Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

SAVING BURIED OYSTERS

D. Buzan1, C. K. Weber1, B. Rodney2, and B. Legare2

ABSTRACT

Oysters are a keystone species in estuarine ecosystems. The reefs they create provide habitat for myriad estuarine invertebrates and fish. They also provide other ecosystem services. Oysters feed by filtering water thus helping to cleanse coastal waters. Oyster reefs also help reduce shoreline erosion by attenuating wave energy. In addition to these ecological benefits, a considerable economic benefit is realized through their harvest and consumption. The U. S. production of oysters neared $130 million in 2008. Recent research indicates the economic value of oyster reef ecosystem services may exceed the commercial harvest value. Hurricanes and other strong storms can bury thousands of acres of oyster reefs under a layer of sediments in a matter of hours. These layers can range from inches to feet thick. The primary approach used to recover the productivity of these impacted habitats is referred to as “cultch planting” with the various materials used collectively called “cultch”. This involves placing hard substrate like limestone or oyster shell on top of the buried reefs. Cultch planting can range from about $22,000 per acre for large uncomplicated projects to more than $100,000 per acre for small complicated projects. Different techniques to remove sediment quickly over broad areas have been conceptually explored. One conceptual method to reclaim buried oyster habitats includes dredging sediments and buried shell, separating shell from sediments, and pumping sediments to beneficial use sites. The reclaimed shell can then be used to construct oyster reefs. Another possible method explored uses dredge equipment in reverse to blow sediment off of buried reefs. A third, passive method, involves placing dredge pipe over buried reefs to increase erosion rates over the tops of the reefs. Alternative methods of oyster reef restoration are vitally needed due to the high cost of restoring deeply buried oyster reefs using cultch planting methods. Keywords: cultch, oyster reef sedimentation, dredging, oyster ecosystem services, Texas Parks and Wildlife Department

INTRODUCTION

Reduced freshwater inflow, anoxia, substrate removal, changes in water circulation, disease, predation, storms, and burial under sediments can damage or destroy reefs. TPWD has managed oysters in Texas since 1895 when the 24th Legislature created the Office of the Fish and Oyster Commissioner (House Bill 55, Regular Session) (Texas State Archives 2014). Duties included protecting fish, turtles and terrapin of the state’s coastal waters, and protecting natural and private oyster beds. Texas oysters have been studied since at least 1905 (Moore 1907; Moore and Danglade 1915) and cultch planting to enhance commercial harvest occurred earlier. Recent studies of oysters in Texas and the Gulf of Mexico include the Gulf States Marine Fisheries Commission’s 2012 revision of the regional management plan (VanderKooy (ed.) (2012)) and Culbertson (2008). Oysters’ contributions to increased habitat diversity and improved water quality are documented in voluminous scientific literature. In addition to playing a critical role in healthy estuarine ecosystems as a keystone species, oysters contribute to the economic vitality of the state. Dockside value of commercially harvested oysters in Texas averaged $14.3 million a year from 2000 to 2008 (VanderKooy (ed.) 2012). Economic benefits extend directly to processors, wholesalers, transporters, restaurants, and grocery stores. 1 Aquatic ecologist, Freese and Nichols, Inc., 10431 Morado Circle, Suite 300, Austin, TX 78759, USA, T: 512-617-3164, Fax: 512-617-3101, Email: david.buzan@freese.com. 1 Engineer, Freese and Nichols, Inc., 10431 Morado Circle, Suite 300, Austin, TX 78759, USA, T: 512-617-3156, Fax: 512-617-3101, Email: cris.weber@freese.com. 2 Oyster restoration coordinator, Texas Parks and Wildlife Department, 1502 FM 517 East, Dickinson, TX 77539, USA, T: 281-534-0127, Email: Bill.rodney@tpwd.texas.gov. 2 Oyster restoration biologist, Texas Parks and Wildlife Department, 1502 FM 517 East, Dickinson, TX 77539, USA, T: 281-534-0101, Email: bryan.legare@tpwd.texas.gov.

Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

Ecological services provided by oysters generate indirect economic benefits through recreational angling, boating, water quality enhancement, and shoreline protection (Tables 1, 2, and 3). Some ecosystem services (ex. shoreline protection) are reduced or nonexistent on repeatedly harvested reefs.

Table 1. Ecological services provided to recreation by oysters.

Ecological Service Economic Value Explanation Recreational fishing $2,000,000 About 23% of annual coastal fishing days occurred over oyster

reefs. Based on 2003 dollars for Louisiana coastal waters. Recreational boating $8,000,000 Based on an estimated 20% improvement in water quality that

would increase boating by those who trailer boats. Based on 2003 dollars for Chesapeake Bay.

Swimming $56,000,000 Based on an estimated 20% increase in swimming resulting from an estimated 20% reduction in nitrogen and phosphorus. Based on 2003 dollars for Chesapeake Bay beaches in Maryland.

Source: Henderson and O’Neil (2003)

Table 2. Value of ecological services for 3.6 Miles of oyster restoration shoreline protection in Mobile Bay, Alabama.

Ecological Service Economic Value Explanation

Commercial and recreational fisheries (finfish, crabs, and oysters)

$84,000 to $89,000 per year (or $599,000 per mile of reef over 50 years)

An additional 6,900 pounds per year of fish and crab with a value from $38,000 to $46,000 may be caught by recreational and commercial fishers. This extra catch will generate $39,000 per year of local economic output.

Reef construction economic impacts

$11,200,000 $8.4 million in local economic output and $2.8 million in earnings.

Erosion reduction Up to $2,132,000 per mile of reef over 50 years, based on avoided armoring costs

Wave height could be reduced up to 90% and wave energy lowered as much as 99%.

Nitrogen reduction $3,600 to $25,000 per mile of reef over 50 years, based on property value enhancement

Oyster reef breakwaters would remove between 280 and 4,160 pounds of nitrogen per year.

Source: Kroeger (2012); Kroeger and Guannel (2012)

Table 3. Economic value of ecosystem services provided by oyster reefs per acre per year for reefs that are not commercially harvested (2011 dollars).

Ecological Service Minimum Maximum Average Recreational fishing Not applicable Not applicable Not applicable Commercial fishing $1,669 $1,669 $1,669 Chlorophyll α removal1 0 0 0 Nitrogen removal2 $561 $2,718 $1,639 Recreational use Not applicable Not applicable Not applicable Submerged aquatic vegetation enhancement3 0 $1,046 $523 Bacterial removal Not applicable Not applicable Not applicable Carbon burial Not applicable Not applicable Not applicable Shoreline protection 0 $34,803 $348 Habitat for epibenthic organisms 0 0 0

Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

Not applicable – indicates data were insufficient to assess economic value of a service. 1 Chlorophyll removal values were not included “because this service is considered potentially redundant if nitrogen removal through denitrification is also considered.” 2 Nitrogen removal value was estimated from “the value of enhanced denitrification rates on oyster growth.” 3 “The average submerged aquatic vegetation (SAV) enhancement and shoreline stabilization was valued assuming that 1% of the linear length of reefs perform this function.”

Hurricanes and other storms may catastrophically impact oyster reefs, affecting commercial harvest and ecological services provided by oysters. In 2008, Hurricane Ike struck Galveston Bay, burying 8,000 acres of oyster reef under sediment and triggering TPWD’s desire for a tool to rapidly guide restoration of buried oysters. Some reefs were buried under 1-3 feet of sediment. Hurricane Ike’s impacts to oysters gave TPWD a significant incentive to develop an oyster reef restoration decision tool to help guide restoration/creation of oyster reefs.

METHODS

Information about different restoration techniques was compiled from phone interviews with oyster reef restoration practitioners, dredging industry representatives, and extensive review of the scientific literature. Nineteen experts who practice oyster reef creation from Chesapeake Bay, North Carolina, and the states bordering the northern Gulf of Mexico were interviewed. One hundred and sixty documents were compiled and searched for information. In addition to expert information and literature review, TPWD requested exploration of possible ways which had never before been used to uncover oysters buried by sediment. Bill Rodney, TPWD, managed the project and Freese and Nichols, Inc. constructed the restoration decision tool. Two lessons were learned during the decision tool development:

1. Prices for materials and services, as well as values of ecosystem services, will vary considerably based upon location, timing of construction, size of project, and many other factors.

