Beneficial Use and Estuarine Island Creation: Intracoastal Waterway Maintenance Dredging Project Aids Lake Worth Lagoon
In May, Orion Marine completed a maintenance project to dredge the Intracoastal Waterway (IWW) channel to -10 feet Mean Lower Low Water (MLLW), its federally authorized depth, in a 4.5-mile section from the Port of Palm Beach to the Town of Palm Beach docks in Palm Beach County, Florida. The Florida Inland Navigation District (FIND) is the local sponsor for the 407-mile federally authorized Florida Atlantic Intracoastal Waterway (AIWW), the IWW and the eastern 98 miles of the Okeechobee Waterway (OWW), and sponsored the maintenance dredging project. This portion of the IWW channel had not been dredged since its construction in the 1960s. The material was beneficially used to restore a deep dredge hole in Tarpon Cove Restoration Area.
FIND formulated the project to provide recreational boaters and commercial vessels safer access to the area’s marinas, boatyards and shipping facilities. The project’s success came from the work between many project stakeholders and environmental regulatory agencies — including FIND, the Port of Palm Beach, Palm Beach County, state and federal permitting agencies, local boating and commercial industry groups, as well as the FIND engineering firm Taylor Engineering Inc. and the dredging contractor Orion Marine Construction Inc.
FIND’s IWW channel dredging permits authorized upland containment of dredged material in FIND’s Peanut Island Dredged Material Management Area (DMMA). However, to support an overall cost-effective strategy to leverage beneficial sand sources for Palm Beach County’s Tarpon Cove restoration project, Taylor Engineering facilitated coordination between the county and FIND to modify FIND’s permits to allow placement of the IWW material in the county’s restoration site. Palm Beach County had previously acquired Florida Department of Environmental Protection (FDEP) and U.S. Army Corps of Engineers permits authorizing restoration and enhancement of Tarpon Cove — a 46-acre site located approximately 1.2 miles south of the Town of Palm Beach docks. The project would cap muck sediments and create seagrass, mangrove, and oyster reef habitat where poor sediment quality and dredged holes prevented development of high-quality habitats.
Orion began dredging on a 24-hour, 7-days per week schedule in March 2019 and ended in May 2019. Orion mechanically dredged and transferred 84,650 cubic yards of material from the IWW channel to the Tarpon Cove restoration project.
Partnership History: Beneficial Use and Ecosystem Restoration
The Lake Worth Lagoon estuary in Palm Beach County runs approximately 20 miles along the southeast coastline of Florida. The lagoon is an urban estuary that has suffered extensive loss of estuarine habitats and degraded water quality due to human development activities over the past century. Approximately 81 percent of the lagoon’s shoreline is developed with seawalls for private residences and businesses (Source: Palm Beach County Department of Environmental Resources Management (PBC ERM). 2016. Summary of Projects and Fiscal Year 2016 Legislative Funding Request. West Palm Beach, Florida.)
Sediments throughout the lagoon were dredged, decades ago, to support local development. The dredging created large benthic ‘holes’ that now impair the lagoon’s ecosystem, as they are well below adjacent grade, often anoxic, and generally do not support seagrass or other submerged resources. Additionally, canals that drain into the lagoon have introduced fine, silty sediments that settle in these holes, hindering recruitment of seagrasses and diminishing water quality.
FIND and the Palm Beach County Department of Environmental Resources Management (PBC ERM) are two members of the Lake Worth Lagoon Initiative, a multi-agency effort to increase awareness, support and funding assistance for projects to improve and protect natural resources within the watershed of the lagoon. The initiative has successfully promoted interagency coordination and commitment to lagoon restoration and protection. The initiative was the genesis to the FIND and PBC ERM partnership that enabled IWW maintenance dredged material placement at the county’s Tarpon Cove restoration project.
