This is considered in the context of the challenges posed from climate change over the next 100 years and beyond, particularly sea level rise and more extreme weather events.

The sections, strategic pathways, financial case and economic case, consolidate the recent reports into a preferred strategic pathway to managing coastal flooding and erosion risks.

Short term implementation can be defined with a reasonable level of confidence given the recent studies and reports, whilst the longer-term approach needed in the second half of this century should allow for a range of possible scenarios whilst still achieving the overall objective.

Factors which could influence the longer-term approach in the coming decades include;

• availability of national funding to deliver different possible future options
• availability of local funding / partnership funding contributions
• the rate of sea level rise
• the frequency of flooding and erosion incidents
• the rate of beach narrowing along the seafront
• the rate of degradation in the condition of harbour walls
• willingness/acceptability for specific future options
• spatial planning direction and drivers
• future economic need and tourism

This report has been reviewed and is supported by the Environment Agency who maintain strategic oversight on flood and coastal risk matters in England and who also manage the majority of government investment into reducing flood and coastal risk.

Weymouth has the attention of the Wessex Regional Flood and Coast Committee and features as a priority location within its committee strategy.

Coastal management schemes must account for accelerated sea level rise caused by global warming.

This is normally informed by the latest climate change projections, which are currently those released in November 2018 by the UK Climate Predictions 2018 (UKCP18) project.

That project was undertaken by the Met Office and funded by Defra, with the purpose of reviewing and updating climate change projections for the UK.

Projected rise in the 1 in 200-year water level at Weymouth to 2120 under the
UKCP18 ‘High’ emissions projection (WSP, 2019).

Sea level rise is expected to exceed the 2.5m flood defence elevation level in comparison to the current 2.3m Ordnance Datum (OD) crest level over the next 100 years. 

The target Standard of Protection (SoP) against coastal flooding at Weymouth is 1 in 200 years (0.5% annual probability of exceedance).

The water level is rising with the upper limit of the UKCP18 ‘High’ emissions scenario (RCP 8.5 95th Percentile) and this represents a conservative estimate.

Over this time period, the 1 in 200-year level can be seen to increase from a present day level of +2.43m Ordnance Datum (OD) to a level of +3.74mOD; a rise of 1.3m over the next 100 years in the worst case UKCP18 projections.

The current typical defence level is +2.30mOD around the harbour and between +3.0mOD and +3.5mOD along the esplanade frontage.

Current harbour walls below the desired standard of protection means increased level of risk and stifles development without specific mitigation measures.

The most recent flood protection scheme constructed in Weymouth Harbour was that built in 2001/2002 by the Environment Agency. It was designed to a 1 in 200-year Standard of Protection which at that time required a crest level of +2.30mOD.

The wall heights around the harbour vary and some are higher, and some are lower than the original scheme level. There are multiple construction forms and types of wall assets built over centuries and are accordingly in variable condition.

Corresponding residual asset life for wall sections range from less than a year up to greater than 60 years. Residual life refers to the length of time before the asset is deemed to have reached failure/unserviceable state and is based on individual condition assessment surveys undertaken.

However, even walls with reasonable residual life may require raising or replacement in order to achieve the required crest level to afford flood risk protection. There needs to be a consistent wall height throughout the town to safeguard against the risk.

If a 1 in 200-year flood event were to occur, various technical reports (which include computer flood modelling simulations) have estimated the number of residential and non-residential properties around the harbour and behind the esplanade to be at risk of flooding.

The flood risk mechanism could be either, or a combination of, extreme still water level and/or wave overtopping. Extreme still water level refers to an exceptionally large tidal event independent of any waves. In addition, the flood risk impacts from any failure of individual sections of harbour wall have been analysed.

In the present day (2020), this could be as many as 440 properties at flood risk (JBA, 2019c), in turn rising to over 2,000 properties by 2120.

 

Within the strategy area, erosion risk is most prevalent to the northern part of the Weymouth seafront area, between the Pier Bandstand and the Greenhill Groyne. The risk would increase if the seawall were to fail as a result of being undermined, particularly during storm events.

Once defences have failed and coupled with sea level rise, a period of initial ‘coastal catchup’ would most likely occur. Coastal catch up describes the behaviour of the coast which can exhibit an increased level of short-term shore retreat in the immediate period following the loss of coastal protection before recession falls to a lower and more constant rate.

