Coastal Structures, Waste Materials and Fishery Enhancement

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COASTAL STRUCTURES, WASTE MATERIALS AND FISHERY ENHANCEMENT

K. J, Collins, A. C. Jensen, A. P. M, Lockwood and S. J. Lockwood

ABSTRACT

Current U.K. practice relating to the disposal of material at sea is reviewed. The usc of stabilization technology relating to bulk waste materials, coal ash, oil ash and incinerator ash is discussed. The extension of this technology to inert minestone waste and tailings, contaminated dredged sediments and phosphogypsum is explored. Uses of stabilized wastes arc considered in the areas of habitat restoration, coastal defense and fishery enhancement. It is suggested that rehabilitation of marine dump sites receiving loose waste such as pulverized fuel ash (PFA) could be enhanced by the continued dumping of the material but in a stabilized block form, so creating new habitat diversity. Global warming predictions include sea It:vel rise and increased storm frequency. This is of particular concern along the southern and eastern coasts of the U.K. The emphasis of coastal defenses is changing from "hard" seawalls to "soft" options which include offshore barriers to reduce wave energy reaching the coast. Stabilized waste materials could be included in these and other marine constructions with possible economic benefit. Ministry of Agriculture, Fisheries and Food (MAf'F), the regu- latory authority in England and Wales for marine disposal/construction, policy regarding marine structures and fishery enhancement is outlined. A case is made for the inclusion of fishery enhancement features in future coastal structures. Examples of the producti vity of man-made structures are given. Slight modification of planned structures and inclusion of suitable habitat niches could allow for the cultivation of kelp, molluscs, crustacea and fish.

This paper provides an account of marine disposal practice in the U.K. in relation to the requirements of international conventions. Consideration is also given to the potential for stabilization of some of the wastes which are currently dumped loose at sea or in landfill sites. The possible use of such stabilized material in marine construction, particularly in relation to coastal protection works, is discussed,

CURRENT U.K. MARINE DISPOSAL The U.K. is a signatory to the London and Oslo dumping conventions. Within the provisions of these agreements dumping of materials in the marine environment is licensed by the Ministry of Agriculture, Fisheries and Food (MAJ:

1240 COLLINS ET AI..: COASTAL STRUCfURES FROM WASTES 1241

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- , •...• -' '-::::-\~~ West B.y " Highelltfe c::;0 Poole B8Y.rtffle'.' reef Figure I. Map showing locations described in the text and areas vulnerable to sea level rise (shaded portions) identified by Borman et a!. (1989).

are necessarily freely available to marine organisms as some components may be bound within the mineral structure of the sediments. The practice of disposing of dredged spoil at sea is likely to continue in the U.K.

Solid Waste.-In 1989 4,835,6] 0 tons wet weight solid industrial waste were licensed for disposal at sea (MAFF, ]99]), The bulk of this material was stone extracted from coal mines, considered chemically inert in the marine environment. Dumping of mine tailings, a slurry of finely ground stone arising from the washing of coal, has aroused considerable concern at certain disposal sites (e.g., the beach disposal site at Durham on the east coast of Britain). In response to this a condition of the ]988 and 1989 British Coal licenses to dispose at sea was to inves- 1242 BULLETIN OF MARINE SCIENCE. VOL 55. NO. 2-3. 1994 tigate the practicality of disposing of colliery waste on land to terminate beach disposal at Durham (a particularly sensitive site) as soon as possible. Similarly, disposal of pulverized fuel ash (PFA) at sea from the coal-fired power-stations of Blythe (309,000 tons per annum) and Stella on the northeast coast of England was recently allowed to continue only on the condition that it should be terminated as soon as practicable, in line with the declaration of the Second International Conference on the Protection of the North Sea, London 1987 (De- partment of the Environment, 1987). Only 50% of the PFA produced in the U.K. is sold commercially (e.g., for road bases, cement filler, etc.). The remainder has to be disposed of by other means. It is currently expected that both loose PFA and minestone waste disposal at sea will be discontinued by 1995. Sewage Sludge.-In 1989 9,642,847 wet tons of sewage sludge were dumped under license into the coastal waters of England and Wales (MAFF, 1991). At present licenses are linked to the quality of sludge, which is related to the amount and type of industrial effluent released into the sewers. This disposal at sea will be stopped by 1998. Liquid Waste.-In 1989 248,454 tons of liquid industrial waste were licensed to be disposed to the marine environment (MAFF, 1991). Following the second In- ternational Conference on the Protection of the North Sea, London 1987, an agree- ment to reduce the number of licenses relating to marine disposal was reached (Department of the Environment, 1987). This has encouraged the development of alternative disposal methods.