2. Success of any restoration effort depends on the careful consideration of site-specific factors and the goal (s) of the project. Approaches that work in one area may not be effective somewhere else in the same bay.

Fourteen categories of oyster reef recovery methods were identified which could be used to recover or create oyster reefs for different purposes (Table 4). This report focuses on categories involving recovery of oysters buried by sediment.

Table 4. Restoration goals and associated recovery methods.

Recovery Method

Goals Recovery of

Buried Reefs

Commercial Harvest

Shoreline Protection

Ecological Enhancement

Recreational Fishing

Bagged/enclosed shell X X X Bag-less dredging X Chain-link fence X Cultch planting (low relief reefs) X X X X X Cultivation X Electrolysis X X X Escalator harvesting X High relief reefs X X X Increased water velocity X

Landscape processes 0 0 0 Total $2,230 $40,236 $4,179 Source: Grabowski et al. (2012)

Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

Low pressure dredging X Premanufactured structures X X X Pressure washing X Rotational harvest X Timing X

RESULTS

Four methods that involve removal of sediment from buried oyster reefs are explored: bag-less dredging, increased water velocity, low pressure dredging, and pressure washing. Bag-less dredging is the only method which is not considered experimental. It is widely used in the northern Gulf of Mexico by commercial oystermen or agencies responsible for supporting commercial harvest of oysters. Methods suggested for increasing water velocity, low pressure dredging, and pressure washing have not been documented by experts or in the scientific literature. Each method is described in more detail in the following subsections. Bag-less Dredging Bag-less dredging involves pulling an oyster dredge with the bag removed (Figure 1) through soft, shallow sediment covering oysters or oyster shell. The process exposes oyster shell buried under a relatively thin layer of sediment or vegetative matter. This is the most commonly used mechanical method used to uncover shell covered with sediment in the Gulf of Mexico.

Figure 1. Photograph of bag-less dredge from Mississippi Department of Natural Resources, 2013 (MDMR 2013).

Opinions differ among restoration practitioners regarding this method’s effectiveness. The process disturbs sediment that may rebury any shell uncovered by the process (Westby, personal communication). This technique is not frequently used in the Chesapeake Bay area (Westby, personal communication). Despite questions about its

Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

effectiveness, it has been used in all five Gulf states and parts of the Chesapeake Bay system. It is considered effective in Mississippi and Texas (Figure 2).

Figure 2. Galveston Bay oyster reefs partially buried by sediment during Hurricane Ike in 2008. Side-scan sonar image on left was taken before bag-less dredging. Side-scan sonar image on the right was taken after bag-less dredging (Hons and Robinson, TPWD). Yellow polygons in the image on the right indicate areas

where shell has been exposed. Factors likely to increase the success of bag-less dredging are listed below (Luckenbach, personal communication). These factors are relevant to the other restoration methods described in this report.

1. Larval oyster attachment rates are adequate to colonize exposed shell. 2. Work should be done shortly before oysters are recruiting to substrate. This prevents other organisms like

barnacles from colonizing the shell before spat can settle. 3. A thinner layer of sediment increases likelihood of success. This technique may be most effective when the

sediment layer is only a fraction of an inch deep over the oysters or shell. 4. Burial results from a unique event like a storm.

To the extent possible, bag-less dredging should be conducted when strong currents are present. It should begin at the up-current side of the reef with dredges pulled perpendicular to the current. This will move disturbed sediment down-current and away from shell uncovered by the dredging. Possible constraints that should be considered when using bag-less dredging include:

• Oysters buried under less than 6 inches of sediment, • Best performance with fine silt, sand, and clay,

Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

• Probably less effective for compacted sediments, • Although this process may increase turbidity and disturb bottom habitat, its use in the past as a method of

recovering oyster habitat after a significant disturbance (storm or hurricane), increases likelihood of approval by regulatory agencies.

• Ecological impacts of this method may be minimal if conducted as soon as possible after the sedimentation event. Fine, recently deposited sediment is likely to be disturbed naturally by currents and benthic animal communities may not have re-established in recently deposited sediments.