FIND has historically supported county restoration and public use projects by providing dredged material for beneficial reuse, or through project grant funding cost-share participation via FIND’s Waterway Assistance Program. For example, 1.2 million cubic yards of material from Peanut Island DMMA was transferred to the Snook Islands Natural Area from 2003 to 2005 to create a 100 acres of shallow water estuarine habitat of seagrass, mangroves, spartina and oyster reefs. From 2009 to 2010, 47,000 cubic yards of material from FIND’s Juno Dunes DMMA area was used to create and enhance 14 acres of mangrove habitat and create 3.2 acres of shallow water seagrass area accompanying the construction of boardwalks, floating docks, an observation tower and picnic areas. The material excavated to create the wetlands was used to fill dredged holes to create intertidal mangrove islands at the county’s South Cove Natural Area in West Palm Beach. Also, in 2010 FIND expedited and completed a small (16,250 cubic yards) IWW maintenance dredging project in West Palm Beach to provide fill for the South Cove Natural Area project, which had the capacity to beneficially reuse dredged material.
The successful restoration of the dredged holes at Snook Islands and South Cove Natural Areas did not rely solely on a partnership with FIND to provide material; the local marine community (i.e., Rybovich Marine Center, Palm Harbor Marina, and Lockheed Martin) also provided material for the projects as a cost-effective alternative for the placement of beneficial dredged materials. Seeing the positive results of these public-private partnerships, the county saw a need to have additional dredged holes, such as Tarpon Cove, permitted for future restoration and beneficial use of dredged materials.
Permitting and Design: IWW Maintenance Dredging and Tarpon Cove Restoration Area
In 2015, Taylor Engineering began permitting the project. State and federal agencies issued environmental permits in 2018, and permit modifications for altering the final placement area were completed in 2019.
Taylor Engineering faced significant permitting and design challenges, which resulted in a two-year permitting timeframe. The challenges stemmed from (1) the modification of the original project from a deepening to a maintenance dredging project, (2) the identification of seagrass and hardbottom impact, (3) surveying and performing diving investigations for 32 utility crossings, and (4) the modification of the final dredged material placement area.
A March 2001 Corps project report made a case for a 5.2-mile-long deepening project that would increase the channel depth from -10 ft MLLW to -18 ft MLLW, inclusive of the area between the Port of Palm Beach and Town of Palm Beach Docks (Source: U.S. Army Corps of Engineers (USACE). March 2001. Detailed Project Report. Palm Beach Harbor Lake Worth Access Channel Expansion. Section 107 Small Navigation Project. Palm Beach County, Florida. (Jacksonville, Florida).)
To reevaluate the project need, nearly two decades later, FIND and Taylor Engineering evaluated several channel design alternatives — including an existing adjacent federally authorized 2.8-mile side channel and basin east of the IWW, extending south between Lake Worth Inlet and the shoreline of the Town of Palm Beach — for project depths ranging between -10 and -20 ft MLLW, with an assumed allowable 2-foot overdepth for dredging (Source: U.S. Army Corps of Engineers. June 1971. Palm Beach, FL. Side Channel and Basin. Jacksonville, Florida.). Evaluation criteria included variable project lengths, dredge quantities (as compared to the Peanut Island DMMA capacity of 366,000 cubic yards), conflicting submerged utility crossings, and submerged natural resource impacts. The 2001 Corps report recommendation entailed the greatest dredging volume (1.2 million cubic yards) at -18 feet MLLW, 32 possible utility crossings, and submerged natural resources impact. Based on a current lack of substantial marina and megayacht facilities south of the Port of Palm Beach, 16 of the 32 identified utilities requiring relocation, and impacts to submerged environmental resources, FIND elected to move forward with a project to maintenance dredge 4.5 miles of the existing IWW channel to a depth of -10 ft MLLW (with an additional 2-foot of allowable overdepth) to serve the immediate needs and use of the IWW.
In 2014, the county implemented a scoping effort to identify the dredged holes in the lagoon and determine potential environmental enhancement projects and options for possible future mitigation needs. The first component of that effort was to create a sub-committee from the county’s Artificial Reef and Estuarine Enhancement Committee to get the groups’ feedback on the potential restoration sites, eliminate from consideration some of the holes that have substantial recreational/fishing value, and get a consensus on which holes to study for potential restoration.
The sub-committee identified the Tarpon Cove project area as a section with high wave energy associated with an unrestricted wake zone and good shoreline fishing. These conditions offered an ideal area for island creation to provide wetland habitat, protect the adjacent shoreline, and enhance fisheries utilization. The committee recommended to keep all structures and enhancements 150 feet from the shoreline and stated that clean fill and restoration components would cap fine grain (muck) sediments within the dredged hole and provide for suitable estuarine habitats.
