Total Summary of long list

1 Do nothing 31

No maintenance of existing defences. Does not meet technical requirements and is detremental to all social, political and legal factors.

2 Do minimum 37

Maintain existing defences. This will provide the baseline against which further options will be tested.

3 New sea wall 40

A new wall could be built of concrete, steel piles or masonry. This option would seek to replace the existing defence, or could be placed seaward of the existing defence in order to advance the line. To adapt to climate change, the wall would need to be taller than the current defence.

This option seeks to replace the existing sea wall and can achicve the technical requirements without compromising on social, environmental, political and legal factors. Beach access can be maintained and the footprint of the 'hard' structure will be minimal.

4 Raise existing defences 38

Raising the existing defence would increase the flood protection performance of the defence in the short tomid-term. However, as this option relies on the existing structure it can only practically be raised so farwithout a complete re-build. In areas where the existing structures are currently in poor condition aconcrete 'shroud' would be used to encase the existing defence to prevent premature failure of the newraised defence.

Option discounted as reliance on existing defences and increasing maintanence costs is not considered viable in the medium to long-term.

5 Rock armour revetment 35

Rock armour could be installed at the base of the existing defence to increase flood protection performance. This option may or may not include a wall on top.

Due to the larger footprint of the structure and resultant loss of beach / amenity space the option has been discounted.

6 Setback walls with flood gates 42

Flood protection walls could be installed set-back from the existing coastal defences. This option would help prevent flooding to the town through a secondary defence line; while it does not help reduce wave overtopping, it would prevent flood water from inundating roads and properties. In the long-term this option will be less effective due to the extreme sea levels expected and it does not seek to improve the condition of existing defences. However, if used in conjunction with other defence improvements it could effectively work in the long-term.

Option shortlisted as the technical requirements can be met without impacting the beach areas. The existing promenade area provides an excellent opportunity for renewing the existing raised secondary defences.

7 New stepped or sloping revetment 38

A new stepped revetment or similar modular blockwork structure could be constructed. All solutions could be designed such that their wave overtopping performance is suitable into the long-term scenario; this may or may not include a wall on top. This option would seek to replace the existing defence, or could be placed seaward of the existing defence in order to advance the line.

Option discounted due the increased footprint on the beach and large capital costs.

10 Property relocation 22

Properties at immediate flood risk behind the current coastal defences could be relocated, reducing potential flood damages while also providing additional space for flood protection improvement schemes behind the existing defences.

Option not feasible due to significant disruption - social and political factors.

11 Property Flood Resistance and Resilience 43

Property Flood Resitance and Resilience measures could be a valuable option to incorporate into those properties at risk of flooding. This could be in conjunction with automated traffic signs to advise of diversions on roads.

Shortlisted option as can provide efficient short-term benefits.

12 Helensburgh Seafront Development Partnership (HSDP) lagoon 35

HSDP have a proposal to create a lagoon to the west of Helensburgh pier. This would be formed by a series of breakwaters and offer protection to part of the West Clyde Street benefit zone.

Option not shortlisted as it does not provide protection to the whole benefit area. The option could be progressed in tandem, but would not be considerd a flood protection scheme at this stage.

Key reason for shortlisting / discounting Short-termPresent day

to 2030

Mid-termPresent day

to 2070

Long-termPresent day

to 2118

Standard of Protection Short list options in green

Option Description

The map shows the modelled flood extents for the West Clyde Street benefit zone for the 2 year event along with the 200 year event under present day conditions and with climate change taken into account. It can be seen that the 2 year event shows coastal flooding to part of the promenade and across on to the main road. During the higher return period, 200 year event, flooding occurs along the full length of the benefit zone and affects properties.

The table below summarises the number of properties that the modelling shows to be at coastal flood risk for a range of different events.

