EROSION of the CLIFF at SHOTLEY GATE Shotley Peninsula Shoreline CIC, April 2020 INTRODUCTION

EROSION OF THE CLIFF AT SHOTLEY GATE Shotley Peninsula Shoreline CIC, April 2020 INTRODUCTION

Figure 1. Map of the local river system 1. Shotley lies on a peninsula bounded by the rivers Stour and Orwell – the Stour, which, for the majority of its length, marks the county boundary between Essex and Suffolk flows east to west and joins the Orwell at Shotley; Shotley lies on the Suffolk shoreline. The two rivers then flow out to the North Sea between Felixstowe and Harwich. The saline estuary thus formed at Shotley has a mean tidal range of about 3.5m. The estuary basin is predominantly silt over London clay. 2. The quay at Harwich International, formerly Parkeston Quay, occupies the southern bank – the Essex shoreline. The channel from Harwich International to the sea is subject to dredging and locally it is believed that this has contributed to the observed loss of sand and silt at Shotley. A fresh dredging operation is planned for 2020. Some of the dredged material may be available for local re-use. 3. Although all part of the parish, Shotley comprises three distinct areas, known locally but not officially as ‘The Street’, ‘Shotley’ and ‘Shotley Gate’. Shotley Gate, which lies on the southern edge of the parish covers approximately 1000m along the northern bank of the Stour. Construction of sea defences in this region began around the opening of the shore establishment of HMS Ganges in 1906 and they have been successively enhanced since then. These defences are now in urgent need of attention. 4. Although tidal shores up to the high-water mark are Crown property by default, the shoreline at Shotley is an exception – the only known other exception is in Bristol. Ownership is distributed across the RSPB, Shotley Parish Council (SPC), and possibly the Marchioness of Bristol. The shoreline lies within an Area of Outstanding Natural Beauty (AONB) and contains a Site of Special Scientific Interest (SSSI). 5. The Coastal Protection Act of 1949, which assigns responsibility for erosion protection, excludes the region to the west of a line drawn between Felixstowe and Harwich. The Environment Agency likewise is not responsible for protection from where the River Stour widens into the estuary. No statutory body has proved willing or able to take responsibility for the sea defences at Shotley, see Appendix 2. 6. The Shotley Peninsula Shoreline Community Interest Company (SPSCIC) was formed by local volunteers in 2018 to fill this void. SPSCIC responds to the wishes of the community via a steering group (SPS SG) that also consists of local volunteers.

1 V2.2 17 April 2020 Figure 2 - Location of settlements, structures and boreholes 7. Any work that is performed on the sea defences will require the approval of relevant organisations. An attempt has been made to list these in Appendix 2. PURPOSE 8. This document is a concise technical statement of the recent history and current condition of the cliffs and defences at Shotley Gate. It serves to inform interested parties and support discussion of what could be done in the near future to manage erosion. SCOPE 9. This document includes facts and projections as they are presently known to SPSCIC, and that are considered relevant to the design, costing and life expectancy of developments to manage cliff erosion. It covers the shoreline west from the slipway at the bottom of Bristol Hill and east of the start of the gabions, a total distance of 780m. This has been divided into three regions which reflect the nature of the existing defences, as follows: a. concrete sea wall 0m - 180m. b. pilings 180m - 525m. c. gabions 525m - 780m. It describes the topography of the landward side to the first civil construction (roadway or building) and the seaward side to the mean low water mark. It includes the superficial geology to the extent of such sources that have been found.

