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

Background 2

Policy Unit 15.1 Sub-units A – B – C Sub-unit A (~500-600m) Sub-unit B (~1200-1300km) Sub-unit C (~900-1000m) 3

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 of no breach and an aim of maintaining the status quo for as long as possible 4

Phase 1 has developed Scope options and outline costs It has also reviewed previous plans and studies 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. 5

Key features of shoreline behaviour Assessments of coastal processes and evolution were also used to inform the development and assessment of potentially viable options 6

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 See report App B2 for explanation - 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) 7

‘No Active Intervention’ 8

Sub-unit C No Active Intervention Wide crest Wide foreshore – multiple ridges Vegetated backslope Little risk of breaching so NAI policy applies here 9

No Active Intervention (Do Nothing) Even if revetment maintained, still breach in sub-unit B Doing nothing likely to SMP suggested breakwater lead to breaching type structure at breach 10

Sub-unit A 11

Revetment and timber groynes Note narrow ridge Note proximity of estuary channel 12

1. Slumping and displacement of rocks 2. Erosion of crest 4. Washover of shingle from crest 3. Damage to crest from overtopping 13 Ongoing issues – existing defences not sufficient

Sub-unit A Rejected Options Issues with holding a beach in exposed location, also with access to maintain structures • Maintain/develop a beach (A2) • New Seawall (A4) Highly reflective – will end up 14 with adding revetment too.

Sub-unit A Revetment (A3) Initially £ 3 to 4 Million Future £ 0.5 to 1 Million Rebuild revetment Maintenance of revetment - Unpick and reprofile - Additional rock - Add toe Needs to be bigger and better - Repair crest than what is there now to ensure stability over time. 15

Sub-unit A Widen Defence (A5) Buffer of shingle on landward face sufficient to prevent breach under overtopping Initially £ 1 Million Future £ 4 to 6 Million Large nourishment on landward side Repairs to crest and shingle buffer Re-instate crest Maintain revetment and £3 to 4 Million £1 to £2 Million to 2055, Eventually rebuild revetment ( as A3 ) £3 to £4 Million thereafter 16

Sub-unit A New Embankment(A6) Initially £ 5 Million Future £ 0.5 to 1 Million New turfed embankment Maintenance of embankment Protection on front face Storm damage repairs Alternatives are to leave existing revetment in and £1.5 to 2 Million place, or remove and allow beach material to Rock ‘headland’ & Protect embankment accumulate Seawall termination at ‘pinch point’ 17 Greater beach stability possible

Sub-unit B 18

Wider shingle ridge (mostly) Further to estuary channel (mostly) But still issues (haul route erosion evident) 19

And more obvious recent issues (2013) 20

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 21

Sub-unit B Some variations on this are possible, e.g. allow Revetment (B6) some realignment of the shingle ridge first 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) Future £ 0.5 to 1 Million Maintenance of revetment and crest and £ 5 to 6 Million If phased As with sub-unit A this needs to be larger than existing revetments. 22

Sub-unit B New Embankment (B7 & B8) Various alignments Space for natural beach evolution in front 23

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 Uncertainty over ground Maintenance of embankment conditions for initial construction But low future costs 24

Likely to consider as part of an approach Sub-unit B that commits to future breach repairs Works to Shingle Ridge (B2, B4 & B5) Hold (B2) Widen (B4) Manage (B5) (nourish front face) (nourish rear face) (‘natural’ response) Not preventing Highly intensive and need to Allow rollback and erosion of crest but keep pace with rate of lowering, but intervene 25 reduces risk of breach shingle movement if necessary

Sub-unit B Works to Shingle Ridge (B2 & B4) Considerable efforts needed to maintain a beach in its present position Resulting high but narrow and @Mike Page steep beach also not that resilient 26

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 27

Due to volumes required, costs for B2 and B4 assume shingle Sub-unit B would need to be imported, i.e. from offshore dredging Works to Shingle Ridge (B2, B4 & B5) Future £ 6 to 10 Million Initially £ 1 to 2 Million Widen (B4) Occasional reinstatements and Large nourishment on landward (nourish rear face) replacement of shingle buffer side Emergency response to breaches £1.5 to £2.5 Million to 2055, £5 to £7 Million thereafter Future £ 15 to 30 Million Initially £ 2 to 3 Million Hold (B2) Large nourishments on beach Regular re-nourishments on beach (nourish front face) (regular) Emergency response to breaches £7 to £12 Million to 2055, >£10 to £20 Million thereafter Future £ 2 Million Initially £ 0.5 Million Manage (B5) Occasional reinstatement and repairs Initial nourishments and stockpile (‘natural’ response) Emergency response to breaches £0.5 Million to 2055, £1.5 Million thereafter Although these each have low initial costs, they Assume can be locally sourced have quite different long term commitments 28

Combined Options 29

A range of different permutations can deliver a ‘No Breach’ outcome 30

A range of different approaches to deliver a ‘Temporary Breach’ outcome 31

Whole Frontage Shingle Engine Initially > £ 15 to 20 Million Dredge and place 1.2Mm 3 of shingle - Costs may be dependent upon sources and nature of operations Future £ 5 to 20 Million Redistribution of mobilised shingle, or re-do shingle engine Based upon rates for other ‘large’ beach nourishment operations 50 year design life Initial plan shape closer to a beach scheme (125m wide, 2km long) 32