Present Day Climate Change2 year 0 050 year 0 12100 year 0 12200 year 5 14

Present Day Climate Change2 year 0 650 year 6 11100 year 7 12200 year 7 13

Present Day Climate Change2 year 1 2350 year 25 57100 year 26 67200 year 26 77

Present Day Climate Change2 year 0 1750 year 18 65100 year 29 79200 year 35 83

Present Day Climate Change2 year 0 050 year 2 56100 year 2 63200 year 9 69

Rhu

Return PeriodProperty Count

West Clyde Street

Return PeriodProperty Count

Sailing Club

Return PeriodProperty Count

Craigendoran

Return PeriodProperty Count

East Clyde Street

Return PeriodProperty Count

Evaluating coastal flood risk within Helensburgh, Craigendoran and Rhu

West Clyde Street Benefit Zone Overview

West Clyde Street Long List Assessment

The West Clyde Street benefit zone runs from Kidston Park in the east to Helensburgh Pier in the west. The existing defences include sloping concrete and masonry revetments and a concrete recurve wall; each of these can be seen in the photographs below:

West Clyde Street Flood Extents

Recurve wall Masonry revetment Masonry revetmentSloping concrete

A range of potential options were considered for the West Clyde Street benefit zone; these are detailed within the table on the left. These options were assessed against technical, economic, environmental, social, political and legal criteria, with each category being assigned a score based on whether the option met the aims of the assessment criteria. A summary of the total scores is provided for each option considered, with those taken through to the short list phase for further assessment highlighted in green.

LEGEND

EXISTING GROUND

ROCK ARMOUR

TOPSOIL MINIMUM 150mm

ASPHALT

BLINDING

MASONRY WALL

RC CONCRETE

GRANULAR FILL

ST2 CONCRETE TO APPENDIX 26/1

COMPACTED SUB GRADE

WEST CLYDE STREET

DEFENCES TIEINTO SAILINGCLUB FRONTAGE

DEFENCES TIE INTOHELENSBURGH PIER

OPTION TO REDUCESIZE OF DEFENCE IN

AREA OF HIGH GROUND

A

AEXISTING BEACH ACCESSPOINTS MAINTAINEDWITHIN NEW DEFENCEALIGNMENT

PIER

1824.665

SET BACK WALL BETWEENPROMENADE FOOTPATH AND ROAD

SPILLWAY ACCESS MAINTAINEDWITH FLOOD GATES

NEW MODULAR BLOCKOR PRECAST CONCRETESEA WALL WITHMASONRY APPEARANCE

BEACH

BLINDING

GEOTEXTILE

ROCK ARMOUR SCOURPROTECTION BURIEDBENEATH BEACH

5.48mAOD

4.28mAOD4.50mAOD 1.

20

NEW DEFENCE INSTALLEDIN FRONT OF EXISTING

PROMENADE AREA RAISED BY APPROXIMATELY 0.3m TO MINIMISERELATIVE HEIGHT OF NEW WALL FROM THE PROMENADE ASHALT SURFACE

TO MATCH EXISTINGPROMENADEEXISTING PROMENADE

4.042.36MASONRY APPEARANCETO PARAPET WALL FACE

SECTION A-A (OPTION 1): NEW WALL1:50

COMPACTED FREEDRAINING FILL

SUB BASE

REINFORCED CONCRETE FOUNDATION

VEGETATED AREA

-0.21mAOD-0.44mAOD

4.76mOD 1 in 200 Year ESL, 2118

1.78mOD MHWS

1.18mOD MHWN

REPAIRS REQUIRED TO EXTENDRESIDUAL LIFE OF DEFENCE

EXISTING SEA WALL

EXISTING PROMENADE

VEGETATED AREA

MASONRY CLADDING

NEW REINFORCED CONCRETE SET-BACK WALLCOPING STONE

ROAD

SET BACK DISTANCE VARIES (MINIMUM 3000)

SECTION A-A (OPTION 2): SET-BACK WALL1:50

0.70

5.23mAOD

WALL HEIGHT VARIES BETWEEN0.7m AND 1.2m ALONG FRONTAGE

1.34mAOD

4.50mAOD

0.40

BLINDING

4.76mOD 1 in 200 Year ESL, 2118

1.78mOD MHWS

1.18mOD MHWN

4.00mAOD

WEST CLYDE STREET WALL

GEOTEXTILE

DRAFT

1

2

No. Construction Risk Maintenance Risk Demolition Risk

In addition to the hazards/risks normally associated with the types of work detailed on thisdrawing take note of the above.

