mta-dot236-2_WinifredNorth_Hydraulics_Memo_Final.pdf

Prepared for:

WESTERN FEDERAL LANDS HIGHWAY DIVISION

610 East Fifth Street, Vancouver, WA 98661

FINAL HYDRAULICS DESIGN

MEMORANDUM

Winifred North

MT FLAP DOT 236(2)

IDIQ Contract No. 69056721D000008 Task Order No. 69056722F00105N

May 2024

Prepared by:

ROBERT PECCIA &

ASSOCIATES

Helena, Montana

Stephen

Robert Peccia and Associates Final Hydraulics Design Memorandum May 2024 i

TABLE OF CONTENTS

1.0 Introduction

2.0 Purpose and Need

3.0 Roadway Characteristics

4.0 Drainage Characteristics

5.0 Existing Major Drainage Structures

6.0 Hydrology

6.1 Drainage Basin Delineation

6.2 Design Flood Frequency

6.3 Drainage Culvert Hydrologic Estimates

7.0 Hydraulic Analysis

8.0 Design Considerations

8.1 Riprap Stabilization

8.2 Impacts

Appendices

Appendix A: Project Map Appendix B: StreamStats Report Appendix C: PN Bridge Road, M.P. 31.64 – Drainage Crossing Hydraulic Analyses

May 2024 ii

ABBREVIATIONS/ACRONYMS

ADT average daily traffic cfs cubic feet per second

CMP corrugated metal pipe

FEMA Federal Emergency Management Agency

FHWA Federal Highway Administration

MDT Montana Department of Transportation

M.P. mile post mph miles per hour

PDDM Project Development and Design Manual

Q2 2-year design flow

Q10 10-year design flow

Q25 25-year design flow

Q50 50-year design flow

Q100 100-year design flow

RCP reinforced concrete pipe

RCPA reinforced concrete pipe arch

RP MDT reference post

RPA Robert Peccia and Associates

S-236 Montana State Secondary Highway 236

SIR Scientific Investigations Report

USGS United States Geological Survey

WFLHD Western Federal Lands Highway Division

May 2024 1

1.0 INTRODUCTION

The Western Federal Lands Highway Division (WFLHD) of the Federal Highway Administration (FHWA), in cooperation with the Montana Department of Transportation (MDT) and Fergus County, is proposing to complete the design documentation for the Winifred North improvement project (MT FLAP DOT 236(2)).

The proposed project actions consist of improvements to subgrade, aggregate surfacing, roadside drainage, signing, and guardrail along Montana State Secondary Highway 236 (S-236). Robert Peccia and Associates (RPA) was selected by FHWA to assist in the development of the project.

The project route consists of 18.6 miles along S-236, also known as the PN Bridge Road, beginning at the US Air Force missile launch facility at MDT reference post (RP) 28.1 and ending at the PN Bridge over the Missouri River at RP 47.8. The PN Bridge Road is located within the Billings District of MDT and is included in the Montana state highway system. However, as it is a gravel-surfaced roadway, Fergus County oversees day-to-day maintenance.

Since MDT reference posts are based on as-built data as well as existing RP sign locations, the resulting values do not always match on-the-ground distances. The location data noted in this report has been calculated to be continuous from the beginning reference/mile post (M.P.) 28.1 to the project end at the Missouri River bridge (M.P. 46.7). The resulting mile post notations will be carried forward to project plans and specifications for ease of construction.

See the vicinity map in Appendix A for the general location of the project.

2.0 PURPOSE AND NEED

The project Culvert Inspection Report, based on field observations taken by RPA during October of 2022, outlined existing drainage patterns and contained general assessments of the condition and performance of all in-place drainage structures. Three major drainage crossings were identified along the project route, all draining an area greater than one square mile and with existing culvert sizes of at least 48 inches in diameter or equivalent.

The purpose of this memorandum is to describe and document the hydraulic analysis at selected drainage crossings within the proposed project limits. Per the outlined scope, all hydrology is based on the United States Geological Survey (USGS) StreamStats program.

No impacts beyond the existing right-of-way limits or road profile adjustments are allowed for the project.

The proposed drainage improvements of this memorandum are limited by these two requirements.

