Reef Ball Beach Enhancement
The St. Lucia Golf Resort & Country Club
January 10, 2006
(A division of the Reef Ball Foundation)
With Team Partners Including
-Todd Barber, President, Reef Beach and Chairman Reef Ball Foundation
-Lee Harris, Ph.D., P.E. Consulting Coastal/Ocean/Engineer
Cap Estate is situated on the northern coast of St. Lucia. The property has two stable beaches; the largest beach is directly exposed to the Atlantic Ocean and called “Donkey Beach”. This beach has a steep slope, very “fluffy” and soft, biological based, sand (broken shells and corals) and often has very large waves breaking on it.
Left: Donkey Beach….note the depth of the footprints indicating the softness of the sand. Dr. Harris commented after making those footprints, “This is perhaps the softest sand I have ever walked on.”
The second stable beach, [for purposes of this report we will call “Hidden Beach”] is located just inside the northern point of Fayolle bay. It has a mixture of biological and terrestrial based sands making a soft beach with moderate slope, it is bounded on both sides by rocks/cliffs.
Above: View from one cliff overlooking Hidden Beach. (Note: dark colors in the middle of the bay are loose semi-floating seaweeds not rocks)
Below: Panoramic view of both cliffs surrounding Hidden Beach.
Just off the property, the northwestern portion of Fayolle Bay also has an existing stable beach, Casenbas Beach, that is composed of very fine grain sand from terrestrial sources and is flat and fairly hard packed sand. It contains a mangrove “estuary” that serves for drainage that is likely providing most of the fine-grained terrestrial sands for the beach. Construction is occurring on Casenbas Beach that may be exaggerating the sedimentation at the present moment.
Casenbas Beach: note the flat hard packed fine sands. The beach is so hard that horses use it regularly.
Below: Mangrove estuary draining into Casenbas Beach.
Sidebar on Red Mangrove Health: Although many mangroves were damaged during the construction of a hotel on this site, new seedlings are sprouting as seen on the photo to the right. These will be important for the long-term water quality in the bay because drainage needs biological filtration before it hits the reefs for coral health. Unfortunately, this is not on the property of Cap Estates and therefore Cap Estates will have little control over the development of this drainage point. However, an attempt should be made to contact the owners of this resort and make sure they understand the importance of the red mangroves that surround it.
Our investigation identified two sites, indicated in the picture on page 2, where beaches occasionally exist that could be permanently stabilized [for this report referred to as “Hotel” and “Condominiums” beach].
The beaches will need to be initially filled with sand with an appropriate grain size distribution to weld to the beach for the specific wave energies of the individual beaches. The maximum width of these beaches cannot yet be computed until the bottom survey work is completed.
Before filling, both Hotel Beach and Condominiums Beach sites will require breakwater protection to hold the filled sand. Logical choices for long-term breakwater protection include submerged Reef Balls, submerged rock breakwater, emergent local rocks [either parallel to shore, in a European “crab claw” style, or perpendicular as groins]. This report only addresses the feasibility of the Reef Ball option.
Biologically, breakwaters for the Hotel beach would support a typical “live bottom” marine community that would include a variety of fish, marine invertebrates, plants/algae and some corals. Water quality is slightly better for Condominiums Beach and it is possible that there would be a few more corals on a breakwater built there.
There are several factors that need to be considered to choose the best breakwater option for these beaches;
- Look and Feel: Each option would produce a different visual view. Reef Balls or a submerged rock breakwater would be the most unobtrusive and hardly noticeable providing a “natural” look. Parallel emergent rocks could be designed to have somewhat of a similar appearance to rocks that already stick out in the bay, but they would be highly visible from many views on the property. Groins, in this report writer’s opinion, are just plain ugly and from our understanding of the project they can probably be eliminated on this point alone. “Crab claws” can be done tastefully, and can be used to make a “formal” look.
Above: Hotel Beach View Top, After Reef Balls Rendering Bottom
Below: Condominiums Beach View Top, After Reef Balls Rendering Bottom.
- Cost: Each option would have different costs. Submerged rock breakwaters are typically the most expensive due to the large volume of rocks need to have the crest and width needed to be effective. Typically, Reef Balls or emergent parallel rock breakwaters are the second most expensive options and they are usually fairly comparable price wise. Groins and “crab claws” are often less expensive since the work can be typically performed from a land base instead of a barge.