2 V2.2 17 April 2020 Figure 3. Detail of site and existing defences 10. All positions along the shore are measured in a straight line from the west edge of the slipway at the foot of Bristol Hill except where noted otherwise. 11. All heights are expressed as metres above ordnance datum Newlyn (mAODN), abbreviated to OD in this report. Measurements against other reference data (e.g. 'above sea level') are approximated to this and are identified with an asterisk. 12. Except where stated, the document does not include: a. the potential impact of or on the environment, including the effects of global warming. b. the limitations that may be imposed by statutory bodies. c. legal or financial matters. d. developments elsewhere in the estuary or on the peninsula. GENERAL 13. Geology: The beach is a mixture of sand and silt with pebbles and rubble, to a depth of at least 1m where test pits have been dug. Hard, dark clay is exposed in those regions where the sand has been lost by wave action. The land immediately adjoining the sea defences is described under each section below. 14. The only detailed information from local test bores is covered under Piling. Three boreholes within 1km of the site are recorded as SW15-17 by the British Geological Survey 1. The nearest is 640m inland at 22.6m OD* . All boreholes report several metres of red crag or glacial sand and gravel overlying London clay. Details in Appendix 3. One more borehole is SW19 at 890m inland and 20m OD* 2. Taken to a depth of 45m, this reports Harwich formation down to 23m below ground level (BGL), Reading formation to 35m BGL, Upnor formation to 39m BGL and finally Ormesby clay. 15. One local seismic event above magnitude 1.5 has been recorded in the last 20 years: August 2008, magnitude 2.7, 32 km offshore, bearing 103 degrees, depth 10km 3. It was not reported in local media.

1 ALLENDER, R. and HOLLYER, S. E. 1973. The sand and gravel resources of the country around Shotley and Felixstowe: Description of 1 : 25 000 resource sheet TM 23. Rep. Znst. Geol. Sci. No. 73/13.71pp.

2ENTWISTLE D C et al, 2013. Engineering Geology of British Rocks and Soils - Lambeth Group. British Geological Survey Open Report, OR/13/006. 316pp

3https://earthquaketrack.com/gb-eng-ipswich/recent

3 V2.2 17 April 2020 16. The land in this region is falling as a result of post-glacial rebound. Combined with effects of global warming this accounts for a rise in sea level estimated between 29cm and 115cm by 2100.4 17. Hydrology: Tidal action is estimated as follows5 (all heights OD): a) Highest astronomical tide +2.58m b) Mean high water springs +2.13m c) Mean high water neaps +1.32m d) Mean low water neaps -0.9m e) Mean low water springs -1.57m f) Lowest astronomical tide -2.13m The strongest wave action is seen when the wind sweeps across in a direct line from Copperas Bay, which lies 5800m ESE. The chart below6 shows the theoretical extreme sea level frequency, neglecting atmospheric effects, at the nearest location to the cliff for which it has been published.

Figure 4. Estimated Extreme Sea Level (ESL) in m OD by return interval (years) for Harwich. The abbreviation in the legend identifies the source of the data, for details see the original reference. 18. Topography: The beach slopes down from +1m OD to 0m OD over a distance of between 15m and 60m from the wall, and then a more gradual slope over mudflats to the low water mark, which is mostly within 10m of the -1m OD map contour. The nearest point opposite on the river is the quay wall at Harwich International 900m SSW. The landward topography varies along the site and is described individually. 19. Flora and Fauna: Birds and mammals regularly seen in the river and mudflats attest to its health. The undeveloped land and shore are designated an AONB.

4 https://www.metoffice.gov.uk/binaries/content/assets/metofficegovuk/pdf/research/ukcp/ukcp18-fact-sheet-sea-level-rise-and-storm-surge.pdf

5MLM Consulting Engineers Ltd, 2018, Stage 1 Assessment of Deflected River Wall at Shotley Gate, Suffolk, ref 619742-MLM-ZZ-XX-RP-C-0001

6https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/827778/ Coastal_flood_boundary_conditions_for_the_UK_2018_update_-_technical_report.pdf