3.0 ROADWAY CHARACTERISTICS

The project Road Log Report outlines the existing road conditions along S-236 based on data collected in October of 2022. The existing gravel-surfaced roadway has an average top width of 28 feet, with numerous locations of minimal gravel and poor subgrade material which can cause difficulty to the traveling public during precipitation events or spring thaw. The proposed roadway configuration, post-construction, is for a 22-foot top width, 5% crown, four to nine inches of additional surface aggregate, areas of subgrade stabilization, and a surface stabilization treatment of calcium chloride.

S-236 is classified as a Major Collector roadway within the State highway system and has a recommended design speed of 50 miles per hour (mph) according to MDT’s geometric design guide, the Baseline Criteria Practitioner’s Guide. The route is an important connection to northern Montana, as it is one of the few

May 2024 2 routes to have a Missouri River bridge crossing within the Upper Missouri River Breaks National Monument area. Sticking to State highway routes, the nearest detour routes that would cross the Missouri River and get back to the project area would be through Big Sandy, either via Denton and Fort Benton or via the Fred Robinson Bridge and Havre.

4.0 DRAINAGE CHARACTERISTICS

The project is located within the Upper Missouri River watershed northwest of Winifred, Montana and situated adjacent to the Dog Creek and Judith River drainages. Surface flow is generally from south/southwest to north/northeast. Intermittent and ephemeral drainages intersecting the roadway are predominantly tributaries of Dog Creek. Dog Creek empties into the Missouri River just downstream of the PN Bridge (project’s terminus). General drainage patterns are depicted in the project map of Appendix A.

From M.P. 28.1 to M.P. 34.5, the roadway is generally adjacent to private agricultural land and conveys flow from numerous intermittent and ephemeral drainages. From M.P. 34.5 to the end of the project, the roadway mostly stays along the dividing ridgeline between the Dog Creek and Judith River drainages, before dropping down to the Missouri River. Numerous drainages have been dammed to create stockponds throughout the project area, both upstream and downstream of the roadway.

The entire project corridor is located within Federal Emergency Management Agency (FEMA) floodplain “Zone D” for unmapped areas.

5.0 EXISTING MAJOR DRAINAGE STRUCTURES

As presented within the project Culvert Inspection Report, three locations were noted as being major drainages in the project area. The locations are noted below:

Major Drainage – Drainage Culverts 48” and Greater:

o M.P. 31.64 – Existing 48” culvert o M.P. 31.94 – Existing 48” culvert o M.P. 32.75 – Existing 24” culvert and 30” overflow culvert

All three locations were reviewed with FHWA, Fergus County, and MDT in May 2023.

The crossing at M.P. 32.75 was recently replaced by Fergus County. The crossing at M.P. 31.94 is under eight to ten feet of embankment, likely making replacement within the existing right-of-way limits infeasible. Both locations also have upstream ponds within the drainage, likely modulating runoff flow to the culverts during typical runoff years. Both the County and MDT thought these features were functioning as intended and did not warrant further hydrologic or hydraulic investigation.

The crossing at M.P. 31.64, however, was determined to be a good candidate for replacement. Runoff has been severely eroding the embankment slopes and could cause roadway failure during a high runoff flow.

In addition, the embankment height at this crossing makes replacement of the culvert within the existing right-of-way feasible and within the project scope. A topographic survey was completed at the M.P. 31.64 drainage crossing in July 2023. The following hydraulic analyses are based on this project data and focus on the design of the M.P. 31.64 crossing replacement.

The existing drainage crossing at M.P. 31.64 consists of one 48-inch diameter corrugated metal pipe (CMP). The culvert has approximately two feet of existing cover and both the inlet and outlet are within three feet of the road shoulder, resulting in near-vertical fill slopes at the culvert. Shoulder erosion, either as a result of high runoff flows inundating the culvert or surface runoff from the roadway, was observed to

May 2024 3 be encroaching on the traveled way. A scour hole, approximately one foot deep, has also developed at the culvert outlet. Fences on either side closely mirror the existing 60-foot right-of-way limit. An underground fiber optic line is located outside the fenceline on the outlet side (east). An overhead power line is situated about 15 feet inside of the existing fenceline on the inlet side (west) but does not have any poles near the culvert itself.

