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SeawallConnect

Symptom guide

Why Is Soil Washing Out Behind My Seawall?

Sand disappearing near the wall, a soft patch in the lawn, a paver that has dropped — these usually share one mechanism. Here is how it works and what it means for your property.

Request a Seawall QuoteIdentify the Problem
Collapsed section of lawn beside a residential canal seawall exposing a cavity where soil has been lost

The sequence, step by step

1Water movementTide, rain and groundwater move through the soil behind the wall.2Opening or failed jointA gap at a panel joint, cap crack or penetration creates a path.3Soil migrationFine sand travels through the opening and out into the waterway.4Void formsA cavity develops behind the wall where the soil used to be.5SettlementThe surface drops — a depression, soft spot or hole appears in the yard.
How a small opening becomes a yard problem. Each stage can run for months before anything is visible at the surface, which is why a depression in the lawn is often a late symptom rather than an early one.

A seawall retains soil. It does not, on its own, stop water from moving through that soil. Rain, irrigation and tidal cycles keep groundwater moving behind the wall, and that water will exit wherever it can. If it can only exit through a designed drainage path, it carries very little material with it. If it can exit through a joint, crack or failed penetration, it carries fine sand with it every time.

That is the whole problem. Each individual event moves a trivial amount of material. Repeated over years, it produces a cavity — and eventually the surface above the cavity gives way.

What a void behind the wall looks like

VoidSurface settlementRemaining soilWaterwaySoil escaping through joint
A void behind the wall. Because the cavity is hidden, the first evidence is often a dip in the lawn, a sunken paver, or a settled pool deck edge rather than anything visible on the wall itself.

Warning signs

Things owners notice, in roughly the order they tend to appear

  • Water staining, seepage or weeping at a joint or crack in the wall face
  • Sand fanning out at the base of the wall on the water side, especially after heavy rain
  • A visible gap opening between two panels
  • Grass that stays soft or spongy near the wall long after the rest of the lawn dries
  • A shallow depression in the lawn parallel to the wall
  • Pavers, stepping stones or a pool deck edge that has dropped or tilted
  • A hole appearing suddenly, sometimes after a storm
  • Cracks in a slab, patio or pool cage footing near the wall
  • Irrigation lines exposed or broken by ground movement

Possible causes → possible repair categories → next steps

Possible causeRepair category commonly consideredNext step
Separated or failed panel jointJoint sealing or localized panel work, plus fill behind the wallJoint & panel repair
Crack through a panel or the capCrack repair; investigation of whether it is structuralCracked wall & cap
Failed or unsealed penetration (pipe, conduit, drain outfall)Sealing the penetration correctlyOnsite evaluation
Existing cavity behind the wallVoid filling and soil stabilisation, alongside closing the pathVoid filling
Scour or loss of material at the toe of the wallStructural evaluation of embedment and supportInspection
Movement of the wall opening gapsStructural assessment before anything elseLeaning walls

What to do now

  1. Keep people, pets and vehicles off any soft or depressed ground near the wall.
  2. Photograph the area, the wall face at that location, and the water side at low tide if it is safe to do so. Date the photos.
  3. Check your irrigation and any downspouts discharging near the wall — concentrated water makes an existing path worse.
  4. Do not fill the depression before someone has looked at it; filling hides the evidence.
  5. Arrange an evaluation and ask specifically where the water is exiting.
Seawall inspectionWhat an evaluation covers and what it should tell you.Void filling & stabilisationMethods, and where they do not apply.Repair cost factorsHow this kind of scope tends to be priced.All failure signsThe full symptom hub.

Frequently asked

Why is soil washing out behind my seawall?
Because water moving through the soil has found a path out through the wall — most often a separated joint, a crack, a failed penetration, or a gap below the structure. Fine sand travels with the water and ends up in the waterway, leaving a cavity behind.
Is a sinking spot in my yard urgent?
It should be looked at rather than watched. A surface depression usually means material has already been lost below, and the size of the cavity is not something you can judge from above. Keep people and vehicles off the area until it has been assessed.
Can I just fill the hole with sand?
Topping up the surface hides the symptom without closing the path that caused it, so the material generally continues to escape. Filling has a place as part of a scope that also addresses the opening.

Get soil loss looked at properly

Photos of the wall face, the water side and the affected ground make a real difference to the quality of the responses you receive.

Request a Seawall Quote
Request a Seawall Quote