Appendix IV Initial Project Risk Appraisal – Boscombe Multi-Purpose Reef
(From Black et al., 2004)

Executive Summary

An initial project risk appraisal for the Boscombe multi-purpose reef examined the risks associated with field studies, design, construction and the eventual use of the reef, particularly surfing safety.

The surfing reef is a low risk, but technically innovative scheme. Risks have been minimised by using surfer “friendly” materials, with construction materials that have been proven elsewhere. Further reducing any construction risk, it is anticipated that three reefs in New Zealand and one reef in USA will be constructed under ASR Ltd supervision prior to the Boscombe Reef.

While data on life cycle performance and sustainability is relatively limited, there are several cases worldwide that support geotextile manufacturer’s warranties of around 25 years. It would be advisable to establish the maintenance programme with the geotextile supplier at the time of construction.

Some operation and guarding methods may need to be developed. It will be necessary to ensure that the lifesavers have appropriate equipment for rescues offshore (e.g. fast inflatable boats, binoculars etc.). It may also be appropriate to keep swimmers that are not wearing fins away from the reef, although experienced body surfers may want to use the reef. It is not expected that substantial operational management will be required, as serious conflicts of use are not expected to occur and no management (other than lifeguards) is present at other surfing breaks worldwide. Surfing competitions will need to be given permits and rights to clear the water of non-competitors.

Surfing is a relatively safe sport and the Borough presently provides facilities for a full range of sports (.e.g. rugby fields, tennis and basketball courts, golf courses etc.). As such, the creation of an artificial surf reef should not materially change the risk exposure of the Council, bearing in mind that surfing activities currently occur at locations that are far less benign, with larger waves and more dangerous reefs. However, it is recommended that legal advice be obtained.

Introduction Feasibility Study

A feasibility study was undertaken to determine if sites along the Bournemouth foreshore would be suitable for the development of an offshore multi-purpose reef (Black et al., 2000). Two sites were identified: Southbourne and near the Boscombe Pier. The study showed that the reef would provide acceptable surfing conditions for 30-40% of the year. While the wave climate is relatively small (compared to surf breaks around the world), the waves were sufficiently large to justify the reef, although the wave heights at Boscombe are typically less than 20-30% of the wave height in Cornwall, for example.

There is a strong surfing community in Britain (including Bournemouth) and many of the surfers are highly experienced. They commonly surf around the Bournemouth and Boscombe Piers and the many wooden groynes along the coast. It is suggested below that these existing hard features are inherently more dangerous than the proposed surf reef.

Reef Construction Methods

The reef at Boscombe is likely to be constructed using large, compartmentalised geotextile units that are custom made to provide a smooth and accurate reef surface.  The same technique is being adopted by ASR Ltd in New Zealand for a reef at Mt Maunganui. The full reef structure is divided into strips or elements which run across the full width of the reef.  Each element consists of a number of large sand-filled compartmentalised geotextile containers that are joined together to make up the single element.  The entire reef volume will be built by placing these elements one beside the other. 

Within each element will be a number of compartments, which increase in height from the toe to the crest.  When the compartments are filled by pumping them up with sand, the reef “inflates” to its full height creating a smooth profile rising from the toe to the crest, thereby allowing accurate reproduction of the designed profile. Further details on the methods will be provided in the detailed design reports at the completion of the construction methods investigation.

Possible Location & Size of Surf Reef

The reef is to be located about 200 m to the east of the Boscombe Pier in about 3 m depth, as shown on Figure 9.8A and B. The reef will have a volume of about 15,000 m3 and will project up from the seabed to around low tide line (0.5-0.9 m above CD). The reef consists of a smooth reef face, rising at a gradient of about 1:20 (i.e. the wave face which is being surfed). The back of the reef (lee face) drops off quickly with a gradient of about 1:1.5 into deeper water. Thus, the reef is not sharply protruding from the seabed; it is better described as a smooth mound with a steep lee face (Fig. 9.8A). Figure 9.9 shows a typical cross section of the structure resting on the underlying stable sea bed, with the relative heights of the crest for high/low tide levels. The reef is expected to be underwater mostly, but there will be times when the crest of the reef will be shallow or exposed. However, it should be noted that waves break in water depth that is about equal to the wave height. That means - as the wave gets bigger it breaks in deeper water. Consequently, surfers will always be in relatively deep water when the waves are large. They will only surf near the crest when the waves are very small (say less than 0.5 m high).

