SMP 7 Policy Review Policy Unit 15.1 Sudbourne Beach Phase 1 - - PowerPoint PPT Presentation

SMP 7 Policy Review Policy Unit 15.1 – Sudbourne Beach

Phase 1 Assessment Findings Presentation to Suffolk Coast Forum – 9 January 2018 by Kevin Burgess, CH2M (now part of Jacobs)

With key points from speakers presentation included as notes herein

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Background

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Policy Unit 15.1 Sub-units A – B – C

Sub-unit A (~500-600m) Sub-unit B (~1200-1300km) Sub-unit C (~900-1000m)

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Policy Unit 15.1 Current SMP Policy

To 2025: Hold The Line 2025 – 2055: No Active Intervention 2055 – 2105: No Active Intervention Noted however as: ‘An interim policy pending an agreed Management and Investment Plan for the Alde and Ore area’

AEOP does not address coastal defence – it looks to others to resolve management of the coast AEOP based upon a presumption

• f no breach and an aim of

maintaining the status quo for as long as possible

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Scope

Phase 1 (current): High-level review and assessment to provide a baseline appreciation of aspects that are key to identification of a viable policy, with a focus on implementation measures. Informed by this high-level assessment the CSG can conclude a preferred way forward, i.e. whether to pursue any policy change and what the nature of that change might be. Phase 2: Further detailed assessments, including more detailed environmental appraisals to be undertaken as required to fully appraise the proposed policy change, including formal engagement with statutory consultees required as part of that process. Phase 3: Upon completion of necessary studies the proposals will be subject to wider consultation, to review and agree the policy changes. Following this, and taking responses into account, the policy change process can be finalised accordingly.

Phase 1 has developed

• ptions and outline costs

It has also reviewed previous plans and studies

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Key features of shoreline behaviour

Assessments of coastal processes and evolution were also used to inform the development and assessment of potentially viable

• ptions

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Option Cost Estimates

• Indicative costs built up from a combination of actual costs and rates from

previous schemes involving similar works or operations

• Includes published information and details from other sources
• High level estimates, so contingency allowance also has to be included to

account for uncertainties, risks, and a range of other items

• This is referred to as ‘Optimism Bias’
• Sufficient to provide an order of magnitude expectation and enable a

relative comparison between different approaches to be made

• Presented as estimated initial costs (assumed up to 2025) and future costs

– typically assumed to be 100 years although report also breaks down to end of epoch 2 (2055) – but not discounted to PV (present value) See report App B2 for explanation

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‘No Active Intervention’

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Sub-unit C No Active Intervention

Wide foreshore – multiple ridges Wide crest Vegetated backslope Little risk of breaching so NAI policy applies here

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No Active Intervention (Do Nothing)

SMP suggested breakwater type structure at breach Doing nothing likely to lead to breaching Even if revetment maintained, still breach in sub-unit B

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Sub-unit A

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Note proximity of estuary channel Note narrow ridge Revetment and timber groynes

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• 1. Slumping and displacement of rocks
• 3. Damage to crest from overtopping
• 2. Erosion of crest
• 4. Washover of shingle from crest

Ongoing issues – existing defences not sufficient

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Sub-unit A Rejected Options

• Maintain/develop a beach (A2)
• New Seawall (A4)

Issues with holding a beach in exposed location, also with access to maintain structures Highly reflective – will end up with adding revetment too.

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Sub-unit A Revetment (A3)

Future £ 0.5 to 1 Million Maintenance of revetment Initially £ 3 to 4 Million Rebuild revetment

• Unpick and reprofile
• Additional rock
• Add toe
• Repair crest

Needs to be bigger and better than what is there now to ensure stability over time.

