Recommendation for Reef Ball Submerged Breakwater
 with Beach, Safety, Aesthetic and Biological Enhancement on Windward Beach, and Alternative Breakwater Technologies for Leeward Beach 

For

Maiden Island, Antigua.
July 16, 2003

 

Submitted to

 

The Stanford Development Company of the
SFG logo banner

By The

With Team Partners Including

 


      
 Advanced Coastal Technology   


 

Preface

 

Terms used in this report refer to beach names and modeling results presented in several reports by the Caribbean Oceanography Group (COG).  Therefore, any reader of this report should, as a pre-requisite, read the “Maiden Island Beach Protection Study Executive Summary” by the COG and preferably have familiarity with the entire set of reports prepared by COG for this site/project.  Every attempt has been made to use wording in this report, which is understandable, by non-engineers and non-scientists, however some familiarity with engineering, scientific and biological terminology can be helpful to interpret this report since some subjects are necessarily complex due to the many variables that need to be considered to make good recommendations.  When technical terms help in the understanding of the subject they will sometimes be included in italic parenthesis in addition to the common explanation, for clarification.  The author(s) welcomes questions to clarify any ambiguities that may arise from this approach. Email reefball@reefball.com and reference this report for a quick answer.

 

Executive Summary

 

Historical data indicates that the beaches and near shore (littoral) zones of Maiden Island were altered approximately 50 years ago when a shipping channel was dug (dredged) near the island and the sand (fill) from the digging (dredging) operations was added to the Windward beach. This change impacted various parts of the island’s beaches and near shore (littoral) zones in different ways. 

 

Leeward Beach became susceptible to erosion due to periodic bursts of higher energy which are a result of the deepened (dredged) channel acting as a “wave lens” (wave refraction/diffraction) capable of focusing occasional big swells from distant storms (periodic cyclical bursts of long period ground swell waves) or random (chaotic) hurricanes waves directly on the trade wind protected (leeward) side of Maiden Island.  In addition to Caribbean Oceanography Group (COG) scientific modeling to support this theory, an eroded and collapsing shoreline or embankment (escarpment) over one meter high behind Leeward beach records at least one such major event.  There are at least four other intermediate erosion scars (escarpments levels) easily visible on the shoreline between the lighthouse point (Maiden Cay) and the boat dock that confirm that the leeward side of Maiden Island is exposed periodically to erosional events.  Although there may be some debate as to magnitude of energy that the “wave lens” is capable of focusing on the leeward side of the island, the physical evidence confirms that erosion is a fact. Eroding islands are perilous to oceanic ecosystems due to increased sedimentation that stresses corals and physical burying that can kill coral reefs, seagrass beds and other aquatic habitats. There are valid human and economic reasons to preserve precious land and aquatic resources in Antigua, so our recommendation for Leeward Beach is to undertake environmentally friendly erosion control measures.

 

 

Windward Beach faces a different set of circumstances.  Trade winds provide a daily onslaught of moderately sized wind generated waves that set up a slow flow of sand along the beach (longshore) as depicted by this picture:

 

 

 

Because this area was filled with mix of various types of sand, shells, dead corals, and other materials that came from the bottom of the channel (non-beach compatible sand), the sand did not flow in the same manner as it did before (stratification occurred).  Heavier grains of sand, and larger or irregular shaped shell fragments and coral skeletons did not move as easily (coarser materials wielded themselves to the beach) and stayed on the beach whereas the lighter and smaller sand grains washed away (native sands where displaced by incompatible sand). 

 

Client only section: consider removing before public distribution

Removal of the coarse material is presently underway, with the intention of adding natural fine sand (beach renourishment) after the coarse material has been removed.  However, the finer sand will continue to be washed away by the wave activity, and frequent renourishment of the beach will be required.  Beach renourishment is not only expensive; it is intrusive both to human activities and plant and animal life.  In addition, the finer sands are lifted by the wave activity (suspended-load sediment transport) and reduce the clarity of the water.  A submerged offshore barrier (artificial reef) is therefore recommended to reduce the wave activity at the beach and help keep the sand on the beach and help maintain water clarity

 

 

The Stanford Development Company wants the beach to return to the original state of natural fine sand which is easier to walk on with bare feet and more comfortable for beach activities.  However, there have been some interesting positive biological changes in the area as a result of the beach changing to coarser sand and shell materials over the last fifty years that complicates the situation. 

