How Do You Design a Concrete Seawall That Holds the Line?

A concrete seawall is designed as a coastal retaining structure: wave forces on the face, soil pressure behind, scour at the toe, and salt attacking the concrete itself. Every element — the wall section, the foundation depth, the toe armor, the drainage, the concrete mix — addresses a specific failure mode. Seawalls fail at their weakest link, so the design has to be complete, not just strong in one direction.

Wave loading is the defining demand: breaking or non-breaking wave pressures on the wall face, uplift on any horizontal surfaces, and overtopping that sends water — and energy — over the top to erode the backfill. The wave climate comes from coastal analysis of the site's exposure, water depths, and storm history. Stability is checked like a retaining wall — overturning, sliding, bearing — but with the water-side soil potentially scoured away, which is the critical difference from a land retaining wall. Hydrostatic pressure behind the wall is managed with drainage layers and weeps, and the backfill is specified as free-draining material so it can't trap water. The concrete is designed for the marine exposure class: low water-cement ratio, adequate cover, and crack-width control, because the reinforcement's lifespan is set by how well the concrete protects it.

The failures I've investigated were preventable — and they were prevented on the projects where the owner invested in proper coastal analysis and refused to cut the protection details. My seawall checklist.

• Wave climate established: design waves from coastal analysis, not guesswork
• Toe below scour depth: foundation and armor designed against undermining
• Drainage detailed: weeps, filters, and free-draining backfill relieve pressure
• Marine concrete specified: low permeability and cover for salt exposure
• Overtopping managed: crest elevation and back-of-wall erosion protection
• Post-storm inspection plan: the owner knows what to check after every major storm