Attachment 10 - Hydraulics Memo.pdf

FHWA: S. Jurek:3549:JS: 05/20/24: RF: M:\PROJECTS\_FWS\BAKN\100(1)\Techserv\Hydra\Reports CC: Hydraulics, Geotech, Env, HD Engineer, TS Engineer, Bridge

Form FHWA-201 U.S. DEPARTMENT OF TRANSPORTATION (Rev. 11-87) FEDERAL HIGHWAY ADMINISTRATION

MINUTE - MEMO

Use this form in lieu of transmittal slips within Dept. of Trans. when message comment is to be retained as file material. Do not prepare carbons. Not to be used in lieu of Form FHWA-121 for informal correspondence.

SUBJECT: AR FW BLD 11(1) Culvert Memo

TO MESSAGE/COMMENT FROM/DATE

Yanina

Kirtley

Project

Manager

Rachel

Wright

Highway

Design

Manager

We have completed the hydrology and hydraulics for the AR FW BLD 11(1) project. The project involved the replacement of major culvert on MP 3.4 on

Granary South Road (Route 011) within the Bald Knob National Wildlife

Refuge in Searcy, Arkansas. The existing crossing had been identified by the

FWS as a point with frequent overtopping and flooding. The hydraulic analysis was performed using HY-8 version 7.7, which is based on the HDS-

5 (Hydraulic Design of Highway Culvert, Third Edition).

The project is located within a FEMA flood hazard area categorized as Zone

A, which indicates that there are no base flood elevations determined by a detailed study at this location. The area has been designated as a high-risk area with a high incidence of floods by FEMA in their Flood Insurance Rate

Map (FIRM). The FIRM for the site is panel # 05145C0500E.

The flow rates calculated for various return periods are shown in Table 1.

The total contributing drainage area at the site is 323 acres. The drainage area was delineated using Open Road Designer with geo-referenced the

USGS quad maps into the software for the project site. Hydrology is based on the U.S. Geological Survey (USGS) National Streamflow Statistics application, using regression equations developed by USGS. The hydraulic design for the culvert was based on the 25-year design storm according to

Chapter 7 of the Project Development and Design Manual (PDDM). HY-8 version 7.80.0.2 software, which is based on the HDS-5 (Hydraulic Design of Highway Culvert, Third Edition) was used to design the culvert. Scour countermeasure were designed using the Riprap Analysis Hydraulic

Toolbox (V4.4), which is based on HEC-14 (Hydraulic Design of Energy

Dissipators for Culverts and Channels, Third Edition).

Table 1. Design Flow Rates

Station 2-year

(cfs)

10-year

(cfs)

25-year

(cfs)

50-year

(cfs)

100-year

(cfs)

MP 3.4 117 345 496 626 761

Sam Jurek

Hydraulics

Engineer

THROUGH

Wendy Hiciano

Hydraulics Team

Leader

05/20/24

Culvert at MP 3.4 (35°12'35.8"N, 91°34'22.2"W)

Based on the hydraulics analysis and site visit observations, the existing 72 inch culvert does not meet the required capacity during the design storm event. During the site visit on 06/16/2021, there was flood debris found on the road and the subgrade of the road was eroding, both of which are caused by overtopping and frequent flooding.

Recommendations:

We recommend replacing the existing structure with a 8 ft (96”) diameter steel pipe culvert. We also recommend the pipe be lengthened to 50 feet to prevent further erosion and allow for a proper shoulder on the road.

Based on the hydraulic analysis results, the proposed pipe outlet velocity is higher than the downstream channel velocity. Therefore, outlet protection is needed. We recommend installing a

Class 3 Riprap (D50=12”) at the outfall as scour countermeasure with a length of 20 ft, a width of

50 ft at apron end, and a minimum thickness of 2.5 ft. The rirprap apron should follow the bank contours.

Please refer to Attachment 2 for the proposed culvert profile and Attachment 3 for the riprap layout. For a summary of the culvert data, please refer to Table 2.

Table 2. Culvert Parameters

Size Material Inlet El. (ft) Outlet El. (ft) Length (ft)

96” Corrugated Steel Pipe 185.36 184.76 50

The slopes of the banks should be 1V:4H. The required cover for the pipe is 2 feet, which is met with the proposed inlet/outlet elevations. At the shallowest point on the inlet side, the cover between the pipe and the bottom of the road subgrade should be 2 feet.

If you should have any questions or comments, please feel free to contact us.

