20170566 Ver 1_050047_HYD_SMPv2 07_(20170216) (Oct 2016)_20170522

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I�II�;hWc1y North Carolina Department of Transportation
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STORMWATER MANAGEMENT PLAN �`"'��
(Version 2.07; Released October 2016) FOR NCDOT PROJECTS
WBS Element: 17BP.11.R.173 TIP No.: SF-050047 County(ies): Avery Page 1 of 2
General Project Information
WBS Element: 17BP.11.R.173 TIP Number: SF-050047 Project Type: Bridge Replacement Date: 2/16/2017
NCDOT Contact: Heath Slaughter Contractor / Designer: RK&K Engineers - Corey Cavalier, PE
Address: g01 Statesville Road Address: g00 Ridgefield Drive
North Wilkesboro, NC 28659 Suite 350
Ralei h, NC 27609
Phone: [phone] Phone: [phone]
Email: hslau hter ncdot. ov Email: [e-mail]
Cit ITown: N/A Count ies : Ave
River Basin s: Watau a CAMA County? No
Wetlands within Project Limits? No
Pro'ect Description
Pro'ect Len th lin. miles or feet : 0.047 mi Surrounding Land Use: Rural
Proposed Pro'ect Existin Site
Pro'ect Built-Upon Area ac. 0.1 ac. 0.1 ac.
Typical Cross Section Description: 2-lanes at 9'-0" each with 2'-0" paved shoulder 2-lanes at 8'-0" each with 2'-0" to 6'-0" grassed shoulder
Annual Avg Daily Traffic (veh/hr/day): Desi n/Future: 170 Year: 2012 Existin : 170 Year: 2012
General Project Narrative: This project replaces existing bridge #050047, a 16'-6" single span timber floor on timber joists with timber caps / post and sills, 20'-0" wide out to out. The proposed
(Description of Minimization of Water replacement structure will be a 16'-0"x4'-0" bottomless (3-sided) culvert with wingwalis approximately 49' long along the centerline of culvert. The proposed culvert will have cast
Quality Impacts) in-place concrete footings founded on rock. The footings will be constructed up to the floodplain bench elevation to alleviate constructability issues. The floodplain bench will be
armored along the stream side and within the culvert with Class I riprap while coir fiber matting will be placed along the top outside of the culvert for stability. The proposed
culvert will have 41 LF of inlet improvements and 41 LF of outlet improvements to help stabilize the stream banks and direct the flow into the culvert. There is a slight increase
in the impervious area of the project, however there is no significant increase in the discharge from the roadway runoff. The stormwater runoff is being discharged into a rip rap
bank of the outlet channel improvements associated with the proposed culvert.
Waterbody Information
Surface Water Body (1): Poga Springs (Flat Springs Branch) NCDWR Stream Index No.: 8-20-5
NCDWR Surface Water Classification for Water Body Primary Classification: Class C
Supplemental Classification: Trout Waters (Tr No�e
Other Stream Classification: None
Impairments: None
Aquatic T&E Species? No Comments:
NRTR Stream ID: Buffer Rules in Effect: N/A
Project Includes Bridge Spanning Water Body? No Deck Drains Discharge Over Buffer? No Dissipator Pads Provided in Buffer? N/A
Deck Drains Discharge Over Water Body? No (If yes, provide justification in the General Project Narrative) (If yes, describe in the General Project Narrative; if no, justify in the
(If yes, provide justification in the General Project Narrative) General Project Narrative)

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STORMWATER MANAGEMENT PLAN --�
(Version 2.07; Released October 2016) FOR NCDOT PROJECTS
WBS Element: 17BP.11.R.1 � TIP No.: SF-050047 County(ies): Avery Page 2 of 2
Bridge to Culvert Avoidance and Minimization
Proposed Structure Summary
Sheet No. & Station Sheet No.: 4 Station: -L- 12+08.4 Number of Barrels: 1
Drainage Area (ac or sq mi): 1.4 Sq. Miles Barrel Width/Diameter (ft): 16
Surface Water Body: 1 Po a S rin s Flat Sprin s Branch Barrel Hei ht ft : 4
Culvert T e: Bottomless 3-Sided Culvert Culvert Len th ft 49
Avoidance and Minimization Efforts: The proposed culvert is bottomless to accomodate aquatic passage and wide enough to accomodate normal channel width. The slope is
(Bridge to Culvert) consistent with the existing stream slope and the low flow velocities are minimized. Sills and baffles are not required because the culvert is
bottomless. The length of the Bottomless (3-Sided) Culvert is the minimum required for clear recovery without guardrail that may block flow in
overtopping events and the alignment avoids a significant bend at the inlet.
Stream Slope Fish and/or Aquatic Life Passage
Existing Average Stream Slope (°/a): 6.32 % Existing Low Flow Channel Dimensions 8' wide from BOB to BOB and 2.3' deep. 15'
Proposed Culvert Slope (%): 6.32 % in the Stream: from TOB to TOB with 1.5:1 bank slopes.
Culvert Burial
Proposed Culvert Burial Depth (ft): N/A
Existing Streambed Material: Sand with cobbles and boulders Proposed Low Flow Dimensions 8' wide from BOB to BOB and 0.5'-1.3' deep.
Through the Culvert: 9'-13' from TOB to TOB with 1.5:1 bank slopes.
Proposed Sills/Baffles: N/A Floodplain bench is at top of footing.
Existing Low Flow Velocities in the
Stream (ft/s): 9.33
ropose ow ow e oci ies roug
the Culvert (fUs): 10.73
Alternating Low Flow Sills/Baffles: N/A
Culvert/Stream Alignment
Stream Patterns Upstream and Downstream The culvert lies just downstream of a kink in a generally straight section of stream flowing East - Northeast. There also appears to be a slight pool
of the Culvert that Could Affect Fish at the inlet end of the culvert.
Passage and Bank Stability:
Bed Forms Impacted by Culvert (riffles, A slight pool appears to be located at the inlet end of the culvert, but the rest of the stream seems to hold a fairly constant grade.
pools, glides, etc.):
Low Flow Floodplain Bench Required? Yes Excavation is necessary to the top of the culvert footing. Fill is not possible once the culvert is put in place due to the low
(provide justification) clearance.
Bends at Inlet/Outlet? Yes There is a 56° turn at the culvert inlet. The turn is completed over a distance of approximately 30 to 35 feet.
(describe culvert alignment with stream)
Stream Realignment Necessary? (provide No
justification)
Bank Stabilization: Class I rip rap is used to stabilize the disturbed channel banks up to 41 feet upstream and 41 feet downstream of the culvert.
Outlet Velocities
Natural Stream Channel 2-yr Velocity (ft/s): 6.89 Natural Stream Channel 70-yr Velocity (ft/s): 8.57
Proposed Culvert 2-yr Outlet Velocity (ft/s): 8.3 Proposed Culvert 10-yr Outlet Velocity (ft/s): 12.18
Roadway Geometric Considerations
Evaluate/Describe Roadway Geometric Constraints:
This roadway section closely borders mountains on its northwest and southeast corners.