 

A natural beach has finer sands than the present Windward Beach, and when the waves strike the beach, these sands move around more and silt up the water near the beach.  Therefore, hard corals don’t normally grow very close to the soft sand beaches.  But at Windward Beach which no longer has these finer sands, there are now a number of hard coral species growing fairly close to shore …we observed finger corals, staghorn/elkhorn corals, brain corals, rose corals, mound corals, yellow pencil coral, fire corals and soft corals (acropora cervicornis, acropora prolifera, acropora palmate, porites porites/divaricata, madracis mirabilis, stephanocoenia intersepts, meandrina meandrites, Madracis Mirabili , porites astreoides and plexaurella.). [Note: Species identification was not a purpose of the initial survey and is based on observational notes only and may not be totally accurate since many species require in depth examination for positive identification].  However with the exception of a few soft corals, most were very small, since there is no hard bottom on which to attach, and therefore they can only get a few inches tall before they fall over.  So in one sense, the coarse sand beach has allowed hard corals to grow where they would not normally be present….but the physical layout of the near-shore water (no hard bottom) does not allow these precious corals to develop into an adult size where they could function as a coral reef or breed (sufficient fecundity) to reproduce more corals.

 

 

 

Picture of Yellow Pencil Coral (Madracis Mirabili) that is from Windward Beach.  Note the dead part at the base where it was in the sand and note the size…all Yellow Pencil Corals in the area are about this size and are unable to get any larger due to the lack of a stable substrate to attach.  

 

 

 

Left: Yellow Pencil Coral (Madracis Mirabili) in adult form when it is able to attach to a hard bottom.

 

Our recommendation for this beach is therefore a bit complex. To obtain a restoration to the original natural sand beach, the coarse materials near the shoreline need to be removed so that they will no longer be able to displace natural sands.  After removal, the sand would need to be replaced with natural sand (beach compatible sand).  However, doing this could harm the near shore corals.  Therefore, two additional steps need to be taken.  1) The corals need to be stabilized to a hard substrate so they can mature into adult corals, and 2) The energy level of the waves need to be reduced (attenuated) enough to allow the added natural sands to be unable to add too much cloudiness (sedimentation) to the water to which could harm the corals.  Any device used to reduce (attenuate) the wave energy must also be able to provide adequate circulation to the beach to maintain the present high water quality that is required for coral and general reef health.

 

Potential Solutions

 

It is important to note that we tried to take into consideration the widest possible design considerations as follows: a) to balance architectural beauty; b) enhancement of the uniqueness of the property; c) long term stability of the beach; d) safety for water entry/use; e) protection and enhancement of the environment; physical protection of Maiden Island during storm events f) regulatory, governmental and resident considerations; g) long term property value; h) engineering requirements; i) integration with the current planned designs and functionality; j) and desired outcomes (i.e. the creation and retention of a natural beach look, feel, width and slope). 

 

Although the team has a great deal of combined experience, we did lack a first-hand knowledge of Mr. Stanford’s personal tastes and preferences which we believe should be an important consideration in our recommended solutions since Maiden Island will serve as one of Mr. Stanford’s personal residences.  Noting this, we wrote this report using the assumption “What I would do if it were MY property?”  (Noting, that being a environmental founded company we would error toward the side of environmental protection). We also made some basic assumptions based on informal discussions that should be corrected if they are inconsistent with Mr. Stanford’s profile.

-Mr. Stanford is a scuba diver and snorkeler, but has a wide variety of interests and would prefer a balanced property rather than a focus on a single passion or interest. He cares about the community and desires that his projects are a positive contribution to the island.

-In addition to personal friends and family, guests would include potential business associates that might have a wide variety of interests (i.e. the property would be used for a mixture of business and personal use).

-Mr. Stanford plans on spending a significant amount of time on this property (as opposed to being a casually used vacation property).

-The budget for proposed beach protection solutions should be less than or equal to the originally engineered armor stone breakwaters (unless there are very strong and clear additional advantages that might warrant budget revisions).

-The primary goal is erosion control of the restored beaches on Maiden Island. Whereas creation of a coral reef to increases property value, reduction of maintenance, additional “bells and whistles”, more environmentally friendly methods, community acceptance and more aesthetically pleasing solutions are all considered secondary goals.