Attachments

The following attachments can be found in the following folder path:

M:\PROJECTS\_FWS\BAKN\11(1)\Techserv\Hydra\Reports\Culvert Memo Attachments

Attachment 1: Water Surface Profile

Attachment 2: Proposed Culvert Profile

Attachment 3: Riprap Layout

Attachment 4: HYD Toolbox Riprap Analysis file://///fhfl15fileserve.flhd.fhwa.dot.gov/data/PROJECTS/_FWS/BAKN/11(1)/Techserv/Hydra/Reports/Culvert%20Memo%20Attachments

Offset = 25'

Ele. = 184.76'

Proposed invert outlet Offset = 25'

Ele. = 185.36'

Proposed invert inlet

1.19%

Skew =13.68°

Length = 50.00' aluminum pipe culvert

Install 96" x 50' Approx. 20'

Grade to drain

Existing ground

LC

30" Depth

20' Length

Class III

Riprap Apron

Grade to drain

NO. DATE BY REVISIONS

OFFICE OF FEDERAL LANDS HIGHWAY

FEDERAL HIGHWAY ADMINISTRATION

U.S. DEPARTMENT OF TRANSPORTATION

PIPE CULVERT CROSS SECTION

SCHEDULE A

SCALE IN FEET

0 5 10

1:4 1:4

284+34.89

-50 -40 -30 -20 -10 0 10 20 30 40 50 60

140 140

150 150

160 160

170 170

180 180

190 190

200 200

210 210

220 220

1:4

196.12 Des Grade =

195.62 Subgrade =

-4%+4%

-50 -40 -30 -20 -10 0 10 20 30 40 50 60

140 140

150 150

160 160

170 170

180 180

190 190

200 200

210 210

220 220

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DRAINAGE CROSS SECTION

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NUMBER

SHEET

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NPS Drwg No. XXX/XXXX NPS PMIS No. 000000

Not To Scale

ELE

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'AR FW BLD 11(1)

Attachment: Riprap Layout

96" x 50' Pipe Culvert Corrugated Steel

30" Depth 20' Length 55' Width at apron end Class III Riprap Riprap Apron

Hydraulic Analysis Report

Project Data Project Title:

Designer:

Project Date: Monday, May 20, 2024

Project Units: U.S. Customary Units

Notes:

Riprap Analysis: Pipe Outlet - 8ft - USE Notes:

Input Parameters

Riprap Type: Culvert Outlet Protection

Flow: 496 cfs

Culvert Diameter: 8 ft

Normal Depth in Culvert: 7.92 ft

Tailwater Depth: 2.9 ft

If tailwater is unknown, use 0.4D flow is supercritical

Result Parameters

Tailwater Depth Used in Computations: 3.184 ft

Culvert Diameter Used in Computations: 7.96 ft

Computed D50: 288.144 mm

Riprap Class

Riprap shape should be angular

Riprap Class Name:CLASS III

Riprap Class Order:3

The following values are an 'average' of the size fraction range for the selected riprap class.

D100: 609.60 mm

D85: 431.80 mm

D50: 317.50 mm

D15: 228.60 mm

Layout Recommendations

Apron Length: 40 ft

Apron Depth: 2.5 ft

Apron Width (at end): 50.5467 ft

Report for channel

Channel Analysis: Channel Analysis

Notes:

Input Parameters

Channel Type: Custom Cross Section

Cross Section Data

Station (ft Elevation (ft) Manning's n

0.00 190.20 0.0330

12.10 190.00 0.0330

16.79 189.00 0.0330

20.10 188.00 0.0330

33.33 187.00 0.0330

44.38 185.66 0.0330

52.72 185.66 0.0330

57.33 185.66 0.0330

62.91 187.00 0.0330

67.62 188.00 0.0330

69.91 189.00 0.0330

71.30 190.00 0.0330

72.60 191.00 -----

Longitudinal Slope: 0.0060 ft/ft

Flow 496.0000 cfs

Result Parameters

Depth 2.8998 ft

Area of Flow 94.5337 ft^2

Wetted Perimeter 51.2407 ft

Hydraulic Radius 1.8449 ft

Average Velocity 5.2468 ft/s

Top Width 50.6586 ft

Froude Number: 0.6769

Critical Depth 2.4353 ft

Critical Velocity 6.9267 ft/s

Critical Slope: 0.0141 ft/ft

Critical Top Width 48.06 ft

Calculated Max Shear Stress 1.0857 lb/ft^2

Calculated Avg Shear Stress 0.6907 lb/ft^2

Composite Manning's n Equation: Lotter method

Manning's n: 0.0330