4 V2.2 17 April 2020 20. Rights of way: There are registered public footpaths along the entire length of the cliff. The most used path lies at the foot of the cliff, although this is not a registered footpath. It is however a recognised long-distance path, shown for example on an Ordnance Survey map 7 as part of the Suffolk Coast and Heaths Path. There are two other paths which run east to west through the Heritage Park. One runs along the top of the cliff and the second around halfway up. CONCRETE SEA WALL 21. Description: The sea wall forms a barrier between the beach and a flat gravelled pedestrian area, known locally as the Pinic Area. The wall starts at a narrow concrete slipway and ends 180m west at the remains of a military defensive structure (pillbox) adjoining the next section. The 20m central section of the wall was built as a retaining wall for a metalled highway and has foundations beyond the depth of any exploratory pit. The sides are smooth vertical concrete cast prior to 1906 8. Subsequently a 5m section of the wall was rebuilt in the same style to incorporate a wastewater settling tank – now decommissioned. The rest of the wall is rubble aggregated with concrete which follows the curve of erosion around the central section. The slope of these sections varies between 30 and 50 degrees from horizontal. These sections do not appear to have an engineered foundation. Piecemeal repairs are visible throughout the length. 22. Topography: The gravelled area is approximately 3m OD and 2m to 6m width, with a straight boundary on the north side. This is the southern edge of gardens of properties in Estuary Road, which lies between 59m and 77m further away. The properties start at 4m OD at the eastern end and rise to 18m OD at the western end. The overall slope of the developed land behind the path increases uniformly from east to west. The shape of the inverventing terrain varies considerably due to landscaping efforts by the occupants. The steepest slope is 39°. See Appendix 4 for more detail. 23. Geology: The gravelled area is on made-up ground, incorporating the remains of a road (Queen Victoria Drive) that was, it is believed, largely destroyed in the flood of 1953 – see under ‘Pilings’ for an estimate of the soil structure. 24. Flora and Fauna: There is little in the way of uncultivated land in this section, but the area is popular with anglers who will cast from the sea wall at high tide. 25. Ownership: The land seaward of the property boundaries has not been formally registered. An estate agent acting for the Marchioness of Bristol has previously asserted9 that the area from the foot of the gardens out to mean low water is part of that estate. It was the subject of a claim for adverse possession in 2014. Permission is needed from the owner of the land before any work starts. 26. Principal threat: Tidal surges overtop the defences and flood the gravelled area. The returning water washes the gravel out onto the beach. Wave action scours the sand from under the concreted rubble. The unsupported concrete then breaks off and falls onto the beach. Water is forced up into the structure from below and expels pieces of rubble, exposing more area to the elements. Freezing water in the crevices from piecework repairs expands and breaks pieces off. The wall suffered significant damage during winter storms early in 2020. PILINGS 27. Existing structure: The pilings start where the concrete sea wall ends at 180m and run in a series of four straight sections for 325m to the start of the gabions. The top of the piling wall is reported10 to be 3.0m OD. For the remainder of this section distances are given from the west end of the pilings, since they do not follow a straight line. The height of the pilings above the beach and the path varies considerably along the length as shown below.

7Explorer 197 (Ipswich Felixstowe and Harwich, Woodbridge and Manningtree) 1:25000, 1999, Ordnance Survey ISBN 0-319-21828-7

8Photograph dated 1906 showing continuation of Victoria Drive.

9Letter dated August 1998 offering to sell this land to owners of adjacent properties.

10 MLM Consulting Engineers Ltd, 2018, Stage 1 Assessment of Deflected River Wall at Shotley Gate, Suffolk, ref 619742-MLM-ZZ-XX-RP-C-0001