 

Windward Beach (Part I)

Our proposed solution for Windward Beach is 3-7 rows of 5 feet tall Reef Balls placed along the 5-6 foot low tide bathometric profile line off Windward Beach in a natural looking pattern incorporating numerous snorkeling pathways, and optional snorkeling and scuba trails featuring several different Reef Ball molding patterns for uniqueness.  The Reef Balls would be transplanted with a variety of soft and hard corals rescued from the path of beach restoration project and actual footprint of the Reef Balls.  Photo renderings on next 2 pages represents our vision of the project, look closely to see Reef Balls. 



The optional Reef Balls outside of the main breakwater structure used for the snorkeling, and scuba trails could be of a variety of sizes to represent a natural system (Reef Balls are available in 8 other standard sizes besides the 5 foot tall Reef Ball being used for the actual breakwater).  As depicted in the photo above, snorkeling trails could start at each guesthouse and lead to gaps in the breakwater to go past the breakwater if desired.  Look closely at the photo and you will also see a diving trail on the seaward side of the breakwater.  Conceptually, the submerged breakwater is designed to be like an ideal natural barrier reef (that one would look for in high-value oceanfront property).  There are a number of features shown in the photo that are included in our recommended design…for example, the Reef Balls could approach the shore near the primary residency house because water currents are dangerous on the other side of this end of the island and they would provide a signal or “fence” to inexperienced guests to make their way to the beach rather than getting caught in sweeping currents past the main house point. The photo also shows several prevailing wave perpendicular gaps in the breakwater to allow for easy exit/ingress for snorkelers or small boats. 

 

Our biological assessment found very high water quality on the Windward Beach.  (Some of the highest coral reef water quality we have encountered in the Caribbean) Therefore, this site is ideal for coral transplants that will turn the breakwater into a nearly natural coral reef over time. Based on an observed high tropical fish load on the few small coral heads in the area, we are 100% confident that the breakwater will be populated with a large amount and variety of tropical fish.  Therefore we expect this particular location will yield an incredible snorkeling reef.  So, our design recommendation is for the Reef Balls rows to be spread out more than our previous Reef Ball projects that used tightly spaced rows.  Dr. Ward is modeling suggested maximum distances between the Reef Balls for obtaining optimal wave attenuation for the Miami 63rd Street Hotspot submerged Reef Ball breakwater project. From this we can work the Caribbean Oceanography Group can suggest an exact design.  There is current scientific debate on how far Reef Balls can be spaced without reducing (and perhaps even increasing) wave attenuation. i.e. “Can you use less Reef Balls and yield the same attenuation result as tightly packed Reef Balls?”  Dr. Ward’s modeling will hopefully provide us with a way of using less Reef Balls in this manner to reduce the total project cost for Stanford.  However, if Dr. Ward’s modeling yields poor results for increased row spacing then we would change our recommendation to a tighter rows of Reef Balls (at the expense of some snorkeling access), as seen in this photo, or we would have to expand the number of rows  (More Reef Balls but better access for snorkeling).

 

 

 A working group of Dr. Lee Harris, Reef Ball Development Group, Ltd., The Caribbean Oceanography Group, and Dr. Don Ward can form an expert opinion on the number of rows of Reef Balls recommended to best balance sand accretion with sand loss from the long shore currents taking into account Stanford’s project goals.  This will help to insure that the equilibrium balance of the beach will not be too wide or too narrow, on average.  (Note that storms, such as hurricanes, will change the beach from time to time and that recovery to the equilibrium depends on a variety of natural factors including time, sand budget and wave climates.  Also note that all submerged breakwaters are still considered experimental in nature and results can never be guaranteed in terms of predicting the exact effects on a beach.  This is one reason why we have pulled together the large team of experts to provide Stanford with an accurate assessment of advantages and risks associated with submerged breakwaters).  Since the recommendation of this group is dependent on not yet completed wave tank testing using scaled Reef Ball models by Dr. Ward and a review of the data by Dr. Lee Harris, we suggest a preliminary working hypothesis that 4 rows will be required for purposes of budget estimates based on our “best guess” from prior projects.  (Prior projects have used between 3-7 rows of Reef Balls)

 

One other important variable to note is that the number of rows must be increased as the depth from the top of the Reef Balls to the waterline increases or conversely if the Reef Balls are placed where the top of the units are closer to the surface of the water less rows can be used.  Typically, clients do not like Reef Balls to be exposed at low tides for visual reasons.  Therefore, our standard initial recommendation is to leave about 1 foot above the Reef Balls at low tide as shown in the picture to the left.    This small amount of water above the Reef Balls is one reason tightly packed Reef Balls restricts the snorkeling.  However, if we are able to space the Reef Balls out some to allow for snorkeling access between the Reef Balls, it might be acceptable for the Reef Balls to be even closer to the surface requiring less Reef Balls for similar wave attenuation.  The trade off between visual aesthetics, snorkeling access, required swimming area size and project budget are factors best decided by an educated client so the design team can make the best choices for final breakwater design.