Pros and cons of bag-less dredges are summarized in Table 5.

Table 5. Pros and cons of using bag-less dredges to uncover buried oysters.

Pros Cons • Substantially less expensive than placing cultch (Herrmann, personal

communication). • No quantitative data

showing it is effective in exposing shell

• TPWD hired oystermen to pull bag-less dredges following Hurricane Ike. An estimated 1,100 acres of reef were considered restored over a 5-month period of bag-less dredging at an average cost of $740 per acre (Drake 2012).

• Can be implemented quickly relative to other methods

• Has wide support of commercial oystering industry

• Paying or allowing commercial oystermen to voluntarily pull bag-less dredges has positive social and emotional value. It actively engages the commercial industry in the process of trying to improve both the ecological and economical condition of the bay after a sedimentation event like a hurricane. It engages them in doing something positive for their community.

Increased Water Velocity This technique would build or place structures in the water to constrict the cross-sectional area of the water column through which water is flowing. When cross-sectional area of the water column is constricted, water velocity increases. Increased water velocity may help erode recently deposited sediment from buried oysters. This technique is experimental and there is no readily available evidence it has been used to remove sediment from buried cultch. Two variations are proposed:

1. Placement of floating flexible boom or turbidity curtain over the reef (Figure 3). This process would place a substantial length of boom perpendicular to the prevailing direction of wind or tide-generated currents over buried oysters. There would be substantial slack in the boom allowing it to sweep back and forth over the buried reef as the current direction changes. For example, if water velocity is 1 foot per second in water that is 2 feet deep, a 12-inch deep boom reduces the effective depth of water to about 1 foot. Velocity may nearly double to about 2 feet per second, creating greater erosive capacity to remove sediment covering the shell. This is expected to be a relatively low cost method since it may not require specialized equipment or personnel to implement. It may be possible to use retired oil spill boom or have neutrally buoyant dredge pipe deployed for this purpose.

2. Construction of mounds (Figure 4). Mounds would be constructed in a complex of mounds. Mounds may be constructed with a suction or clam shell dredge or a barge or boat-mounted excavator. As wind or tide-generated currents flow between mounds, increased velocity would remove fine sediments from shell between the mounds and from the sides of mounds. The height and spacing of mounds would depend on water depth and expected current velocities. This technique is expected to be more expensive than placement of floating boom due to the specialized equipment and increased labor that may be required.

Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

Figure 3. Conceptual view from the side of a boom or floating pipe illustrating how sediment may be expected to erode under the floating device depending on water depth and velocity. Fine sediment is represented by the

brown color and oyster shell is represented by gray.

Figure 4. Conceptual view of created mounds. Fine sediment is represented by the brown color and oyster shell is represented by gray.

Several considerations should be made regarding placement of boom (dredge pipe, oil spill boom, or turbidity curtains) to increase velocity and erosion.

• Water depth should be less than 3 feet. Oil boom typically extends about 12 to 18 inches below the surface of the water.

• Sediment depth over the oysters should be less than a foot and relatively soft. • Sources of boom should be identified prior to a sedimentation event, with boom obtained and staged

prior to a sedimentation event.

Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

• Deployment of boom does not required highly specialized equipment or training however this technique

should be practiced to ensure equipment and personnel with some experience with its use are available after a sedimentation event.

• Boom should be placed perpendicular to the expected wind or tide generated currents and with enough slack to allow them to sweep back and forth with current movement. This method may uncover a smaller area when currents are steady from one direction. A greater area may be exposed if currents change directions periodically and push the boom back and forth.

• The boom could be left in place, unattended for days, and moved to a different location after enough cultch had been exposed.

• There would be potential navigation concerns associated with leaving boom in the water for days. Placement and maintenance of the boom should be coordinated with the U.S. Coast Guard which may require an application for a Private Aids to Navigation permit.

• Depending on resources available, it may be possible to place and maintain multiple booms at the same time to maximize area benefited.

• Agreements with dredging companies should be made in advance of any sedimentation event to minimize time between the incident and having dredge pipe on site if dredge pipe is used instead of oil spill boom.