Coastal erosion at rates between 0.5-1.0m/year poses risk to properties (Jacobs, 2019), Greenhill Gardens and the B3155 highway which runs parallel to the shoreline.

Should the existing defences fail, erosion loss of between 25 and 50m could be expected after 50 years. This would rise to between 50 and 100m after 100 years. An erosion loss of just 25m would render the loss of the promenade as well as the majority of properties located between the beach and the B3155 road.

The narrowing or loss of the beach would not only increase erosion risk but would also exacerbate flood risk through increased wave overtopping.

 

The basic idea behind adaptive planning is to generate a wide array of "pathways" through which policy objectives are achieved under changing climate and socio-economic conditions.

Three key elements are central to the adaptation pathways concept:

1. responses to changes that are effective under the widest set of all plausible future scenarios;
2. responses do not foreclose future options or unnecessarily constrain future choice;
3. relevant changes are foreseen through targeted monitoring and scenarios of the future are continuously being reassessed.

Proposed strategic adaptive pathways were considered in recent studies (WSP, 2019), all seeking to provide a 1 in 200-year standard of protection from sea flooding and preventing erosion until at least 2120.

This time horizon is important to allow development to be brought forward with adequate flood and coast risk management.

Pathways were made up of grouped interventions, optimised to ensure that the standard of protection is maintained for the 100-year duration. Financial and economic impacts of such pathways were assessed to look for an optimal approach.

All harbour and esplanade assets have undergone further recent condition inspection and appraisal (JBA, 2019a&b and Jacobs, 2019) to determine anticipated residual life and detailed crest heights.

The scheduling of interventions has then been calculated by the earlier of either; the exceedance of the existing crest level by the corresponding 1 in 200 year flood level; or, the existing structure reaches the end of its residual life.

The pathways included phased approaches to wall raising, wall replacements and the possible inclusion of a future tidal barrier. Further consideration of these options has resulted in a leading strategy pathway. 

The next section describes this pathway in more detail 

 

Phase 1 (2020 to 2039) £47 million capital works, inclusive risk, £1 million maintenance

Harbour sea defence walls (2020 to 2030)

• replace seven sections of harbour walls (eg North Quay Rd, Custom House Quay, Westwey Rd) and raise nine sections (eg Commercial Rd,Cove Row, Nothe Parade) (2020 to 2030)

Esplanade sea defence (2030 to 2026 )

• capital repair to Greenhill section sea wall foundation Continue ongoing beach recycling activities
• Greenhill section sea wall with associated promenade works (2034 to 2035)

Harbour walls general

• replace four sections of peninsula walls (2020 to 2027)

Phase 2 (2040 to 2059) £9m Capital Works, Inclusive Risk, £1m Maintenance

Harbour sea defence walls (2040 to 2059)

• replace nine sections of harbour walls (eg Nothe Parade, Commercial Rd, Cove Row) (2040 to 2045)

Esplanade sea defence (2040 to 2059)

• consider potential future beach recharge to replace /delay future capital

Phase 3 (2060 to 2120) £59M Capital Works costed on further wall raising / replacements, Inclusive Risk, £5m Maintenance

Harbour sea defence walls (2060  to 2120)

• decision Gateway - Consider Further wall raising or tidal barrier choice? – 2060
• further wall raising – 2070
• tidal barrier between Custom House Key and Nothe Parade – 2070

Esplanade sea defence  (2060 to 2120)

• replace Pavilion to Brunswick sea wall with associated promenade works and set back walls (2065 to 2067)

Harbour walls general (2060 to 2120) 

• replace and/or major capital refurbishment to 8 wall sections (eg Nothe Parade, Ferry Berths, Stone Pier) (2060 to 2075)

There will be strategic reviews in

• 2039
• 2059

To fulfil the identified adaptive pathways, it is essential that clear responsibilities and liabilities are understood, and it is necessary to categorise the assets requiring ongoing management and upgrade. The harbour and esplanade assets can be split into three categories as follows;.

Harbour Sea Defence Walls

A significant number of harbour walls (approximately 2.5km in plan length) form not only a functional harbour quay wall but also provide a flood risk function to mitigate tidal flooding to residential and commercial property.

It is therefore essential that these walls are replaced and/or raised at the appropriate intervention timings to ensure the desired standard of protection is maintained. In addition, a number of locations are known to suffer from tidal water rising up behind the defences contributing to the flood risk.

