City of Naples 3.4 Acre Habitat Island

Summary: Erickson Consulting Engineers, Inc. (ECE) is responsible for managing all design, permitting, engineering, construction and post-construction monitoring for a 3.5 acre habitat island located in Naples Bay.

The habitat island was designed to achieve:

    1. Reduction of shoreline erosion of an existing mangrove shoreline;
    2. Increased flows and therefore improve circulation within an embayment; and
    3. Creation of an enhanced habitat for birds, fish and invertebrates.

The island was designed to support three different habitats based on elevation and target biological and vegetative species as follows: (1) coastal upland, (2) low wetland and (3) oyster reef. The sediment source to construct the island is from a nearby canal system. This provides an added benefit of restoring the navigable canal system for the community and constructing a sustainable project based upon sustainability’s triple bottom line (environmental, economic and social benefits). To obtain enough volume to achieve the full 3.5 acres, the sediment source may be supplemented from an upland sand mine. The Project is expected to be funded using Restore Act funding under a $1.5M grant. Construction is pending for 2013.

Design Concept: Sediment filled geotextile containers will be used to stabilize the island perimeter. Several small interior containment baffles will also be constructed using geotextile containers to control dewatering and formation of the island. Further, an 8 inch geoweb layer with crushed shell infill will be installed to cap the finer grained material and maintain the stability of the island during overwash events. A polymer/flocculent will be introduced to aid in dewatering and settlement of the large fraction of fines. Finally, the island will be planted with mangroves and marsh grasses for habitat enhancement and island stabilization.

Key Project Elements:

  • Project Design Basis
  • Topographic and Bathymetric Surveys
  • Geotechnical Studies (Jet Probes and Vibracores)
  • Environmental Surveys & Sampling (seagrass, oyster beds, Macro Invertebrate)
  • Water Quality Sampling and Analysis
  • Geotextile Containers Design
  • Dewatering Design
  • Assessment of Polymer for Dewatering of Fine Sediments
  • Sediment Analysis and Development of a Sediment Management Plan
  • Construction Methods & Sequencing Plan
  • Dredge Pipeline Plan
  • Current Velocity Measurements and Tidal Prism Calculations
  • Estimation of Quantities, Costs, & Construction Schedules
  • Assessment of Project Impacts (Environmental, Social and Economic)
  • Vegetation Plans and Assessment of Target Biological Species
  • Acquire all County, State and Federal Permits
  • Construction Plans and Specifications
  • Bidding Assistance
  • Construction Monitoring and Administration
Challenges: The two primary challenges associated with the design included (1) the use of very fine sediment from the adjacent canal bottoms to construct the island (fines content exceeding 80% in some locations) and (2) construction of the island adjacent to a federal navigation channel which required intensive coordination with the USACE.

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