Coastal Defence Strategy

Options for the River Itchen, Weston Shore, Netley and River Hamble

Mouchel Parkman has been commissioned by a partnership with Southampton City Council, Eastleigh Borough Council and Fareham Borough Council to develop a ‘Coastal Defence Strategy’ for the sustainable management of coastal defences. The study frontage includes the east bank of the River Itchen as far upstream as Woodmill, the Weston, Netley and Hamble Le Rice frontage, and both banks of the River Hamble as far upstream as the Bursledon railway bridge.

• Coastal Defence Strategy (The estuary process study) 29MB pdf  (right click and save target as to speed download)

• Coastal Defence Strategy Part B (Regime modelling) 20MB pdf (right click and save target as to speed download)

• Geomorphological Survey Report  5MB pdf (right click and save target as to speed download)

• Proposal for Appropriate Assessment pdf

How does the Coastal Defence Strategy fit in with the Shoreline Management Plan?

The Strategy adopted will fall within the framework already developed for the Weston Solent and Southampton Water Shoreline Management Plan (SMP) 1998 which looks at a much wider area, but in less detail. The Coastal Defence Strategy reviews the strategic coastal defence options recommended by the SMP for each management unit in more detail and determines whether the SMP options have to be revised. The Shoreline Management Plan for the Solent is also currently under review and is likely to be revised in 2008.

Provisional Coastal Defence Options for each Management Unit

The study area has been divided into several ‘Management Units’. Provisional coastal defence options for each Management Unit have been suggested for the next 100 years. These are shown on three separate display maps and have been divided into the following areas:

• The River Itchen frontage
• The Weston, Netley and Hamble Le Rice frontage
• The River Hamble frontage

Defence Options Definitions – what does it mean for the frontage?

• ‘Do Nothing’: (also called No Active Intervention) This means that no coastal defence activities are carried out except for safety measures.

• ‘Hold the Line’:  This means the existing defence line is held in its current position. This may involve intervention including maintenance. Future proposed engineering works required to Hold the Line would be subject to further consenting requirements during the detailed design stage.

• ‘Retreat the Line’:  This means the existing defence line would be set back landwards, away from the sea. This could mean either:

1. Building an embankment inland and letting the existing defences fall into disrepair (with monitoring), or;
2. Building an embankment inland and dismantling the existing defences.

Once again, specific engineering works required to Retreat the Line would be subject to further consenting requirements during the detailed design stage.

It is estimated that sea level could rise by approximately 0.6m over the next 100 years so a Retreat the Line policy may need to be considered for some frontages in the long term. A  Hold the Line policy may become unsustainable along many frontages, resulting in a Retreat the Line policy adopted where possible.

Process to finalise Coastal Defence Strategy options

• Environmental Appraisal of Coastal Defence Options

A Strategic Environmental Assessment (SEA) of the coastal defence strategy is currently being carried out. This will ensure that the environmental implications of the coastal defence options are understood and suitable mitigation measures are taken account of in the selection of the preferred coastal defence options.

The coastal and river frontages have National and European nature conservation designations:- Legislation protecting the sites of European importance requires that the provisional defence options are subject to an ‘Appropriate Assessment’ which will be carried out in May 2007.

The objective of the Appropriate Assessment is to ensure that the proposed defence options will not have an adverse effect on the important features of the nature conservation site. If this is the case, and there are no viable alternative options, compensatory habitats must be secured elsewhere before the defence options can be approved.

• Economic Appraisal

An economic appraisal of the recommended options will be carried out in accordance with the latest Defra guidance using cost-benefit analysis.

Programme

The Draft Coastal Defence Strategy is due to be completed in August 2007 and will include the Strategic Environmental Assessment, Appropriate Assessment and economic appraisal.

Do you have any comments on the defence Options?

If you have any comments please  fill in our online comments form.

Rob Crighton, Coastal Projects Officer, Southampton City Council, Planning and Sustainability Division, Southampton City Council, Civic Centre, Southampton  SO14 7LS

Netley shore

Recommended Strategies for Each Management

ITCH 3

• Undefended frontage: Do nothing and monitor.
• Defended frontage:  Hold the Line.  Retreat the Line in long term.

ITCH 4

• Hold the Line assuming maintenance by private landowners. 
• Retreat the Line in long term.

NET 1

• E frontage:  Defend the land fill frontage with new defences.
• Central and W frontage:  Hold the Line.  Retreat the Line in long term.

NET 2

• Hold the Line assuming maintenance by private landowners.
• Retreat the Line in long term

NET 3

• Defended Frontage:  Hold the Line and Monitor assuming Hamphire CC will maintain defences.  In the longer term Retreat the Line.
• Undefended Frontage: Do Nothing and Monitor

NET 4

• Do Nothing and Monitor
• Retreat the Line in long term

NET 5

Hold the Line assuming maintenance by private landowners.

Retreat the Line in long term

NET6

• Defended Frontage:  Hold the Line assuming maintenance by private landowners.  Retreat the Line in long term
• Hamble Common:  Do Nothing and Monitor.  Retreat the Line in long term

HAM 1

• Defended Frontage:  Hold the Line assuming maintenance by private landowners.  Retreat the Line in long term.
• Hamble Common:  Do Nothing and Monitor
• Retreat the Line in long term.

HAM 2

• Mercury Marina:  Hold the Line assuming maintenance by private land owners.  Retreat the Line in long term.
• Undefended frontage:  Do Nothing and Monitor.   Retreat the Line in long term.

HAM 3

• Do Nothing and Monitor.
• Retreat the Line in long term.

HAM 4

• Hold the Line assuming maintenance by land owners.  Retreat the Line in long term.

HAM 5

• Undefended frontage:  Do Nothing and Monitor.
• Defended frontage:  Hold the Line assuming maintenance by private land owners.  Retreat the Line in long term.

HAM 6

• Hold the Line assuming maintenance by private land owners.

HAM 7

• Do Nothing and Monitor.
• Hampshire CC wish to maintain existing footpath.

HAM 8

• Defended frontage: Hold the Line assuming maintenance by land owners.  Retreat the Line in long term.
• Undefended frontage:  Do Nothing and Monitor.  Retreat the Line in long term.

• Map showing Ham3 Ham4 Ham5 Ham6  (opens in new window, hover over image to enlarge)
• Map showing Ham1 Ham2 Ham7 Ham8  (opens in new window, hover over image to enlarge)
• Map showing Net1 Net2 Net 3  (opens in new window, hover over image to enlarge)
• Map showing Net4 Net5 Net6   (opens in new window, hover over image to enlarge)
• Map showing ITCH3, ITCH4    (opens in new window, hover over image to enlarge)

Reproduced from the Ordnance Survey mapping with the permission of Her Majesty’s Stationery Office © Crown copyright. Unauthorised reproduction infringes Crown copyright and may lead to prosecution or civil proceedings.  Southampton City Council LA 100019679 2006.

Definition of Defence Options

Do Nothing:  Carry out no coastal defence activity except for safety measures.

Hold the Line:  Hold the existing defence line where it is by intervention including maintenance subject to the proposed works meeting the funding benefit costs requirements and environmental appropriate assessment requirements.

Retreat the Line:  Retreat the existing defence line landward by intervention subject to the proposed works meeting the funding benefit costs requirements and environmental appropriate assessment requirements.

Time Scales Short to medium 25-50 years. Medium to Long 50-100