Stabilization of Wastes Landfill.-The simplest method used to stabilize otherwise mobile wastes is to bury material at a landfill site. This is particularly attractive where disused quarries and mine workings are available. The economics of disposal dictate that while a low cost landfill alternative is available little effort will be made to find alternative, environmentally acceptable practices. Current (1990) U.K. landfi II prices are in the region of £2·m-3 for inert materials and £ 10'01 3 for controlled materials. It would seem likely that as U.K. landfill sites are filled, and the price to dispose increases, that there will be a greater willingness to pursue other options. Stabilization of Urban Waste Material.-Nagasaka et al. (1985) describe a process by which Japanese urban waste can be stabilized by press packaging in steel mesh and encasement in concrete. These materials could then be used to build artificial reefs. Stabilization of Ash.-Research groups in the U.S. and Europe are investigating the use of cement-stabilized waste from coal-fired power-stations (Woodhead et aI., 1985, 1986; Collins et aI., 1990, 1991a, 1991c). Groups in the U.S. are investigating cement stabilized oil ash (Metz and Trefry, 1988; Nelson et aI., 1988) and incinerator ash (Breslin et aI., 1988). The common theme running through this work is the construction of artificial reefs from this stabilized material. In Japan it is usual for artificial reefs to be constructed from prime (not waste) materials. However, Suzuki (1985) describes plans for artificial ridges, designed to enhance nutrient upwelling and improve fishing grounds constructed from a hardened mixture of 65% coal ash, 23% water and 12% cement. Use of this stabilized material would have half the cost of similar structures made from concrete. COLLINS ET AL.: COASTAL STRUCTURES "ROM WASTES 1243

Stabilization of Contaminated Sediments.-Some harbor dredgings contain high levels of toxic materials. In the Netherlands some 45 million m3 of sediment is dredged annually, over half from the River Rhine. Scouten and Rang (1989) have described a system for high temperature (up to 1,200°C) processing of dredged muds. Organic micro-pollutants are destroyed. Heavy metal loss is slowed by the formation of a glass-like matrix of metal silicates and scintering which reduces the overall surface area of the material. A gravel-sized particulate is produced. Other Materia/s.-At present bulk wastes such as minestone waste and tailings with inherent low toxicity, small particle size which are currently disposed of at sea seem to be ideal subjects for cement stabilization technology. It is possible that other materials, such as phosphogypsum, which pose greater environmental problems, may be suitable for disposal in the sea after stabilization. Phosphogyp- sum is a by-product of the production of phosphate fertilizers from ores which may contain trace constituents such as cadmium and natural radionuc1ides of the uranium-238 family. The conversion of ore to phosphoric acid by sulfuric acid leaves calcium sulfate as a waste product. Some 2 million tons per year of this slurry are discharged, via the Nieuwe Waterweg in the Netherlands into the North Sea (van del' Heijde et a!., 1990). In France some 840,000 tons per year of phosphogypsum are disposed of directly into the marine environment off Le Harvre (Commission Baie de la Seine, 1990). The future of this practice is not known. The experience of the Poole Bay artificial reef project (Collins et a!., 1990, 1991 a, 1991 c, 1992a) with stabilized PFA/gypsum blocks suggests that phosphogypsum could be successfully stabilized.

