environment agency update climping beach frontage march 2020 agency... · 2020. 5. 30. · purple...
TRANSCRIPT
Environment Agency updateClimping beach frontage – March 2020
Introduction
• This update has been produced to communicate information to Climping Parish Council and community instead of the meeting scheduled for 24th March 2020. This meeting was cancelled due to Coronavirus.
• This update contains the following;• Work the EA have been doing since 12th February• Comparisons between the 2015 Strategy and storm Ciara• The Environment Agency’s current position• Outline options for the frontage as requested• Resilience of the current beach
Climping beach: work since 12th Feb
Working with Littlehampton Harbour Board and using emergency funds, we have been recycling shingle to increase the size of the shingle bank which has been constructed north of Mill Lane in an area where shingle has naturally migrated during the storms.
The new bank contains extra shingle and is now more stable than the previous narrow embankment. The more landward position means waves lose more energy before reaching the beach (More detail in the section Resilience of the current beach).
The bay shape allows for additional natural accumulation of shingle that, in the past would have moved straight past this location.
Our recycling work has extended this bund through the Eastern Car Park field to cut off the flood route from the recently toppled concrete wall and in anticipation of further damage to the wall in future storms.
In recent weeks we have met with our partners at Arun District Council, West Sussex County Council and the
Emergency Services to update plans which cover the risk from a breach in the defences at Climping.
The Environment Agency have robust contingency plans which include; using a bulldozer to re-profile the beach
and deploying pumps to help discharge water into the River Arun as was actioned following Storm Ciara.
There remains a risk that access to The Mill is difficult and may become cut off during high tides, the owner is
aware of this risk and should register to the flood warning service and self-evacuate if required.
We continue to monitor the condition of Climping Beach alongside weather and tidal forecasts to understand
when we may see impacts. For the most up to date information on flood alerts and flood warnings, see our
website ; https://flood-warning-information.service.gov.uk/warnings. To sign up to receive free Flood Warnings
please call Floodline on 0345 988 1188.
Climping Beach: Work since 12th FebContingency and Emergency plans
Climping beach: work since 12th FebGeomorphological report and JBA update
Geomorphological Report:
Following the community request to make this report available as soon as possible it was released on 12th March.
JBA consultant modelling work:
Our consultants JBA have created a flood model that replicates closely the events seen over storm Ciara. Some
maps are shared in the next section which explores the difference in the strategy assumptions compared with the
reality of what has happened on the beach. The maps can be found on slides 10 and 11. The model will now be
used to assess the future options in relation to flood risk reduction.
Outcome comparison: Strategy vs Reality How long would it take?
Strategy assumptions What happened
On one hand, without ‘patch & repair’ there was and expectation of a 50-50
chance for a ‘breach’ to happen before 2020.1
On the other hand, with ‘patch & repair’ the ‘breach’ should be delayed until
~2030 to 2050. 2
• Deterioration of timber structures and natural transport of shingle away
from the frontage could not be delayed as might have been envisaged
through the funds available.
• Damage to the Mill Road embankment incrementally increased from
2006, but especially since Storm Imogen (4/5 January 2018)
• wave and water level conditions needed to be less severe for it to
fail than for an ‘undamaged’ structure as anticipated in the strategy
Outcome comparison: Strategy vs Reality Resistance of beach and embankmentStrategy assumptions What happened
The overtopping calculations assumed 3
• a shingle beach with the associated roughness that reduce the run-up
of the waves
• an overtopping rate that leads to damage at the rear of the
embankment (which is based on clay dikes covered with turf (e.g. in
the Netherlands or in Germany)
• The storms have exposed the clay slope (A) under the beach that was
much closer to the beach surface than assumed. Wave run-up over a
clay slope reaches higher than on a deep shingle beach.