SAFETY, HEALTH AND ENVIRONMENTAL INFORMATIONBOX

Drawing Notes

1. This drawing is to be read in conjunction with:-2. Crest heights are post settlement and consolidation. Dimensions and levels are

subject to change.3. CROSS SECTION 9: Would require landraising landward side of wall by

approximately 0.4m.

West Clyde New Wall

Setback-Wall

2018s0549-JBAU-XX-XX-DR-C-1003

As Shown @ A1

S0 P01.05

A Coad 19/04/19

The property of this drawing and design vested in Jeremy Benn Associates Ltd. It shall not be reproduced in whole or in part,nor disclosed to a third party, without the prior written consent of Jeremy Benn Associates Ltd.

Project

Title

Clientfor

Unit 2.1Quantum CourtResearch Avenue SouthHeriot Watt UniversityEDINBURGHEH14 4APUnited Kingdom

T +44 (0)131 3192 940E info@jbaconsulting.com

Designed:

Approved:

Drawn:

Checked:

Project Reference: Scale:

Drawing Number: Sheet Size:Status: Revision:

A1

www.jbaconsulting.comTwitter @JBAConsulting

Cowal and Lomond FLRMP

2018s0549

ARGYLL & BUTE COUNCIL

General Notes

A. All dimensions shown are in metres unless otherwise stated and levels in metres toOrdnance Datum.

B. Do not scale from this drawing. All dimensions must be checked/verified on site.C. Any discrepancies noted on site are to be reported to the Supervisor immediately.D. The locations of any known services shown on drawing are approximate and for

guidance only. The Contractor will confirm the location of any services prior to thecommencement of any works.

E. The electronic version of this drawing is not to be used for setting out.F. Refer to Contract Specification for details of materials and workmanship to be used

for the works shown on this drawing.

PLAN1:5000

0 20 20050 100

LEGEND

EXISTING GROUND

ROCK ARMOUR

TOPSOIL MINIMUM 150mm

ASPHALT

BLINDING

MASONRY WALL

RC CONCRETE

GRANULAR FILL

ST2 CONCRETE TO APPENDIX 26/1

COMPACTED SUB GRADE

WEST CLYDE STREET

DEFENCES TIEINTO SAILINGCLUB FRONTAGE

DEFENCES TIE INTOHELENSBURGH PIER

OPTION TO REDUCESIZE OF DEFENCE IN

AREA OF HIGH GROUND

A

AEXISTING BEACH ACCESSPOINTS MAINTAINEDWITHIN NEW DEFENCEALIGNMENT

PIER

1824.665

SET BACK WALL BETWEENPROMENADE FOOTPATH AND ROAD

SPILLWAY ACCESS MAINTAINEDWITH FLOOD GATES

NEW MODULAR BLOCKOR PRECAST CONCRETESEA WALL WITHMASONRY APPEARANCE

BEACH

BLINDING

GEOTEXTILE

ROCK ARMOUR SCOURPROTECTION BURIEDBENEATH BEACH

5.48mAOD

4.28mAOD4.50mAOD 1.

20

NEW DEFENCE INSTALLEDIN FRONT OF EXISTING

PROMENADE AREA RAISED BY APPROXIMATELY 0.3m TO MINIMISERELATIVE HEIGHT OF NEW WALL FROM THE PROMENADE ASHALT SURFACE

TO MATCH EXISTINGPROMENADEEXISTING PROMENADE

4.042.36MASONRY APPEARANCETO PARAPET WALL FACE

SECTION A-A (OPTION 1): NEW WALL1:50

COMPACTED FREEDRAINING FILL

SUB BASE

REINFORCED CONCRETE FOUNDATION

VEGETATED AREA

-0.21mAOD-0.44mAOD

4.76mOD 1 in 200 Year ESL, 2118

1.78mOD MHWS

1.18mOD MHWN

REPAIRS REQUIRED TO EXTENDRESIDUAL LIFE OF DEFENCE

EXISTING SEA WALL

EXISTING PROMENADE

VEGETATED AREA

MASONRY CLADDING

NEW REINFORCED CONCRETE SET-BACK WALLCOPING STONE

ROAD

SET BACK DISTANCE VARIES (MINIMUM 3000)