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Sub-unit A Widen Defence (A5)

Future £ 4 to 6 Million Repairs to crest and shingle buffer Maintain revetment and £3 to 4 Million Eventually rebuild revetment (as A3) Initially £ 1 Million Large nourishment on landward side Re-instate crest

Buffer of shingle on landward face sufficient to prevent breach under overtopping £1 to £2 Million to 2055, £3 to £4 Million thereafter

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Sub-unit A New Embankment(A6)

Initially £ 5 Million New turfed embankment Protection on front face Alternatives are to leave existing revetment in place, or remove and allow beach material to accumulate Future £ 0.5 to 1 Million Maintenance of embankment Storm damage repairs and £1.5 to 2 Million Rock ‘headland’ & Seawall termination

Greater beach stability possible Protect embankment at ‘pinch point’

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Sub-unit B

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Wider shingle ridge (mostly) Further to estuary channel (mostly) But still issues (haul route erosion evident)

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And more obvious recent issues (2013)

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Sub-unit B Rejected Options

• Maintain/develop a beach (B3)

As sub-unit A: Not likely to be too successful – potentially further south but limited effectiveness further north Beach position is being driven landward by natural forces, deepening offshore, and will be exacerbated by rising sea levels – the position is not in a natural equilibrium

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Sub-unit B Revetment (B6)

Future £ 0.5 to 1 Million Maintenance of revetment and crest and £ 5 to 6 Million If phased Initially £ 13 to 19 Million Import rock/blocks to build new revetment

• Full length or phased (only build first

800m initially) (extra 400m may not be required if sub-unit

C continues with northward migration) Some variations on this are possible, e.g. allow some realignment of the shingle ridge first As with sub-unit A this needs to be larger than existing revetments.

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Sub-unit B New Embankment (B7 & B8)

Various alignments Space for natural beach evolution in front

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Sub-unit B New Embankment (B7 & B8)

Initially £ 5 to 7 Million New turfed embankment and £2 to 3 Million Rock ‘headland’ Future £ 0.5 to 1 Million Maintenance of embankment

Uncertainty over ground conditions for initial construction But low future costs

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Sub-unit B Works to Shingle Ridge (B2, B4 & B5)

Widen (B4) (nourish rear face) Hold (B2) (nourish front face) Manage (B5) (‘natural’ response) Likely to consider as part of an approach that commits to future breach repairs Not preventing erosion of crest but reduces risk of breach Highly intensive and need to keep pace with rate of shingle movement Allow rollback and lowering, but intervene if necessary

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Sub-unit B Works to Shingle Ridge (B2 & B4)

@Mike Page

Considerable efforts needed to maintain a beach in its present position Resulting high but narrow and steep beach also not that resilient

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Sub-unit B ‘Natural’Shingle Ridge (B5)

Aerial Photos @Mike Page

• 1. Flatter and lower, but wider

beach can be much more resilient

• 3. But a commitment to repair ….

although that may occur naturally

• 2. Will be overwashed at times

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Sub-unit B Works to Shingle Ridge (B2, B4 & B5)

Widen (B4) (nourish rear face) Hold (B2) (nourish front face) Manage (B5) (‘natural’ response)

Initially £ 1 to 2 Million Large nourishment on landward side Future £ 6 to 10 Million Occasional reinstatements and replacement of shingle buffer Emergency response to breaches Initially £ 2 to 3 Million Large nourishments on beach (regular) Future £ 15 to 30 Million Regular re-nourishments on beach Emergency response to breaches Initially £ 0.5 Million Initial nourishments and stockpile Future £ 2 Million Occasional reinstatement and repairs Emergency response to breaches

Although these each have low initial costs, they have quite different long term commitments Due to volumes required, costs for B2 and B4 assume shingle would need to be imported, i.e. from offshore dredging £1.5 to £2.5 Million to 2055, £5 to £7 Million thereafter £7 to £12 Million to 2055, >£10 to £20 Million thereafter £0.5 Million to 2055, £1.5 Million thereafter Assume can be locally sourced

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Combined Options

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A range of different permutations can deliver a ‘No Breach’ outcome

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A range of different approaches to deliver a ‘Temporary Breach’ outcome

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Whole Frontage Shingle Engine

Future £ 5 to 20 Million Redistribution of mobilised shingle,

• r re-do shingle engine

Initially > £ 15 to 20 Million Dredge and place 1.2Mm3 of shingle

• Costs may be dependent upon sources

and nature of operations

Based upon rates for other ‘large’ beach nourishment operations Initial plan shape closer to a beach scheme (125m wide, 2km long) 50 year design life