6.0 HYDROLOGY

6.1 DRAINAGE BASIN DELINEATION

The area falls within Montana’s Northeast Plains Hydrologic Region as described in the USGS Scientific Investigation Report (SIR) 2015-5019, otherwise known as Montana StreamStats. The USGS StreamStats application (version 4.16.1) was used to identify and delineate the drainage area contributing flow to the crossing location along S-236 at M.P. 31.64. The delineated drainage basin encompasses 1.1 square miles. Areas of agricultural stockponds exist upstream of the culvert crossing, however, recent aerial imagery shows the damming structures either having failed or purposefully excavated. Therefore, the hydrologic analysis conducted for the drainage basin does not factor in the presence of upstream ponds in flow rate calculations. A map of the delineated drainage basin for the M.P. 31.64 drainage crossing is included in the StreamStats report of Appendix B.

6.2 DESIGN FLOOD FREQUENCY

The project design speed of 50 mph is based on the MDT State highway classification of Major Collector.

The route has a design year average daily traffic (ADT) of less than 400 vehicles per day. MDT traffic counts published for 2022 indicate traffic volumes of between 40 and 160 vehicles per day within the project area. The route is currently signed for a speed limit of 45 mph, with warning signs and advisory speed limits in areas of reduced sight distance or substandard alignment.

The design speed is greater than 45 miles per hour. Therefore, per Section 7.1.6.1 of the FHWA Project Development and Design Manual (PDDM), the roadway is classified as a High-Standard Road, and the resulting design flood frequency is the 50-year event (Q50).

According to Chapter 9 of the MDT Hydraulics Manual, the design flood frequency for an MDT route would be determined based on ADT and the length of potential detour along routes of equal or higher classification. Potential detour routes along paved State routes would all be over 200 miles and would also indicate a Q50 design flood frequency. Gravel routes exist between Winifred and Denton that are considered Major Collectors and would reduce the detour length to approximately 100 miles, which could potentially indicate a 25-year design event (Q25) would be acceptable. However, these routes have similar concerns with the surface conditions under precipitation events and are not considered a reliable detour route. As such, the Q50 design flow is carried forward for this analysis.

6.3 DRAINAGE CULVERT HYDROLOGIC ESTIMATES

Peak discharges for the drainage basin associated with the M.P. 31.64 culvert crossing were determined by the StreamStats program utilizing the USGS Rural Regression Equations (Basin and Climatic Characteristics) as described in Chapter F of USGS SIR 2015-5019. These equations are a valid and accepted method for estimating peak flows for ungaged watersheds in Montana. The variables used in the USGS regression equations include the drainage basin area and the percent of the drainage basin area with an elevation greater than 5,000 feet. Elevations along the drainage basins discussed in this memorandum are all under 5,000 feet. Results of the StreamStats USGS regression equation analysis are

May 2024 4 summarized in Table 1 and included in Appendix B. Peak runoff volumes are shown as cubic feet per second (cfs).

Table 1: USGS Regression Equation Analysis – Hydrologic Peak Flow Summary

Basin M.P.

Existing Culvert Size & Type

Function Drainage

Area

(sq. mi.)

StreamStats, USGS Regression Analysis (cfs)

Q2 Q10 Q25 Q50 Q100

31.64 48”

CMP

Drainage 1.1 8.8 66.3 128.0 197.0 271.0

(Blue designates design flow)

7.0 HYDRAULIC ANALYSIS

The existing drainage structure at the unnamed stream crossing at M.P. 31.64 is a 48-inch diameter CMP that is 30.8 feet long and sloped at 0.57%. The flow capacity of the existing culvert was calculated with HY8 (version 7.80.0.2). This analysis utilized an existing roadway elevation of 3,312.08 feet as the controlling headwater elevation. The controlling headwater elevation corresponds to a low point along the existing road approximately 60 feet south of the existing 48-inch diameter CMP. The calculated flow capacity of the existing 48-inch CMP culvert is 93.6 cfs. This flow rate corresponds to a hydrologic peak flow between the 10-year and 25-year event indicating that the existing roadway will be overtopped prior to the 50-year event design flow. Existing culvert capacity calculations are shown in Appendix C.

Design constraints for a new drainage structure at this location include limited available cover and corrosive soils. Soil corrosivity was tested and documented in the project Final Geotechnical Report. Samples taken along the route indicate resistivity levels around 500 ohm-centimeters. These test results indicate that area soils are highly corrosive to steel and aluminum pipe materials, based on pipe service life calculations in Section 7.3.6 of the PDDM as well as Chapter 11 of the MDT Hydraulics Manual. Given the measured resistivity of the soil samples, only reinforced concrete pipe (RCP) culverts are recommended at the project site. Sulfate testing was not completed for the soil samples.