An example of such an asset is Wall 7 (spanning part Commercial Road and part Custom House Quay) 

Whilst the concrete flood wall was added in the early 2000’s by the Environment Agency, the supporting harbour wall itself has a residual life of around twenty years. In addition, the current crest height of 2.30mOD would be exceeded even in a present day (2020) 1 in 200-year tidal flood event.

It should be noted that the present-day flood levels are based on the most up-to-date guidance which has changed significantly since the Environment Agency scheme was designed in 2001.

Harbour Walls General

A further number of harbour walls (approximately 2.0km in plan length) provide limited Flood and Coastal erosion Risk Management (FCRM) benefit. However, in order to consider the total harbour wall requirements and to ensure coherent and efficient delivery, they should be included within the strategic approach.

An example of such an asset is Wall G (northern side of the Pavilion Peninsula).

The condition of this wall is poor and has reached the end of its effective design life. When it is replaced, it will not need its crest level raising for flood defence purposes.

However, should development be brought forward on the peninsula, mitigation measures funded by developers may be required.

Esplanade Sea Defences

The Esplanade Sea Defences provide a dual purpose in terms of offering flood risk benefit and also mitigating erosion risk. They are important to protect against wave overtopping for the low-lying areas of the town set behind the Esplanade frontage.

An example of such an asset is the seawall and beach along the frontage of the Esplanade within Section 2 (Jubilee Clock to the Pier Bandstand).

Here, future interventions are anticipated in approximately 45 years with the installation of set-back defences to manage flood risk. If the beach levels lower, further structural measures may be required including potential replacement of the Promenade seawall.

Other Esplanade assets such as Section 3 (Pier Bandstand to Greenhill Groyne) are impacted to a greater extent by coastal erosion. As such, interventions here include for considering undermining and erosion of the wall structures.

Current beach management activities should continue which includes recycling of sand and reprofiling of the beach. This provides a cost-effective measure of delaying more significant capital interventions.

Cost assessment

The capital costs for each of the interventions to deliver the adaptive pathway were calculated using the rates provided in the Environment Agency’s ‘Long-Term Costing Tool’.

This provides unit costs for FCRM measures based on previously undertaken schemes.

The rates within the tool were uplifted to present day value using the Consumer Price Index.

A number of variations for costing options were undertaken to provide a sensitivity analysis around potential cost estimates. These include simple or defined approaches and lower, average and upper percentiles.

Cost outputs from the Environment Agency’s ‘Long-Term Costing Tool’ have been benchmarked and validated against recent works at Wall C of Weymouth harbour.

Good correlation was found, adding to the confidence of the cost assessment.

Maintenance costs have been considered to ensure whole life costs are inclusive of routine repairs and inspections.

In line with HM Treasury guidance and FCRM industry best practice, an ‘Optimism Bias’ uplift of 60% has been added to all costs.

Funding - general

At the present time, Department for Environment, Food & Rural Affairs (Defra) allocates funding to FCRM projects through the Environment Agency.

Flood and coastal erosion resilience partnership funding or ‘partnership funding’ (Environment Agency, 2020a) aims to share the costs between national and local sources of funding. This approach allows any worthwhile project (where benefits are greater than costs) to qualify for Government money, known as Flood Defence Grant-in-Aid (FDGiA).

The success of this approach depends on:

• creating strong partnerships;
• clearly defining roles for responsible organisations and their partners; and
• securing and managing contributions to help reduce flood and coastal erosion risks
• and achieve more benefits for the economy, local people and the environment.

It is a condition from Defra that the Government’s FDGiA funding settlement will realise a minimum of 15% ‘Partnership Funding’ contributions to its overall FCRM capital investment programme.

In addition, the current rationale is that those that are set to benefit from FDGiA scheme investment should likewise contribute to scheme cost.

Contributions are considered from all groups and organisations that will benefit the most from the project. Private or third sector contributors (voluntary organisations) are encouraged, as this reduces the amount of funding needed from other local government spending.

Accordingly, the Grant Memorandum for Local Authorities (Environment Agency, 2018) sets out the prerequisite to secure reliable commitments from funding partners.

A tool, known as the partnership funding calculator (PF Calculator), is used to work out the amount of FDGiA a project is entitled to and the minimum amount of contribution it needs to obtain.

 

 

Dorset Council would be expected to be a significant contributor in the development and delivery of this strategy.

