PRE – PROPOSAL
NATIONAL SHORELINE EROSION CONTROL DEVELOPMENT AND DEMONSTRATION PROPRAM
INNOVATIVE EROSION CONTROL SOLUTIONS
GULF SHORES, ALABAMA
CITY OF MIAMI BEACH, FLORIDA
August 28, 2002
TABLE OF CONTENTS
The National Shoreline Erosion Control Development and Demonstration Program of the U.S. Army Corps of Engineers was authorized under Section 227 of the Water Resources and Development Act (WRDA) of 1996. The multi-year Program began in 2000. The goal of the Section 227 Program is to evaluate the functional and structural performance of innovative or non-traditional ways of abating coastal erosion. The Program is intended to advance the state-of-the-art of shoreline erosion control technology, encourage the development of innovative solutions, and provide technical and public information designed to further the use of well-engineered alternative approaches.
A minimum of seven primary demonstration projects will be selected for the Program. Two on the Atlantic, one on the Gulf Coast, two on the Great Lakes, and two on the Pacific Ocean. For design and construction of each major 227 project, it is anticipated the Corps will allocate between 2 and 4 million dollars.
Under the Corps selection process, the private sector has been invited to submit proposals for the innovative technologies that might be installed at Gulf Shores, AL and Miami Beach, FL. Based on several factors, the Corps will choose several of these innovative solutions for further conceptual development. Only one of these will be selected for implementation in the demonstration program. The criteria will include: local community interest; environmental suitability; and the ability to make use of the same technology in other coastal locations. The solution can take the form of a proprietary product, non-proprietary structure, or emerging state-of-the-art methodology.
URS cordially submits the following pre-proposal for innovative shoreline protection designs aimed at alleviating the Gulf Shores and Miami Beach sand erosion issues.
As described, in some detail, in the Broad Agency Announcement (BAA) and “State-of-the-Beaches” (Douglass, 2001), the highly fluctuating beaches of Gulf Shores State Park Hotel, Alabama, have been suffering significant “hot-spot” erosion in recent years. The beach is frequented by the public, thus requires a unique erosion solution that does not interfere with or hinder the esthetic and recreational use of the beach.
The technical description of the proposed sand retention design can be found in Section 2.7. In layman terms, the sand retention design will consist of two to three pile supported piers, which will be evenly spaced along the beach, creating boardwalks to the open ocean. These boardwalks, approximately 200 feet long, serve their own recreational use as scenic walkways, dolphin and turtle viewing areas, as well as providing increased ADA access. These piers will also serve as the structural base for the sand retention structures.
The sand retention will be accomplished by placing high strength polyester bands at the very bottom of the piles of the pier, creating a short, submerged, barrier. These barriers create a weir effect, causing sand to deposit in front of them and at the same time allowing currents moving along the shoreline to pass over the top, sustaining the up-shore and down-shore sand budgets. This “soft structure”, called the Shore Perpendicular Template Structure (SPTS) provides several key benefits.
A. The height of the submerged barrier is highly adjustable both up and down, inshore and offshore. This allows very accurate tuning of the system based on measured performance. If more sand retention is required, the height of the barrier can be increased. In contrast, if less retention is needed to pass sand to the adjacent shoreline, the barrier can be lowered. This variability in retention allows the design to provide accurate control of the beach material throughout the structures lifetime, not just solve today’s needs.
B. Structurally, the barriers do not try to block all of the flow, thus the forces applied to the structure are dramatically reduced. This decreases the required structure strength requirement making it less expensive to build and increases the projected life span.
C. If the sand retention requirement completely abates (not anticipated), the public still has valuable structures that will continue to provide recreational services.
It is these reasons and others that make the Shore Perpendicular Template Structure (SPTS) design the favorite of URS for providing solutions to the sand retention issues plaguing Gulf Shores State Park Hotel, Alabama.
Please see Section 4.1 for company information.
The principal investigators for the development of the shoreline stabilization design for Gulf Shores State Park Hotel, Alabama, are George F. Turk, P.E and Clinton S. Thurlow.
The proposed design primarily consists of two components, the pier structures and any beach nourishment, if necessary. These two components can be designed and worked independently of each other with some coordination required if done simultaneously. The design duration required for the pier structures, including geotechnical investigations, structural analysis, and initiation of the permitting processes is estimated at 45 calendar days. Permitting aside, it is anticipated that each of the pier structures would take an estimated 60 days to construct (400 piles @ 10 piles per day + planking), resulting in either a 120 or 180-day project construction duration based on 2 or 3 piers respectively.
Beach fill is more nebulous as it depends greatly on the local availability of sand. Once a source (barrow) has been identified and quantified, the beach fill design, including drawings and specifications, dredge method determination, overfill calculations, typical profiles, transitions, and solicitation support, would require an estimated 180 days for the nourishment design. If a local source is available and is reachable by hydraulic means, the nourishment construction could be completed in the same 180-day period as the pier construction, depending on required volumes, permits, and environmental blackout windows.
Pier construction has been estimated at $1,000/linear foot. At 200 foot, each pier is estimated to cost $200,000 to construct. The pier design is estimated at $85,000, including permit applications, drawings and specifications.
The primary objective for the adjustable pile mounted weir structure is to provide fine tuned control of the retained sediments, as well as provide added value to the beach areas recreational use.
