Stock photo (Unsplash), not a job photo.
You fill it with a few bags of topsoil, and two weeks later it’s back, a little bigger. That’s the classic sign. The hole isn’t the problem. It’s the symptom. Soil behind the wall is leaving with the tide.
The four usual causes
- Gaps in the face of the wall. Old timber boards shrink, split and separate. Vinyl or steel sheets can lose their interlock. Every high tide pushes water in, and every low tide pulls soil out.
- Torn or missing filter fabric. Fabric behind the sheathing lets water through but holds soil back. When it tears or degrades, fine soil escapes even through small gaps.
- Scour at the toe. Waves, boat wakes or currents dig out the bottom of the wall until soil can run out underneath it.
- A failed return. The short wall that ties your bulkhead to the neighbor’s separates or rots, and soil escapes at the corner.
How each one gets fixed
| Cause | Typical fix |
|---|---|
| Gaps in sheathing | Reface (resheath) the wall. DEC limits this to 4 inches seaward for timber or 8 inches for vinyl or steel. Or replace the section. |
| Torn fabric | Excavate behind the wall, install new fabric, then backfill and compact |
| Toe scour | Extend or replace the sheathing deeper, or add toe protection, depending on permits |
| Failed return | Rebuild the return, ideally coordinated with the neighbor |
What it costs (Long Island, 2026)
- Minor repair (cap boards, a tie-back, a local patch): $3,000–$8,000
- Significant repair (section replacement, backfill restoration): $10,000–$30,000
- Repair or partial replacement by length: about $150–$300 a foot
If sinkholes keep appearing along much of the wall, or the timber is near the end of its 25–30-year life, a full replacement usually costs less per year. The calculator compares both.
In the meantime
Rope off the area, keep vehicles and equipment back, and don’t keep dumping fill into the hole. It feeds the leak and hides how big the void is. Get it looked at.
Need it done? See bulkhead repair on Long Island.