• Agreements with regulatory agencies should be made to test this approach prior to a sedimentation event. In order to minimize costs of a pilot test, it may be possible to test erosion in shallow water under dredge pipes when a dredging company is dredging for another project.

• There should be some increase in turbidity with this activity however it is expected to be lower than turbidity generated by dredges. Since the method is intended to remove recently deposited sediments from oysters, regulatory concern about water quality or habitat impacts may be relatively low.

• Cost examples: o $511 for 100 feet of 3 feet deep turbidity curtain o $1,156 for 100 feet of Simplex oil boom. Simplex oil booms are usually used for low energy

environments. Several considerations should be made before building mounds to increase water velocity.

• Arrangements should be made prior to a sedimentation event with companies who would construct the mounds and with the regulatory agencies about possible impacts from mound construction.

• Mound construction may be more effective in increasing water velocity in shallow water where mounds can be built to the surface of the water.

• Water depths should be greater than 3 feet to limit impacts to the bottom from dredges or excavators accessing the site.

• Increased velocities would be expected to remove sediments most readily from the tops of mounds, followed by the upper sides of the mound, and then from the bottom between the mound (Lenihan 1999).

• Sediment depth and degree of compaction are not expected to be significant constraints to sediment removal from the tops and sides of mounds since any sediment placed in the mounds will be loosened in the process. Thick or compacted sediment on the bottom will be less likely to be moved by increased velocities.

• Depending on water depth and mound height, there may be concerns about impacts to navigation. Coordination with U.S. Coast Guard will be important. Depending on location, coordination with commercial fishermen and recreational anglers may be necessary.

• This technique should be practiced and tested for effectiveness prior to a sedimentation event. • This method may require a permit from the U.S. Army Corps of Engineers since it is a dredging operation. • Cost: A rough cost estimate for dredging (including mobilization and demobilization) is about $20 cubic yard

of sediment. Low Pressure Dredging Low pressure dredging would use a dredge to vacuum sediment from a recently-buried reef. Interviews with restoration practitioners and review of the scientific literature did not find any examples of this method being used. Dredging companies work in difficult environments and find effective solutions to dredging challenges. Although this may be considered an experimental approach, it is expected that dredging companies can find ways that work. The increased difficulty or novelty associated with dredging sediment from buried oysters will likely affect project costs.

Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

A modification of this approach which was used in parts of Chesapeake Bay (Wesson, personal communication). Oystermen would vacuum sediment and shell, onto a vessel and wash the sediment off the shell. Shell would be returned to the shore and mounded where it was exposed to sun and rain and reused after about a year. This technique has not been used for decades. It may be possible to use a small dredge if the reef is in shallow water, less than 6 feet deep (Saenz, personal communication). Several constraints make it potentially difficult and costly to use a small dredge. Small dredges typically have low freeboard (1 to 2 feet) and it may be difficult for them to reach the site or remain on site in the open bay where wave conditions may be rougher than in sheltered areas. If there is increased possibility they will capsize, they may not be willing to operate, or may charge a higher rate for their services. If the layer of sediment is relatively shallow and varies considerably in depth over the oysters, it may be difficult to operate the dredge without repeatedly encountering the oyster shell. Making relatively fine adjustments to cutter head height to minimize damage to a reef would cost more because of the more frequent, minor adjustments in cutter head height. When a thin layer of sediment (less than a foot deep) covers cultch, the dredger may operate the dredge pump without the cutter head (Elms, personal communication), essentially vacuuming sediment off the reef. If shell is frequently encountered during dredging, cutter head replacement may be needed more often. Small dredges tend to have smaller diameter pipes which may be more likely to clog with shell. Two variations may be considered depending on the reef structure:

1. For more massive reefs that are 1 foot or greater in height with oysters cemented together, low pressure dredging may effectively remove sediment from the reef without removing substantial amounts of shell (Figure 5).

2. For reefs which are relatively low, with cultch material relatively scattered, it may be appropriate to remove the sediment and the cultch and deposit the cultch into mounds, separate from the fine sediment (Figure 4).

