Seawall replacement in Islamorada

When replacement makes sense

Replacement is the answer when panels are cracked through, the wall leans, repairs would cost more than half of a new wall, or the wall is too low for your city's new standard.

• Panels cracked through or leaning
• Repeated sinkholes despite repairs
• A city notice to raise or rebuild
• Planned dock or lift work that needs a sound wall

Bay side and ocean side tides differ fourfold

NOAA's Florida Bay gauge at Upper Matecumbe Key shows a great diurnal range of only 0.61 ft, with mean higher high water about 0.41 ft below NAVD 88, while the Hawk Channel gauge a short way across the key shows 2.28 ft (1983 to 2001 epoch). A lift or floating dock sized for one side of Islamorada is wrong for the other.

The tide also sets how much of the wall can be worked on dry at low water, which changes crew time.[1][2]

Watch the datum: about 1.5 ft

The Village notes that converting from NGVD29 to NAVD88 shifts elevations by about -1.5 ft on average in Monroe County, and the shift varies from place to place. Old plans and new maps use different datums, so a cap or floor height has to be converted before anyone compares numbers.

A replacement wall is built to the current height from the start, so the panels, piles and cap are sized for it.[3]

Flood maps from 2005, new ones pending

Islamorada still builds to effective flood maps dated 18 February 2005. Preliminary maps went through appeals between March and June 2021, FEMA has not announced when they take effect, and the Village has promised six months' notice once it does.[3]

Seawalls and riprap inside the setback

Islamorada's shoreline setback keeps buildings 20 to 50 ft from mean high water, but it does not apply to seawalls, riprap and bulkheads whose purpose is erosion control or upland protection. Because the Keys are an area of critical state concern, the 2024 ordinance was approved by the Florida Department of Commerce.

A full replacement needs the complete permit set, so we start on drawings and surveys early.[4]

What makes Islamorada different

Principal buildings sit 20 ft from the mean high water line on altered shorelines such as canals, 30 ft on open water with conditions, and 50 ft on unaltered shorelines. Docks, lifts, davits, seawalls and riprap are water-dependent structures that may sit inside that setback under the Village's standards.[4]

Sanctuary and manatee layers

The federal small-project permit, SPGP VI, required Sanctuary sign-off before any Islamorada project in Keys waters, and crews follow the state manatee conditions on every in-water job.[5][6]

Permits in Islamorada

• Islamorada, Village of Islands, Planning and Development Services: Docks, lifts and shoreline structures under Village Code Chapter 30.
• Florida Keys National Marine Sanctuary: Sanctuary waters surround every Islamorada key from the mean high water mark; we confirm what Sanctuary approval each project needs.
• Florida DEP or South Florida Water Management District: State permit or exemption; part of the Village's water is the Lignumvitae Key Aquatic Preserve.
• US Army Corps of Engineers, Jacksonville District: Federal authorisation for work in the Sanctuary waters around the Village.

What a seawall replacement involves

A Florida engineer designs the wall to the site's soil, water depth and the local top elevation. Most replacements go in front of the old wall, which stays in place as backing, because removing it can undermine the yard.

1. Survey and engineered drawings
2. DERM, city and state approvals
3. Turbidity barrier and manatee watch in the water
4. New panels or sheet piles, tiebacks and cap
5. Backfill, drainage and yard restoration

How far out can the new wall go?

Florida Statute 403.813 exempts restoring a seawall at its previous location, upland of it, or within 18 inches waterward of it. Miami-Dade's short form and the federal SPGP VI use the same 18 inch line, measured wet face to wet face, and need no seagrass survey within it.[10][9][5]

Federal permits

Under SPGP VI, the Florida DEP could verify the federal Army Corps authorisation for qualifying seawall work along with the state decision. That permit's stated expiration date was 27 July 2026, and we have not been able to confirm a replacement, so for each job we confirm the federal route with the agencies before we file.[5][11]

Working around manatees

Permits attach the state's Standard Manatee Conditions: all in-water work stops if a manatee comes within 50 ft, and resumes only once it has moved beyond 50 ft or 30 minutes pass without it reappearing. Turbidity barriers must not entangle or block manatees.[6]

Frequently asked questions