Bulkhead problem
Soil Washing Out Behind a Seawall or Bulkhead
Dips, depressions or disappearing yard along the wall
The short answer
Soil washing out behind a seawall almost always means water is passing through or under the wall and carrying backfill with it. The water movement is the problem; the sinking yard is the symptom. Left alone, the resulting voids tend to enlarge and can undermine the wall, slabs, pools and walkways behind it.
What this usually indicates
- Joints between panels have opened, or the filter fabric behind them has failed
- Water is moving through the wall on tide cycles and carrying fines out with it
- Weep holes are missing, blocked, or were installed without adequate filtration
- Scour at the toe of the wall is letting soil migrate underneath rather than through
- 1Backfill lost from the yard — the depression is the last stage, not the first
- 2Open joint — water takes the easiest route out, and it widens each cycle
- 3Sediment carried into the waterway — your soil, in transit
What causes it
Failed or absent filter fabric
Most walls rely on geotextile fabric behind the panel joints to let water pass while holding soil back. Fabric degrades, tears, or was never lapped correctly at the joints — and once it fails, every tide cycle removes a little more backfill.
Open panel joints
Vinyl and concrete panels interlock, but differential movement, impact and ground settlement can work those joints apart. An opening the width of a pencil is enough to move a surprising volume of sand over a season.
Blocked or missing weep holes
Weep holes relieve the hydrostatic pressure that builds behind a wall when the tide drops. When they clog, pressure finds another path — usually through a joint, taking soil with it.
Toe scour
Boat wake, tidal current and storm flow can excavate the sediment at the base of a wall. Once the toe is undermined, backfill migrates down and out beneath the panels.
Surface water discharging at the wall
Downspouts, pool deck drains and regraded yards that dump stormwater at the top of a wall will erode backfill from above, independent of anything happening at the waterline.
What an assessment looks at
These are the specific questions an inspection is trying to answer for this symptom.
- Where the depressions sit relative to panel joints and weep holes
- Whether soil loss is isolated to one area or distributed along the whole wall
- Probe or sounding results behind the cap to estimate void extent
- Condition of the toe and whether scour is present at low tide
- Where surface water and roof runoff currently discharge
What tends to happen if it is left
Voids behind a wall rarely stay the same size. As more backfill leaves, the soil that remains loses the lateral support it was providing to the wall, which transfers load onto panels and tiebacks that were not designed to carry it. Repairs that would have been localised often become structural.
Frequently asked questions
Is a sinking spot in my yard always a seawall problem?
Not always. Settlement over an old utility trench, a collapsed drain line, or decaying buried organic material can produce similar depressions. What points toward the wall is the location — soil loss that tracks along the wall line, concentrates near panel joints, or worsens after high tides and heavy rain.
Can I just fill the low spots with dirt?
Topping up the surface hides the symptom without addressing the water path that is removing the soil. The fill usually disappears again, and in the meantime the void underneath keeps growing where nobody can see it. Filling makes sense as part of a repair that also closes the path the water is taking.
How fast does soil loss progress?
It varies with tide range, how open the pathway is, and how much stormwater reaches the area. Some walls lose material slowly over years; others open up noticeably after a single storm season. That variability is exactly why an in-person look matters before deciding how to respond.
Next
Services that address this
Seawall erosion repair
Erosion behind a wall is a plumbing problem before it is a structural one. Water found a route out, and it has been taking soil with it.
Learn moreSeawall void filling
Voids behind a seawall are almost always bigger than the hole you can see. The surface is the last thing to go.
Learn moreSoil stabilization
The soil behind a wall is a structural component. When it loses density, both the wall and anything built on top of it lose support.
Learn moreOther symptoms
Seeing more than one of these?
Problems rarely arrive alone — several symptoms together usually point at a single mechanism.
Wall leaning or bowing
The wall is tipping waterward or bulging outward
Learn moreCracks in concrete
Cracked panels, cap or returns
Learn moreWater coming through the wall
Seepage, jets or streams through joints and cracks
Learn moreDeteriorating wood or vinyl
Rot, splitting, brittleness or UV damage
Learn moreNext step
Seeing soil washing out behind the wall?
Send photographs and a short description. You will get help understanding what the symptoms point to and which repair options are realistic.