- Permitting: Governmental permitting might influence the choice by limits, permit costs or mitigation requirements.
- Feasibility: We have determined that Reef Balls are suitable for the site. It is not clear if a barge could be used in the shallow bays to place local rock parallel to shore making offshore rock breakwaters (submerged or emerged) difficult to build or non-cost effective.
- Environmental Impact: Reef Balls or submerged rock breakwaters would offer positive biological enhancement, emergent rocks have positive and negative impacts as they offer some biological enhancement but also limit water flows causing some biological changes, and “crab claw” and groin designs are generally considered as negative environmental impacts.
- Maintenance Considerations: All designs carry the risk that hurricanes or other unusual storm events might cause some erosion that would necessitate renourishment of the beach sands. The most effective reduction of this risk is emergent rocks since nearly all energy is blocked from reaching the beach. Reef Balls and submerged rock breakwaters are less effective because attenuated wave energy is still transmitted to the beach. This is especially true if there is a high storm surge that can render submerged breakwaters much less effective since they must be close to the surface to function properly. The number of rows of Reef Balls affects how well Reef Balls will function in larger wave events but also affects project costs so there are client based decisions that must be made in terms of risk/costs. Groins and “crab claws” work by physically keeping the sand from moving in a long shore direction but they allow full wave energy on the beach and sand can be lost to the offshore direction. Dr. Harris’s report should contain information about the relative risks involved for the specific beaches and breakwater type.
The first photo depicts the anticipated “look” of the beaches and Reef Balls although the actual color of the sand would be dependant on the color of the selected fill sand (The photo depicts a color of sand similar to Donkey and Hidden beaches to keep the property distinct from Casenbas Beach.
This photo rendering is available in screen resolution at http://www.reefball.org/album/stlucia/capdevstlucia/mergedphotosandrenderings/slides/beachzonesredered.jpg or we have a high-resolution version available on our computer system [file:///G: /imagesrbf/stlucia/capdevstlucia/mergedphotosandrenderings/ beachzonesredered.jpg It is 3.6 megabytes that can be emailed upon request from email@example.com.]
We have also created a rendering on the master satellite photo and uploaded it via FTP to Paul Krone firstname.lastname@example.org. Unfortunately the file is too large (27 megs) for our computers to resize it for use in this document.
The second graphic is the current master plan for Cap Estates. Note that the possible beaches do not exactly match the master plan so accommodation will have to be made to reflect what is feasible.
Due to the uniqueness of this property, we believe that aesthetics are an important engineering requirement. In particular, the layout of Condominiums beach is designed to leave the existing sea facing cliffs intact that are a spectacular view (Below).
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 and during occasional very low tide events where natural corals are often see at the surface too. They would typically be visible as a dark line below the surface.
Ultra sized 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 Cap Estates.
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.
Physically, the site experiences a significant wave climate and St. Lucia faces threats from hurricanes. Although Reef Balls can be engineered heavier, and/or with modular bases for extra weight, Dr. Harris concluded that directly anchoring the Reef Balls to the seafloor would be the best solution for this wave climate. However, Dr. Harris needs additional data before he can determine what types of anchors should be used. Whichever anchoring method is recommended, they are typically designed to make sure that the Reef Balls endure up to at least Category III hurricanes.
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 designed with this goal in areas where there is sufficient long shore sand transports.
Above Right: Natural accumulation of sand in the Reef Ball Dominican Republic Beach Creation Project after 4 months.5
However, neither the “Hotel Beach” nor “Condominium Beach” sites have an active sand transport system. The sand in the systems is very fine which is not ideal for a soft beach, therefore we recommend an initial sand nourishment. The Reef Balls will help to protect the sand filled and will reduce the requirement for periodic filling. Note that some sand will nearly always be lost initially after the fill due to the sand resorting its grain size characteristics. Dr. Lee Harris will be able to take measurements of this to compute the exact amount of sand for the initial fill so that it gives the desired beach width. The width of the beach may be limited by the final selected location of the breakwater that has not yet been determined until the bathometric data is provided to Dr. Harris. Maintenance fills may still be required after hurricanes or other unusual events.