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Comparison of shingle nourishment requirements

APPROACH Initial Requirement Future Commitment Total quantity (100 years) Current Recycling Operation Typically averages 10,000 m3 every 3 years 330,000 m3 (A5) Widen 30,000 m3 Top up every 10 to 20 years 200,000 m3 (B4) Widen 60,000 m3 (+ 20,000 m3 stockpile for interim repairs) Repeat every 10 to 20 years 530,000 m3 (B2) Beach recharge 40,000 m3 Re-nourish every 3 to 5 years ~ 1 Million m3 (B6) ‘Natural’ 10,000 m3 (provisional) (+ 10,000 m3 stockpile for interim repairs) Repeat every 10 to 20 years 130,000 m3 Shingle Engine 1.2 Million m3 Repeat after 50 years ~ 2 Million m3

Benchmark < 50% x3 x2 x6

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Moving Forward

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Three Basic Outcomes

‘Breach’

• Certain options would lead to a permanent opening along the shingle barrier,

with significant changes in the wider estuary system and adjacent shorelines

• No direct costs for this policy unit, but some may be incurred to secure

Slaughden frontage to the north

‘No Breach’

• Various approaches and combinations possible to continue to provide a

continuous barrier between the estuary and the sea

• Typically, initial costs range between £10 and £20 Million
• Ongoing costs (to 2055) are typically a further £0.5 to £2 Million

‘Temporary Breach’ (repaired)

• Although a barrier will remain in some form, it may be occasionally breached

(in sub-unit B) meaning a temporary interaction between the sea and estuary

• Typically, initial costs would be between £5 and £8 Million
• Ongoing costs (to 2055) range, but typically a further £2 to £3 Million
• There will be some correlation between level of cost and level of breach risk

Variety of approaches, but just three broad outcomes for the estuary Albeit not necessarily on current alignment But would be repaired

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Potential considerations for different outcomes

Hydrodynamic modelling? Morphological modelling? Flood risk assessment? Habitat surveys? Environmental appraisal? Economic study? Economic appraisal?

Impacts on estuary dynamics?

• Potential for changes in water levels and impacts upon affected areas
• Potential for morphological changes and to hydrodynamic regime

Impacts on ecology?

• Effects of changes in estuary dynamics, or resultant changes in estuary

management to accommodate impacts of different outcomes

• Effects of changes in coastal management practices on shoreline and marshes

Impacts on socio economic environment?

• Flood risk to land and property
• Tourism
• Local use of the environment (e.g. boating)
• Heritage and archaeology
• Agriculture

Some modelling suggests water levels could reduce! Currently no assessments of impacts

• f a breach upon habitats

No studies so far explicitly link economic damages to a

• breach. 65% of houses are in just 2 flood cells.

Tourism and Agriculture impacts important.

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Discussion points on requirements going forward

All outcomes will require an updated economic appraisal and some level of environmental appraisal. But also to consider…. If preferred option is one with ‘Breach’ outcome

• Arguably no change from provisional SMP policy (so no further study?)
• But Estuary Management Plan would need to be revisited
• That could require additional studies for the AEOP (rather than SMP)

If preferred option is one with ‘ No Breach’ outcome

• Although change from SMP policy, the estuary-wide impacts do not result
• So, possible that only assessments looking at local impacts are required

If preferred option is one with ‘ Temporary Breach’ outcome

• No change from the existing management practice over recent years
• So, have temporary breaches had any wider detrimental effects?
• If not, then perhaps wider additional studies are not needed
• Also AOEP may not need to be revisited
• Again, possible that only assessments looking at local impacts are required

What needs to be done next depends on which outcomes are to be considered further

SMP 7 Policy Review Policy Unit 15.1 – Sudbourne Beach

Phase 1 Assessment Findings Presentation to Suffolk Coast Forum – 9 January 2018 by Kevin Burgess, CH2M (now part of Jacobs)