Summary 5: BEACH RECYCLING AND REPROFILING

Appropriate locations All locations, including those with limited blown sand for natural recovery.
Costs Low to moderate, but requires ongoing maintenance (£1000- £20,000 /100m length plus fencing, transplanting, etc, with similar repeat costs).
Effectiveness Short term defence against erosion, and enhancement of natural recovery. Moderate resistance to single storms. Enhanced by fencing and vegetation transplanting, and can be successfully used to bury hard defences.
Benefits Accelerates natural recovery of foredunes and provides short term defence against single severe storms.
Problems Removes material from other sites, possibly transferring erosion or environmental damage to a different frontage. May introduce beach debris, non-indigenous sediment and/or vegetation, potentially damaging local ecology.

General description

Recycling is the mechanical shifting of sand, shingle or even boulders from an area of accretion to an area of erosion. Normally recycling would be undertaken at a local level, with sediment being taken from an accreting ridge, the lower beach or an estuary bar, and transported a short distance to an eroding dune face or a blow out. Alternatively the donor area may be to landward if sand is blown onto roads or other areas where it is not wanted and from where it can be recovered.

Reprofiling is an alternative term, usually referring to the direct transfer of material from the lower to the upper beach or, occasionally, the transfer of sand down the dune face from crest to toe.

If large structures, such as harbour breakwaters or river training walls, cross the beach then sediment may accumulate on the updrift side. This material can either be returned to the beach in the updrift direction, or can be mechanically bypassed around the structure to feed a downdrift beach.

Recycling sand or shingle can be undertaken to repair minor erosion problems such as blowouts, or it can be used to rebuild long lengths of upper beach. Use of boulders is usually restricted to relocating small numbers up the beach face to provide temporary armouring of a short length of dune face suffering minor erosion.

If material is imported from a source not related to the eroding site the approach is known as beach nourishment or recharging (Summary 7).

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Reprofiled dune face following storm erosion. Sand taken from inter-tidal bar formed after storm event.

Function

Recycling provides an artificial buffer between the dune face and the erosive forces of the sea. Where erosion is active this buffer provides a short-term defence of the dunes, possibly only lasting through a single storm. Where the beach is stable or recovering, recycling accelerates the development of new foredunes. The success of this approach will be enhanced if combined with vegetation transplanting (Summary 2) and dune thatching (Summary 3) or fencing (Summary 4).

Recycling can also be used to enhance the coastal landscape by burying hard defences (sand bags, rock, gabions or timber), with the understanding that those defences may become re-exposed and active during storms. This will only be successful if the defences are high on the beach face - structures within the normally active foreshore zone will not be successfully buried as waves will rapidly remove the recycled material.

Methods

Recycling should only be undertaken where the shoreline manager has a good knowledge of local processes and beach movements developed from measurements and observations over at least several years. Sand or gravel should be sourced from areas known to be accreting, and scraping should not remove sufficient material to create a new erosion problem or to cause any significant environmental damage.

Relocating boulders from the foreshore to the dune toe may be an option for minor erosion problems, but the boulders will only provide a temporary defence against minor storm events, unless they are placed in sufficient quantity as a properly engineered rock revetment (Summary 14). Removal of rocks from the foreshore may well be damaging to local intertidal habitats, and will make an unattractive and largely ineffective addition to the dune face.

Prior to planning a beach recycling operation the ownership of the donor area must be established and appropriate consents sought. The intertidal area may be owned by the Crown Estates, a private estate, the Local Authority, the National Trust or other organisations.

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Recycled sand or gravel placed along an eroding dune face

The recycled material should be as similar as possible to the indigenous sediment. Sediment size, grading, shell content and material should match the upper beach and dune face. The material should also be clean and free of seeds. If these conditions are not met then the nourishment may cause unwanted changes to the beach and dune profiles, to the dune ecology and the dune appearance. Coarser sediments can be used, and may be more stable, but they are likely to cause the beach gradient to increase and will be less likely to form new foredunes. Ideally, environmental and hydraulic assessments should be carried out to determine the acceptability of sediments that do not meet the optimal criteria.

Scraping from a lower beach bar directly to seaward of an eroding dune face may well exacerbate existing problems. The bar will normally be a transient feature that acts to reduce wave attack by causing waves to break or refract before they reach the dune face. Any scraping should only remove a surface layer, say 200mm in depth.

Extraction may also be from other accreting areas, such as dunes, upper beach ridges or from estuary bars. Whatever the source it is important that the operation will not create a new erosion problem or habitat damage, and that the recycled material is acceptable in terms of environmental impact, hydraulic performance and appearance. Careful management should ensure that the donor site remains an area of net accretion into the future.

There is some debate as to the most effective position to place recycled sediment to achieve optimum protection. Possible locations include the upper beach and dune face, the mid to lower beach and the shallow nearshore zone. The former is most obvious as the benefits of recycling are immediate, but, if the sediment is primarily sand, it will be rapidly redistributed alongshore or across the beach face by waves and currents to form a new equilibrium profile (shingle tends to remain on the upper beach, but may be redistributed alongshore). Placement on the mid-beach anticipates this redistribution, and provides shoreline protection by helping to dissipate wave energy before it reaches the dunes. Placement below the water line also anticipates the redistribution and allows sand to be fed into the beach system gradually; this approach is more applicable to very large recharge schemes and is unlikely to be considered for dune management.