The profile grade of the existing roadway will not be significantly modified with this project. However, the roadway will be reconditioned to provide a 5% crown prior to aggregate placement, which will likely reduce the elevation of the subgrade by up to six inches at the shoulder. Nine inches of new aggregate surfacing is proposed to be added. The design headwater overtopping elevation for the proposed drainage culvert is set at an elevation of 3,311.44 feet. This elevation is lower than the controlling headwater used to evaluate the existing culvert and corresponds to the new bottom of subgrade at the roadway low point previously noted. With the given constraints, multiple single and double RCP configurations were analyzed with HY8 including both round and arch culvert options.

A single RCP culvert, large enough to convey the 50-year design flow at this drainage crossing, is not possible due to cover limitations. Likewise, a configuration of double round RCPs are not hydraulically adequate to convey the 50-year design flow. Therefore, double 54-inch equivalent diameter reinforced concrete pipe arch (RCPA) culverts are the recommended replacement structures at this location.

The proposed double 54-inch equivalent diameter RCPA culverts are 58 feet long and sloped at 0.74% and 0.79%, with a minimum of 1.4 feet of cover. The capacity of the proposed RCPA culverts is calculated at

205.1 cfs and is adequate to convey the 50-year design flow. The proposed drainage culverts are designed

May 2024 5 in accordance with Chapter 7 of the PDDM and would meet all headwater criteria. The hydraulic analysis of the proposed RCPA culverts is summarized in Appendix C.

8.0 DESIGN CONSIDERATIONS

8.1 RIPRAP STABILIZATION

Headwater depths at the Q50 runoff event would extend above the top of the proposed culverts. In addition, the low point along the roadway is close to the M.P. 31.64 culvert crossing and runoff from the roadway surface itself could concentrate and travel down the embankment slopes in situations where snow deposits along the roadside. Both situations would indicate riprap headwall stabilization may be beneficial for the installation.

The outlet scour hole will need to be filled during construction of the new culvert crossing at M.P. 31.64.

Design flow velocities, however, do not indicate the need for riprap aprons at the inlet or outlet under the proposed configuration.

8.2 IMPACTS

Impacts to right-of-way and utilities are not anticipated. To stay within the existing 60-foot right-of-way limits with the design, the proposed embankment slopes are 2:1. The project Final Geotechnical Report indicates that the recommended fill slope for native soils within the project is 3:1, with 2:1 being the maximum slope recommended. The proposed slopes will predominantly be constructed with Section 704 Backfill Material and will also have riprap stabilization measures.

An underground fiber optic line is located outside the existing fenceline at the M.P. 31.64 culvert crossing, on the outlet side (east), and should be five to ten feet from the proposed excavation limits. From discussions with Triangle Communications, there may also be an abandoned phone line buried just beyond the fenceline. Utility locates will be required prior to starting excavation to verify existing conditions.

No downstream structures were noted during the field visits to the project, so the increased flow capacity of the crossing is unlikely to negatively impact the adjacent landowner. An agricultural stockpond within the intermittent drainage does exist about a half-mile downstream of the crossing.

