Riprap Installation on Hilton Head Island, SC

It works as a sloped system, not a wall — the slope itself is part of what absorbs energy, spreading the wave's force across a larger area instead of concentrating it against one vertical face. That's also why riprap needs more lateral space than a bulkhead: it can't do its job compressed into a narrow footprint.

Riprap also ages differently than a bulkhead: a wall tends to fail suddenly once its tie-back system gives way, while a stone revetment more often degrades gradually — a stone shifts, then another — which generally gives more warning before a real problem develops, provided someone is actually looking.

Stone size and gradation are matched to the site's wave climate — undersized stone gets displaced by the first significant blow, while a well-graded mix of sizes locks together and resists movement far better than uniform stone of any single size.

A revetment exposed to open sound frontage and boat wake needs larger, heavier stone than one on a sheltered lagoon or a narrow tidal creek. Getting this wrong is the most common cause of early riprap failure — stone that looked adequate on delivery but was undersized for the actual wave energy the site sees.

Gradation matters as much as the maximum stone size: a mix that's too uniform leaves larger voids between stones, which lets more wave energy through to the layers underneath rather than dissipating it at the surface. A well-graded mix — smaller stones filling the gaps between larger ones — performs better than the same total tonnage of uniformly sized stone.

A revetment without filter fabric and proper bedding fails from the inside: waves pump water in and out of the stone layer, and without fabric to hold it back, the soil behind the stone washes out through the voids until the bank subsides and the stones settle into the resulting hole.

Filter fabric goes down before the stone, sized and overlapped correctly at seams so soil can't migrate through a gap. Bedding stone beneath the larger armor stone spreads the load and keeps the whole system from settling unevenly into softer pluff mud.

This failure mode is deceptive because the stone itself often still looks intact from a distance even as the bank behind it is actively washing out — a revetment that appears stable on a casual look can already have a significant void developing beneath it.

The toe — the base of the slope where it meets the channel bottom — takes the most concentrated wave and current energy on the whole structure, and a revetment that fails almost always fails there first, undermined from below before the rest of the slope shows any problem.

A properly designed toe extends below the anticipated scour depth or keys into firmer material, so the base of the slope can't be undercut. This is a detail that doesn't show in a finished photo but is the difference between a revetment that holds for decades and one that unravels from the bottom up within a few storm seasons.

Riprap suits a site with room for a sloped footprint and a bank that can be laid back rather than held vertically; a bulkhead suits a tight property line where space for a slope doesn't exist. Wave exposure, available width, and what SCDES will permit on that specific shoreline all factor into which one fits.

We assess the bank profile, the available lateral space, and the site's wave and wake exposure before recommending either — riprap is often the better-performing and better-permitting choice where the site allows it, but the site has to allow it.

Where a lot has room for either, riprap generally asks less of the maintenance schedule over the structure's life than a bulkhead does, since there's no buried tie-back system to fail — the tradeoff most owners are weighing is footprint against long-term upkeep.

Stone revetment is reviewed under the same Critical Area standard as a bulkhead: conformance to the Critical Area line, siting relative to the existing escarpment, and the same erosion-justification requirement that marsh already serving as a buffer takes precedence over a new structure.

We prepare that determination and the supporting drawings as part of the project scope, the same process used for bulkhead and dock work.