20170343 Ver 1_Bridge 990259 Yancey SMP_20170324

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Highway Stormwater Program
„ STORMWATER MANAGEMENT PLAN p``',•�':=�
(Version 2.04; Released November 2015) FOR NCDOT PROJECTS
WBS Element: 17.BP.13.R.9 TIP No.: 990259 County(ies): Yancey Page 3 of 3
Bridge to Culvert Avoidance and Minimization
Proposed Structure Summary
Sheet No. & Station Sheet No.: 4 Station: 13+03.9 Number of Barrels: 2
Drainage Area (ac or sq mi): 1 Sq. Miles Barrel Width/Diameter (ft): 7
Surface Water Body: 1 Baile Branch Barrel Height (ft : 5
Culvert T e: RCBC Culvert Length ft 46
Avoidance and Minimization Efforts: Bridge Replacement of Structure 990259 with DBL 7' x 5' RCBC. 50 LF of downstream and 40 LF of upstream channel improvements are
(Bridge to Culvert) proposed. Limiting Riprap Embankments to above Ordinary High Water will minimize stream impacts. Rock Cross Vanes will be used. The
existing stream bed slope will be maintained. Proposed low flow channel has similar geometry to existing. Culverts will be buried 1'.
Stream Slope Fish and/or Aquatic Life Passage
Existing Average Stream Slope (°/a): 4.90 % Existing Low Flow Channel Dimensions 5' Wide (WE to WE); Normal Depth = 0.5' -
Proposed Culvert Slope (%): 4.90 % in the Stream: 0.8'; Banks are 2' - 4' High
Culvert Burial
Proposed Culvert Burial Depth (ft): 1
Existing Streambed Material: Silt & Cobbles Proposed Low Flow Dimensions 5' - 7' wide; 0.5' High
Through the Culvert:
Proposed Sills/Baffles: Low flow sills = 1.0'; High flow sills = 1.5'; Sills placed
at inlet and outlet of both barrels with an additional sill Existing Low Flow Velocities in the
at the centerline of the low flow barrel. Stream (ft/s): 3
ropose ow ow e oci ies roug
the Culvert (fUs): 3
Alternating Low Flow Sills/Baffles: Yes
Culvert/Stream Alignment
Stream Patterns Upstream and Downstream Stream runs parallel to road embankment upstream and downstream
of the Culvert that Could Affect Fish
Passage and Bank Stability:
Bed Forms Impacted by Culvert (riffles, N/A
pools, glides, etc.):
Low Flow Floodplain Bench Required? No High Flow Bench provided
(provide justification)
Sharp Bends at Inlet/Outlet? Yes Stream runs parallel to road embankment upstream and downstream
(describe culvert alignment with stream)
Stream Realignment Necessary? (provide No
justification)
Bank Stabilization: Bank stabilization required 40 LF upstream & 50 LF downstream
Outlet Velocities
Natural Stream Channel 2-yr Velocity (ft/s): 7.2 Natural Stream Channel 10-yr Velocity (ft/s): 8.2
Proposed Culvert 2-yr Outlet Velocity (ft/s): 7.3 Proposed Culvert 10-yr Outlet Velocity (ft/s): 11.5
Roadway Geometric Considerations
Evaluate/Describe Roadway Geometric Constraints:
Combination of topographic constraints & existing buildings located within NCDOT ROW limited the roadway and culvert design. Staged construction required.