May 2024 6

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May 2024 1

APPENDIX A: PROJECT MAP

2 1 0 2 4

SCALE IN MILES

ROSE CREEK

MI

SS

OURI

R

IV

ER

M

IS

S O

U R I

R

IV

E R

A R

R O

W C

R E

E K

C O

F F E E C

R E E

K

W O

L F C

R E

E K

J U

D I T

H R I V

E R

DOG CREEK

SALT CREEK

CU

TBAN

K CREEK

TAFFY C

REEK

79 COULEE

B

IR

C H C

R E E K

FLAT CREEK

CHIP COULEE

PN BRIDGE RD

MORRIS LN

DERKS LN PEIRCE LN

LINSE LN

JUDITH RIVER RD

PARADISE RD

ROSE CREEK RD

D Y TRL

SIMAC RDKJORLIEN RD

TUSS LN

BLACKWELDER RD

HEGGEM LN

WHISKEY RIDGE RD

D Y TRL

B E

A R S

P R I N

G S R

D

M U

R P

H Y

L N

SMITH LN

K U

C E

R A

L N

T O

B

IN

L N

P N

B R

ID

G

E R

D

E V

E R

S O

N L

N

K

JO

R L

IE

N R

D

H W

Y W

IN

IF

R

E D

S T

A F F

O R

D F

E R

R Y R

D

LL

OYD

RD

EIGHT MILE BENCH RD

PN BRIDGE RD

O L

D P

N B

R

ID

G E

R D

L

N

H E

L L

E R

R E

P P

E H

IL

L

R D

T H

R

IL

L H

IL

L

S R

D

STULC LN

END PROJECT

BEGIN PROJECT

CLYDES CREEK

FACILITY APPROACH LT

E-11 MISSILE LAUNCH

RIVER BRIDGE

MISSOURI

N

C H

O T

E A

U C

O

B L

A

IN

E C

O

FERGUS CO.

CHOTEAU CO.

FERGUS CO.

BLAINE CO.

109°37'34" W

47°44'14" N

=MDT RP 47.85

M.P. 46.69

109°26'23" W

47°35'01" N

MDT RP 28.09

M.P. 28.09 =

B ig S a n d y

M ile s ± to

H ilg e r

M ile s to

WINIFRED

NATIONAL MONUMENT

UPPER MISSOURI RIVER BREAKS

:0

P

M

N o v e m b e r

V ic in it y M a p

R

P A

-H L

N -0

\S h a re d \h ig h w a y s \F

H W

A \2 m t-a -d o t2

W in if re d

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\R e p o rt s \D e s ig n \H y d ra u li c s \F in a l\ m t-a -d o t2

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CULVERT REPLACEMENT

M.P. 31.64

S-236

PROJECT

NUMBER

SHEET

A.3

MT FLAP DOT 236(2)

8/3/23, 2:32 PM

M.P. 31.64 StreamStats Report

Region ID: MT Workspace ID: MT20230803202906776000 Clicked Point (Latitude, Longitude): 47.59813, -109.49414 Time: 2023-08-03 14:29:30-0600

M.P. 31.64 Culvert Replacement Hydrology

> Basin Characteristics

Parameter Code Parameter Description

StreamStats

Value Unit

CHANWD_RS Channel width determined from remotely sensed data sources, including aerial imagery

CONTDA Area that contributes flow to a point on a stream

EL5000 Percent of area above 5000 ft

WACTCH Width of active channel

WBANKFULL Width of channel at bankfull

General Disclaimers

Upstream regulation was checked for this watershed.

> Peak-Flow Statistics

Peak-Flow Statistics Parameters [NE Plains Region BasinC 2015 5019F)

1.1 feet square miles percent

Parameter Code

CONTDA

EL5000

https://streamstats.usgs.gov/ss/

Parameter Name

Contributing Drainage Area

Percent_above_5000_ft

Value

1.1

Units square miles percent

Min Limit

0.18

Max Limit

30.6

1/2

8/3/23, 2:32 PM StreamStats

Peak-Flow Statistics Flow Report [NE Plains Region BasinC 2015 5019F]

PII: Prediction Interval-Lower, Plu: Prediction Interval-Upper, ASEp: Average Standard Error of Prediction, SE: Standard Error (other --see report)

Statistic Value Unit PII Plu ASEp

66.7-percent AEP flood 5.33 ft•3/s 1.24 23 107

50-percent AEP flood 8.8 ft•3/s 2.29 33.8 95.7

42.9-percent AEP flood 11.7 ft•3/s 3.33 41.1 87.4

20-percent AEP flood 34.1 ft•3/s 13 89.5 62.5

10-percent AEP flood 66.3 ft•3/s 28.7 153 53.1

4-percent AEP flood 128 ft•3/s 58.2 281 49.2

2-percent AEP flood 197 ft•3/s 85.6 426 50.7

1-percent AEP flood 271 ft•3/s 115 637 54.5

0.5-percent AEP flood 369 ft•3/s 147 928 59.6

0.2-percent AEP flood 532 ft•3/s 191 1480 67.3

Peak-Flow Statistics Flow Report [Area-Averaged]

PII: Prediction Interval-Lower, Plu: Prediction Interval-Upper, ASEp: Average Standard Error of Prediction, SE: Standard Error (other --see report)

