Base PDH

Living Shorelines: Marsh Sill and Breakwater Design and Application

Sustainability

Last Updated: April 19, 2026

PDH_CREDITS
2 Hours
PRICE
$20.00

Summary

This course introduces the engineering principles and design methodology of living shorelines, drawing on guidance developed for coastal practitioners in alignment with USACE natural and nature-based features frameworks and New Jersey Coastal General Permit 24. The course covers the four categories of site design parameters, the scoping-through-operations project lifecycle, and structural design methods for marsh sills, ecologically enhanced revetments, and breakwaters, including armor stone sizing using the Hudson and Van der Meer formulas. Students will develop the technical foundation to assess sites, select appropriate living shoreline techniques, and produce defensible designs for coastal stabilization projects.

Learning Objectives

  1. Define living shorelines and explain how they differ from traditional hard stabilization approaches, including the regulatory context established by USACE resilience guidance and state coastal general permit frameworks.

  2. Identify the four categories of living shoreline design parameters — system, hydrodynamic, terrestrial, and ecological — and describe how each influences site assessment, technique selection, and structure configuration.

  3. Apply engineering design methods for marsh sills, ecologically enhanced revetments, and breakwaters, including crest elevation determination, armor stone sizing using the Hudson and Van der Meer formulas, and mitigation of geotechnical and scour conditions.

  4. Analyze segmented breakwater layout geometry using empirical relationships to evaluate expected shoreline response, including salient and tombolo formation, relative to longshore sediment transport continuity.

Notice: Our courses do not yet qualify for PDH credit for engineers licensed in Florida, Indiana, Maryland, New Jersey, and New York. Check your state requirements for details.

Course Reading Material

Living Shorelines: Marsh Sill and Breakwater Design and Application

BasePDH  |  Course No. 008  |  2 PDH

Source: NJDEP Living Shorelines Guidance

Publisher: New Jersey Department of Environmental Protection (NJDEP), Division of Land Resource Protection
Permit framework: NJDEP Coastal General Permit 24
Supporting references: USACE Coastal Engineering Manual (2002), The Rock Manual (CIRIA/CUR/CETMF, 2012), Chesapeake Bay Foundation sill guidance, Van der Meer et al. (1995) toe berm stability formula

Marsh Sill

Description

Sills are low-elevation structures constructed parallel to the shoreline for the purpose of reducing the erosional pressure along the natural shoreline. Sills are often used as armoring for fringe marshes or wetlands that require a higher degree of protection or shallow water nearshore breakwaters. Sills dissipate wave energy and reduce bank erosion, causing waves to break on the structure, rather than on the natural, more fragile shore. The quiescent area of water that is created by the sill often allows sand and sediment to accumulate between the structure and the shoreline. With time this process can eventually raise the elevation of the bottom and create a perched beach or cause the marsh to build out to the structure. This unique effect not only serves to further stabilize the shoreline or marsh behind the sill but replaces lost and eroded land. Often the area between the sill and the shoreline is filled during construction to accelerate the development of the perched beach. Marsh plantings are often added to further stabilize the reclaimed land.

Design Guidance System Parameters

Erosion History

Sills are appropriate at sites with a low-moderate erosion rate. The Chesapeake Bay Foundation suggests hybrid approaches such as sills are appropriate at sites with erosion rates of between 2 and 8 ft/yr (Chesapeake Bay Foundation, 2007). Based on the success of several New Jersey projects along higher energy shorelines, the recommended limit in New Jersey has been raised from 4 ft/yr to 6 ft/yr.

Sea Level Rise

Sills rely on their exposed crest to reduce wave energy on shore. In general, the effectiveness of a sill will be reduced over time as sea level rise gradually reduces the freeboard of the structure. If sea level increases rapidly, eventually the structure may become submerged at which point its ability to reduce wave heights will be reduced significantly. Sea level rise will also allow larger waves to impact the structure and may change the location and characteristics of the breaking waves. These possibilities should be considered during design. It is recommended that the latest sea level rise guidance provided by your state's coastal management agency be used to design marsh sills. As a reference, New Jersey's 2021 guidance recommends using sea level rise estimates associated with the moderate emissions scenario. Depending on the project setting and risk tolerance, values in the low-end to likely range may be appropriate for marsh sills. Engineers should verify the current guidance issued by the relevant state agency prior to applying specific values to a project. Adaptive management should be considered at the design phase, to mitigate any unexpected impacts from sea level rise.

Tidal Range

Sills are generally constructed at sites with a small to moderate tidal range. Sills are intended to be low-crested structures with a freeboard of between 0 and 1 ft above MHW. Wave attenuation is highly dependent on relative crest width and relative freeboard. Recent work by Bredes, et al. (2022) highlighted the variability in wave attenuation characteristics for a sill structure in Delaware Bay with a six-foot tidal range.

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