• The historic bank turned out to mainly consist of a shingle ridge faced
with a single layer of block work and relatively thin layer of clay on the
top and the rear slope (B). Overtopping water running down the rear
slope quickly stripped vegetation and clay and then washed out/eroded
the bank from the back
A) 10-02-2020 B) 12-3-2020
Outcome comparison: Strategy vs Reality Breach dimensions and storm durationStrategy assumptions What happened
The Strategy assumed
• a ‘catastrophic failure’ to be a >15 m wide opening 4
• Storms would only last over one high tide with beach recovery after the
storm
• The gap width increased gradually and exceeded the 15 m measure
already in 2016
• From 2018 onwards gaps were patched with shingle in bags which
were more resistant than just loose shingle but were outflanked on
every storm a little bit more either side
• Storm Imogen in January 2018 lasted over 4 high tides
• Storm Ciara in February 2020 lasted over 4 high tides
Cumulative gap width/widths at Mill Road over time
Outcome comparison: Strategy vs Reality ‘Breach’ size
Strategy assumptions What happened
• A broad range for the variables going into a model is acknowledged
• The size of a ‘breach’ is limited by the existing topography 5
• The selection of a representative opening is a key area of uncertainty 6
• Many of the assumptions that went into a model have turned out to be
different from reality (see preceding slides)
• The size of the opening was limited by the topography and the coastal
processes, ie the sill level was higher than that used in the model
• The range of openings investigated in the strategy covered the opening
observed during Ciara and the ‘centrally representative values’ covered
the first high tide of storm Ciara (see preceding slide) which had a width
of ~80 m but a sill level of only 3.5 to 3.9 mOD. However, with three
more high tides to follow the damage length increased and the sill level
dropped in placed to the level of 3 mOD
Outcome comparison: Strategy vs Reality Inundation extent
The background shows a
satellite image of the area on
11-02-2020 at 11:16 (just
before over washing at high
tide started on the 2nd day of
Storm Ciara).
Apart from the field north of
the A259, the flooded area is
within the extent under a 1 in
50 year breach event
southwest of Ferry Road and
within the 1 in 200 year
breach event in the remainder.
Previous modelling did not
account for the large culvert
under the A259.
Purple is the area under >~0.2m of water, bright green is dry land and vegetation, white are clouds; transitions
to lighter purple and purple/green is water <~0.2m deep
Outcome comparison: Strategy vs Reality New modelling
The consultancy company
JBA have created a new
model calibrated with all
available observations over
the four days of Storm Ciara
which shows a very good
agreement between the area
flooded in the satellite image
and the modelled extent.
This can be seen in the map.
The model will be used to
assess the risk and protection
potential of options.
Purple is the area under >~0.2m of water, bright green is dry land and vegetation, white are clouds; transitions
to lighter purple and purple/green is water <~0.2m deep
Climping beach: EA’s current position
• Our shingle reprofiling and recycling works are complete and operational activity has now
stopped on the beach.
• We will be doing public safety works shortly and in the future to remove the wooden groynes
and structures which have been exposed by recent storm surges and are posing a hazard.
Please be careful to avoid these structures when visiting the beach.
• Approximate spend: 2018/19 Maintenance : £22k
2019/20 Maintenance : £60k
2019/20 Emergency funding : £50k
• The Arun to Pagham strategy has a 'do minimum' (patch and repair) approach to this frontage.
It is clear that we are reaching the end of this stage as the beach structures can no longer be
repaired. At this stage, the strategy recommends that we cease maintaining the frontage. We
are currently reviewing our position with respect to this and we welcome your feedback to help
inform our decisions around what should happen next. At the same time, we are doing what we
can, within the limited funding available, to make the beach as resilient as possible.
The Environment Agency work within certain guidelines, which shape what we can do and the money
available for us to do it. Our Arun to Pagham Strategy sets the direction for our activities on the Climping
frontage.
The community have requested options on what others are available and these are presented in this
document. These options fall outside our parameters and would prove a challenge for us to justify and fund.
Arun to Pagham Strategy - Economic
The strategy recommended do minimum approach for the Climping beach ‘non-legal’ section. This is a
reactive patch and repair approach to maintenance of the beach and structures, whilst acknowledging that at
some point in the future the costs of maintaining the beach will exceed what we can justify spending under
government rules, at that point our maintenance activities will cease.
Shoreline Management Plan - Environmental
The recommended long-term plan for Littlehampton Harbour to Poole Place is to allow the coastline to realign
to a more naturally functioning system, whilst continuing to provide flood defence to the large hinterland
floodplain.
Climping beach: Outline options for the community
Option Cost (£m) Life span Pros Cons
Timber groynes 1.2 to 1.5 30 to 40
years
Similar to current Requires maintenance and
replacement
Rock groynes 2.1 100 years Long life span, low
maintenance needs
Visual impact, construction
impact
Alternative material
groynes (steel/concrete)
2.5 to 6.6 < 40 to 75
years
Safe to construct,
good life span
Deterioration, high carbon
footprint, inflexible.