 

 

Client only section: consider removing before public distribution

On our inspection of the site, we found dredging operations that are removing seagrasses that are filled with numerous coral species that can be saved and then transplanted onto the Reef Balls.  Of particular importance were a few colonies of Elkhorn coral that is facing massive decline in most of the Caribbean and is considered endangered.  We also found a few colonies of Staghorn coral.  These two (Acropora) species are very important for transplanting onto Reef Balls in that they represent the fastest growing coral species in the world with growth rates of up to 6 inches per branch per year (and since multiple branches form, this growth is therefore exponential each year in terms of coral mass).  They also represent the “classic” coral shapes that people associate with high quality snorkeling and diving sites.  The Elkhorn was already broken by the barge but is salvageable.  I recommend A.S.A.P. movement of these corals to a safe location for later replanting on the Reef Balls or changes in the barges work schedules or methods to make sure these particular corals survive.  Compared to slow growing corals that can be quite robust, Acropora species are very sensitive to infection (Rapid Tissue Necrosis) and poor water quality so experts should only handle Acroporas.  All of the Acropora species were found offshore near the point opposite the Residence House (see below).

 

Left: 14 months growth of Staghorn coral (Acropora Cervicornis) transplanted on a Reef Ball as a 1 inch tall fragment in Curacao. Right: Classic Elkhorn coral (Acropora Palmata).

 

 

Optional Enhancement Features

 

There are various other special features one could design into the Reef Balls:

 

 











Photo looking into the inside at the base of a Reef Ball cast with Conch Holes and minimal seagrass footprint style


(Top of an EcoReef™ ceramic unit that could be embedded
 into various types of Reef Balls to mimic adult branching corals)

 

With the possible exceptions of underwater lighting and expenses of the coral transplanting teams, most of these options would not significantly affect the overall project costs. Therefore we recommend the client use as many of these options that are a good fit with the overall goals of the project.

 

Possible Project Concerns

 

Aesthetics of Project

 

Due to the uniqueness of the Maiden Island, we believe that aesthetics is an important engineering requirement.  The Reef Balls are symmetrical domes that would only be exposed during low tides in the trough of waves similar to the appearance of natural barrier reefs. 

 

 

Ultra Reef Balls being deployed at Gran Dominicas Hotel in the Dominican Republic, note the appearance of the Reef Ball submerged breakwater as only a dark line in the water.  This would be the same look generated at the Maiden Island except your Reef Balls would be spread out a bit more and would not form such an obvious line.

 

The proposed Reef Ball project would look much more natural than the initially proposed rock breakwater.

 

 

Longevity

Reef Ball has a long history of using high tech concrete to engineer structures designed to last centuries rather than decades.  Our work has required this because longevity is an important design criterion when building coral reefs that potentially last for thousands of years. By using specially designed, high strength concrete and using W.R. Grace admixtures, we will create a high strength, abrasion resistant concrete, (without iron rebar in the modules), that will have an engineering life of hundreds of years.  Therefore, the client can consider this solution a final one.   Our authorized contractors are trained to meet our concrete standards.

 

Stability

 

Physically, the site experiences a significant wave climate and Antigua faces threats from hurricanes.  Although Reef Balls can be engineered heavier, and/or with modular bases for extra weight, we concluded that directly anchoring the Reef Balls to the seafloor is the best solution.

 

Beach Creation

There are three options to obtaining the beach sand; sand nourishment, natural accumulation of sand, or a hybrid approach of seeding some while accumulating the rest. 


In most cases, a natural accumulation of sand is desired and Reef Ball submerged breakwaters are normally set up with this system.

 

Right: Natural accumulation of sand in the Reef Ball Dominican Republic Beach Creation Project after 4 months.5

 

However, due to the beach not having beach compatible sand as discussed earlier in this report the current sand must be removed and natural sand renourished.  This is the basis for our recommendation to conduct a hybrid sand renourishment and natural replenishment project rather than relying solely on the natural build up of sand over time.