Possible Increase in Natural Surfable Waves

There is expected to be an increase in the number of surfable days, but the most important benefit of the reef is that the waves will break with a form suitable for surfing more often. Along the Bournemouth shoreline, when the waves arrive at the beach they break simultaneously over a long length of their crest (known as “closing out” to the surfer), making it very difficult to get up to the standing position and successfully ride the wave. The reef will be easier to ride because the breaking section of the wave will run down the reef (known to the surfer as “peeling”). The breaking section will be adjacent to an unbroken section along the length of the reef and the surfer will often ride on the easier-to-ride unbroken section.

Comparison With Existing Waves & Other British Locations

In comparison with existing waves at Bournemouth, the wave should be safer than the regular closeouts. It is expected to be similar in danger to the waves that are commonly ridden adjacent to the Bournemouth Pier. In comparison to international surfing sites (e.g. Australia, Indonesia, Hawaii, parts of Britain), the wave will be extremely safe due to the small wave climate. It is noted that the reef will be made of geotextiles filled with sands. These materials have no sharp edges and form a smooth surface which is much safer than the many coral reefs or rock ledges around the world that are commonly surfed on and produce much bigger waves than at Boscombe.

Identification of hazards & possible methods of mitigation:
Design Phase:

• Initial on shore investigation, including installation of current meter (area of investigation & hazards)

• Core drilling (area of operation & hazards).

Construction Phase:

• Selection of appropriate contractor

• Professional oversight

• Location & impact on the area during construction period

• Consultation with effected parties

Post Construction Phase:

• Design performance – risk minimisation (quality/experience of design team, robust solution etc.)

• Hazards to users – surfers & other users of the surf zone, including bathers

• Location, time of year, nature of probable user, assessment of additional risk created by ‘surf reef’ in comparison with existing levels of hazard – groynes etc

• Hazards to beach staff – lifeguards and cleaning team

• Durability of installed structure and tolerance of storm damage

• Maintenance regime – cost characteristics

• Conflicts of use

These matters are dealt with in turn in Table 1. The table identifies the risks, suggests mitigation and makes comparisons to other hazards that are common in the environment.

Discussion is presented next about reef construction/durability, reef safety for water users and areas for future investigation.

Modern geotextiles are durable materials with a postulated life of up to 100 years when submerged, even in a challenging marine environment.  Tests by Naue Fasertechnik and other large geotextile manufacturers have shown that the material is resistant to chemical and biological influences and can be effectively protected from ultra violet degradation by utilising UV-stabilised materials in the geotextiles.  The materials used on the Narrowneck reef have experienced no recorded degradation from UV light, this is in part due to the fact that the reef is constantly submerged.  However, even when installed above the water level, geotextiles can be easily protected from UV degradation to give them a long useful life.  Testing has shown that geotextiles installed in the UK suffer little or no danger from UV degradation, especially when submerged and covered with marine life. 

To further improve the durability of standard geotextile materials, soft armour products are available which will provide additional protection to the geotextile material while maintaining a soft reef surface.  The guaranteed life of the geotextile material will depend on the fabric used. By way of example, the material specified for the Noosa Artificial Surfing Reef in Australia carried a 25-year manufacturer’s guarantee.

There is some risk to the geotextile fabric from deliberate vandalism or boat damage.  However, geotextile fabrics require some determination to cut in their natural state and when installed on the seabed, the material quickly builds up a layer of dense sand on its surface which increases puncture resistance by up to three times.  This high puncture resistance, along with the fact that the reef will be a considerable distance offshore, means that the main risk would come from more determined “saboteurs” rather than random acts of vandalism.  It is hoped that boat damage will be avoided by marking the area of the reef with buoys and banning the use of anchors.  In the event that the material is damaged, experience on previous projects has shown that torn tubes only lose sediment within a small area either side of the tear and so caused no serious damage to the structure (Davis and Landin,1997).  Damage to the geotextile units can be repaired using geotextile patches and chemical bonding agents and it is suggested that the contract for provision of the geotextile material would include periodic maintenance of the fabric once installed. 