5 V2.2 17 April 2020 Figure 5. Beach and path height relative to top of pilings, January 2020 28. Structure Detail: 0-265m is an embedded cantilever steel sheet piling, which appears to be Frodingham section 1B 11, with 50mm weep holes at 7m intervals. 265 - 285m is constructed of interlocking reinforced concrete slabs with steel waling. 285-290m appear to be Frodingham section 3. 290-348m returns to Frodingham section 1B. 348-358m are interlocking concrete slabs with steel waling. There are no records of its construction but evidence 12 that the entire piling was installed between 1964 and 1968. 29. Condition: The steel piles are heavily corroded; this is worst in the splash zone, above mean high water, typically the top 1.2m. The pilings have been completely perforated in places, with piecemeal repairs over the worst damage. Vertical cracks exist between the piles’ flanges and web. The original thickness of the 1B steel sections was 9.5mm which has been reduced by corrosion to an estimated effective 4.5mm in the tidal zone. The effective life is listed by manufacturers of this type of pile as 60 years in sea water. 30. In addition, the steel piles from 160 to 193m are leaning seaward by up to 7 degrees from the vertical. This is the region which was subject to a series of escapes of drilling mud in October 2017. A survey 13 conducted for UK Power Networks did not conclude that the lean was caused by the spillage. 31. Topography: The gravelled area behind the pilings varies from 0.6 to 2m wide and averages 0.4m below the top of the pilings. The terrain then rises steeply to the top of the cliff 17m OD to 19m OD and 65- 73m further back and this area forms the Heritage Park. The steepest slope is 44°. See Appendix 4 for more detail. 32. Geology: The only local samples are from boreholes taken from the landward side near the centre of the pilings. We believe these are typical of the shoreline. Made ground was encountered between 1.6 and 2.4m BGL. This was of silt and clay-bearing gravelly sand of variable composition. Beneath this was soft to firm silty clay of the Thames group; the deepest bore was 5.0m BGL. See Appendix 3 for estimated engineering properties of the soil. 33. According to a newspaper article in the ‘Evening Star’ 14 it was well known that part of the cliff was used by HMS Ganges as a rubbish dump. There are no records of the specific location or the quantity or nature of the rubbish. However the location is inferred to lie along the edge of the area then controlled by Ganges, which has since been developed for housing. This starts at the east limit of the piling and ends at 258m west. The width of the dump can be estimated from the accompanying image as about 30m.

11 Frodingham Steel Piling, 1966, The British Steel Piling Co Ltd, London SW1. 26pp

12 Evening Star, 12th June 1964, p11

13 MLM Consulting Engineers Ltd, 2018, Stage 1 Assessment of Deflected River Wall at Shotley Gate, Suffolk, ref 619742-MLM-ZZ-XX-RP-C-0001

14Evening Star, 12th June 1964, p11

6 V2.2 17 April 2020 34. Hydrology: Groundwater seepages during the boring ranged from 1.0 to 3.6m BGL. There is a copious flow from most of the weep holes in the pilings after heavy rain and if a storm surge overtops the pilings. In the latter case the water is distinctly saline. The path floods readily under these circumstances. 35. Flora and Fauna: The slope is populated by mature trees and shrubs. There is bare earth where paths have been created by pedestrian traffic and subsequently enlarged by runoff. The ground is heavily shaded by the tree foliage, which appears to prevent the establishment of undergrowth. Elsewhere the vegetation is well established to bind the soil. The largest wild animals seen in the Heritage Park are muntjac deer. There is no visible ground disturbance, such as burrows, caused by the fauna. 36. Ownership: The land adjacent to this section comprising the Heritage Park and the beach down to the low water mark is owned by SPC. The SPC has indicated it will permit work on the defences. 37. Principal threat: The beach is below the original level due to scouring, which increases the bending moment on the cantilever. Water from runoff and storm surges collecting behind the pilings washes soil through perforations in the metal. That which is retained makes the soil heavier and more plastic. Tree roots are exposed by runoff; when a tree falls it releases several tons of soil which accumulates behind the pilings. The corroded pilings will eventually fail under the load from retained soil. GABIONS 38. Structure: The gabions start at the western end of the pilings (525m from the slipway) and continue to the western limit of a rock outcrop that marks the end of the beach (780m from the slipway). The gabions are plastic coated, galvanised steel wire cages of 1m cube filled with rubble. They were installed by the SPC in 2012. The 197m eastern section of gabions are stepped two high and two wide, supported on a sand-filled geotextile pad. The 58m western section are a single cage high and wide laid directly on unsecured geotextile. 39. Condition: The eastern section has remained largely upright and stable, although the shoreward cages have lost around 25% of their fill and some of the steel has been exposed and is rusting. The western section has been badly undermined and has rolled forward up to 90 degrees in some places. This has exposed the edge of the geotextile and dragged the endmost cages of the other section out of true by approximately 5 degrees. 40. When originally proposed it was generally believed that the gabions have a 25 year life expectancy. 41. Topography: Very similar to that described under Pilings. The cliff height is maintained at 19m OD along most of its length, sloping uniformly to 8m OD over the final 80m. The steepest river-facing slope is 42°. See Appendix 4 for more detail. 42. Geology: No specific information is available: see under ‘Pilings’ for an estimate of the soil structure. 43. Hydrology: No specific information is available: see under ‘Pilings’ for an estimate of the shoreward hydrology. 44. Flora and Fauna: Will be the same as described under ‘Pilings’. 45. Ownership: The land adjacent to the eastern section is owned by SPC (see above). The beach west and shoreward from a marker post (destroyed in storms early 2020) is owned and controlled by the RSPB. This part of the beach is an SSSI for overwintering of birds on the mudflats. The RSPB have in the past objected to work that might adversely affect the wildlife. The area landwards of the western gabions is owned by a local farmer, who has indicated he will permit work on the defences. 46. Principal threat: Tumbling of the infill by wave action breaks down the rubble so it is washed out onto the beach. The tumbling also abrades the plastic coating so that seawater attacks the metal underneath. Uprooted trees - see above. Scouring removes the supporting beach so the cages roll forward under the pressure from the retained soil.