Over the next three years, the county implemented benthic surveys, bathymetric surveys, and seagrass surveys to assess project feasibility. A conceptual design was created considering the view from the adjacent neighborhood, navigation, fishing from the seawall, costs and the development of a large site for the marine community to use for the beneficial placement of dredged material. The project received positive feedback from all the stakeholders, and in May 2017, the county submitted a joint Environmental Resource Permit Application to the FDEP and the Corps. The county received the FDEP permit on June 23, 2017, and the federal permit on February 15, 2018.
The 46-acre Tarpon Cove project was designed to fill in a deep dredge hole. This will restore and enhance critical shallow estuarine subtidal vegetation (seagrass) habitat by capping the muck, which will allow for the natural recruitment of seagrasses, including Johnson’s seagrass (Halophila johnsonii), a federally threatened species, which occurs near the project area. Additionally, the project will result in five intertidal islands consisting of mangrove, emergent (tidal marsh), unconsolidated sand (tidal flat), reef (oyster), and coastal nesting bird island habitats. These islands should support a wide variety of fish, invertebrates and birds.
Other benefits of the project include downstream water-quality improvements, improved wildlife-oriented recreational opportunities, increased protection of shorelines from sea level rise, and increased carbon sequestration capabilities. The project will also serve as a natural buffer between the IWW and existing shoreline, providing for both refuge and safer passage by listed species, such as manatees and sea turtles, outside of the busy IWW channel.
Overall, the project:
• Restored 39.9 acres of estuarine habitat;
• Capped 15.9 acres of muck sediments while allowing for deep-water refuge landward of the project;
• Created 34.8 acres of seagrass habitat;
• Created 2.7 acres of emergent islands with intertidal mangrove and spartina habitat;
• Created 0.3 acres of habitat for coastal nesting birds;
• Created 2.1 acres of oyster and artificial reef habitat.
The project required approximately 418,600 cubic yards of sand; the FIND IWW Palm Beach Maintenance Dredging project provided 20 percent of that amount. Construction of the Tarpon Cove project began in February 2018 with the placement of beneficial material generated from the Town of Palm Beach Channel Maintenance Dredging project and Rybovich Super Yacht Marina Center expansion in West Palm Beach. Construction continued with the placement of the FIND IWW maintenance dredging material in 2019. Future phases of the project will occur as funding and other beneficial use sources of fill material become available.
CONSTRUCTION: Equipment and Procedures
Orion completed the construction phase of the IWW Maintenance Dredging project between March 2019 and May 2019, approximately two months before the required completion date. Orion removed 86,450 cubic yards of material.
Orion used a mechanical dredge equipped with 15-cubic-yard environmental clamshell and 6-cubic-yard heavy duty bucket to dredge the channel. A tender tug relocated the dredge during the dredging operation. The environmental bucket minimized sediment suspension and impacts to water quality.
The mechanical dredge — a Liebherr HS 895 HD crane — was able to break through the weathered limestone encountered along some sections of the channel. To facilitate movement of larger vessels during the March 2019 Palm Beach International Boat Show, Orion began dredging in shoal areas targeted by FIND and the marine industry at the south end of the project area. Orion then continued working northward toward Peanut Island.
Hopper barges (260 feet x 52 feet x 12 feet) transported the material from the dredging location to the Tarpon Cove restoration project, located about one mile south of the southern project limit. When filled to capacity the hopper barges could hold 3,900 tons of material; however, shallow depths in the offloading area restricted barges to a maximum of 1,850 tons. At the Tarpon Cove restoration project, Orion moored the loaded barges to an offloader barge. The offloader barge — a large excavator equipped with a hydraulic environmental bucket — began placing material from the southern portion of the placement area moving north. A turbidity barrier enclosed the placement area to prevent water quality standards exceedances. The excavator released the material below the waterline to further minimize turbidity.
The contractor experienced substantial variability in daily production rates due to (1) weather and mechanical delays, (2) difficulty in dredging coquina and hard packed sand; (3) attempting to mechanically dredge a relatively thin-layer of material spread out over several miles; and (4) increased vessel traffic associated with the Palm Beach International Boat Show.
