Seawall raising in Key Largo

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

Where a seawall is allowed at all

Monroe County allows vertical seawalls only to stabilise severely eroding shorelines on man-made canals, channels or basins, and never on open water. Lawfully existing walls may be repaired or replaced on the same footprint, the yard behind must sit at least 6 in below the top of the wall, and riprap goes at the toe wherever feasible.

A raise is designed to that number, measured in the right datum, and checked by survey before the cap pour.[1]

Class 3 for unincorporated Monroe

Key Largo is unincorporated, so it shares Monroe County's flood insurance rating, and the County lists its current Community Rating System class as 3. Monroe takes part in the program on behalf of homeowners in unincorporated areas, and the discount depends on whether a home is inside the Special Flood Hazard Area.

Raising the wall stops tidal overtopping, but the home behind it still relies on its own flood protection.[2]

Ocean side tide at Rock Harbor

NOAA's Rock Harbor station on the Atlantic side of Key Largo records a 2.09 ft mean range and a 2.37 ft great diurnal range, with mean higher high water about 0.25 ft above NAVD 88 (1983 to 2001 epoch). There is no NOAA datum station on the bay side near Key Largo, so for bay side lots we measure the water on site.

Those numbers show how much margin a raised wall really gives above an ordinary high tide.[3]

What makes Key Largo different

The special exception application asks owners to describe the submerged lands the dock crosses, such as sand, seagrass or coral, and the minimum extra length needed to reach adequate water depth. The site plan must be prepared by a Florida registered architect, engineer or landscape architect and show the mean high water line and shoreline setbacks.[4]

Sanctuary, seagrass and manatees

Projects inside the Florida Keys National Marine Sanctuary needed prior Sanctuary approval under SPGP VI. The same permit let boat lifts and minor structures in Monroe County go into existing boat slips without a seagrass survey. All in-water work follows the state manatee conditions.[5][6]

Permits in Key Largo

• Monroe County Planning and Environmental Resources Department: Dock length special exceptions under County Code section 118-12(m)(15).
• Florida Keys National Marine Sanctuary: The Sanctuary starts at mean high water, so Key Largo canal and bay work is inside it; SPGP VI required its prior approval.
• Florida DEP or South Florida Water Management District: State permit or exemption, which Monroe County needs to see before it issues a Notice to Proceed for docks, seawalls and ramps.
• US Army Corps of Engineers, Jacksonville District: Federal permit, also required before the County's Notice to Proceed.

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