Uses of Stabilized Waste Habitat Restoration.-The principal impact of dumping many powdered or loose wastes, capable of being stabilized, is that of smothering, characterized by a reduced faunal abundance and diversity. Eagle et a!. (l979) described the effects of disposal of colliery waste, fly ash and harbor dredgings off the Northumberland coast (northeast coast of England). They found severe depletion of the benthos in terms of species number and diversity. The dumping was thought to cause direct interference with commercial trawling and potting. The productivity of the fishery was reduced as rocky areas, formerly suitable crab and lobster habitat, were smothered. At the Wear dump site (licensed for 0.85 million tons of colliery waste and 0.75 million tons of harbor dredgings) an area of some 10 km2 was affected. The impact was expressed as a severe depletion of the bottom fauna. Bamber (1984) found a negative correlation between faunistic diversity and sediment ash content at the Blythe PFA dumping site. This relationship was significant over an area of 43 km2 around the center of the site at which some I million tons of PFA is dumped per year. Nunny (l978) described the dispersal of beach-tipped colliery waste at Lyne- mouth, Northumberland. The waste established an area of soft-medium pan, pre- sumably with a similar effect to that of PFA dumping. Even when dumping is discontinued (projected as 1995), it will take an un- known length of time (probably decades) for the sea bed to be rehabilitated and exhibit a typical biological productivity. Even then it is unlikely that it would ever return to its original condition. From the preliminary results of the Poole Bay reef (Collins et a!., 1990, 1991a, 1991c) it is suggested that the process of rehabilitation could be accelerated significantly by continuing to dump fly-ash but in the form of stabilized blocks, creating a new substratum with considerable niche diversity. The authors suggest that it would be more environmentally re- ]244 BULLETIN OF MARINE SCIENCE, VOL. 55, NO. 2-3, 1994 sponsible to continue with this form of modified disposal than to cease dumping altogether and wait for natural processes to restore biological productivity in the area. Non-dispersive sewage sludge dump-sites also have a very restricted fauna, although biomass may be high. Reef building might restore such an area to fuller productivity with the additional possibility that the soft underlying substratum would become suitable for colonization by post-larval lobsters. It is believed that stabilized PFA reefs are not simply a means of waste disposal but can contribute positively in ameliorating some of the environmental problems bequeathed by earlier dumping.