Sediments moving along shore are typically controlled by “hard structures” such as jetties. These “hard structures” typically disrupt the sediment budget down shore of the project site and are undesirable in areas of heavy recreational activity. The Shore Perpendicular Template Structure (SPTS), with small “weir type” blocking structures at the base of the piles, traps long shore sediment transport. The shoreline retains sediment by controlling the height of the submerged weir structure. This “training” can be as gradual or as radical as required, and can be set for almost complete retaining of sediment if required by placing blocking material throughout the entire water column. The material used to construct the weir will be high strength polyester strapping, as timber has proven difficult to adjust and handle in the surf zone. The pier is constructed with conventional techniques with some attention paid to the added lateral load on the piles.
The Shore Perpendicular Template Structure (SPTS) can be constructed in almost any coastal region with the exception of northern areas that suffer from ice events. Otherwise, the SPTS structure is widely applicable and can provide increased sediment stability in areas ranging from lake and inland areas suffering from boat wakes and riverine currents to ocean side beaches under duress from ocean wave activity. In additional to providing a highly tunable sediment trap, the pier structure provides addition recreational benefit.
Please see Section 4.2 for the curriculum vitae.
The 63rd Street “hot spot” has suffered excessive shoreline recession rates, documented since the early 1980’s. While northern winter storms result in net transport to the south, the beach is exposed to significant wave energy from the southeast. As in many locations around the country, traditional rubble structures have fallen out of favor, and are deemed to have a substantial, unacceptable impact, often on adjacent shorelines.
The URS proposed submerged reef extensions are constructed using a matrix of artificial reef structures creating submerged terminal groins. The submerged reefs will be designed to blend with the underwater landscape. These structures, in and of themselves, do not constitute a complete shore protection system. If a beach were experiencing a sand deficit, an initial surcharge of sand would be required. The structures proposed are intended to retain sand and increase the length of time between sand re-nourishment cycles. The individual structures will be atypical. They will be designed as a porous matrix of individual artificial dome-shaped reef units. These would have limited visual impact, as they are semi-emergent and only a portion visible as the units approach the foreshore. The matrix will be designed to limit primarily longshore movement and will have a noticeable influence on the offshore migration of sand by providing some reduction in local wave energy. The structure is also considered a “soft structure” as it will not negatively result in the dramatic and immediate halt of sand transport to the adjacent beaches.
As with other URS concepts, this structure serves multiple purposes, as it is envisioned the structures will not only act to retain sand in the “cove”, but also increase the native underwater habitat. South Florida’s ocean recreational use is one of the largest in the world. By providing additional aquatic habitat, accessible by boaters and beach goers alike, the cost to benefit ratio of this type of structure is in a class of its own when compared to typical groin structures.
Please see Section 4.1 for company information.
The principal investigators for the development of the shoreline stabilization design for Miami Beach, Florida, are George F. Turk, P.E and Clinton S. Thurlow.
The engineering and design of the project primarily consists of collection of field data (waves, currents, bathymetry, geology, and biology), moderate numerical modeling, permit applications, and development of plans and specifications. It is estimated this effort will take 150 calendar days. Aside from permit approvals, the construction time for placing approximately 800 reef units at 5 units a day is 160 days. Adding setup and interruption time, the construction window extends to approximately 180 days. This design is highly scaleable and can be done in phases, thus smaller time windows may be achieved to avoid any environmental black out periods or other schedule conflicts.
The engineering and design of the submerged reef extensions is estimated at $130,00, including field data collection, modeling and development of engineering plans and specifications. The project construction, as defined herein, with approximately 800 artificial reef units, is expected to cost approximately $1,040,000 ($300 ea. + $1,000 install * 800 units).
The project objective for this structure is to provide a sand retention design that does not “stop”, but “slows” longshore sediment transport, and adds value to the aquatic region by providing increased habitat. The submerged reef extensions provide the required “soft” barrier where it is required to “slow” the longshore sediment transport and is integrated with the existing reef, increasing both structures ability to retain sand.
Wave action causes sand to become suspended in the water column, the smaller the grain size the longer the material stays in suspension and moves where the predominant current carries it. Low impact (visually and environmentally) sand retention or sand training structures, in combination with beach fills hold promise of abating or at least attenuating the sand losses to coastal systems. It is this class of structure that URS will investigate for the City of Miami Beach.
Sand enters the project site from the up-current side and exits the down-current side, creating a dependency to the adjacent beaches. It is intended that the introduction of the submerged reef extensions will increase the holding capacity of the project site. This is accomplished by creating a more stable ocean bottom by reducing the currents at depth, allowing increased sedimentation or reduced scour. The artificial reef structure creates a resistance to submerged currents moving along the shoreline that carry the suspending sands offsite. The currents are slowed, or rather redirected to the surface, or offshore, by the introduction of the artificial reef structures. Spacing these units in the appropriate matrix creates an increased flow resistance on the sea bottom, increasing the boundary layer, and thus decreasing the flow velocities near the bottom. When coupled with the existing reef, the bottom currents are further reduced; creating a “bathtub” effect that provides increased sand holding capacity.
The primary associated benefit is the retention of sand. However, this design gains significant merit when considering the dramatic increase in marine habitat. At a minimum, the artificial reef structure will provide increased protective habitat for marine organisms. However, it is expected that some artificial reef structures will provide additional coral growth substrate.
Please see Section 4.2 for the curriculum vitae.
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