SECTION A-A (OPTION 2): SET-BACK WALL1:50

0.70

5.23mAOD

WALL HEIGHT VARIES BETWEEN0.7m AND 1.2m ALONG FRONTAGE

1.34mAOD

4.50mAOD

0.40

BLINDING

4.76mOD 1 in 200 Year ESL, 2118

1.78mOD MHWS

1.18mOD MHWN

4.00mAOD

WEST CLYDE STREET WALL

GEOTEXTILE

DRAFT

1

2

No. Construction Risk Maintenance Risk Demolition Risk

In addition to the hazards/risks normally associated with the types of work detailed on thisdrawing take note of the above.

SAFETY, HEALTH AND ENVIRONMENTAL INFORMATIONBOX

Drawing Notes

1. This drawing is to be read in conjunction with:-2. Crest heights are post settlement and consolidation. Dimensions and levels are

subject to change.3. CROSS SECTION 9: Would require landraising landward side of wall by

approximately 0.4m.

West Clyde New Wall

Setback-Wall

2018s0549-JBAU-XX-XX-DR-C-1003

As Shown @ A1

S0 P01.05

A Coad 19/04/19

The property of this drawing and design vested in Jeremy Benn Associates Ltd. It shall not be reproduced in whole or in part,nor disclosed to a third party, without the prior written consent of Jeremy Benn Associates Ltd.

Project

Title

Clientfor

Unit 2.1Quantum CourtResearch Avenue SouthHeriot Watt UniversityEDINBURGHEH14 4APUnited Kingdom

T +44 (0)131 3192 940E info@jbaconsulting.com

Designed:

Approved:

Drawn:

Checked:

Project Reference: Scale:

Drawing Number: Sheet Size:Status: Revision:

A1

www.jbaconsulting.comTwitter @JBAConsulting

Cowal and Lomond FLRMP

2018s0549

ARGYLL & BUTE COUNCIL

General Notes

A. All dimensions shown are in metres unless otherwise stated and levels in metres toOrdnance Datum.

B. Do not scale from this drawing. All dimensions must be checked/verified on site.C. Any discrepancies noted on site are to be reported to the Supervisor immediately.D. The locations of any known services shown on drawing are approximate and for

guidance only. The Contractor will confirm the location of any services prior to thecommencement of any works.

E. The electronic version of this drawing is not to be used for setting out.F. Refer to Contract Specification for details of materials and workmanship to be used

for the works shown on this drawing.

PLAN1:5000

0 20 20050 100

Evaluating coastal flood risk within Helensburgh, Craigendoran and Rhu

There are three short listed options for the West Clyde Street benefit zone:

- New sea wall - New stepped or sloping revetment - Property Level Resistance and Resilience

This poster presents details of the two engineered options, with the plan view to the left showing the extent of the potential defences.

The setback walls must be a minimum of 3m back from the crest of the existing defences, and could be located between here and the edge of the road, as indicated by the dotted line.

A schematic section of the options is then presented below along with some example photographs of this type of defence.

Examples of Property Level Resistance and Resilience are shown in the final poster, with further information also available from the Scottish Flood Forum representative present here today.

Aerial plan of proposed extent of flood defences along West Clyde Street.

Not to Scale

Please note that this drawing is not to scale and all dimensions and materials are indicative at this stage and may be subject to change prior to final construction.

Please note that this drawing is not to scale and all dimensions and materials are indicative at this stage and may be subject to change prior to final construction.

Section A-A (Option 1)

Setback alignment examples

Section A-A (Option 2)

West Clyde Street Options

Proposed Option 1 - New modular block wall in front of the existing revetment resulting in a widening of the existing promenade.

This image shows the existing alignment, promenade and amenity grass area along West Clyde Street, near to the junction with Cairndhu Gardens.

This montage provides an indication of how the wall might look if it follows the indicative alignment (set back by 3m).

This montage provides an indication of the new wall alignment if it were set back as far as possible from the indicative alignment.

Proposed Option 2 - A new wall with masonry cladding will be set back by a minimum of 3m from the current alignment.

Key:

Indicative alignment

Furthest possible indicative Set back alignment