20210589 Ver 1_Scientific Street Bridge to Culvert Justification_20210423

17BP.7.R.114
40 — GUILFORD Br# 400052
SR1332 S Scientific St.
BRANCH
The project consists of replacing 33-foot-long Structurally Deficient Bridge that has a Sufficiency Rating
of 17 in Guilford County. The current structure was metal deck on I-beams setting on concrete
abutments. The Deck, Superstructure and Substructure all have a grade of 4. This makes every
component of the bridge Deficient therefore, the immediate need for replacement.
The proposed structure consists of a 2 @ 12' X 10' Reinforced Concrete Box Culvert. This structure
meets the hydrological requirements of the drainage area and matches or reduces upstream backwater
in all events analyzed including the 100 Year event for FEMA compliance. The proposed culvert will
function similarly to that of the existing bridge, which consists of concrete vertical abutments and long
wingwalls. The existing stream also approaches the upstream side of the bridge at a sharp skew with
some locations of bank erosion. The culvert option proposes to better align the stream and allow the
banks to stabilize. Smaller streams in the Piedmont area are often best suited for culverts to minimize
raising the roadway grade.
Justification for bridge to culvert:
• The basin drainage area and estimated discharges are compatible with a culvert structure. And
as mentioned, typically prefer culverts due to longer service life and reduced maintenance vs a
bridge.
• The proposed culvert and existing bridge (with vertical concrete abutments) have similar
hydraulic type openings and properties. Hydraulic function including backwater, outlet
velocities, etc will remain similar.
• The outlet channel looks stable. The upstream, inlet channel has some erosion on the south
bank. We would anticipate the culvert will allow the outlet channel to remain stable as well as
improve upstream bank stability.
fE