For example, the harbour wall component has wider benefits for the Council and therefore Dorset Council’s contribution should be at least equal or exceed the capital cost of the ‘Harbour Walls – General’ in addition to the routine maintenance costs that are usually incurred directly.

The significant value of tourism and amenity benefit realised locally from harbour and esplanade works would also support the need for investment by Dorset Council or other major beneficences.

The Council has recognised the need for flood defence investment and mechanisms are already in place for collecting and contributing to projects such as this. One such example is the Council’s Community Infrastructure Levy which collects money as a result of new development.

Completion of the PF Calculator demonstrated that the delivery of the strategy could attract in excess of £50m PVc (Present Value Cost) of FDGiA (WSP, 2019).

Updated PF arrangements and a revised calculator were released by Defra on 17/04/20 (Environment Agency, 2020b). The latest changes increase the funding payment rates available and allow for the inclusion of specific additional benefits not previously eligible for quantification.

This will only help to strengthen the case for FDGiA investment in Weymouth at the point of individual business case submissions. The revised PF Calculator will be utilised in all future business cases and investment making decisions.

The adaptive pathway should be considered in phases to ensure cohesive delivery packages whilst still providing opportunity for further future adaptation and variability.

It is intended that the strategy be reviewed at least twelve months prior to the commencement of each future phase of the pathway. In addition, it is anticipated that a light touch ‘refresh’ of the strategy be undertaken every five years. The information below below indicates the anticipated cost profile across the phases and potential scale of contributions required.

Phased Forecast Cost Profile

Phase 1, 2020 to 2039 

• estimated Dorset Council contribution (£m) = 7 million 
• estimated FDGiA/local levy/other (£m) = 40 million 
• estimated total costs (£m) = 47 million 

Phase 2, 2040 to 2059 

• estimated Dorset Council contribution (£m) = 2 million 
• estimated FDGiA/local levy/other (£m) = 7 million 
• estimated total costs (£m) = 9 million 

Phase 3, 2060 to 2120  

• estimated Dorset Council contribution (£m) = 17 million 
• estimated FDGiA/local levy/other (£m) = 42 million 
• estimated total costs (£m) = 59 million 

Totals 

• estimated Dorset Council contribution (£m) = 26 million 
• estimated FDGiA/local levy/other (£m) = 89 million 
• estimated total costs (£m) = 115 million 

To provide a comparison against additional costs associated with a tidal barrier option, the below information presents a similar phased approach but with the inclusion of a barrier from 2070.

Phased Forecast Cost Profile – Provided for comparison with inclusion of Phase 3 barrier costs

Phase 1, 2020 to 2039 

• estimated Dorset Council contribution (£m) = 7 million 
• estimated FDGiA/local levy/other (£m) = 40 million 
• estimated total costs (£m) = 47 million 

Phase 2, 2040 to 2059 

• estimated Dorset Council contribution (£m) = 2 million 
• estimated FDGiA/local levy/other (£m) = 7 million 
• estimated total costs (£m) = 9 million 

Phase 3, 2060 to 2120  

• estimated Dorset Council contribution (£m) = 43 million 
• estimated FDGiA/local levy/other (£m) = 42 million 
• estimated total costs (£m) = 85 million 

Totals 

• estimated Dorset Council contribution (£m) = 52 million 
• estimated FDGiA/local levy/other (£m) = 89 million 
• estimated total costs (£m) = 141 million 

Following local government re-organisation in April 2019, Dorset Council has started work on preparing a new local plan which will replace those adopted local plans of the predecessor District and Borough Councils.

The Council intends to undertake a consultation on the emerging plan in autumn/winter 2020, publish a pre-submission draft of the local plan in autumn/winter 2021 and adopt the new local plan in spring 2023.

As part of preparations for the new local plan the Council will be undertaking a Level 1 Strategic Flood Risk Assessment (SFRA) that covers the entire Council area and a Level 2 SFRA for Weymouth.

The risks from flooding and coastal erosion around Weymouth Town Centre need to be effectively managed and mitigated in order to secure re-development of parts of the town, and to encourage regeneration and investment.

The policies in the emerging local plan that relate to Weymouth will take account of both the Level 1 and 2 SFRA, in addition to this Harbour and Esplanade FCRM strategy.

