Why is there a sinkhole behind my bulkhead?
Sand is leaving through a gap in the wall, torn filter fabric, a leaking pipe or under the toe. Filling the hole hides the problem; the fix is closing the path the sand is taking.
Behind every bulkhead is a mass of sand. Water moves through it with waves, wind and rain. A sound wall lets water pass while it holds the sand back.
When a joint opens or the fabric tears, each flow carries a little sand out. The hole you see is the last stage. The void under the surface is often wider than the dip in the lawn.
Where does the sand escape?
These are the usual leak paths. Several can act at once.
- Open panel joints: the seal between panels has failed.
- Filter fabric: the woven cloth behind the wall that lets water out but keeps sand in. Once torn or worn out, it stops doing either job well.
- Weep holes: small drains through the wall. Without a filter behind them, they can pass sand.
- Pipes through the wall: yard and stormwater pipes can leak around their edges.
- The toe: the base of the wall below the bottom. If the bottom scours away in front, sand can run out underneath.
- Cracks and spalls: broken concrete near the waterline.
Drainage and filtration are designed together: one relieves water pressure, the other keeps soil in place. Coastal engineering guidance
Why is filling the hole not the fix?
New sand goes out the same way the old sand did. Owners often fill the same spot every few months.
- The leak path stays open, so the loss continues.
- The real void may run along the wall, well past the visible dip.
- Heavy fill, or a truck on the soft spot, can load a weak wall.
- Covering the dip hides the change you need to track.
Filling is fine as a short-term safety step to remove a trip hazard. Mark and photograph the spot first, so the assessor can see what happened.
How does stormwater make it worse?
Rain that runs to the wall has to go somewhere. If it soaks in behind the cap, or pours out of a pipe beside it, it pulls sand along. Fort Walton Beach requires docks, piers and seawalls to be built so they do not channel runoff straight into the water. FWB LDC 5.01.15
Public drainage reaches many bulkhead lots. Destin says one outfall at Mattie Kelly Park on Joe’s Bayou drains over 200 lots. The city sought state money for a bigger pipe and settling basin. Destin funding request The city has also repaired poorly performing culverts in the Destin Harbor, Joe’s Bayou and Indian Bayou drainage areas. NFWF project summary
Isaias added a lot of water. A rain gauge near Fort Walton Beach caught about 11 inches, and one near Mary Esther nearly 12 inches. NWS Isaias report NWS Isaias rainfall Watch for new soft spots in the weeks after a storm like that.
- Where do your gutters, yard drains and pool overflow empty?
- Does a public pipe or ditch discharge beside your wall?
- Does water pond behind the cap after rain?
The Joe’s Bayou and Indian Bayou guides cover those shorelines.
What fixes soil loss for good?
| Leak path | Typical fix | Ask |
|---|---|---|
Open panel joint | Seal the joint and replace filter fabric behind it | How far back will you dig, and which fabric will you use? |
Torn or missing filter fabric | Dig out behind the wall, install new fabric, backfill with clean sand | How will you protect the wall while it is open? |
Weep hole passing sand | Add a filter behind the weep, or rebuild the drain | Which openings must stay open? |
Leak around a pipe | Seal around the pipe, or reroute it | Who owns the pipe: you, a neighbor or the city? |
Scour at the toe | Toe protection, such as riprap | Is there seagrass in front, and which permit applies? |
Confirmed void, leak already fixed | Fill with clean sand or polyurethane foam | How was the size of the void measured? |
Foam can fill a confirmed void, but it should come after the leak is closed. See foam injection. For scour at the base, see riprap and toe protection.
What does a lasting fix cost?
Far less than a new wall, when the wall itself is sound. Here is one local example. A 2026 contractor letter in an Okaloosa County packet covered a public shoreline at 901 Eglin Parkway in Shalimar. It estimated $20,000 to $30,000 to dig along the wall, install new filter fabric and backfill. Okaloosa County agenda packet
County staff put the full touch-up there at around $50,000 and said keeping the existing wall would save over $1 million. That was one site, with a rough estimate. Your length, access and findings will differ, so use the cost guide to build your own budget.
Do I need a permit to fix soil loss?
Usually yes, when the work touches the wall. Destin requires a permit to repair bulkheads and seawalls. Destin permit rule Okaloosa County’s October 2026 post-storm guide lists seawall repair as work that generally needs a permit. Okaloosa storm guide
Rock at the toe of an existing vertical wall can qualify for a state general permit. It must stay within 10 feet of the toe, at a slope of 2 to 1 or flatter, and off seagrass. Rule 62-330.431 DEP’s fee to verify a general permit is $250. Rule 62-4.050
Find your office in the permit guide, or read the Okaloosa and Walton county guides.
What to ask before you sign
- Where is the sand leaving, and how did you confirm it?
- How big is the void, and how did you measure it?
- Does the price include new filter fabric, or only filling?
- How will drains and weep holes work after the repair?
- What happens if you dig and find a failed tieback or cracked panel?
- What does the warranty cover if a sinkhole comes back?
- For a job over $5,000, will a Notice of Commencement be recorded before the first inspection? s. 713.135
Show sourcesHide sources
- Coastal Erosion Control DesignSource reviewed 2026-10-27
- Land Development Code, City of Fort Walton Beach (Municode, Supp. No. 17, codified through Ord. No. 2194, enacted January 27, 2026), Sec. 5.01.15Source reviewed 2026-10-27
- Florida House funding request #2959: Mattie Kelly outfallSource reviewed 2026-10-27
- Gulf Environmental Benefit Fund, Florida at a Glance: Destin Harbor, Joe's Bayou, and Indian BayouSource reviewed 2026-10-27
- Post Tropical Cyclone Report - Isaias (NWS Mobile/Pensacola)Source reviewed 2026-10-27
- Okaloosa County BCC Agenda Request: Review of Due Diligence Requirements for the Waterfront Property in Shalimar (July 14, 2026), with attached Seawall Inspection Report dated April 15, 2026Source reviewed 2026-10-27
- Building DivisionSource reviewed 2026-10-27
- Okaloosa County Storm Post-storm Permitting Guide/PlanSource reviewed 2026-10-27
- 62-330.431 General Permit for Installation of RiprapSource reviewed 2026-10-27
- 62-4.050 Procedure to Obtain Permits and Other Authorizations; ApplicationsSource reviewed 2026-10-27
- Section 713.135, Florida Statutes (2026), Notice of commencement and applicability of lienSource reviewed 2026-10-27