7 V2.2 17 April 2020 SUMMARY 47. The protection of the cliff is presently provided by several technologies, all of which are demonstrably inadequate and at imminent risk of failure. The credibility of any remedial plan is essential to raise the considerable funds needed. This in turn depends on the viability of the solutions which are proposed. This document was produced by Dr. JM Howell on behalf of SPSCIC.

Appendices 1. Glossary 2. Roles and responsibilities for flood and erosion protection. 3. Geological data 4. Detailed topology

8 V2.2 17 April 2020 Appendix 1 Glossary AONB - Area of Outstanding Natural Beauty BGL - below ground level DC - District Council EA - Environment Agency ESL - Extreme Sea Level OD - Ordnance datum (abbr. for Above Ordbance Datum Newlyn) RSPB - Royal Society for the Protection of Birds SPC - Shotley Parish Council SPSCIC - Shotley Peninsula Shoreline Community Interest Company SPS SG - Shotley Peninsula Shoreline Steering Group SSSI - Site of Special Scientific Interest

9 V2.2 17 April 2020 Appendix 2

Roles and responsibilities for flood and erosion protection. The following legislation places the lead for flood risk matters with the Environment Agency: 1. Water Resources Act (1991) 2. Land Drainage Act (1991/4) 3. Flood & Water Management Act (2010). The following legislation places the lead for erosion matters with the local District Council (Suffolk) as the Coastal Protection Authority: 1. Coastal Protection Act 1949. The Flood & Water Management Act (2010) makes the DC the Lead Local Flood Authority, but gives the EA an over-riding responsibility to co-ordinate flood & coastal erosion risk matters. Other organisations that may need to be consulted for permission to work on the defences: 1. AONB

2. RSPB 3. Marine Management Organisation (MMO)

4. Harwich Haven Authority (HHA) 5. Natural England (NE)

6. Highways Authority Shotley cliff is located within one of the 111 sites listed in Schedule 4 (Waters excluded for purposes of definintions of "sea" and "seashore") of the Coastal Protection Act. The exact text is: "17. The Rivers Orwell and Stour, above the ferry between Felixstowe Pier and Harwich Landing Stage."