 

 

 

Client only section: consider removing before public distribution

 

Reef Balls have never been used on an existing seagrass beds before since this is typically a prohibited activity from a permitting standpoint.  On a hard bottom, the main concern is lateral movement (sliding) by hurricanes that is solved with simple fiberglass rebar anchoring pins drilled into the rock.  On a pure sand bottom, lateral movement is unlikely due to the suction effects of sand, however there is a concern that the Reef Balls will sink (subsidence) into the sand loosing design height and becoming less effective at protecting the beach.  This has been addressed by an articulating concrete mat below the Reef Balls for Miami, by a geo-textile under-layment in Tampa, and by planned settlement depths in Porto Progresso.  The problem we face is that as long as the seagrasses below the Reef Balls remain healthy, the area will act much like a hard bottom.  However, if the seagrasses below the Reef Balls die, the area may revert to the characteristics of a sand bottom.  It is a further unknown if the waves breaking on the Reef Balls might cause a scour trenches on either side into the seagrass beds.  There are several ways to approach this.  The safest thing to would be for us to quickly ship a container full of Reef Balls from one of our currently producing distributors and to deploy a short segment of the Reef to see what impact, if any, the Reef Balls would have on the seagrass beds.  If there are no problems then we can continue with simple anchoring techniques placing the Reef Ball directly on the seagrasses. [Note: we recommend double helix screw anchors for sand or seagrasses bottoms which will provide similar stability to fiberglass rebar in rock.  A sufficient length of fiberglass rebar may also suffice for lateral movement concerns.   If, however, there are problems with either scouring or seagrass health affecting stability, then it would be advisable to dredge the area where Reef Balls are to be placed and fill in the dredge hole with sand or rock.  In this case, we would again need to modify our recommendations to tighter packed Reef Balls rows to minimize seagrass impacts.  Another alternative might be to place Reef Balls closer in to shore where the seagrasses are already planned to be dredged.  This may require a different sized Reef Ball.                                            

Stability Testing at Florida
Institute of Technology by Dr. Harris

 

Note: There are unanchored Reef Balls at the Iberostar in the Dominican Republic which rely only upon the weight and natural stability of Reef Balls.  So far, these units have not experienced movement against some strong storms, but they have not been tested by the direct hit of a hurricane like we have experienced in other locations. If you have questions about stability, and the risks/costs associated with different techniques for anchoring or stability Dr. Harris is our team expert on stability. 

 
 

Client only section: consider removing before public distribution

Environmental Responsibility

This project has a many activities that will impact the seagrasses and corals around Maiden Island.  In terms of the corals, the beach dredging and renourishment process is creating siltation that can harm corals.  Fortunately, the corals around the island are in good heath and they can handle short-term increases in siltation.  (Note: this is not the case in much of the world).   We recommend that either 1) Silt guards are used, 2) dredging and renourishment activities span no more than 2 months in any given area of the island, or 3) If more than two months are needed to accomplish work then provide at least a one month gap each 2 month construction period. (i.e. move the dredge to the other side of the island and work in another place to give the corals some time to recuperate between silty periods which stress them.

 

Picture of sedimentation as a result of dredging and other activities

The seagrasses on the windward side that are impacted will be mitigated by the higher quality reef habitat that is being provided.  On the leeward side, we recommend minimal impacts to the seagrasses because structures on that side will not offer high level reef habitat in return.

 

Right: A small sized Reef Ball

(3 feet x 2 feet).  This Bay Ball sized Reef Ball was deployed in Cancun, Mexico.  This picture was taken 3 years later and shows only natural growth (no coral transplants were added to this Reef Ball).

 

The Reef Balls in Maiden Island will look similar to this photograph with much larger corals in 3 years. This high diversity coral reef type habitat is more threatened worldwide than seagrass beds and is justifications for habitat upgrading.

 

 

Client only section: consider removing before public distribution

 

Before additional dredging of the seagrasses occur, we also suggest a coral rescue team moves the corals out of these areas to deeper water for temporary storage until they can be transplanted onto the Reef Balls.  We believe this could be done with one or two compensated coral experts and a group of volunteers in a short period of time (i.e. one week).  Most or all of the coral plug preparations could be done at this time saving work when it becomes time to populate the Reef Balls with corals.