Coastal Defense.-There are many estimates of global mean sea level risco In the southern U.K. two factors are at work; climatic factors and isostatic subsidence. It is suggested (U.K. Climate Change Impacts Review Group, 1991) that by 2030 higher temperatures (by some 1.5°-2.IOC), will result in warmer winters than at present, a higher incidence of extreme hot summers and increased precip- itation (5% higher during the winter of 2030). This combination of effects will result in a sea level rise of some 20 cm (to be adjusted for vertical land move- ments). An increased incidence of storms is predicted, so promoting the possibility of enhanced wave heights and generation of storm surges. The importance of these phenomena is reflected in the large financial investment made in the Thames barrage. Following a storm surge in 1953, floods in the U.K. cost between £240 million and £400 million at 1982 values (Arnell et aI., 1984). East Anglia, one of the more prosperous farming regions of the U.K., is an area of low-lying land separated from the North Sea by stretches of soft, erodible cliffs. The 1953 floods claimed over 300 lives (Karas et aI., 1991) in East Anglia. More recently, in February 1990, storms breached the seawall at Towyn, North Wales, causing considerable damage to the low-lying area behind the wall. Areas at risk in the U.K. have been reviewed by Borman et al. (1989) (Fig. I). Complementary to predicted climatic increase in sea level the southeast of England experiences isostatic subsidence at the rate of I mm·year I (Huntley, 1980). The cost of protecting the U.K. from sea level rise has been estimated as £6 billion for a I m rise in level (IPCC: Delft Hydraulics, 1990). Modern coastal defense philosophy is turning away from the "hard" defenses typified by concrete seawalls towards a "soft engineering" approach, absorbing wave energy before it impacts easily erodible beaches and cliffs. A recently proposed scheme to protect the coastline between the Humber estuary and the Thames (Milne, 1991) will not utilize seawalls, instead emphasis will be placed on beach replenishment schemes. To protect the Norfolk Broads, a wetland area in East Anglia, a proposal, detailing the building of offshore reefs between Hap- pisburg and Winterton (Halcrow, 199I), has been submitted to the coastal defense section of MAFF. The scheme involves construction of 16 reefs, each 200 m long with a gap of 300 m between each reef, 300 m off, and parallel to, the shore along some 8 km of coastline. Each reef will have a crest elevation some 3 m above Ordnance Datum. There will be a gradation of rock sizes from 100-500 mm rocks at the base, through 1-2 ton rocks in the center to a capping of either 8. I6 ton rocks or 20 ton concrete accropodes. This range of material sizes will be valuable in the provision of habitats for marine life. It is thought that incident wave height will be reduced by 50%. These reefs will be cheaper to construct than fish-tail breakwaters (an extension of the groin concept), and will interfere less with longshore drift, so minimizing the risk of beach starvation downstream of the scheme. Net cost of reef production is estimated at £30 million. Stabilized COLLINS ET AL.: COASTAL STRUCTURES FROM WASTES 1245 ash products could replace the smaller rocks and possibly the concrete accropodes assuming that the mechanical properties were satisfactory. Wang (1978) describes significant reductions in beach erosion with rocky-toe structures to protect beaches. On the south coast of England, Christchurch Council is investigating the possibility of constructing fish-tail groins at Highcliffe, replacing the groin core with high PFAIconcrete (80% PFA) blocks. One method of forming or handling this material would be to use geotextile bags rather than conventional blocks. On the North HumbersidelEast Yorkshire coast the soft clay cliffs of Holder- ness, northeast of Hull, are disappearing at a rate of 2 m every year (Withington, 1988). Proposals have been made to use minestone banks offshore in a beach protection scheme. The scheme was rejected because loose minestone would not be stable along this exposed coast. It would seem more realistic to stabilize the small minestone waste particles and create nearshore reefs with the intention of reducing wave energy as a longterm effect rather than providing a shortterm replenishment material.

Marine Construction.-Stabilized materials could be used as a replacement for the large boulders used in marine construction projects. At present in the U.K. much of the rock for marine construction is imported from Scandinavia and Spain. The quarrying of such rock will have environmental implications in the countries of origin. HARBOR WALLS. The proposed harbor wall/breakwater at the south coast port of West Bay, Dorset (Anon., 1990) is a £10 million project to construct a 12 m deep breakwater using 7-15 ton blocks (at surface) of Spanish granite at some £50 per ton. The use of stabilized material and a design to create sufficient hollows and crevices for commercially important species such as lobsters and crabs would create a multifunctional structure with a longterm benefit to the local fishing community, with the potential financial saving linked to the use of a stabilized waste product. ARTIFICIALISLANDS.Johnson et al. (1978) described the colonization of an artificial island, Rincorn Island off the Californian coast. It is bounded by rock armor, using many lypes and gradations of quarry rock and concrete tetrapods on its exposed side. The sea bed is a silty sand. New habitats were created with a net increase in species diversity. Stabilized material could be utilized in a similar fashion in the future, with block design optimizing the fishery opportunities. Plans for an oil production island in Poole Bay, recently cancelled, had recognized this potential and consideration had been given to a fishery enhancement program. OFFSHOREWINDFARMS.As the demand for "clean energy" increases, the economic viability of an offshore wind farm for electricity generation becomes more likely. Aesthetic and environmental considerations are likely to restrict land-based farms. Marine-based generating structures will need to be supported by an un- derwater foundation which is analogous to an artificial reef. The use of stabilized waste for a large structure offshore, supporting wind generators and acting as a purpose designed fishery area is certainly futuristic but would provide multiple benefits from the environmentally sensitive use of a waste material. FISHERYMANAGEMENT.Trawling and dredging at best disturbs the sea bed and the communities on, and in it. Where fishing effort is most intense and persistent, e.g., the German and Southern Bights of the North Sea, the impact of fishing can be particularly disruptive. The construction of artificial reefs as a conservation measure to prevent trawling over reserve areas (say spawning or nursery grounds) could increase fisheries productivity. An Italian reef complex of 2 m cube concrete 1246 BULLETIN OF MARINE SCIENCE. VOL. 55. NO. 2-3. 1994

