The proposed project involved the replacement of the existing structurally deficient two lane, three span bridge carrying S.R. 0533 (Orrstown Road) over the Muddy Run and an unnamed tributary to Muddy Run which meandered under the existing structure. The new structure was designed with two, rather than three, spans. The single center pier in the proposed design intersected the flow of the unnamed tributary, causing the relocation of the unnamed tributary. N&W designed the unnamed tributary relocation, including grading plan (with a low flow channel and elevated floodplain bench), planting plan, cross sections, profile, details, and notes. N&W worked with the Pennsylvania Fish and Boat Commission and the Department of Environmental Protection to develop the typical stream cross section to handle the variable stream hydrology and improve the stream bank stability, including the use of non-woven geotextile and willow plantings. A gravel stream bottom was incorporated into the design of the relocated channel to provide enhanced benthic stratum for the colonization of macroinvertebrates and other epifauna,as compared to the original silt stream bottom. The existing stream channel was backfilled to match existing grade and planted with a wetland seed mix. Compensatory mitigation for the relocation of the unnamed tributary was provided by shrub plantings with a high wildlife value in the floodplain. Additionally, root wads (recycled from necessary cuttings for temporary construction access) were utilized in the main channel of Muddy Run for stream bank stabilization and aquatic habitat improvement.