 

Picture of Yellow Pencil Coral (Madracis Mirabili) which is common in the seagrasses on the Windward Beach and Mangrove Beach. (Ideal for transplanting onto Reef Balls).

 
 

 

Why Reef Balls Work Better than Solid or Rock Submerged Breakwaters

 

Reef Balls were initially designed to be biologically active and to be stable in hurricanes.  Essentially, Reef Balls needed to be the base of a natural reef.  To do this, we had to design our holes to create whirlpools so that corals could be fed better by passing currents.   Additionally, we created a large hole in the top of the Reef Ball so that waves and currents would be jetted from the top, adding to the stability of Reef Balls.  Our goal was to use the least amount of concrete to make a unit that was stable in hurricanes. 

 

Traditional and barrier submerged breakwaters work by making waves break.  As a wave breaks, it loses some of its energy. The problem with these systems is that this is the primary mechanism for wave attenuation. Additionally, as the wave is lifted over the submerged breakwater the acceleration of water as a wave breaks can create washout/scouring. 

 

Reef Balls work to break waves too, but they also add a significant amount of drag or friction on water flow around them by creating water whirlpools (vortexes).  Reef Balls are full of holes that are designed to create whirlpools, and offer a variety of angles of reflection from the round shape, so that any wave that traverses a field of Reef Balls has to “fight itself” and therefore looses energy in relation to the number of rows of Reef Balls that are transversed.  For smaller, non-breaking waves, waves may keep their shape; but the drag forces will make them smaller as it passes through the Reef Balls.  

 

 

 

Wind tunnel demonstrating whirlpool effect of Reef Balls      

With major storm events, the width of the Reef Ball fields must be wide enough to cause a break on the larger waves like a traditional submerged breakwater.  This attenuates the wave by the normal breaking process but also reduces the energy of each wave further by fighting (drag) the wave by creating whirlpools/wave reflections (friction).  Note: In major storm events, wash out (scour) is possible because the breaking waves can create washout (scour) even with drag (attenuation/drag). 

 

Safety & Property Protection

 

Safety is usually always an issue for our clients.  Certainly, children, elderly and other potential waders/swimmers who snorkel or swim on windward beach would be subject to getting caught in the strong currents near the point where the Mr. Stanford’s house will be placed.  There are dangerous fire corals in the area that is often to cloudy to see clearly because of the high currents and waves bouncing off the rocky point.  We therefore propose that a line or two of Reef Balls are brought all the way into the shoreline to serve as a visual warning to exit to the beach at that point.

 

For the entire length of the beach, the submerged breakwater will reduce the energy of the waves to make swimming and wading safer.  Reef Balls may also provide a physical barrier to reduce the loss of a swimmer to sea. 

 

Protection from wave run-up and damage to the guest houses might also be another benefit of a submerged breakwater.  This cannot be relied upon for submerged breakwaters since a high storm surge can render submerged breakwaters less effective for that period of time.  Therefore Caribbean Oceanography Group’s recommendation of foundation heights should be followed.

 

Leeward Beach (Part II)

 

Leeward Beach is a very challenging area and we have spent hours working on and researching possible solutions.  Long period waves are particularly tough to attenuate for any submerged breakwater system due to the corresponding wide submerged breakwater that is required to break them.  From an environmental perspective, it is a difficult challenge to minimize the impact on the seagrasses in this area because of the necessary width of the submerged breakwater.  Furthermore, all submerged breakwater designs either cause breaking waves or fast moving water that may impact nearby seagrasses.  Following are a list of the major options that we evaluated. 

1)      ACT S.D.R.S. Erosion Control System

2)      Beach Renourishment(s) ONLY

3)      Beach Renourshment(s) with ACT S.D.R.S. Erosion Control System

4)      Perched Beach with ACT ProTecTube

5)      Perched Beach with ACT ProTecTube  & ACT S.D.R.S. Erosion Control System

6)      Beach Renourishment and Reef Ball Submerged Breakwater System

7)      Beach Renourishment and Armor Stone Breakwater System

8)      Submerged ProTecReef with a small Reef Ball pinned to surface

9)      Beach Renourishment and Submerged ProTecReef with seagrassed re-transplanted over most of the breakwater except for some small sized Reef Balls (2 feet wide) pinned to the breakwater system on the offshore slope for additional drag.