offshore wind farms for electricity generation ".~ ..~ .~ artificial Islands for 011extraction

offshore breakwaters ~

Figure 2. Diagram showing areas of potential use of stabilized waste materials in the marine environment. blocks spread out over 6 ha has been described by Gravina et al. (1989). Such a deployment has been used to protect Posidonia beds in the Mediterranean. Some of these uses are summarized in Figure 2. FISHERYENHANCEMENT.The potential benefit of fishery enhancement around structures has already been mentioned. In the U.K. all "dumping" is licensed by fisheries departments, including MAFF (England and Wales). Construction work below high water level, whether civil engineering or rig construction is licensed as if it were dumping. MAFF's current position is that it will not license reef construction purely for fisheries reasons, even though it carries government re- sponsibility for fisheries. The department's view is that there must be some well founded reason for reef construction in the first instance, such as coastal protection or environmental rehabilitation, before it will consider approval. If this constraint is met, MAFF will then look to maximize the benefits to fisheries from individual proposals. Current U.K. legislation is only able to grant exclusive fishing rights over an area of seabed to mollusc fishermen (a fishery order). At present the fishing on an artificial reef would be open to all. If structures are to be developed with fishery enhancement in mind this lack of legal protection may act as a disincentive to constructors hoping to gain an income from the lobster harvest and to any group wishing to enhance the fishery population artificially. MAFF could, however, make "public fishery enhancement" a condition of granting a license for construction. The use of artificially created structures, both purpose designed and those of opportunity, are already being considered or exploited elsewhere. The establishment of a mussel community on newly constructed rock breakwater jetties was described by Reish (1964). This natural settlement has been advantageous to the Dutch mussel industry. The colonization of artificial rocky shores, dykes and storm surge barriers in the Netherlands is described by Leewis and Waardenburg (1990). Colonization of a range of substrate types from natural rock (limestone and granite) and concrete to wastes: minestone, various slags COLLINS ET AL.: COASTAL STRUCTURES FROM WASTES 1247

(steel, phosphorus, manganese, copper) has also been followed (Leewis et aI., 1989; Leewis and Waardenburg, 1989). Recommendations given for artificial shore elements include large size of components (>30 em), loose packing and utilization of concrete blocks designed to provide optimal conditions for flora and fauna. Jones and Holt (1985) and Moreley (1985) envisage the cultivation of large brown algae, Saccorhiza polyscides, Laminaria saccharina and Alaria esculenta) on horizontal ropes anchored between structures such as wind turbine towers. An annual productivity of 15 kg weed per m of rope (equivalent to 1 kg of coal when used as a power source) is envisaged, together with a wave reduction capability. Kain and Dawes (1987) present further data on seaward productivity, describing production of 9 tons·ha I from anchored rope off the Isle of Man. Japanese coastal aquaculture of seaweeds for rearing sea urchins is described by Mottet (1985) and Neushul et al. (1985) describe the construction of a chain and rope network over one acre of seabed to cultivate the giant kelp Macrocystis. Suto (1968) describes propagation of seaweeds and considers the suitability of breakwaters and tetrapods as substrata for growing seaweeds. The artificial reef in Poole Bay, Dorset, U.K. (Collins et aI., 1990, 1991a, 1991b, 1991c) has successfully attracted lobsters (Homarus gammarus) and crabs (Cancer pagurus) to a previously sandy area of seabed some 3 km from the nearest significant hard substrate. The first animal was recorded on the reef 3 weeks after deployment. The large amount of internal void space in the 1 m high by 4 m diam conical piles is estimated to be about 22% of total volume. Potting, tagging and acoustic tagging work (Collins et aI., 1991b, 1992b) has established that lobsters continued to be attracted to the reef and one specimen has an established residency time of over 368 days. For the maximum advantage to be taken from marine construction activities there is a need to research the design of marine structures to optimize habitat for selected species.

