Select Sill Material. Sand filled bags were chosen because the sill is only needed temporarily
while the vegetation becomes established. The bag material and seams should be ultraviolet resistant. To
insure better bag-to-bag contact, they should be filled to about 75 percent capacity and stacked.
Settlement should not be a problem because the bags are underlain with a suitable filter cloth that
provides a foundation. The splash apron is provided to prevent sand fill from being eroded when a wave
breaks over the sill. Toe protection for the sill is provided by a row of sandbags on the edge of the filter
cloth.
Sand Fill. Medium sand is imported from a nearby site for the beach fill. The sand is intended
to provide a suitable substrate for the vegetation. The sill will retain the sand initially and when it
deteriorates, the vegetation should be able to retain the beach.
Veqetation. Two types of plants are used, smooth cordgrass (Spatina alterniflora) and saltmeadow
cordgrass (Spartina patens). Smooth cordgrass seedlings are planted in the zone between MHW and the
sill at spacings of 1. 5 feet. The saltmeadow cordgrass is planted from above MHW to the toe of the
revetment. Individual sprigs are spaced 3.0 feet apart. Fertilizer is applied at two month intervals from
planting at a rate of 1.25 pounds of 10-10-10 per 100 square feet until the plants are well established
(perhaps 4 applications). Fertilizer may be applied if needed during successive years, especially if there
are signs of plant stress.
Revetment Design. Due to the presence of the perched beach, the originally calculated design
wave height (4.0 feet) no longer applies. A new wave height must be determined with respect to the
perched beach. Using the same design Stillwater level (+3.6 feet MLW), the depth at the sill should be
about 2.5 feet, assuming that the sill is roughly 1.5 feet high. The design wave height (H) is, therefore,
0.8 x 2.5 = 2.0 feet. Gabions are used to form a stepped face revetment. Using Table 4, for a 1 on 1. 5
slope, the expected runup, R = 2. 0 H or 2. 0 x 2. 0 = 4. 0 feet. The proposed design provides more than
enough height (5.4 feet) above the design Stillwater level to accommodate the runup. To construct the
revetment, the existing bluff does not have to be graded to a milder slope; however, some excavation is
needed for the top tier of baskets. The baskets should be PVC-coated and packed tightly with stones at
least four inches in diameter.
Filter Cloth. Two filter cloths are used in the design. The cloth for he sill should be sized to
match the sand fill and insitu bottom material. The filter cloth for the revetment should be sized to retain
the bluff material. To insure continuity, the cloth should have an 18-inch overlap at the seams.
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