Geotextiles are not as resistant to mechanical damage as other coastal construction materials (i.e. rock or concrete), so care must be taken when designing and handling geotextile systems.  Experience suggests that most geotextile failures occur through careless handling during the installation process but, when correctly installed, failures are rare.  The use of a compartmentalised reef structure means that failure of a single compartment of the reef does not lead to failure of the whole reef.  In the event that a large amount of sediment is lost from one reef compartment due to a large cut in the fabric, the compartment can be repaired and hydraulically re-filled with sand.

While the materials are puncture resistant, if it becomes necessary to remove the reef due to unforeseen detrimental effects the geotextile containers can be cut using industrial cutting tools to allow the contained sand to escape.  Once the sand has dispersed, the empty geotextile containers can be pulled up from the seabed and disposed of.

Case Studies

A wide range of sand-filled geotextile construction units in a variety of shapes and sizes have been used for coastal projects around the world.  On the Gold Coast, Australia, an artificial surfing reef was constructed using large 160-300 tonne sand-filled containers dropped onto the seabed from a spilt-hull barge.  The reef at Narrowneck in Australia has proven the suitability of the use of sand-filled geotextiles for the construction of surfing reefs in large wave climates by standing up to storm waves in excess of 10 m on occasion.

At other locations much smaller units have been used, for example the artificial reef at El Segundo, USA used 13 tonne containers (Borrero, 2001) while the units used for a reef rehabilitation project on the island of Sylt, Germany weighed just 5 tonnes (Naue Fasertechnic, 2001).  A number of exposed groynes along the Australian coast have been built using 5-10 tonne sand-filled containers, the oldest of these at Russell Heads has performed very well since its installation in 1993 despite constant exposure to ultra-violet and wave attack.  In Florida, USA, a number of coastal protection projects have been successfully completed using compartmentalised geotextile units that were custom designed to suit the required application.  These units have been installed along hundreds of miles of coastline with no known damage due to waveborne debris. 

As the reef is well offshore and beyond the normal surf zone where beach goers swim, the additional risk of injury to bathers at the reef is small. There is expected to be a region of deeper water (where the waves are not breaking) between the reef and the inshore surf zone which means that loose surfboards are unlikely to be carried across from the reef to the beach. Also, the surfing on the reef is completely separate from the beach.

However, the reef is expected to improve the sand banks for surfing inshore of the reef at the beach. Thus, it may be appropriate to warn swimmers about increased surfing use in this area. A second effect relates to surfers paddling through the surf zone to and from the reef. It is expected that more surfer “traffic” will occur. However, it is noted that surfers are presently paddling around the surf zone at Boscombe, and that they are riding the waves in the surf zone with swimmers present. It is well known that surfers are not allowed to enter swimmer’s regions that are marked by life guard flags and so it may be appropriate to consider special regions for swimmers, which could be determined after reef construction in consultation with the local lifeguards.

In comparison to other sporting activities, surfing is a relatively safe past time.  This Section provides a background review of the existing literature that has addressed this aspect of surfing, as well as the physical aspects of the Boscombe reef itself.

The Boscombe surfing reef will be constructed of sand-filled geotextile bags.  With respect to the safety of surfers, this method of construction is advantageous, as the reef face will be relatively flat, with the convex reef profile meaning that the shallower regions are flatter than the deeper regions.  Large pinnacles or rocks protruding up from the reef, that often create a hazard at natural surfing breaks, will be absent.  In addition, when compared to rocky reefs, geotextile bags are relatively soft.  It must be noted that surfers rarely hit the seabed when they are surfing and if contact with the bottom does occur it is normally not with great force due to passing through the water column.  Waves break due to their height relative to the depth, generally at a ratio of wave height over water depth of 0.78.  This means that a 1m wave breaks in ~1.2m of water, and so the bigger the wave, the deeper the water it breaks in (e.g. 4m wave would break in 5m of water), lessening the chances of contact with the bottom.

A brief review of existing literature directed at injuries to surfers found that relative to other sports surfing is very safe and that impacts with the bottom are rare (SMA, undated; Renneker et al., 1993; Alfaro, 2000; Frisby, 2001).  Surfing injuries (minor, moderate and major combined) have been estimated at 4.5 injuries per 1000 surfing days for the Otago and Southland areas of New Zealand (Frisby, 2001), 4 injuries per 1000 days in the USA (Renneker et al., 1993) and 3.5 per 1000 surfing days world-wide (Booth and Facrm, 1989 – cited SMA, undated).  Most board surfing injuries result from surfers being hit by the surfboard resulting in lacerations (SMA, undated; Alfaro, 2000).  A two-year Australian study demonstrates the low injury rate of surfers.  Of all injuries sustained and reported at an Australian summer beach resort over a two-year period it was found that the same the number injuries due to surfing occurred in this period as those caused by litter and rocks (Renneker, 1987; Grenfell, 1993 - cited SMA, undated).

