20090367_Stormwater Plans_20090128

STORMWATER MANAGEMENT PLAN
NCDOT Project 32579 (B-1037) Date: 01/28/09
Ashe County
Bridge No. 39 on US 221 over South Fork New River
Hydraulics Project Manager: Andrew Nottingham, PE
PROJECT DESCRIPTION
The NC Department of Transportation proposes to replace bridge no. 39 with a bridge.
The existing structure is a ten span bridge 462' long with a clear roadway width of 20'.
The proposed structure will be a five span bridge with MBT girders totaling 455' long
with a clear roadway width of 28'. US 221 is a rural major collector route with an 18'
pavement width and 2' grassed shoulders. The proposed typical roadway will have a 22'
pavement width and 4' grassed shoulders (7' shoulders in guardrail areas). Traffic will
be maintained on the existing bridge during the proposed bridge construction. The
existing bridge will be removed upon completion of the proposed bridge. Roadway
improvements will result in an additional impervious area of approximately 8543 square
feet (0.20 acre).
ENVIRONMENTAL DESCRIPTION
The project is located in the New River Basin in the mountainous physiographic
province. The normal depth of South Fork New River at the site is 6.4'. The best usage
classification is B, ORW. The surrounding area is generally mountainous, with natural
ground elevations between approximately 2550 and 2690. The land usage is primarily
agricultural and residential in nature. This portion of the river has been designated as a
Wild and Scenic River and is used for recreation, such as rafting and canoeing.
BEST MANAGEMENT PRACTICES
• The roadway typical section will match the existing roadway section, which consists
of grassed shoulders, fill slopes and grass lined roadway ditches.
• Bridge deck drains will be connected to a closed drainage system and will be
discharged into a hazardous spill basin before discharging into a tributary to the river.
• The hazardous spill basin is approximately 100 feet long, has 3:1 side slopes and is on
a 0.4% slope and will also provide grass swale treatment of the storm water coming
off the bridge.
• The hazardous spill basin and stormwater treatment have been designed to the
maximum extent practicable considering the mountainous terrain and limited area to
provide treatment.