DISCUSSION In the U.K. the practice of dumping waste material at sea is currently being phased out in favor of land disposal. However, the simple landfill option will increase in cost over the next decade as suitable sites become scarce and alternative, environmentally acceptable, means of disposal will ultimately become nec- essary. Pilot schemes such as the Poole Bay artificial reef have shown that stabilized PFA/gypsum appears to be environmentally acceptable and can be used to build a fishery enhancing structure, suggesting that waste materials can be used constructively. It must be stressed that any stabilized waste material used in the construction of artificial habitats must be fully investigated over a realistic time- scale, years rather than months. The Poole Bay reef continues to be monitored for block heavy-metal content and the possibility of epifaunal uptake of these metals. Investigations into the utilization of reefs for lobster fishery management are producing encouraging results. Artificial reef block composition is an area which warrants further inves- tigation, so to maximize the mechanical strength of the material. Blocks constructed from other ashes, e.g., commercial domestic refuse incinerator ash, have been shown (Rothel and Breslin, pers. comm.) to have strengths comparable to concrete blocks used for the construction of buildings. Environmental aspects of reef building with waste materials do not always receive the attention that they deserve. For example, waste tires have been used as a reef building material throughout the world for several decades apparently 1248 BULLETIN OF MARINE SCIENCE, VOL. 55, NO. 2-3, 1994 without any specific assessment of their chemical stability. There appears to be no published environmental impact assessment of the possible leachates from tires in the marine environment, even from areas still actively building tire reefs (Pol- lard, pers. comm.; Branden, pers. comm.). The proposed use of offshore reefs (using conventional materials) to minimize coastal erosion off part of the East Anglian coast indicates that coastal engineers now believe that this type of structure can be of positive benefit in combatting the effects of storm damage. MAFF policy at this time indicates that any artificial reef structure should be multipurpose, one possible secondary role being that of fishery enhancement. The use of structures of opportunity elsewhere in the world confirms that this approach is feasible. In the U.K. several problems need to be addressed if effective, multipurpose marine structures are to become a reality. Work must be continued to establish the exact function of an artificial reef in terms of biomass productivity. The legislation relating to the ownership of seabed structures must be modified to include "all shellfish" rather than only molluscs. The true economic case for artificial reefs must be established, a complex task involving social issues (such as the creation of employment and the effects of coastal erosion) and the true cost of recycling waste materials rather than dumping them in a landfill site. Research into optimal block mixes to maximize block strength must be extended so that engineers have a comparison of prime material and stabilized waste strengths. Finally, block design must be optimized to provide the required mechanical strengths and reef design must address the problem of maximizing the habitat potential for targeted species, such as the lobster, while for filling an additional role, such as coastal defense.

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DATE ACCEPTED: July 12, 1993.

ADDRESSES: (K.J.C" A.C.J. and A.M.P.L.) Department of Oceanography, University of Southampton, Southampton SO/7 IBJ, U. K.; (S.JL) MAFF Fisheries Laboratory, Benarth Road, COl/wy, Gwynedd LL32 8UB, u.K.

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