New Zealand Accident Compensation Corporation (ACC) statistics have been used to compare surfing injuries with other popular sports.  With reference to SMA (undated), Renneker et al. (1993), Alfaro (2000) and Frisby (2001), it is expected that similar low comparative incidents of surfing injuries occur worldwide.  In comparison to other popular sports and recreation in New Zealand, ACC claim statistics also show that claims for surfing related injuries are very low.  For example, in 2000 there were 88 claims for surfing related accidents, while there were 3,201 for rugby, 1,082 for netball, 1,037 for soccer and 691 for skiing/snow-boarding.  Consideration of these data in conjunction with statistics on participation confirms the low injury rate of surfing - i.e. in 1997 there were 219,600 surfers, 159,700 soccer players, 157,700 netballers, 144,700 rugby players and 128,200 skiing/snow-boarders (Hillary Commission, 1998).  Injuries from surfing are also below most other aquatic sports such as pool swimming, ocean swimming, diving, SCUBA diving and Boating (Allen, Eiseman and Straehley, 1987 – cited SMA, undated).

It is expected that SCUBA diving and snorkelling would occur around reef during periods of calm weather.  The smooth geotextile surface of the reef eliminates the possibility of entanglement.

To our knowledge, no coastal Borough in Britain specifically insures for surfing injuries, even though some such as Cornwall receive very large swells at times (far bigger than Boscombe). However, further investigation of practices in Britain and overseas may be warranted. It needs to be recognised that the Borough “supports” many sports, some of which are more dangerous than surfing (see discussion above). Legal advice will be needed.

The discussion about safety indicates that surfing is safer than other sports conducted within the Borough, on Borough facilities (e.g. rugby). In addition, the reef is a lot further offshore than the existing groynes and less likely to cause injury to the casual swimmer than the groynes, which are known to be involved in most rescues along Boscombe foreshore. (Notably, the Borough does not currently insure against injury on the groynes).

The reef will be used mostly by experienced water goers.

It would be advisable to establish the maintenance program with the geotextile supplier at the time of tendering for reef construction. An easy and regular inspection of the reef could be done by the Surf Lifesavers to check for fabric damage and reports will come from surfer observations. A more detailed annual sub-surface and bathymetry survey to review the condition of compartments for fabric damage and displacement of the reef profile would be advisable over the first 3 years. Surveys after that could be less frequent, depending on the early results. There is a high likelihood that student projects will provide invaluable feedback about the reef condition, sand bars and ecology.

The surfing reef is a low risk, but technically innovative scheme. However, it is anticipated that three reefs in New Zealand and one reef in USA will be constructed under ASR Ltd supervision prior to the Boscombe Reef.

While data on life cycle performance and sustainability is relatively limited, there are several cases worldwide that support manufacturer’s warranties of around 25 years. It would be advisable to establish the maintenance programme with the geotextile supplier at the time of construction.

Some operation and guarding methods may need to be developed. It will be necessary to ensure that the lifesavers have appropriate equipment for rescues offshore (e.g. fast inflatable boats, binoculars etc.). It may also be appropriate to keep swimmers that are not wearing fins away from the reef, although experienced body surfers may want to use the reef. It is not expected that substantial operational management will be required, as serious conflicts of use are not expected to occur and no management is present at other surfing breaks worldwide. The exception will be management of surfing competitions, which will need to be given permits and rights to clear the water of non-competitors.

Bearing in mind that BBC is creating an artefact, not promoting a natural phenomenon, particular aspects of Public Liability Insurance may need to be investigated. However, it is noted that surfing is a relatively safe sport and that the Borough presently provides facilities for a full range of sports (.e.g. rugby fields, tennis and basketball courts, golf courses etc.). The creation of an artificial surf reef should not materially change the risk exposure of the Council, bearing in mind that surfing activities currently occur at locations that are far less benign, with larger waves and more dangerous reefs. However, it is recommended that legal advice be obtained.