Statistic Value Unit PII Plu ASEp

66.7-percent AEP flood 5.33 ft'3/s 1.24 23 107

50-percent AEP flood 8.8 ft'3/s 2.29 33.8 95.7

42.9-percent AEP flood 11.7 ft'3/s 3.33 41.1 87.4

20-percent AEP flood 34.1 ft'3/s 13 89.5 62.5

10-percent AEP flood 66.3 ft'3/s 28.7 153 53.1

4-percent AEP flood 128 ft'3/s 58.2 281 49.2

2-percent AEP flood 191 ft'3/s 85.6 426 50.7

1-percent AEP flood 271 ft'3/s 115 637 54.5

0.5-percent AEP flood 369 ft'3/s 147 928 59.6

0.2-percent AEP flood 532 ft'3/s 191 1480 67.3

Peak-Flow Statistics Citations

Sando, Roy, Sando, S.K., McCarthy, P.M., and Dutton, D.M.,2016, Methods for estimating peak-flow frequencies at ungaged sites in

Montana based on data through water year 2011: U.S. Geological Survey Scientific Investigations Report 2015-5019-F, 30 p.

(https://doi.org/10.3133/sir20155019) Chase, K.J., Sando, R., Armstrong, D.W., and McCarthy, P., 2021, Regional regression equations based on channel-width characteristics to estimate peak-flow frequencies at ungaged sites in Montana using peak-flow frequency data through water year

2011 (ver. 1.1, September 2021): U.S. Geological Survey Scientific Investigations Report 2020-5142, 49 p.

(https://doi.org/10.3133/sir20205142)

USGS Data Disclaimer: Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty.

USGS Software Disclaimer: This software has been approved for release by the U.S. Geological Survey (USGS). Although the software has been subjected to rigorous review, the USGS reserves the right to update the software as needed pursuant to further analysis and review. No warranty, expressed or implied, is made by the USGS or the U.S. Government as to the functionality of the software and related material nor shall the fact of release constitute any such warranty. Furthermore, the software is released on condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from its authorized or unauthorized use.

USGS Product Names Disclaimer: Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Application Version: 4.16.1 StreamStats Services Version: 1.2.22 NSS Services Version: 2.2.1 https://streamstats.usgs.gov/ss/ 2/2

Project: Winifred North Project Number: MT FLAP DOT 236(2) By:

Date:

S. Markwardt July 26, 2023

EXISTING CULVERT HYDRAULIC ANALYSIS

FLOWS

Q10 66.3 cfs Q50 197.0 cfs Q100 271.0 cfs

EXISTING CONDITIONS

M.P. 31.64 Area Name Unnamed tributary of Dog Creek Existing Pipe Diameter (in) 48 CMP

PIPE DATA

Inv. In (ft) 3306.51 Inv. Out (ft) 3306.34 Length (ft) 30.79 Slope % 0.57 Skew (deg) 8 LT

ROADWAY DATA / SITE DATA

Overtopping M.P. 31.63 Overtop elevation (ft) 3,312.08 Crest Width (ft) 22 Crest Length (ft) 50 Type Roadway at Sag

OUTLET CHANNEL GEOMETRY

Bottom Width (ft) Irregular channel Channel Slope % -1.47 Lt. Side Slope (_:1) N/A Rt. Side Slope (_:1) N/A Manning's (n) 0.03 Cover

1.82'

Proposed Culvert Capacity per Hy8 Run 93.56 cfs

CMP

CMP CMP

Q50 HW Elev. = 3312.84 Q100 HW Elev. = N/A Q50 HW Depth = 6.33 Q100 HW Depth = N/A D 4.0' D 4.0'

HW/D 1.58 HW/D N/A

Meets Requirements NO Meets Requirements N/A

Notes:

Q50 HW Check Q100 HW Check

HY-8 Culvert Analysis Report Crossing Discharge Data Discharge Selection Method: Specify Minimum, Design, and Maximum Flow

Minimum Flow: 66.30 cfs

Design Flow: 197.00 cfs

Maximum Flow: 271.00 cfs

Table 1 - Summary of Culvert Flows at Crossing: Existing Condition M.P. 31.64 Headwater Elevation (ft)

Total Discharge (cfs)

Ex. 48" CMP Discharge (cfs)

Roadway Discharge (cfs)