Fishtail groynes 6.5 100 years Holds beach position,
low maintenance
Visual impact, construction
impact, down drift sediment
starvation
Rock islands (like
Elmer)
5.0 100 years Continuous beach
access, long life span,
low maintenance
Visual impact, construction
impact, design uncertainty
Concrete or steel wall 7.2 to 10.0 < 40 to 100
years
High certainty of
Standard of Protection
No beach, difficult access,
requires additional protection
and end structures
Climping beach: Outline options for the community
Option Cost (£m) Life span Pros Cons
Containers* 0.325 for 200m
0.560 for 500m
1 to 2 years
(10 to 20 if
permanent)
Relatively quick to
install
Temporary only, uncertain
performance, visual and
environmental impacts
Rock revetment 12.0 100 years Independent of a
beach, most
‘guaranteed’ SoP
No beach, visual impact,
difficult access,
construction impact
Swash aligned bays 5.0 to 10.0 100 years Naturally
functioning, can
evolve
May require beach
management, loss of land
and property
Shingle beach (rolled back) 0.4 to 2.4 100 years Already largely in
place, natural
process, adaptable
Move landward, loss of
land and property
Climping beach: Outline options for the community
• Option descriptions, structure positions and costs are at very high level but provide a way to compare and rank the cost of the different options
• Pro and Con lists are non-exhaustive, non-hierachical and include subjective judgement
• All options would be subject to landowner agreement, permissions and consents
• Options are primarily ‘capital’ schemes, that is new structures would have to be built and depending on structure may require maintenance.
• Almost all options run against the SMP principle “to allow the coastline to realign to a more naturally functioning system”, excluding the
Swash aligned bays and Shingle beach options
• * This was requested by Climping Parish Council as a short term response to Storm Ciara and would not address the long term risk along the
frontage.
Climping beach: Outline options for the community
Structures across the beach Structures along the beach
Timber Rock Fishtail Island Wall* Revetment Beach Swash aligned
Groyne Groyne Groyne Bay
Options not to scale* A more detailed evaluation of the use of shipping containers
on the beach has been provided as a separate document.
Structures across the beach
Structures across the beach, ie groynes are used to (in
ascending order of impact to beaches down drift, e.g.
the SSSI)
• Slow down the rate at which beach material moves
from west to east and thus
• Trap sediment and grow the beach or
• Divide the beach into compartments that are filled
with beach material with little or no sediment
movement between these bays thereafter.
They can be made of timber, rock, concrete steel, or
recycled plastic*.
They can simple lines or more complex forms like T-
Head, L-Head or fishtail.
Nearshore rock islands have a similar impact on the
beach but are covered under “structures along the
beach”.* largely halted due to the issue of releasing plastic into the marine environment
• Timber groynes costs about £110k to £135k
each (60 m long, 60 m apart) , i.e. 11 new
groynes £1.2 to £1.5 million.
• Costs depend on how the piles can be installed
(driving or pre-drilled) which depends on the
ground conditions, the length of groynes and
the size of the beach to ensure they are not
outflanked.
• A beach or a hard structure may be required at
the landward end of groynes and the bays may
need to be filled with shingle (additional costs)
• The beach in the groyne bays has to be
maintained to a certain volume and position,
otherwise the groyne becomes ineffective
(landward outflanking) or the wave load may
damage the groyne.
Climping beach: Outline options: Timber groynes
Pro
• Looks similar to now/in the past
• Proven construction method
• At replacement intervals (30-40 years) there is an
opportunity to relocate groynes and beach landwards
Con
• Plan shape position uncertain to establish
• Risk of outflanking at eastern end / impact on SSSI
• Maintenance required when planks deteriorate
• Will need replacement after 30-40 years
• Reliance on beach material coming from the west or
recycling if the beach size reduces
• Similar to Felpham beach
• Rock groynes are ~£350k each and 6 would be
required (one rock groyne for every 2 timber
groynes) ~£2.1 million
• Costs depend on the amount of excavation
required, the length of groynes and the size of
the beach to ensure they are not outflanked
• A beach or a hard structure may be required at
the landward end of groynes and the bays may
need to be filled with shingle (additional costs)
• The beach in the groyne bays has to be
maintained to a certain volume and position,
otherwise the groyne becomes ineffective
(landward outflanking)
Climping beach: Outline options: Rock groynes
Pro
• Proven construction method
• Rock can be re-arranged
• Last longer than timber groynes
• Low maintenance needs
Con
• Plan shape position uncertain to establish
• More significant visual impact and safety concerns for beach users
• Bigger construction impact (such as Elmer)
• Risk of outflanking at eastern end / impact on SSSI
• Reliance on beach material coming from the west or recycling if the
beach size reduces
Concrete groynes: (6no. 60m long ~£7k/m)
Pro
• Narrower than rock groynes
• Less of the H&S concern than rock
Con
• Excavation required
• Question of stability on the existing ground
• Durable but less flexible to change in future
years
• Large carbon footprint
Climping beach: Outline options: Steel/concrete groynes
Steel groynes: (11no. 60m long ~£10k/m)
Pro
• Easy to install
• No excavation required
Con
• Excavation required
• Question of stability on the existing ground
• Durable but less flexible to change in future
years
• A Fishtail groyne essentially
combines a nearshore rock
island with a groyne by
connecting the island to the
backshore
• Based on Clacton-on-Sea one
groyne +40,000 m3 of recharge
recharge was £1.3 million, five
groynes £6.5 million
(Groyne foot print and position of
shoreline simply transposed from
Clacton-on-Sea.)