Figure 5. Conceptual drawing of fine sediment (brown) being suctioned off oyster shell (gray) with fine sediment being pumped to a beneficial use site.

Factors to consider with low pressure dredging include:

Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

• Water depth should exceed 3 feet to minimize disturbing the bottom when bringing the dredge near the

reef. • Agreements with one or more dredging companies and the regulatory agencies should be made prior to

a sedimentation event in order to: o Pilot test this approach. To minimize costs of a pilot test, it may be possible to incorporate a

test when a dredging company is mobilizing equipment for another project or client. o Minimize the reaction time between time of incident and having the dredge on site.

• Sediment placement sites should be identified in advance of any sedimentation event in order to minimize regulatory agency concern about suitable placement areas.

o If done at low pressure, loose sediment should be removed without removal of shell. It may take time to adjust the dredge so sediment is removed and shell is left behind. This may result in a discharge with a higher water content than typical dredge operations which may be beneficial or detrimental depending on the intended area of placement of the removed sediments.

o If done at a pressure high enough to remove shell with the sediment, it may be possible to configure the dredge system to drop the shell into a pile or mound, separately from the sediment discharge (Figure 6) (Elms, personal communication).

• Length of time buried is not expected to be a significant constraint. • Cost is unknown. Dredging costs are usually based on cubic yards of sediment estimated to be dredged.

Factors affecting cost include: o Area to be uncovered

Relatively small areas, less than 20 acres, which are not deeply buried may require a relatively small, local, dredge operator because it may not be cost-effective for a large dredge operator to mobilize for a small project. A small, local operator may be able to respond more rapidly but may have less capability (i.e. pumping distance, ability to separate shell from fine sediment).

o Depth of water o Depth of sediment overlying the reef o Location in bay relative to potential disposal sites

• Dredge company workload Pressure Washing This technique would wash sediment off buried oysters while currents move resuspended sediments away from the reef before they can resettle (Figure 6). Discussions with oyster restoration practitioners failed to identify anyone who uses this technique. However there are potential technologies that could be tested. These methods would require monitoring the strength and direction of water currents.

Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

Figure 6. Conceptual diagram of how reefs may be uncovered using pressure washing. Pressure washing may be more helpful on long, relatively narrow, transverse reefs when currents could transport resuspended sediments completely across the reef in a relatively short time (minutes to an hour). These methods may be more challenging on relatively wide, low relief reefs or where the oysters are relatively widely scattered and currents are unable to move suspended sediments completely off the reef. To the extent possible, washing should be conducted when there are strong currents present. Washing should begin at the up-current side of the reef and be conducted in the direction of the current. This will help move disturbed sediment down-current and away from uncovered shell. Dredging with water jets is a relatively new technology and many dredging companies may not have it (Saenz, personal communication). Water jets placed at the dredge cutter head blew sediment away that could not be picked up by the cutter head. This is a technique used near piers where it may be difficult to operate the cutter head without damaging the pier or the cutter head. A water ejection dredge has been used on the Houston Ship Channel and Greens Bayou in the upper end of Galveston Bay (Saenz, personal communication). This operation used tidal currents to move the resuspended sediment. The water jet array suspends the sediment 3 to 4 feet above the bottom and ebbing tides sweep the sediment away. In Greens Bayou, it took about a week to dredge 0.1 miles of channel about 350 feet wide with this method. The tug pushing this system drafted about 4.5 feet. Turbidity plumes were not visible when this method was used in the channels. Unproven technologies which may be adaptable to washing sediment off buried reefs include:

• Flyboarding – Flyboarding is a recreational activity created in 2012 which uses jet skis with a large diameter hose attached to a platform. The user stands on the platform and uses hand-controls to shoot water pumped by the jet ski motor out the bottom of the platform at high velocity. This operation can lift a human standing on the platform out of the water up to 30 feet above the water’s surface. It may be possible to modify this system so the platform and jets can be positioned at different angles and maintained underwater. The capability to regulate water jet pressure would be important to avoid washing away cultch or substantially eroding the bottom around oysters.

Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

• X-Subsea designed a number of machines for high pressure dredging. Most of these are used offshore and

require a relatively large platform and deep water for their use. It may be possible to modify one of these instruments for washing sediment off oysters (http://www.x-subsea.com/)

• Prop washing – It may be possible to prop wash sediment off oysters particularly when currents may be more likely to carry suspended sediments away from the reef. Two factors affect the utility of prop washing: 1) It would be difficult to control the effective washing depth in relation to water depth and sediment depth, and 2) There may be more regulatory opposition to this method since it has generally been opposed by state and federal agencies in the past. Convincing resource agencies to accept prop washing as a viable method may be more difficult than convincing them to accept use of a less known, experimental technique.

CONCLUSIONS

None of the methods investigated would be suitable in areas where there are naturally high sedimentation rates. Expert interviews indicated the most commonly used methods to restore buried reefs included placement of oyster shell, limestone, or concrete on top of the buried reef. Placing oyster shell, limestone, or concrete on top of buried reefs is utilized because water quality and circulation patterns are likely to be suitable for oyster growth and the firm bottom created by the oysters under the sediment reduces settling of cultch into the sediment. The cost of placing shell or other hard materials on the bottom in layers that support commercial harvest ranges from $22,000 to $100,000 per acre. Key to recovering reefs buried with sediment during storms is rapid response to make buried shell available to larval oysters. Immediately following a storm, state and federal agencies can be overwhelmed dealing with a multitude of environmental impacts. Paradoxically, this may be the best time to implement recovery methods described in this report (ex. low pressure dredging, pressure washing) and compared in Table 6. These methods involve disturbing the bay bottom and increasing turbidity. Their negative impacts may be insignificant compared to the broader impacts of the storm if these methods can be implemented before benthic communities reestablish on the newly deposited sediment. The costs of implementing these methods although unknown may be exceeded by returning oyster reefs to commercial harvest and the provision of ecosystem services as soon as possible.

Table 6. Restoration methods and qualitative summary of relative costs and benefits for each method.

Restoration Method Impacts and Economic Costs

Benefits Bag-less dredging: Pulling an oyster dredge with the bag removed through soft, shallow sediment covering oysters or oyster shell.

Disturbs bottom habitat and generates localized turbidity. It is not known how much substrate is generated relative to the increased turbidity, fuel and labor costs, and air emissions generated by this process. $740/acre.

Can be done much more quickly than any other method involving placement of material or mobilization of heavy equipment.

Increased water velocity: Building or placing structures in the water to reduce the area of the water column and increase velocity of water over the reef.

This is an experimental method and may receive increased scrutiny from the regulatory community. Turbidity will be generated as currents move sediments. There may be concerns about the effects of any structures used for this method on navigation. May require more time to move sediments than other methods.

Does not require mechanical methods to move sediment.

Low pressure dredging: Using a dredge to vacuum recently-deposited sediment from a buried reef.

This method may take considerable experimentation to design an effective process. Turbidity will be generated during dredging and placement of sediment. If a beneficial use site is not available to place sediment, there will be impacts to bottom habitat from sediment placement.

Uncovers substrate without changing the location of the reef. May generate sediment for beneficial uses.

Proceedings of Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015"

Restoration Method Impacts and Economic Costs

Benefits Pressure washing: Washing sediment off buried oysters.

This is an experimental method and likely to receive increased scrutiny from the regulatory community. Since it is similar to methods like prop washing which have been historically opposed by the regulatory community, regulatory approval may be particularly challenging. This method may generate substantial turbidity plumes.

Uncovers buried reef without changing the location of the reef.

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Kroeger, T., and G. Guannel. 2012. Fishery enhancement, coastal protection and water quality services provided by two restored Gulf of Mexico oyster reefs. 40 pp.

Lenihan, H.S. 1999. Physical-Biological Coupling on Oyster Reefs: How Habitat Structure Influences Individual Performance. Ecological Monographs, 69(3).

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CITATION

Buzan, D., Weber, C., Rodney, B., and Legare, B. “Saving Buried Reefs,” Proceedings of the Western Dredging Association and Texas A&M University Center for Dredging Studies' "Dredging Summit and Expo 2015", Houston, Texas, USA, June 22-25, 2015.