New England Spotlight

Evidence of subsidence behind a revetment.

Our coast is changing at a pace much faster than previously realized and coastal projects are not always properly designed for future projections. On a recent visit to Hull, Massachusetts Woods Hole Group coastal engineers observed a relatively new large stone revetment constructed at Point Allerton is already failing, and will have little chance of reaching its intended design lifetime. Woods Hole Group’s role is to evaluate the structure that was designed and constructed by others, and make recommendations for lasting improvements.

The photo(s) reveal that the rear landward portion of the revetment is subsiding and caving in. This is caused by waves impacting the revetment and infiltrating between and behind the stones. As the waves recede, they erode sediment from behind the stones, which undermines the revetment. While the seaward face of the revetment appears to be stable, the condition will expand over time until enough sediment is eroded that the revetment becomes destabilized and catastrophically slides into the ocean.

Further evidence of subsidence.

Communities are already strapped with increased costs for constructing and maintaining coastal infrastructure, and they cannot afford to incur the costs of inadequately designed coastal projects or their consequences. At Woods Hole Group, Inc. we are on the leading edge of designing our projects based on the best available science. With sea levels rising at rates faster than any historic projections, projects should be designed for the storms of tomorrow, not yesterday.

Proper attention to detail also is essential as related to armor stone sizes and selection, layering with intermediate stones and bedding material, and use of filter fabric to prevent sediment loss from behind the structure. Experience also has proven that designs and specifications must be clearly understood and constructed by the contractor. Having an experienced engineer onsite during construction as the owner’s representative is essential.

Submitted by:

Mitchell Buck, P.E.
Woods Hole Group
81 Technology Park Dr.
East Falmouth, MA 02536

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