Climping beach: Outline options: Fishtail groynes
Pro
• Holds the beach in position
• Does not rely on continued feed of
beach from the west.
• Con
• Not very sightly at low tide (mostly covered at high tide)
• Bigger structure than the breakwater/island (more visual impact and
higher costs)
• High impact on SSSI through starvation of sediment
• More variables in the design and will require extensive modelling
Structures along the beach
Structures along the beach - either
seaward of landward of a beach - are
used to
• Reduce the wave energy that reaches
the beach
• Modify the alignment of the wave
crest reaching the beach
• Provide a hard barrier between sea
and land
They can be made of rock, concrete or
steel.Top right is Elmer showing how wave crests are refracted into a semi circle shape and how wave energy is
much less in the left hand bay than in the right hand (as a function of the gap between the rock islands)
Rock revetment
fronting a concrete
seawall and
promenade
protecting low lying
land at Broomhill
Sands, Kent
• Breakwater foot print and
position of shoreline simply
transposed from Elmer. These
are about 140m long (western
long ones at Elmer)
• One Island is ~£1.2 million, four
islands ~£5 million
• Beach behind will have to be
filled with beach material
(additional cost)
Climping beach: Outline options: Rock Islands
Pro
• Continued access along the
beach without obstacles
• Rock can be moved/rearranged
• Will last a long time
• H&S risk of the rock structure is
more removed from potential
‘users’
• Con
• Not very sightly at low tide (mostly covered at high tide)
• Dimensions and positioning will require significant modelling and design
(additional cost)
• Relies on continued beach feed from the west
• £10k per metre. The line is
1000 metres long ~£10 million
• Cost depends on length of piles
(assumption for 15m long piles,
top of pile at 5mOD)
• Concrete wall ~£7.2k/m, £7.2m.
Climping beach: Outline options: Sheet Pile Wall
Pro
• Independent of a beach
• Provides a ‘guaranteed’
standard of protection
Con
• No beach
• Not very sightly when exposed
• Difficult access across
(additional structures like steps
requiring maintenance)
• High carbon footprint
• Would need additional embankment and promenade behind?
• Will only last a few decades unless protected at the seaward side by rock
• Uncertain development at either end may require future works
• Wave reflection will increase seaward erosion and possible further east
• £0.3 million for 17 parallel to the
Mill Road
• £0.56 million for 42 to also include
the lower lying car park
• £0.8 million for 60 to cover the
entire length as illustrated
• A more detailed evaluation of the
use of shipping containers on the
beach has been provided as a
separate document
Climping beach: Outline options: Containers
Pro
• Installed relatively quickly
Con
• No beach
• Not very sightly when exposed
• Difficult access across (additional
structures like steps)
• High carbon footprint
• Position on top of the beach and
in single units make them likely to
move
• Would need additional embankment and promenade behind?
• Will only last a few decades unless protected at the seaward side by rock
• Unlikely to be permitted as permanent feature
• Uncertain development at either end may require future works
• Wave reflection will increase seaward erosion and possible further east
• 150m all in all is £1.8 million,
the line is 1000 metres long
~£12 million.
Climping beach: Outline options: Rock revetment
Pro
• Independent of a beach
• Works on its own
• Provides the most ‘guaranteed’
standard of protection
Con
• No beach
• Not very sightly when exposed
• Difficult access across
(additional structures like steps
requiring maintenance)
• Bigger safety risk for people climbing across to access
• Would need additional embankment and promenade behind
• Massive construction impact
• Uncertain evolution of the coast at either end may require future works.
• Expanding the principle employed at
Elmer to a larger scale
• Built of rock and requiring large
modelling and design effort the very
Climping beach: Outline options: Swash aligned bays (SMP option)
Pro
• Largely naturally functioning coast
• Works on its own
• Allow the coastline to evolve
rough estimate would
be in the order of
£5m to £10 million
• Options include
adding a third island
between Climping
and the River Arun
(additional cost) or
modify the positions
of the two shown.