10)  Beach Renourishment and low foot print Slotted Submerged Breakwaters

 

We are unable to achieve a protection of vast areas of seagrass (assume a 90-120 foot wide impact the length of the project) using solutions 6, 7 or 8.  Solution 10 impacts at least ˝ of the above square footage. Solution #1 does not solve the client’s primary goal of a beach.  Solutions #2 and #4 do not protect the island from possible erosional events. Solutions #2 and #3 may or may not work and there is not enough data to draw a conclusion in advance.  Solution #5 and #9 are the options that reasonably address all constraints.  Option number #9 is more expensive than option #5 and would likely end up costing more than the original proposed rock breakwater.  Option #9 has never been done before and would also need to be considered experimental.  An experimental solution has both benefits (i.e. Uniqueness, custom solution) and risks (more difficult to predict results, more costly).  All the reviewed options have unique advantages and should be considered based on exact project goals.

 

1) ACT S.D.R.S (Sand Dune Restoration System).  Advanced Coastal Technology offers a defensive erosion control system that works below the sand to be uncovered only during erosional events to protect land from eroding away.  This would be used to prevent Maiden Island’s leeward side from erosion during occasional long period wave events. The system features sand match colors, high-technology geotexiles, welded seams and a number of advanced features.  This system has been successfully used since 1986. 

 

Left, S.D.R.S: multiple rows during installation demonstrating an extremely high vertical profile of protection.

 

 

 

 

 

 

 

 

 

 

 

 Left: Vero Beach, Florida.  S.D.R.S.

 Note natural appearance and sea oat coverage after ten years. Sea oats actually root into the fabric and resist storms better than in sand alone.

 

Typical US based installed cost is $55/linear foot/per row plus engineering.  The leeward side of Maiden Island could use from 3-8+ rows depending upon the level of protection desired.  Total length of this system would depend upon total area desired for protection.

 

2) Beach Renourishment ONLY

 

With this approach, one would simply renourish the beach whenever it became necessary.  Since there is no data on how long a renourishment might last this may end up being either a very good (and inexpensive) solution (if the beach lasts a long time) or only a temporary solution (if the beach erodes away too often to be worth unprotected renourishments).  One distinct disadvantage to this approach is that it does not provide very much erosion control for property protection.  Frequent renourishments could be costly and add stress to the seagrass and reef systems in the area due to siltation and sedimentation. 

 

3) Beach Renourshment(s) with ACT S.D.R.S. Erosion Control System

 

A combination of The S.D.R.S. and Beach Renourishment would provide erosion control for the property.  This would be a complete and good solution if the beach fills are long lasting without protection.

 

4) Perched Beach with ACT ProTecTube

 

Perched beaches are a good solution to hold a beach without breakwater protection.  A perched beach is a beach with a wall around it on the 3 sides facing the sea that holds in the sand during erosion events.  Historically, perched beaches were not very popular because they used large white round sand filled containers (geotubes) that made the interface to the water from the beach to be a leap down to the water rather than a walking entry.  ACT ProTecTubes solved this problem by being a series of tubes forming a 3 to 1 sloped beach face. Literature on the subject calls this a “step faced system.”  

 

Excerpted from a report by Dr. Lee Harris, P.E.,  Consulting Engineer

 

Perched Beach:

“A method to assist with holding sand on the beach is to install a shore parallel structure seaward of the seawall, and fill the area between this structure and the seawall with fill.  The ends of the sill structure must curve back to the seawall at the north and south ends of the property.  This shore parallel structure functions as a sill to hold the sand on the beach. The use of a step-faced sand-filled container such as that shown below allows pedestrian traffic along and up and down the structure when it is exposed. “

 

 


(ProTecTube exposed after a storm)

 

 

 

 


(Artist drawing showing how ProTecTube is placed under the beach)

 


(Protect Tube during installation before it is covered over with sand).

 

The ACT Protect Tube will also provide a measure of erosion control for the shore, but the vertical window of protection would not be enough for protecting the island behind the beach in larger events.

 

The ProTecTube beach has the big advantage of not requiring an offshore breakwater to keep sand fill on the beach.  (Therefore, Leeward Beach seagrass beds would not need to be disturbed).  A standard sized ProTecTube II (4 feet high as shown in the photos above) would cost about $300/foot in the US.

 

5) Perched Beach with ACT ProTecTube  & ACT S.D.R.S. Erosion Control System

 

Combining a filled perched beach with an SDRS will provide full property and beach protection and eliminate the need for a submerged breakwater.  An estimated cost of these combined systems proved that they are comparable to an armor stone breakwater and perhaps less depending upon the total area that needs protect and the height of protection desired.

