GENERATION OF INTERTIDAL AREAS
BETWEEN RECULVER AND BIRCHINGTON

The feasibility of five schemes for the creation of intertidal areas have been assessed. Three schemes involve managed retreat of the existing protected coastline, one scheme involves increasing the width of existing nearshore mudflats and the final scheme involves the creation of new mudflats offshore.

The scheme would create a new 2.5-3 km² intertidal area and would involve the following works:

• Breach existing sea wall in sections
• Build a new 6.5 km long defence adjacent and seaward of the railway line and at each end of the proposed area
• Undertake earth works to develop tidal creeks, tidal flats and/or salt marshes

This scheme is technically feasible and would return the area to a state similar to its natural condition prior to the construction of the existing coastal defences. The scheme also avoids developed areas. Similar, but smaller, schemes have been successfully constructed elsewhere. It would have a limited influence on existing coastal processes (e.g. long shore drift), but this would not necessarily be detrimental. The main disadvantage of the scheme is that it produces a relatively small intertidal area.

Indicative costs:

Land purchase £
Breach existing sea defences £5m
New sea defence £35m
Earthworks £5m

Total £45m (excluding land purchase)

The scheme would create a 6.0-7.0km² intertidal area and would involve the following works:

• Breach existing sea wall in sections
• Build a new 9.5km long defence adjacent and seaward of the A229 and at each end of the proposed area
• Undertake earth works to develop tidal creeks, tidal flats and/or salt marshes
• Protect railway line with flood bunds and culverts and/or raise level

This scheme is technically feasible and would return the area to a state similar to its natural condition prior to the construction of the existing coastal defences. The scheme takes advantage of relatively high ground to the east of the area. Higher costs in comparison to Scheme 1 are primarily due to the issue of protecting the low lying railway line. This scheme would influence coastal processes more than Scheme 1, but this would not necessarily be detrimental. The advantage is that a relatively large area of intertidal is produced.

Indicative costs:

Land purchase £
Breach existing sea defences £5m
New sea defence £35m
Earthworks £10m
Railway protection £25m

Total £75m (excluding land purchase)

The scheme would create a 4.5-5.5 km² intertidal area and would involve the following works:

• Breach existing sea wall in sections
• Build a new 9.0km long defence adjacent and seaward of a relocated railway line (see sketch) and at each end of the proposed area
• Undertake earth works to develop tidal creeks, tidal flats and/or salt marshes
• Relocate 6km of railway line to the south of proposed intertidal area.

This scheme is feasible on a coastal engineering basis but may not be in terms of relocating the railway (SWK Railways to be consulted). In other aspects the scheme is similar to Scheme 2

Indicative costs:

Land purchase £.
Breach existing sea defences £5m
New sea defence £45m
Earthworks £7m
Relocate railway line £ConsultSWKRailways

Total £57m (excluding land purchase & railway relocation)

The scheme would create a 4.0 km² intertidal area and would involve the following works:

• Build shore connected and offshore breakwaters with an approximate length of 5km
• Recharge and extend existing mudflats

This scheme is complex but technically feasible. It is unprecedented in terms of scale. The scheme would be require careful design in order to develop a structure that would sustain a mudflat over long periods. The disadvantages of this scheme include severe disruption to coastal processes, navigation etc and the high costs associated with marine works. It may have significant detrimental environmental impacts for the adjacent coastline. The scheme could be combined with either Scheme 1, 2 or 3.

Indicative costs:

New sea defence £125m
Mudflat recharge £10m

Total £135m

The scheme would create a 4.0 km²intertidal area and would involve the following works:

• Build offshore breakwaters with an approximate length of 6km
• Recharge to create offshore mudflats

The technical feasibility of this scheme is uncertain and is completely unprecedented in terms of scale. Even with carefully designed structures, mudflats areas may prove difficult to sustain offshore. The main advantage of this scheme is that a completely new area of mudflats is constructed. The disadvantages include a severe disruption to coastal processes, navigation etc and the high costs associated with marine works. It may have significant detrimental environmental impacts for the adjacent area and coastline.

Indicative costs:

New sea defence £180m
Mudflat recharge £20m

Total £200m

Schemes 4 and 5 could be increased in size but with associated increases in costs.

As noted above all the options are all unprecedented in terms of scale. Generally UK managed retreat schemes are relatively small and the creation of intertidal mudflat areas is unusual. Examples are as follows:

* Excluding land purchase
** Excluding land purchase and relocation of railway

In order to develop the schemes further a detailed assessment of feasibility would include:

• Detailed bathymetric and topographic assessment
• Assessment of coastal processes
• Review of similar schemes
• Outline Environmental Impact Assessment
• Review of site specific parameters for mudflat/salt marsh design: wave heights, tide levels, exposure time etc
• Engineering option development
• Review of similar schemes

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