10 V2.2 17 April 2020 Appendix 3 Geological survey results 15 16 Height OD Depth Depth Tag Grid reference Type Type m* m m SW15 TM23 2371 3446 23.8 0.6 Red Crag 3.4 London clay SW16 TM23 2450 3438 22.6 0.6 Glacial sand 5.6 London clay SW17 TM23 2414 3497 19.5 0.6 Red Crag 3.4 London clay SW19 TM23 2439 3460 20.0 Thames group deposit ends at 20m

Local bore results 17

Location* Heigh Depth Depth Depth Tag Type Type Type WS Final * t OD m m m WS01 363m 2.68 0 MG 2.00 Sand 2.85 FC 1.0 3.0 WS02 369m 2.87 0 MG 1.60 SC 2.80 SC/FC 2.3 5.0 WS03 377m 2.97 0 MG 2.20 SC 3.75 FC 3.6 5.0 WS04 386m 2.90 0 MG 2.40 SC/FC 3.0 3.0 Abbreviations: WS water strike, MG made ground, SC soft clay, FC firm clay. **Distances from slipway.

15ALLENDER, R. and HOLLYER, S. E. 1973. The sand and gravel resources of the country around Shotley and Felixstowe: Description of 1 : 25 000 resource sheet TM 23. Rep. Znst. Geol. Sci. No. 73/13.71pp.

16 ENTWISTLE D C et al, 2013. Engineering Geology of British Rocks and Soils - Lambeth Group. British Geological Survey Open Report, OR/13/006. 316pp

17 MLM Consulting Engineers Ltd, 2018, Stage 1 Assessment of Deflected River Wall at Shotley Gate, Suffolk, ref 619742-MLM-ZZ-XX- RP-C-0001

11 V2.2 17 April 2020 Mechanical properties Typical values for weathered London clay 18 Property Characteristic First time slope failure Units Bulk density 19.0 19.0 Sat. density 19.0 19.0 E 18000 12000 kN/m2 dE inc 3150 2500 kN/m3 Cu or C' active 0 0 kN/m2 Cu or C' passive 5 5 kN/m2 dC inc. kN/m3 0.0 0.0 kN/m3 Phi 24 20 degrees Wall friction 1.0 1.0 Ka 0.34 0.40 Kac 0.0 0.0 Kp 3.68 2.83 Kpc 5.42 4.76

18 MLM Consulting Engineers Ltd, 2018, Stage 1 Assessment of Deflected River Wall at Shotley Gate, Suffolk, ref 619742-MLM-ZZ-XX- RP-C-0001

12 V2.2 17 April 2020 Appendix 4 Detailed topology. These profiles have been generated from LIDAR measurements at 1m intervals gathered by the Environment Agency and republished by Ordnance Survey. Note that profiles are expanded in the vertical scale. Vertical scale is metres OD. Horizontal scale is metres from sea wall. Location is metres from slipway, and nearest property landwards. Section 1 - Concrete sea wall and gardens backing on to Estuary Road.

0m St Helier/Moorings/Springhill

0 -100.0 -75.0 -50.0 -25.0 0.0 25.0 50.0 75.0

50m Croftdown/Hinkley

0 -100.0 -75.0 -50.0 -25.0 0.0 25.0 50.0 75.0

100m Balaton

0 -100.0 -75.0 -50.0 -25.0 0.0 25.0 50.0 75.0

150m Derwent/Tideway

0 -100.0 -75.0 -50.0 -25.0 0.0 25.0 50.0 75.0

13 V2.2 17 April 2020 Section 2 - Pilings and Heritage Park backing on to Lower Harlings and Stourside

200m 30a Lower Harlings

0 -100.0 -75.0 -50.0 -25.0 0.0 25.0 50.0 75.0

300m 49/51 Kitchener Way

0 -100.0 -75.0 -50.0 -25.0 0.0 25.0 50.0 75.0

400m Whinney Queach

0 -100.0 -75.0 -50.0 -25.0 0.0 25.0 50.0 75.0

500m 3 Stourside

0 -100.0 -75.0 -50.0 -25.0 0.0 25.0 50.0 75.0

14 V2.2 17 April 2020 Section 3 - Gabions and Heritage Park backing on to Stourside and farmland.

600m 8/9 Stourside

0 -100 -75 -50 -25 0 25 50 75

700m Footpath

0 -100 -75 -50 -25 0 25 50 75

780m Gabions end

0 -100 -75 -50 -25 0 25 50 75

15 V2.2 17 April 2020