 

 

6) Beach Renourishment and Reef Ball Submerged Breakwater System

 

Although we reviewed this option, The Reef Ball Development Group, Ltd. has declined to offer a Reef Ball Submerged Breakwater system for the Leeward Beach as it is not a good location (biologically) for reef development (too silty and better as a seagrass area) and the costs involved would not justify Reef Ball use here.  Any breakwater here could also do significant damage to the seagrasses that cover nearly 100% of the area.   Reef Balls would not be able to offer a justifiable trade off to the loss of seagrass from an environmental point of view either. 

 

7) Beach Renourishment and Armor Stone Breakwater System

 

For the same reason as Reef Balls are inappropriate, so would be an armor stone breakwater system.

 

 

 

8) Submerged ProTecReef with a small Reef Ball pinned to surface

 

We also investigated specially shaped sand filled container that is essentially two ProTecTubes back to back as shown below

 

with smaller Reef Balls on the surface of the container to create the desired drag on the waves to provide a perfect “engineering” solution at less cost than armor stone.  This could be a good solution if a breakwater is still desired.  Note that this combination of products has not been done before so it should be considered “experimental.”

 

9) Beach Renourishment and Submerged ProTecReef with seagrasses re-transplanted over most of the breakwater except for some small sized Reef Balls (2 feet wide) pinned to the breakwater system on the offshore slope for additional drag.

 

From an engineering point of view, the majority of drag on waves is created by the Reef Balls on the slope of the ocean side of the submerged breakwater and at the leading edge of the crest.  Therefore, we considered only placing smaller Reef Balls on these areas on top of the sand filled container mentioned in the last option.  The rest of the Reef could then be transplanted with seagrasses taken from below the footprint of the container.  This would preserve most of the seagrasses.  We contacted Seagrass Recovery Services and found that this would be cost prohibitive if we contracted out this work, but that a specialized seagrass transplanting boat could be purchased from Seagrass Recovery Services for about $275,000 (plus training) that could be used for Stanford to manage the transplanting of seagrasses in a somewhat cost effective way.  (The boat cuts a 20 square foot area of seagrass and root system and can move it to replant it in a system similar to sodding a yard).

 

A review of costs indicates that this option would likely be 10-50% more than the originally proposed armor stone breakwater but has the advantage of less environmental impact. 

 

10) Beach Renourishment and low foot print Slotted Submerged Breakwaters

 

To minimize impacts to seagrasses, we also considered low footprint slotted submerged breakwaters.  These are experimental in nature but can be used to attenuate waves.   The breakwater would be made from prefabricated concrete and would need to be custom designed for the site.  COG and Reef Ball Puerto Rico would be able to design and deliver such a solution.  The advantage would be lower cost than an armor stone breakwater and a smaller footprint affecting less seagrasses.  The disadvantage is that such a system could be more vulnerable to destruction by a hurricane if not engineered properly and that the swirling waters created by such a system might disturb seagrasses.

 

 

 

Participating Companies

 

 

 -

Dr. Alfredo Torruell

http://www.reefball.com/map/contractorresumes/alfredotorruell.htm

 

 

 

 

Todd Barber, CEO of the Reef Ball Development Group, will personally oversee this project due to its unique and complex nature.  Mr. Barber is the founder of Reef Ball Development Group, Ltd. and has been working restoring reef systems worldwide since 1992.  Reef Ball has conducted over 3000 projects in over 40 countries worldwide deploying over ˝ a million Reef Balls.  Information on the companies Mr. Barber manages can be found at www.artificialreefs.org, www.reefball.com
http://www.reefball.com/map/contractorresumes/toddbresume2000.htm

 

 

 

www.reefball.com/contractors.htm
      
            P.O. Box 190725
San Juan, Puerto Rico 00919-0725
Tel: (787) 783-2477 / 783-9490
            Fax: (787) 782-5275
             Email: rafael@reefball.com 
             Att: Rafael Semidei, President
            Sonja Newhouse, Vice-President

 

Don Ward, Ph.D., Consulting Coastal/Ocean/Engineer 

http://www.reefball.com/map/antiguiaaerial/CurriculumVitaedonward.htm

 

 

Advanced Coastal Technology   

www.advancedcoastaltechnology.com

Jay Sample, President<