Marsh Sill

Sill vs. Natural Marsh This marsh sill with a planted marsh ({em}foreground{/em}) was designed to increase the width and elevation of an existing marsh ({em}background{/em}) for greater protection of the upland bank.

Marsh Sill - Construction (A) The marsh sill construction sequence starts with establishing construction access to the shoreline, then placing filter cloth under the sill. B Burton

Marsh Sill - Construction (B) The next step is sand fill for equipment to work along the shoreline and to set the stone sill in place. B Burton

Marsh Sill - Construction (C) Before tidal marsh planting, allow the sand fill to settle for about 2 weeks and verify the extent of the new high tides and low tides. B Burton

Marsh Sill - Construction (D) The final step in the construction process is planting tidal marsh vegetation in the low and high marsh zones. B Burton

Marsh Sill - Height The height of marsh sills should be near the mean high water elevation to allow for beneficial tidal inundation, drainage, and sediment accretion in the planted tidal marsh. B Burton

... with Planted Marsh

A marsh sill is another type of low-profile 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

Suitable construction materials include granite quarry stone (riprap) or clean broken concrete free of metal and re-bar; broken concrete is best used as core material capped with quarry stone. Avoid asphalt, demolition debris, or other toxic substances
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 match the expected wave climate and the sand fill should be 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 sill is greater than 100 ft. ; tidal gaps can be designed at shoreline turns, offsets, upland drainages, and for recreation access
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