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 emergent breakwaters work by reflecting wave energy or for larger waves by making them break. As a wave breaks, it loses some of its energy. The problem with these systems is that they cut off currents to the beach during low wave energy periods and can create sand eroding channels around their edges during high wave periods as broken waves cannot return through the solid breakwater. Additionally, as the wave is lifted or reflected back over the emergent breakwater the acceleration of water can create washout/scouring.
Wind tunnel demonstrating whirlpool effect of Reef Balls
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. Because the system is porous, there is no creation of strong currents around the ends of the system. There is also no cut off of normal currents carrying clean water to the beach, so the ecosystem remains intact.
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. Dr. Harris will provide recommends to the number of rows required based on your budget and relative amount of risk of renourishment desired.
From our understanding of the goals of the project, we have concluded that the best options for Cap Estates is either a Reef Ball or submerged rock breakwater. A porous rock submerged breakwater could be designed to perform as well as Reef Balls in terms of reduction of the need for maintenance fills. The downside of rock is that it may be difficult and expensive to place it due to the shallow depth of the bay and therefore an inability to service the area with a barge. Biologically and for stability, large rocks (minimum of 5 tons) would need to be used to construct a breakwater and it would provide similar live bottom habitat. Therefore, both options (Reef Balls or 5 ton+ rock submerged breakwaters) should be considered carefully for cost differences, permitting differences and marketability to buyers in the Condominiums or Hotel management.
Unfortunately, Dr. Harris could not complete his design work during our assessment due to weather conditions so it is difficult to estimate costs. However, we can make a cost estimate based on Dr. Harris’s gut feeling and the measured length of the beaches. Hotel Beach is approximately 210 yards long and Condominium Beach is about 113 yards long. Although the depth profile may allow the use of larger or smaller Reef Balls, a good guess is that the Ultra or Goliath sized Reef Balls will be used. Using these sizes, Dr. Harris reported his gut feel for the wave climate would dictate the need for about 5 rows. Therefore, a reasonable estimate to the number of Reef Ball units would be around 800 units. Based on projects of this size, the price per ball installed with an average anchoring treatment a good estimate would be about $800,000 for the project. This is probably accurate to within 20% plus or minus and includes engineering, mold costs, construction and deployment costs. It does not include the cost for permitting or additional engineering/monitoring work required for permitting or monitoring.
I suggest the best next step is for you to look into the cost of other options then have an internal meeting to determine which path you want to take for final design work and then contractor costing. When Lee turns in his final report, I will update this section with a further refinement of the projected costs and resend it as a final report.
Important Side Note: If desired, this project could qualify as a contribution to a US based charity making it potentially tax deductible. As a developer, you would not need that since it is deductible as an expense but there may be some way to pass the charitable contribution off to buyers of the property, consult with your legal tax team to find out if this may be useful for this project.
Bad weather prevented us from diving or snorkeling so we could not complete our biological assessment, but we are able to make educated guesses based on the biological makeup of what was washed up on the beach and our examination of the fouling community attached to sub-tidal rocks. Pictured below are some examples of the most prevalent species:
Macro Algae Caulerpa (above) Red macroalgae (Below)
Intertidal Green hair algae
In general, we do not believe it is necessary to plant the Reef Balls with reef building corals because our educated guess is that the area will not generally support the faster growing reef building corals. These more delicate species probably would not tolerate the turbidy and fine terrestrial based mud/sand we observed in the bay.
However, natural settlement alone on the Reef Balls will support a variety of fish, marine invertebrates, plants and some corals. The Reef Balls will create a “live bottom” type reef with soft corals, non-reef building hard corals, tunicates (sea squirts), macro algae, sponges and other common members of the live bottom fouling community.
On calm days, the area would make a nice snorkeling site with plenty of tropical fish but it would probably not be considered “world class” snorkeling for more experienced divers/snorkelers.
Our visit was during a time of very strong winds and waves and construction activities were underway on Casenbas Beach so it is possible that normal conditions might be more favorable for coral reef development than we have concluded. Therefore, the biological assessment in this report should be considered a “worst case” scenario.