Andy Bradbury Channel Coastal Observatory, UK

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Andy BradburyChannel Coastal Observatory, UK
Identification of large scale regional trends
within a coastal observation network
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Complex risk scenarios

• High quality data required for beach management
• Strategic planning
• Regional patterns
• Operational management
• Planning new schemes
• Performance evaluation

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Developing management techniques

• Accuracy of nearshore wave climate prediction
• Managed realignment opportunities
• Sediment transport modelling calibration
• Inadequate field data to provide calibration or
  validation of models

Impacts of unsorted recharge materials

• Performance of beach control structures

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Historical approach

• Existing data generally localised at beach
  management sites.

• Inconsistent approach regionally

• Undefended stretches of shoreline infrequently
  monitored, despite potential for local
  interaction with managed sites.

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An approach to regional programme design

• Risk based
• Cost effective
• Coordinated
• Local authority / EA partnership
• 48 local authorities
• Strategic and Operational benefits
• Expandable / transferable

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Risk based design framework

• Geomorphology / geology
• Defence type
• Exposure / flood risk
• Strategic management option

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Programme design issues

• Operational and strategic requirements
• Meeting EU targets
• Research requirements
• Model limitations / validation
• Use of historical data
• Spatial and temporal scales
• Baselines
• Sampling

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Programme structure

• Range of levels of monitoring
• High level on areas with beach management plans
  that require intervention eg recycle, recharge
• Comprehensive programme in actively managed high
  risk areas
• Lower levels in do nothing areas

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• Baseline surveys
• Detailed topographic survey across whole region
• Accessible beaches
• Land survey spot height and ground model plus
  regular profiles
• Inaccessible beaches, cliffs, tidal inlets
• Combination LIDAR and aerial survey
• Baseline orthophoto survey
• Detailed bathymetric survey across whole region
• Repeat baseline after 5 years

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Regular surveys

• Topographic
• Land survey (beaches) profiles
• frequency varies 1-2 times per year
• additional provision for post storm surveys
• spacing varies from 100m-500m
• Over 8000 profile locations

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Beach management plan sites

• Dense spot height surveys and ground models

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Post storm surveys
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Regional distribution of beach management sites
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Beach management impacts
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Christchurch Bay
Poole Bay
Mudeford Sandbank
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extraction area 2004 2005
Location of Extraction and deposition sites
material stockpiled here (2004 2005)
material placed along depleted groyne bays
extraction area in 2006
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Beach management plan scale
DGM created from baseline topographic data
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Baseline DGM difference model 2006 - 2007
Elevation difference (m)
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Increase in cross sectional area
Recycling Event
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Management unit scale
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Impacts of groynes on profile change
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Strategic level analysis
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1946 Lymington marsh
seawall
1946 Lymington marsh
eroding saltmarsh
Integration of historical data sets
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1954 Lymington marsh
seawall
eroding saltmarsh
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1968 Lymington marsh
seawall
1968 Lymington marsh
eroding saltmarsh
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1980 Lymington marsh
seawall
1980 Lymington marsh
eroding saltmarsh
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2001 Lymington marsh
seawall
2001 Lymington marsh
eroding saltmarsh
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1946 Lym photo and chenier positions
seawall
Aerial photograph 1946 Lymington marsh 1946
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1946 Lym photo with 1946 and 1954 chenier
positions
seawall
Aerial photograph 1946 Lymington marsh
1946 Lymington marsh 1954
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1946 Lym photo with 1946, 1954 and 1968 chenier
positions
seawall
Aerial photograph 1946 Lymington marsh
1946 Lymington marsh 1954 Lymington marsh 1968
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1946 Lym photo with 1946, 1954, 1968 and 1980
chenier positions
seawall
Aerial photograph 1946 Lymington marsh
1946 Lymington marsh 1954 Lymington marsh
1968 Lymington marsh 1980
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1946 Lym photo with 1946, 1954, 1968, 1980 and
2001 chenier positions
seawall
Aerial photograph 1946 Lymington marsh
1946 Lymington marsh 1954 Lymington marsh
1968 Lymington marsh 1980 Lymington marsh 2001
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2001 Lym photo with 1946, 1968, 1980 and 2001
chenier positions
seawall
Aerial photograph 2001 Lymington marsh
1946 Lymington marsh 1954 Lymington marsh
1968 Lymington marsh 1980 Lymington marsh 2001
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Saltmarsh Habitat Evaluation

• Hurst
• 18 hectare loss in 33 years (0.5 hectare per
  year)
• 30 loss in 33 years (0.9 per year)
• Keyhaven and Pennington
• 38 hectare loss in 33 years (1.2 hectare per
  year)
• 46 loss in 33 years (1.4 per year)
• Pitts Deep and Sowley
• 31 hectare loss in 55 years (0.6 hectare per
  year)
• 83 loss in 55 years (1.4 per year)
• These figures include the 2.6 hectare gain at
  Sowley since 1955 breach
• Beaulieu
• 84 hectare loss in 47 years (1.8 hectare per
  year)
• 58 loss in 47 years (1.2 per year)
• Calshot
• 16 hectare loss in 61 years (0.3 hectare per
  year)

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Use of LIDAR to identify flood risk areas
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Flood Water at 1.0 metres
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Flood Water at 2.0 metres
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Flood Water at 3.0 metres
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EU habitat requirements
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NOW no sediment accretion
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5 YRS no sediment accretion
6mm per a-1 SLR
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20 YRS no sediment accretion
6mm per a-1 SLR
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50 YRS no sediment accretion
6mm per a-1 SLR
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100 YRS no sediment accretion
6mm per a-1 SLR
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100 YRS 3mm per a-1 sediment accretion
6mm per a-1 SLR
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100 YRS 6mm per a-1 sediment accretion
6mm per a-1 SLR
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Time series comparison
Time Series Data
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Height (m)
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1
0
15/10/1996
29/10/1996
01/10/1996
Inshore Wave Height at Milf Waverider refpt
Offshore Wave Height at Met Data BP11
Offshore Wave Height at Milford on Sea
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Direct Hindcast to buoy site (Hs)
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Wave period
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Impact on wave run-up and profile response

• Variation in Hs
• Variation in Tz

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Empirical profile response modelling impact of
10 change in Hs
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Empirical profile response modelling impact of
10 change in Tz
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Impact on armour stability

• Plunging waves
• Hs/D Dn50 6.2 P 0.18 (S/ÖNZ ) 0.2 x m -0.5
• P notional permeability
• S design damage Ac/Dn502
• Ac erosion area from profile
• Nz number waves
• x m surf similarity parameter
• Surging waves
• Hs/D Dn50 1.0P - 0.13(S/ÖNZ ) 0.2 / cotax m P

Hs3.6m W504.6t Constants Tz9.5s, P0.3, cota
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Hs4.0m W506.2t
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Sediment transport
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Identification of critical beach conditions
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