Redesign Parkway Drainage along Papermill Creek Watershed
Over the past decade, regional development has led to increases in stormwater runoff within the Papermill Creek watershed. Three areas along the Colonial Parkway (Parkway) within the this watershed have been targeted for drainage.
The Environmental Assessment(EA) analyzes the potential environmental impacts associated with implementing the alternatives in accordance with the National Environmental Policy Act of 1969. the main purpose of these alternatives is to maintain the historic Parkway experience while ensuring the safety of Parkway users and the protections of historic design and construction features.
The three sites are defined as Site A, Site B, and Site C. For each site, two separate action alternatives are presented in addition to the No Action Alternative. Project activities common to all action alternatives are also described.
Alternative 1 – No Action Alternative
No action would be taken to alleviate drainage problems at the three targeted sites in the Papermill Creek Watershed. The recurring flood hazard would lead to continued risks to health and human safety, as well as periodic Parkway closures. As the Williamsburg area continues to experience rapid regional growth, the associated stormwater runoff would continue to cause downstream erosion and sedimentation. Adverse flooding impacts to the Parkway would not be mitigated.
Action alternative: At Site A, the NPS proposes to upgrade the existing culvertry by either: (1)Replacing existing 24-inch Culvert with 30-inch RCP pipe or (2)adding a 24" pipe parallel to the existing pipe.
At site B the existing culvert would be upgraded by either (1) replacing the existing culvert with a CON-SPAN structure or (2)upgrading the culvert system by adding an additional culvert system parallel to the existing pipes.
At Site C, the existing culvert system would be upgraded by installing an additional 24-inch RCP adjacent to the existing culvert. The headwall required for this alternative would be incorporated into the existing brick headwall or offset as another headwall. The installation of the parallel 24-inch RCP would require the removal of the road surface, as well as excavation below the road surface.
Alternative 2- Replace Existing Culvert with 24-inch RCP
The culvert system would be upgraded by replacing the existing 15-inch polyvinyl chloride (PVC) pipe with an upgraded 24-inch RCP. The installation of a 24-inch RCP incorporates an open cut excavation and modifications to the existing brick headwalls, in order to accommodate the new, larger pipe.
The colonial Parkway, a national register road of Colonial National Historical Park, extends over 23 miles and links the three historic sites of Yorktown, Williamsburg and Jamestown in southeastern Virginia.