Seawall raising in Islamorada

Who needs a seawall raised

Owners whose walls overtop at king tides, owners who have been cited, and owners planning a repair big enough to trigger the city's height rule.

• Water over the cap at high tide
• A city citation for overtopping
• A repair of $300 or more per linear foot in Miami Beach
• Plans to sell, rebuild or add a dock

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.

Those numbers show how much margin a raised wall really gives above an ordinary high tide.[1][2]

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.

Raising the wall stops tidal overtopping, but the home behind it still relies on its own flood protection.[3]

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 raise is designed to that number, measured in the right datum, and checked by survey before the cap pour.[3]

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.

Seawall height rules by city

Each city sets its own standard, and they do not all use the same vertical datum (NAVD 88 or the older NGVD 1929), so the engineer's survey must state the wall height in the same datum as your city's rule.

Miami Beach: 5.7 ft NAVD for new walls and substantial repairs, or 4 ft NAVD designed to reach 5.7 ft. Coral Gables: a minimum of 6 ft NGVD 1929, structurally able to support 7.5 ft. Fort Lauderdale: a minimum of 5 ft NAVD88, and walls permitted before 1 January 2035 may be built at 4 ft if designed to reach 5 ft by 1 January 2050. Boca Raton: new or replaced walls between 4.0 and 6.0 ft NAVD88, designed to take another 12 to 18 inches.

City of Miami: a 2020 proposal set 6 ft NAVD 88 east of US-1. We have not confirmed it was adopted, so we check with the City for each job.[7][11][13][14][10]

Help with the cost

Miami Beach's Private Property Adaptation program accepts seawall applications on a rolling basis and reimburses 50% of costs up to $20,000, including the $2,500 assessment value; qualifying low to moderate income households need no match up to $17,500. Homes built at least 1 ft above base flood elevation are not eligible. Coral Gables waives a fee for existing homes raising seawalls for sea level rise.[8][12]

Frequently asked questions