Orion was able to remove in-situ coquina and hard packed sand with a 6-cubic-yard heavy duty bucket, equipment typically not required for maintenance dredging projects. In addition, similar variations to Orion’s means and methods were implemented to minimize impacts associated with having thin material layers spread over large areas. Operating a bucket with a smaller footprint allowed Orion to target areas of concern, while minimizing the amount of excess water in the hopper barges, which would have additional detrimental impacts to production.
Through coordination between stakeholders — FIND, Palm Beach County, regulatory agencies and the contractor — Taylor Engineering obtained permit modifications, revised the dredging contract specifications, and issued a change order to Orion to place the dredged material as fill at Palm Beach County’s Tarpon Cove restoration area. Orion completed dredging and transport of 84,650 cubic yards dredged material to Palm Beach County’s restoration project within a consolidated timeframe.
Stakeholder Coordination: Marine Traffic and Mitigation
Partnerships between project stakeholders and environmental regulatory agencies — including FIND, Palm Beach County, the Marine Industries Association of Palm Beach, the Town of Palm Beach, state and federal permitting agencies, local boating and commercial industry groups, and the dredging contractor — were also necessary for the project outcome.
Because the IWW is a key access corridor for many commercial marinas, public outreach and coordination with the local boating and commercial groups was crucial. Providing a daily email update with the construction status, targeted mailings, outreach to the marine industries, public outreach meetings with the historic El Cid neighborhood (lying adjacent to the Tarpon Cove restoration project), and U.S. Coast Guard coordination greatly aided in the overall project success.
This section of the IWW experiences high volumes of marine traffic from the Port of Palm Beach, the Palm Beach International Boat Show, several marinas, a megayacht service facility, and numerous private docks. Combined, the dredge and the barge measured approximately 90 feet in width, which substantially reduced the navigable channel width for marine traffic. To buffer potential maintenance of marine traffic issues, Orion provided daily equipment position reports that helped to notify local mariners of the dredging and offloading locations. These reports were shared via email with the engineer, Port of Palm Beach Pilots, USCG, affected marinas along the IWW, and other stakeholders or individuals that requested this information.
Due to the proximity of the El Cid neighborhood, approximately 500 feet west of the Tarpon Cove restoration project, Orion had to monitor both noise and light disturbance. To reduce noise during the offloading operations, all equipment operating at Tarpon Cove restoration project had muffler systems in place and, as much as practical, Orion minimized noises associated with the mechanical aspects of the offloading procedures. Orion also conducted noise monitoring along the El Cid seawall to measure background and construction noise levels. Readings in the 60 decibels (dB) were recorded for passing cars and 80 dB for planes flying overhead. Construction noise levels were measured between 70 to 75 dB at the seawall, approximately 450 feet from the offloader.
With regard to light mitigation, Orion initially staged the barges in an east to west direction filling the placement area in rows, once a row reached capacity, the offloader barge was moved north to start another row. A few weeks into the dredging operation, the contractor reoriented the barges in a north-south direction. This change (1) reduced light impacts from the tugs on the historic El Cid neighborhood, located along the eastern edge of the IWW and (2) resulted in safer offloading as this orientation facilitated the arrival and departure of the tugs and scows with respect to currents and prevailing winds.
Following the completion of the IWW maintenance project, Palm Beach County residents and the area’s vital marine industry have benefited from easier and safer navigation. This project demonstrated that through proper planning, design, and coordination with the relevant stakeholders, maintenance dredging projects may provide sediment for environmental restoration with economic benefits to both the navigation authority and local government.
L. Brownell is director, waterfront engineering, Taylor Engineering Inc., 904-731-7040, email@example.com; Y. Siddiqui is project engineer, Taylor Engineering Inc., 352-665-0750, firstname.lastname@example.org; E. Anderson is senior environmental analyst, Palm Beach County Environmental Resources Management, 561-233-2514, email@example.com; J. Vannoy is senior project manager, Orion Marine Construction Inc., 813-839-8441; firstname.lastname@example.org; M. Crosley is executive director, Florida Inland Navigation District, 561-627-3386; email@example.com.