Seawall Construction in Davis Shores

A seawall is designed around the energy it absorbs, so the design starts with the water rather than with the wall.

Davis Shores sits at the north end of Anastasia Island, immediately across the Bridge of Lions from downtown St. Augustine. It is a low-lying, densely built waterfront neighbourhood on filled ground, with frontage on both the Matanzas River and Salt Run, and it has a long and well-documented relationship with high water.

Almost entirely armoured, with seawalls and bulkheads along most of the developed frontage. Low elevation relative to the water is the defining characteristic — the margin between a normal high tide and the top of many walls here is slim, and that shapes everything about how structures perform.

Tidal current through the Matanzas and Salt Run, boat wake from a busy stretch of the ICW, and — the dominant concern — storm surge and elevated water levels. Davis Shores is low enough that overtopping is a design case rather than a remote possibility.

Full salt exposure. Hardware, fasteners and embedded reinforcement all corrode faster here than on the fresher inland reaches, so specification is a service-life decision rather than a detail. Tidal range is significant. That matters twice over: it drives a large volume of water in and out through any opening in a wall, and it makes a fixed-only dock awkward to board at the bottom of the tide.

Filled ground over original marsh and river bottom. The organic layers beneath the fill are a central engineering fact here: they provide little resistance, and embedment has to reach past them. Settlement over time is common on properties where it did not. For a seawall it drives section selection, how much toe protection the wall needs, and where the cap has to sit to limit overtopping.

A new seawall on Matanzas River, Salt Run and Intracoastal Waterway has to answer all of these. The ones involving scour and overtopping are the ones most often left out of a cheap design.

• Overtopping during elevated water events, eroding soil from behind walls on the landward side
• Soil loss through wall joints into water that is moving on every tide
• Settlement of fill over organic layers, showing as depressions and tilting hardscape
• Toe scour where current runs along the frontage
• Hydrostatic pressure behind walls where drainage cannot keep up during high water

A seawall is designed around the energy it has to absorb, and that is why we will not quote one by the foot over the phone. Tidal current through the Matanzas and Salt Run, boat wake from a busy stretch of the ICW, and — the dominant concern — storm surge and elevated water levels. Davis Shores is low enough that overtopping is a design case rather than a remote possibility.

On Davis Shores frontage that drives four things: the section selected, how deep it is embedded, whether toe protection is needed and how much, and where the top of the wall sits relative to design water levels.

• Fetch and wake exposure specific to your frontage on the Matanzas River
• Embedment depth, with an allowance for scour rather than for soil load alone
• Toe protection sized for the energy the wall will reflect back into the water
• Cap elevation and freeboard, set to limit overtopping
• Tieback spacing and anchor placement outside the active soil wedge

A vertical wall reflects wave energy downward into the water at its own base, and that reflected energy excavates the material the wall is embedded in. The wall undermines its own foundation, continuously, and none of it is visible from the top.

This is a neighbourhood where cap elevation and freeboard genuinely matter. A seawall here that is only designed for the water in front of it, without regard to what happens when water comes over it, is solving half the problem. Walls in Davis Shores should be assessed with overtopping explicitly in mind.

If you are comparing estimates for Davis Shores and one of them has no toe protection on exposed frontage, that is the question to ask before you compare the totals.

Full salt exposure. Hardware, fasteners and embedded reinforcement all corrode faster here than on the fresher inland reaches, so specification is a service-life decision rather than a detail. We build vinyl and concrete seawalls, and the choice turns on exposure, what sits behind the wall, and how long you intend to own the property.

The important qualifier for vinyl is that wave loading is a larger demand than soil retention, so the section has to be selected for it. A profile adequate on sheltered water is not automatically adequate here. The full construction process is here.

A new seawall here is also a soil-retaining structure, so the bulkhead side of the problem does not go away. Davis Shores bulkheads are retaining fill on low ground against water that regularly comes close to the top of the wall. Full detail: bulkhead construction in Davis Shores and bulkhead repair.

A new wall is the natural moment to resolve a dock tie-in properly rather than working around it. The constraints on this frontage:

More at dock construction in Davis Shores.

• Significant tidal range in a neighbourhood with low freeboard to begin with
• Tidal current in Salt Run and the Matanzas loading piles and scouring foundations
• Dense development limiting the space available for structures and for construction access

Putting that together for a new seawall here:

Davis Shores properties warrant attention to the drainage and the ground behind the wall as much as to the wall itself. Void filling and grout injection are frequently the highest-value work here, because soil loss into fill over organics compounds quickly and the symptoms show up in hardscape before anyone looks at the wall.

Land access is generally workable, but lots are compact and densely developed, with limited laydown space and hardscape close to the water. Protecting and restoring what is in the work corridor is a real part of the scope.

A new seawall is reviewed as new construction, and the toe protection it needs is part of the proposal rather than an afterthought added later.

Low elevation and proximity to a historic district bring considerations beyond the ordinary marine review path, and work on the Matanzas and the ICW carries navigation review. Local requirements here are worth confirming early.

Requirements are revised periodically. Treat this as orientation and confirm current requirements with each reviewing agency before planning work. We handle permitting on the projects we build, and agency review is normally the longest item in the schedule.