A dredge-spoil site of approximately 5 acres (including cobble beach and a dike that surrounded the site), was both a mosquito-breeding area and, due to Phragmites growth, a fire hazard to the nearby houses. Marsh restoration was desirable in order to return the site to salt marsh and salt pond, reduce Phragmites growth, and eliminate mosquito breeding. With cooperation from the U. S. Fish and Wildlife Service, the Rhode Island Office of Mosquito Abatement and the town mosquito-control program, the property owners, the Common Fence Point Improvement Association (CFPIA), set out to restore the marsh.

PROJECT DESCRIPTION

Approximately 21,215 cubic yards of old (45 years+) dredge spoil were removed from 5.1 acres of wet meadow, dike and cobble beach in order to recreate a coastal salt marsh and salt ponds (Table 1 and Figure 1).

1. Tidal Channel and Ponds. A new tidal channel was constructed connecting Mount Hope Bay with two salt ponds within the restored marsh. The channel cut east across the beach at the north end of the site for about 150' from mean sea level to a point where it connects to the main salt pond while turning south for approximately 220 feet to the smaller salt pond. The main salt pond has a surface area of approximately 1/2 acre and the bottom is two feet below mean sea level. The channel connecting the two ponds and the second, smaller pond, also have bottoms at two feet below mean sea level. The smaller pond has a surface area of approximately 1/4th acre.

The salt marsh is graded so that mosquito breeding sites will not develop. The ponds and channels are sufficiently large that mosquito breeding will not occur.

2. Salt Marsh. Approximately 2.6 acres of low and/or high (but excluding tall reed) salt marsh has been created. The marsh surface has been smoothed to a slope varying between 1-to-100 and 1-to-60.

3. Dike. The existing dike was widened to a uniform width of about 40 feet starting from the roads, Montaup Path and the tax assessor's line separating Plat 2 Lot 179 from Plat 8 lot 2. The dike has a maximum elevation of eight feet above MSL or between two and three feet above the road surface. On the north side the dike bends inward slightly to accommodate existing drainage that remains separate from the marsh proper. The dike and mowed area adjacent to the roads take up approximately 1.25 acres.

4. Freshwater Drainage. The runoff from Attleboro Avenue was directed into a sedimentation basin that traps sediment and then allows the water to sheet filter across the marsh surface to the upper pond.

5. Spoil removal. The spoil tested clean and was approved for use as landfill cover by the Division of Waste Management. Over half of the material was removed by the contractor to the Tiverton Landfill, located approximately five miles from the dig site. The remainder was used by the contractor in other projects (the top six to eight inches was skimmed off for such use) and some was used on the dike around the site.

6. Work Period. The work was done between September 1996 and January 1997. Despite heavy rainfall during the construction period, the work went reasonably smoothly. There were no complaints about noise or vehicles coming and going from the site.

7. Vegetative regrowth and Post-dig monitoring. The dike around the marsh will be reseeded to stabilized it. The marsh itself will not be replanted as it is assumed that native salt-marsh plants will recolonize the marsh quickly. The site will be monitored by a team from the University of Rhode Island, led by Dr. Frank Golet, and by the town of Portsmouth Mosquito Control Program. There is money left from the construction phase to do minor work to fine-tune the project. One problem may be Phragmites regrowth. Some herbicide application (by wick to the emerging shoots) may be done.

A primary concern for all was, and is, the possibility that the new marsh will increase the likelihood of flooding during extreme high tides or hurricanes. The site was tested in January, 1997 when a combination of a full-moon tide and winds from the south pushed water over the typical high-high tide (5.0 feet above mean sea level) in Narragansett Bay. There was flooding in Common Fence Point but none of it due to water that came through the restored marsh.

PROJECT FUNDING

This project received local, state and federal funding. Funds from the Rhode Island Mosquito Abatement Grant program were used for the permitting phase. This phase (including the engineering work, mosquito monitoring and plan design and permit application) cost $9,672 plus the cost of advertising for bids and the in-kind service provided by the Portsmouth Finance Office.

Construction-phase funding was received and spent as follows:

Received

Town $1,000 plus support services (Finance Office, etc.)

State $28,000 plus funding for project design and permitting

U.S. Fish & Wildlife $10,000

RI Office of Environmental Coordination $49,000

Total = $88,000

Spent (to 1/20/97)

Contractor $79,899

Engineer $2,500

Christie Mosquito Control $640

Reseeding embankment $250?

Total = $83,289

Remaining unspent funds will be held through the spring of 1997 in case there is a need for additional work or should winter storms cause damage to the marsh before the spring growth can start to stabilize the marsh.

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