Although there is some merit in the alternative locations it is generally considered appropriate that deposition of the recycled material should be along the upper beach, above the high water line and along the eroding dune face. Natural redistribution of the placed material alongshore and cross-shore will occur, particularly for sand. Recycling operations should anticipate this redistribution by ensuring that the volume deposited to the upper beach is in excess of the amount required for immediate protection to the dune. The above figure provides some rough guidance as to appropriate beach profiles that will allow for continued erosion, but each site should be assessed separately. Consideration should be given to the past rates of erosion, the likely rate of redistribution and the intended life of the recycled material before the next recycling operation will be required. Fencing or thatching of the new dune line, followed by vegetation transplanting should enhance the success of the recycling operation (Summaries 2, 3 and 4). Ongoing management will allow the future recycling to be fine tuned for each site.

Recycling gravel can be very effective. A ridge of shingle along the dune face can provide good protection from wave erosion. The gravel may well be partially covered by sand during natural recovery, and may only be exposed by storms. A gravel ridge can be successfully controlled by groynes (Summary 10), although great care must be taken with design of these.

The approximate limits of wave run-up can be established by observing and recording the location of the strand line over Spring tide periods during both winter storms and more normal wave conditions. The toe of a freshly eroded dune face is normally at the run-up limit of the most recent severe sea.

Prior to placing recycled material along the dune face it may be prudent to remove some of the existing foredune vegetation for later transplanting. Vegetation buried by imported shingle or wet sand to a depth of more than a few centimetres may not recover.

Work can either be carried out as an emergency operation immediately after a storm to reduce the risk of follow on erosion, or as a planned maintenance operation in the spring. Maintenance work at this time will provide the greatest benefit to beach users over the summer and will maximise the length of time for establishing vegetation to stabilise the dunes. It is likely that recycling will have to be repeated annually or after severe erosion events.

The dimensions suggested by the accompanying sketch are basic minimums to serve as a guide for small recycling schemes. Greater and longer term success can be achieved by increasing volumes and by undertaking regular top-ups to maintain effective erosion protection. Large schemes should be designed by competent coastal consultants, following preliminary studies of the physical, natural and human environment.

Equipment required varies with the size of the scheme and the duration of the work. A small wheel loader and several dump trucks are suitable for moving a few hundred cubic metres over a couple of days, but recycling larger volumes over several miles of beach will require heavy earth moving equipment.

Mechanical cleaning occurs along some busy public beaches. This process removes some sand along with litter and strand line debris. Simple screening can separate most of the sand allowing it to be placed beneficially back on the upper beach without the debris, which should be disposed of properly.

Costs for recycling vary widely, depending on the scheme objectives, volumes, distances of transport, frequency of ongoing works and the need for beach control structures such as groynes or breakwaters. Minor works to repair blowouts may cost only a few hundred pounds, while large scale works may run to £200,000/km and may need to be repeated annually. Control structures will reduce ongoing maintenance costs but will greatly increase initial construction costs.

Impacts

Sand deposited on the upper beach may be subject to wind erosion, causing an unwanted increase in blown sand across the back shore; fencing and vegetation transplanting will reduce this problem. The deposits may also bury existing vegetation and intertidal invertebrate communities, reducing the natural stability of the foredunes and destroying habitats. As a general rule impacts will be less for regular, small recycling operations than for occasional large operations.

Scraping from the source area may allow erosion of a new area of shoreline. If the source is within an estuary the response to extensive scraping may be difficult to predict, and erosion problems may appear at some distance away.

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Layer of wind-blown sand upon reprofiled dune face. Sand retention and accumulation has been encouraged by re-planting of the reprofiled slope.

Extraction from the source area may also cause local damage to habitats, land forms or amenity. Intertidal scraping or boulder removal is likely to disturb benthic communities, while re-profiling the dune crest will largely destroy the local dune habitat, landform and landscape.

If the source material contains dissimilar sediments relative to the indigenous dune sand (e.g. boulders, gravels or estuary silt), beach debris, or vegetation/seeds that are foreign to the dune system, the dune geomorphology and ecology may be adversely affected. Any fine materials will be washed out of the recycled beach, potentially damaging nearshore fisheries and benthic communities.

Best practice and environmental opportunities

Recycling will enhance the natural recovery of dune face erosion and provide a wider recreational beach. The initial artificial appearance of the upper beach and dune face will quickly be transformed by wind, waves and vegetation to a more natural form. Recycling can be combined with fencing, thatching and transplanting to encourage development of new foredunes and an extended dune habitat. Hard defences built high on the beach face can be buried by recycled material, followed by fencing and transplanting, to create a much more natural shoreline.

In addition to these general guidelines the following are of specific importance to beach recycling: