T.F. Green Airport Improvement Program - FEIS Chapters - PVD

T.F. Green Airport Improvement ProgramEnvironmental Impact Statement and Final Section 4(f) Evaluationcentral box would be filled to the stream bottom elevation with river stone to create a natural bottom. With theelimination of the gravel road along the Airport perimeter, this new culvert can be shortened to approximately60 feet (refer to Site 3 below). Flow velocities would be analyzed to ensure river herring can pass through thestructure during spring flows.This culvert would have an openness ratio of approximately 0.5 which exceeds the minimum recommended0.25 ratio recommended for wildlife passage by the USACE. 487 Lakeshore Drive does not have particularlyheavy traffic and most larger mammals will likely continue to cross over the road to reach habitats north ofWarwick Pond. This culvert would also pass the 10-year storm without overtopping the roadway. Since theexisting Lakeshore Drive road profile would be maintained, no additional permanent wetland impacts wouldbe required to complete this mitigation.Mitigation Site 3Site 3 (Figure 6-5) involves removing existing roads built on fill along Buckeye Brook in Wetland A5 to restoreburied wetlands, and enhancing other road segments constructed in shallow fill that are jurisdictional wetlands.These roads were originally constructed for rescue operations when the first Airport runway was oriented in aneast to west direction parallel to Airport Road. These roads no longer serve this purpose and are not essential tosafe airport operations. This plan was prepared by field delineating wetland limits and using instrument surveyto prepare a topographic plan of the road network that was mostly obscured in the aerial survey. Larger treesestablished in the road fill section were also surveyed so they could be preserved on “hummocks” withexcavation activities excluded from the drip lines. Removal of these roads would not only restore theunderlying wetland, but would also restore the wetland’s floodplain function during smaller, more frequentstorms that do not overtop the existing road fill sections.This mitigation site would provide 1.3 acres of wetland restoration through fill removal from the buriedwetland. In addition 0.2 acres of road which consists of partially filled wetland would be enhanced throughre-grading to provide micro-relief followed by seeding and planting with wetland tree species. Compensationfor forested wetland impacts (0.2 acres) would be nearly immediate as the adjacent wetland is forested andwould provide shade and litter inputs immediately upon the mitigation site project completion.In addition, 49 linear feet of Buckeye Brook presently conveyed through culverts would be day-lighted andplaced in constructed stream channels at two locations. Two other existing culverts under the Airport PerimeterRoad would be removed to provide an additional 49 linear feet of open channel. The perimeter fence whichfollows the Airport boundary currently excludes wildlife from approximately 13 acres of forested upland andwetland and scrub-shrub habitat in Wetland A5. Most of this fence would be removed and relocated to the westof this wetland to connect to the Airfield Maintenance Facility (AMF) access road fence. This would greatlyenhance the wildlife function of Wetland A13 and contiguous habitats north of Warwick Pond. One fencesegment is proposed to remain toward the middle of the wetland to limit future extension of fill slopes fromabutting properties.487New England District, U.S. Army Corps of Engineers Regulatory Division Openness Ratio Spreadsheet (1/4/2006)Chapter 6 – Mitigation 6-29 July 2011\\Mawatr\ev\09228.00\reports\FEIS_Final_July_2011\PVD_CH06_Mitigation_JUL_2011.doc