Iterations

3310.78 66.30 66.30 0.00 1

3311.68 86.77 86.77 0.00 1

3312.27 107.24 96.60 10.59 8

3312.44 127.71 99.25 28.36 6

3312.57 148.18 101.32 46.72 5

3312.69 168.65 103.11 65.45 4

3312.84 197.00 105.26 91.51 4

3312.90 209.59 106.14 103.38 4

3312.99 230.06 107.47 122.52 4

3313.08 250.53 108.72 141.77 4

3313.17 271.00 109.90 160.90 3

3312.08 93.56 93.56 0.00 Overtopping

Site Data - Ex. 48" CMP Site Data Option: Culvert Invert Data

Inlet Station: 0.00 ft

Inlet Elevation: 3306.51 ft

Outlet Station: 30.79 ft

Outlet Elevation: 3306.34 ft

Number of Barrels: 1

Culvert Data Summary - Ex. 48" CMP Barrel Shape: Circular

Barrel Diameter: 4.00 ft

Barrel Material: Corrugated Steel

Embedment: 0.00 in

Barrel Manning's n: 0.0240

Culvert Type: Straight

Inlet Configuration: Thin Edge Projecting (Ke=0.9)

Inlet Depression: None

Roadway Data for Crossing: Existing Condition M.P. 31.64 Roadway Profile Shape: Constant Roadway Elevation

Crest Length: 50.00 ft

Crest Elevation: 3312.08 ft

Roadway Surface: Gravel

Roadway Top Width: 20.00 ft

Project: Winifred North Project Number: MT FLAP DOT 236(2) By: S. Markwardt Date: November 8, 2023

PROPOSED CULVERT HYDRAULIC ANALYSIS

FLOWS

Q10 66.3 cfs Q50 197.0 cfs Q100 271.0 cfs

PROPOSED CONDITIONS

M.P. 31.64 Area Name BASIN 1 Proposed Pipe Diameter (in) 40 65"x40" RCPA

PIPE DATA

Pipe 1 Pipe 2 FETS FETS

Inv. In (ft) 3307.09 3307.04 Inv. Out (ft) 3306.66 3306.59 Length (ft) * 58.00 58.00 LT RT Slope % 0.74 0.79 Skew (deg) 20 20 LT

* Length includes 8 feet of FETS at inlet and outlet (16 feet total)

ROADWAY DATA / SITE DATA

Overtopping M.P. 31.63 Overtop elevation (ft) 3,311.44 Crest Width (ft) 22 Crest Length (ft) 50 Type Roadway at Sag

OUTLET CHANNEL GEOMETRY

Bottom Width (ft) Irregular channel Channel Slope % -1.47 Lt. Side Slope (_:1) N/A Rt. Side Slope (_:1) N/A Manning's (n) 0.03 Cover

1.39'

Proposed Culvert Capacity per Hy8 Run 205.08 cfs

RCP

RCP RCP

Q50 HW Elev. = 3311.27 Q100 HW Elev. = 3311.92 Q50 HW Depth = 4.18 Q100 HW Depth = 4.83 D 3.3' D 3.3'

HW/D 1.25 HW/D 1.45

Meets Requirements YES Meets Requirements YES

Notes:

Q50 HW Check Q100 HW Check

HY-8 Culvert Analysis Report

Crossing Discharge Data

Discharge Selection Method: Specify Minimum, Design, and Maximum Flow

Minimum Flow: 66.30 cfs

Design Flow: 197.00 cfs

Maximum Flow: 271.00 cfs

Table 1 - Summary of Culvert Flows at Crossing: Proposed Dbl. 54" EQ RCPAs with FETs

Headwater Total 1_Prop 54" 2_Prop 54" Roadway Iterations Elevation Discharge RCPA w / RCPA w / Discharge

(ft) (cfs) FETs FETs (cfs) Discharge Discharge cfs cfs

3308.83 66.30 32.46 33.84

3309.19 86.77 42.71 44.06

3309.55 107.24 52.95 54.29

3309.91 127.71 63.20 64.51

3310.29 148.18 73.46 74.72

3310.69 168.65 83.72 84.93

3311.27 197.00 97.92 99.05

3311.50 209.59 103.33 104.42

3311.67 230.06 107.25 108.31

3311.80 250.53 110.19 111.24

3311.92 271.00 112.71 113.74

3311.44 205.08 101.99 103.09

Site Data - Pipe 1: 54

Equiv. RCPA w/ FETs

Site Data Option: Culvert Invert Data

Inlet Station: 0.00 ft

Inlet Elevation: 3307.09 ft

Outlet Station: 58.00 ft

Outlet Elevation: 3306.66 ft

Number of Barrels: 1

0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.76 14.45 29.05 44.52 0.00

Overtoeeing