• Only the rock islands
built and the coastal
alignment with
evolved through
natural processes
over decades.
Con
• Additional beach management may be necessary
• Loss of land and eventually properties
• Requires changing access arrangements
Climping beach: Outline options: Beach (rolling back) (SMP option)
Pro
• Is already largely in place
• Works with natural processes
• Natural beach without structures
• Can change and adapt to sea level
rise (within limits)
• A 1000 metres long
beach, on top of the
existing terrain with an
average 60m2 cross
section (e.g. smaller on
the higher car park and
larger behind Mill Road)
requires 60,000m3 of
shingle.
• Depending on the source
this costs between £40/m3
for offshore supply to
£6/m3 for recycling from
Littlehampton between
£0.4 and £2.4 million
Con
• The beach will move landwards
• Loss of land and eventually properties at
Climping Street
• Requires changing access arrangements
A significant volume of this is already in the beach placed in the
landward position following storm Ciara (white area); the
frontage is east of Bread Lane is already covered with a beach
of those dimensions!
More will be brought in over time by natural feed from the west.
• Will increase the SSSI
• Can be increased in size
length over time in
response to requirements
A shingle beach is a very effective natural defence as is visible just east of Climping and along much of the
Sussex coastline.
Beaches absorb wave energy, for example, through the friction they create for the waves and in the way they
change their shape depending on the wave conditions.
Hard structures like vertical walls work by blocking the wave energy and reflecting it out to sea again which
leads to erosion right in front of them as can be seen in front of the car park wall. It also means that the
structure will eventually be broken down through the wave impact.
However, for a beach to be sustainable into the future it needs the space to change its shape (in a storm the
beach slope becomes longer and shallower) and adjusts to rising sea level by moving landward.
Resilience of the current beach
The map on the right shows the location of the profile
line towards the western part of the overwashing gap
created by storm Ciara crossing the newly created
shingle bank landwards of Mill Road.
The graph shows elevation along the
profile line (red line above) for five
surveys from 15-12-2014 to 12 -03-
2020.
It shows the narrowing of the beach up
to the pre-Ciara situation represented
by the survey on 19-11-2019 and the
progress of re-establishment.
The profiles are almost identical
seawards of ~80 m but the beach crest
is ~20(35) m further landward than in
2019(2014) providing a shallower slope
over which more wave energy is lost.
What will happen in the next storm/spring tide? Re-establishing the beach!
Mill
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Strategy references (slides 6-9)
1. “At present, the shingle ridge on the Climping frontage has a typical 50% probability of breach occurring within the next five years
(following completion of the minor works to reinforce the frontage against mach-stem wave attack in June 2014), assuming no further
maintenance is carried out.” Appendix P:5
2. “The annual benefit of the Do Minimum option at Climping was compared against the annual costs. For the chosen mid-range 3.3mOD sill
level analysis, benefits are greater than the costs until Year 31. Therefore, based on this economic analysis and the best available data, it is
likely to be economically viable to continue to Do Minimum and undertake regular repairs to the Climping frontage until Year 31, unless a
major breach occurs before that time. Minor breach damage variability indicates that this duration should be expected to vary with
a range of 14 to 34 years” Appendix P:65
3. “The resilience of the defence was determined by comparing these likelihoods to critical overtopping threshold values. These threshold
values represent the overtopping rates at which the defence is likely to experience damage or breach.” Appendix P:13
4. “In its relatively recent history (1970’s onwards), there are no known catastrophic failures of the defences leading to large (>15m wide)
openings in the shingle ridge. Localised overtopping and in some cases damage through under wash is common (one to two times per year
in recent years). Such damage is limited in extent with beach berms forming in the shingle as the storm subsides or over the ensuing
period.” Appendix P:31
5. “Breach conditions: Once overtopping rates exceed the breach threshold rate, it is assumed that an opening will develop in the shingle ridge.
The width and sill level of this breach will vary significantly depending on the structural state of the shingle ridge and foreshore, the size and
duration of storm conditions and the prevailing sea conditions immediately following the storm. The range of this variation is broad, but
ultimately constrained by the topography of the area, notably the length of the narrow section of shingle ridge, the rear berm to the
ridge formed by an access road and the ground levels behind this road. In order to determine the volume of water entering the flood cell
through the breach, a representative opening has to be selected. This is a key area of uncertainty in the analysis, so a range of values
for breach width and breach sill level have been tested to identify the stability of the option selection against these parameters.” Appendix
P:8
6. “centrally representative values: […] Width of ensuing breach = 80m, Sill level of ensuing breach = 3.3m.” Appendix P: 37