The local plan is likely to;

• identify the parts of the town that need to be safeguarded to allow coastal and flood defences to be constructed
• require that the design of development adjacent to flood risk and coastal erosion defences should take account of future plans (as outlined in this Strategy) to alter or replace these defences
• require that the Council or developers explore the opportunities to improve the quality of the public realm as part of any flood risk or costal erosion defence works
• require that the design of coastal and flood defences takes account of Weymouth’s heritage assets (including conservation areas, listed buildings and scheduled monuments)

The Council will also be preparing an updated charging schedule for the Community Infrastructure Levy (CIL), and the priorities for spending on infrastructure.
 

Appraisal Introduction

The economic performance of a FCRM scheme is determined through its Benefit Cost Ratio (BCR). Benefits are measured in terms of the present value (PV) of economic damages avoided over the lifespan of the scheme, with the present value of scheme capital and maintenance costs also being estimated over the same period.

The economic appraisal period is typically taken as 100 years and all damages and costs are discounted according to The Green Book, HM Treasury, 2018.

Appraisal Findings

A recent economic appraisal (WSP, 2019), identified that through the provision of a 1 in 200 standard of protection adaptive pathway over a 100-year economic appraisal period, in excess of £750m present value benefit (PVb) can be realised.

The appraisal calculates the economic damages to property, amenity and transport infrastructure caused by flooding and erosion and includes the following;

• the direct flooding damage to properties and vehicles
• the cost of evacuation and clean-up
• the cost to emergency services
• traffic loss assessment
• direct damage to road infrastructure
• recreation amenity assessment
• the impact of flooding on human health
• direct loss of assets due to erosion

Whilst the economic benefit (benefit to the UK) of a coherent Harbour and Esplanade FCRM adaptive pathway are significant at more than £750m, the local financial benefit to the town, wider Dorset and the South West region are likely to be many times greater.

This can be summarised below

Economic Summary

1. Total benefits (£m PVb) = 768 million 
2. Total costs  (£m PVb) = 54 million 
3. Benefit cost ratio (BCR) = 14.2 

Through consideration of previous studies and information, the adaptive pathway approach proposes a comprehensive phased programme of asset replacements, raising and upgrades. 

The implementation of the pathway will ensure that flood and coastal erosion risk is managed whilst ensuring that other wider benefits to Weymouth such as commercial, amenity and recreation can be enhanced.

The approach remains flexible and can be adjusted to manage any future change.

The next steps in progressing Phase 1 of the pathway (2020-2039) should begin immediately with the forming of appropriate project governance and management structures to direct the project. Development and production of an appropriate HM Treasury compliant business case should follow as a priority activity.

Ambition and commitment from all stakeholders is required to ensure that this vital scheme is progressed. Dorset Council and the Environment Agency need to give their full support to the pathway and endorse its progression.

The significant capital investment need will act as a catalyst for delivery of a multi-functional scheme, cementing Weymouth’s reputation as a safe and attractive place to work and visit.

Environment Agency (2020a). Operational principles to follow when setting up funding partnerships to tackle flood and coastal erosion. Environment Agency. April 2020.

Environment Agency (2020b). Calculate grant-in-aid funding for flood and coastal erosion risk management projects. Environment Agency. April 2020.

Jacobs (2019). Weymouth Beach Management Plan. Dorset Council. July 2019. JBA (2019a). Weymouth Masonry Harbour Walls Condition Assessment. Weymouth & Portland BC. June 2019.

JBA (2019b). Weymouth Sheet Pile Harbour Walls Condition Assessment. Weymouth & Portland BC. June 2019.

WSP (2019). Weymouth Harbour & Esplanade Flood & Coastal Risk Management Strategy Update. Weymouth & Portland BC. March 2019.

JBA (2019c). Weymouth Inundation Modelling Report v3. Weymouth & Portland BC. February 2019.

Environment Agency (2018). Memorandum relating to capital grants for local authorities and internal drainage boards in England. Environment Agency. June 2018.

Jackson-Hyder (2018). Weymouth Bay Coastal Processes Study. Weymouth & Portland BC. March 2018.

JBA (2016). Weymouth Model Updates. Weymouth & Portland BC. August 2016.

Halcrow (2011). Durlston Head to Rame Head Shoreline Management Plan Review (SMP2). Shoreline Management Plan (Final). South Devon and Dorset Coastal Advisory Group (SDADCAG). June 2011.

Royal Haskoning (2010). Weymouth Flood Risk Management Strategy. Weymouth & Portland BC. June 2010.