20151048 Ver 1_Bridge to culvert avoidance SMP_Version2.0_20151013

I Ii�;E71�'�]V North Carolina Department of Transportation � �
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„�- .- Highway Stormwater Program �;'
STORMWATER MANAGEMENT PLAN —'��
(Version 2.02; Released April 2015) FOR NCDOT PROJECTS
WBS Element: 17.BP.14. TIP No.: R.90 County(ies): Graham Page 2 of 2
Bridge to Culvert Avoidance and Minimization
Proposed Structure Summary
Sheet No. & Station Sheet No.: 4 Station: 12+66.58 Number of Culverts: 1
Drainage Area (ac or sq mi): 2.8 Sq. Miles Culvert Width/Diameter (ft : 12
Surface Water Body: 1 Mountain Creek Culvert Height (ft): 4
Culvert T e: Reinforced Concrete Box Culvert Culvert Length ft 69
Avoidance and Minimization Efforts: The length of the culvert was minized to the maximum extent possible given the curve of the roadway and the skew of the stream.
(Bridge to Culvert)
Stream Slope Fish and/or Aquatic Life Passage
Existing Average Stream Slope (°/a): 2.69 % Existing Low Flow Channel Dimensions 10' to 12'
Proposed Culvert Slope (%): 2.�� % in the Stream:
Culvert Burial
Proposed Culvert Burial Depth (ft): 1.5
Existing Streambed Material: sand, gravel with medium boulders Proposed Low Flow Dimensions Low flow sill is in the center of the culvert. The
Through the Culvert: low flow sill is 8' wide.
Proposed Sills/Baffles: A low flow sill is created through the center of the
culvert. This low flow sill is 0.5' lower than the high Existing Low Flow Velocities in the
flow sill. Stream (ft/s): 7'6
ropose ow ow e oci ies roug
the Culvert (fUs): 9'�
Alternating Low Flow Sills/Baffles: The low flow sill is in the center of the culvert
all the way through the culvert. The sill does
not alternate through the culvert.
Culvert/Stream Alignment
Stream Patterns Upstream and Downstream The stream is relatively shallow in normal flow conditions and rocking which may prevent spme fish passage during normal flow.
of the Culvert that Could Affect Fish
Passage and Bank Stability:
Bed Forms Impacted by Culvert (riffles, a small riffle
pools, glides, etc.):
Low Flow Floodplain Bench Required? No No floodplain bench is provided
(provide justification)
Sharp Bends at Inlet/Outlet? No There is a bend (not sharp) just upstream of the inlet of the culvert. The culvert has been placed in alignment with the existing
(describe culvert alignment with stream) stream so that existing flow patterns are maintained.
Stream Realignment Necessary? (provide No The culvert is aligned with the direction of flow in the stream therefore no stream realignment is necessary.
justification)
Bank Stabilization: The only bank stabilization required is riprap at the headwalls of the inlet and outlet of the culvert.
Outlet Velocities
Natural Stream Channel 2-yr Velocity (ft/s): 7.6 Natural Stream Channel 10-yr Velocity (ft/s): 9.6
Proposed Culvert 2-yr Outlet Velocity (ft/s): 9.1 Proposed Culvert 10-yr Outlet Velocity (ft/s): 10.4
Roadway Geometric Considerations
Evaluate/Describe Roadway Geometric Constraints:
The roadway is on a curve at the location of the proposed culvert as well as the stream is not perpendicular to the roadway. This creates a longer culvert than would be necessary if the roadway
was straight and the stream was perpendicular to the roadway.