quick links
SILVER CREEK, BRISTOL  

 

Site History

The creek has three tidal restrictions, two at the mouth of the harbor including a former railroad bridge which is currently the EastBay bikepath and Route 114, and one restriction further upstream - a footpath between Creek Lane and Veteran’s Park. These restrictions have created an impoundment and have allowed for the expansion of Phragmites australis above the third tidal restriction. Further impacts to the marsh include historic filling of both sides of the creek and little to no buffer zone along portions of the marsh.

Save The Bay conducted an analysis of the change in area of the Silver Creek salt marsh over time. Results showed that 55% of the native marsh habitat has been lost since 1939. Phragmites now covers 52% of the marsh, and the expansion of Phragmites has constricted the creek and reduced the open water area by 33%. Since 1939, 15% of the marsh has been filled, however a significant portion of the marsh was likely filled prior to 1939 due to the town landfill. 

Due to chronic flooding problems of Route 114 and surrounding properties, the town of Bristol identified the bridge crossing at Silver Creek as their top priority in their Natural Hazard Mitigation Plan to FEMA. The impoundment at Route 114 prevents the freshwater from flowing into Narragansett Bay thereby flooding the state road, one of two main access roads to the town of Bristol. The town is interested in both restoring the salt marsh and mitigating the flooding problem.


Project Goals

  • Reintroduce tidal flow to the marsh in order to reestablish the native high and low marsh plant communities.
  • Decrease the height and vigor of the invasive plant, Phragmites australis
  • Increase fish and bird use of the marsh.


Restoration Planning

In 1996, Silver Creek was identified as a potential salt marsh restoration site through Save The Bay’s evaluation of the ecological integrity of Narragansett Bay salt marshes.

NRCS has completed a full topographic survey of the Silver Creek salt marsh project area including the area around the first two tidal restrictions. NRCS also set out tide data loggers. The data was used to develop a one-dimensional unsteady state flow model using the hydraulic modeling program HEC-RAS. The output from the model is being used by the project partners to determine the optimal size of the openings at the three restrictions to restore tidal hydrology and to improve freshwater drainage. 

The results of NRCS’ hydrologic model determined that the Route 114 restriction is not as restrictive as the first restriction, the bike path bridge. It also determined that a small rock sill upstream of the bike path bridge restricts water flow out of the marsh. This restriction could be removed more easily than resizing the culverts under the road or bike path. NRCS refined the hydrologic model to analyze the restoration benefits and the flooding improvements or impacts of removing the rock sill and opening up the bike path restriction. Their analysis found that there would be no negative impact to flooding by removing the rock sill or resizing the opening at the first tidal restriction.

NRCS has contracted out a consultant to conduct an assessment of the structural integrity of the second tidal restriction, the Route 114 bridge and to design and permit the rock sill removal. The reason for the additional engineering assessment is the Route 114 bridge could be negatively impacted by the removal of the rock sill just downstream of the bridge. The existing bridge abutments are showing signs of degradation. 

The footpath, the third restriction, restricts tidal flow to the upper marsh. Save The Bay’s pre-restoration monitoring data shows lower soil salinity and greater Phragmites coverage upstream of the tidal restriction. NRCS will redesign the third restriction to improve tidal flow upstream of the restriction and decrease the extent and coverage of Phragmites australis.  

Save The Bay, NRCS and the Town have developed a plan for removal of historic fill from the marsh on the northern side of Thomas Park along Silver Creek. The Town is seeking funding from NRCS for this portion of the project. The majority of Thomas Park is historic fill from the 1950s. The Town, NRCS and Save The Bay have identified an area where fill could be removed from the salt marsh and relocated further inland in Thomas Park.   The Parks and Recreation’s Department received funding from RI Department of Environmental Management’s HistoricalPark grant to restore Thomas Park. A portion of these funds could be used to match the NRCS funds for fill removal. 


Environmental Benefits

Restoring the tidal hydrology and habitat connectivity will result in increased use of the marsh by fish, shellfish, and wading and shorebirds. The Silver Creek salt marsh restoration will result in the reestablishment of native salt marsh plants, a decrease in the invasive plant, Phragmites australis, and increased density and diversity of recreational and commercially important fish species. 


Pre-Restoration Monitoring Results

Save The Bay has developed a pre- and post-restoration monitoring plan for Silver Creek. Save The Bay monitored soil salinity, water table depth, and vegetation of the marsh during the 2004 and 2005 growing seasons. Fish and crab monitoring was conducted in July and September of 2005. Pre-restoration monitoring data confirms that plant and animal communities are significantly impacted by the fill and tidal restrictions. Fish and crab usage of the salt marsh is seriously suppressed by existing conditions. Vegetation monitoring has shown that Phragmites australis covers a very small portion of the marsh downstream of the footpath, but a significant portion of the marsh upstream of the footpath in both 2004 and 2005. Phragmites is common in marshes that have been severely degraded by tidal restrictions and eutrophication. Soils also tend to be fresher and more water logged above the third restriction, the foot path. 

 

Project partners include the Town of Bristol, Natural Resources Conservation Service, NOAA, and RI Department of Transportation.