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Living Shorelines: Design Options - Marsh Sill with Planted Marsh

A marsh sill is another type of low-profile stone structure used to contain sand fill to create a new planted marsh where one does not occur naturally.  Marsh sill placement is site-specific depending on bank height and whether bank grading can also be performed, the water depth and bottom type near the shoreline, and the potential for successful marsh vegetation growth.

Suitable Sites

  • Minor upland bank erosion in tidal creeks

  • Failed bulkheads or revetments with lawns

  • Adjacent to graded banks

  • Where plenty of sunlight reaches shoreline without removing a lot of trees

  • Very shallow water extending at least 30 feet offshore with hard sand bottom

  • Where construction access is feasible and navigation will not be interrupted

Guidelines for Marsh Sill

  • Locate near mean low water elevation or landward, determine placement based on level of protection needed and feasibility for bank grading

  • To minimize encroachment, sills should be designed to the needed level of protection elevation and then graded on an average slope (8:1 or 10:1) to the back of the sill

  • The sill should be open ended, it should not tie into the upland bank

  • The height should be near mean high water in low energy settings to allow regular wave overtopping and access for marine organisms

  • The height can be raised 1-2 ft above mean high water in moderate energy settings or where the marsh is less than 15 feet wide and the marsh width cannot be increased. 

  • Strategically place tidal gaps if the total length of marsh toe revetment is greater than 100 ft. ; shoreline turns, offsets, upland drainages, recreation access or geomorphic opportunities can be incorporated as necessary

  • All material stockpiles and equipment storage should be in the upland area

  • Only clean coarse-grained sand fill should be used, no soil amendments are necessary

  • Allow for at least 1-2 weeks of settlement before planting the sand fill area, verify actual tide levels within planting area and adjust slope or height if necessary before planting

Marsh sill vs natural marsh

This marsh sill with a planted marsh (foreground) was designed to increase the width and elevation of an existing marsh (background) for greater protection of the upland bank.
Photo by K. Duhring

Marsh sill before Marsh sill after
Marsh Sill Before Marsh Sill After

This marsh sill project included adding new stone to an existing structure, sand backfill and a planted marsh. This method has effectively prevented upland bank erosion for 15 years with routine planted marsh maintenance by the property owner. 
Photo credits: Marsh Sill Before by B. Roberts, Marsh Sill After by K. Duhring

Marsh sill construction Marsh sill construction 2
(A) Placing filter cloth under the sill (B) sand fill for equipment access and to create a suitable elevation and slope for the planted marsh
Marsh sill construction 3 Marsh sill construction 4
(C) a waiting period to allow the sand to settle and verify where the new mean high water and mean low water elevations are located before planting (D) planting tidal marsh vegetation in the right zones based on actual tidal inundation levels

An example of the marsh sill construction process at Longwood University’s Hull Springs Farm. Photos A, B by B. Burton; C, D by K. Duhring

Marsh sill during storm

The same marsh sill proved how effective this method can be during a Nor’easter storm.  Although the sill and planted marsh were overtopped by storm waves, the wave energy and erosive force was reduced enough that no upland erosion or bank failure occurred like it did before the sill was in place.  Photo by B. Burton

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sill vs natural marsh sill before Marsh sill after Marsh construction Marsh construction Marsh construction continued Marsh construction planting Marsh sill during storm