U.S. National Park Service Seagrass Restoration Program
Seagrass beds provide critical functions that benefit the environment and society, but in many areas are under threat due to overpopulation and vessel traffic. Lally has developed ways to restore seagrass beds safely and cost-effectively.
Among their many benefits, seagrasses create habitat and shelter for juvenile fish and invertebrates. An estimated 20% or more of the world’s most popular commercial and sport fish use seagrass beds as nursery areas. Seagrasses also absorb carbon dioxide, which combats climate change; and release oxygen, which improves water conditions, especially for marine mammals. Further, seagrass beds slow wind and wave-induced water velocities, fostering sediment accretion, and their root network promotes sediment stability. Systemwide, seagrass beds serve to improve water clarity and reduce coastal erosion.
Following a series of severe seagrass bed damage incidents south of Miami, under contract to a large A/E firm, Lally was requested to assist the U.S. National Park Service (NPS) in developing a construction strategy for restoration of major seagrass bed damage caused by commercial and recreational vessel groundings in Biscayne National Park.
Lally investigated the types and extent of scour damage, quantified fill volumes and developed alternative construction approaches for the shallow water sites, many of them remote. Lally also developed production and cost estimates for the restoration approaches based on regional reconnaissance of contractors, equipment and materials. Technical memoranda were prepared summarizing recommendations and best practices for implementation.
The seagrass bed damage was generally classified as propeller scars, caused while vessels are underway; scour holes or “blowouts” caused by propeller jet erosion once grounded; and the resulting mounding created by the displaced substrate material. With an understanding that seagrass bed damage due to vessel groundings was occurring extensively in Biscayne Bay and other shallow waterbodies, like Florida Bay, Lally developed several different seabed restoration approaches ranging from shallow draft crane barge with clamshell bucket, to use of super sacks and manual placement.
Beginning in the early 2000’s, these approaches have been implemented by the National Park Service, proven successful and cost effectively repaired numerous seagrass beds with calcium carbonate sand mixes to pre-existing grades. The NPS has gone on to develop several successful approaches for replanting the submerged grasses, fertilization, and long-term monitoring to complete the seagrass restoration process.
Expertise
Damage Assessment and Quantification
Design Specialized Shallow-draft Sand Placement Methods
Regional Equipment and Materials Reconnaissance
Develop Sand Placement Production and Cost Estimates
Prepare Technical Memo for NPS Implementation
Location
South Florida, Caribbean
Period
2000s