mt-d202101_DAR2021(1)_G-05_Hydraulics_Memo_SIGNOFF.pdf

Prepared for:

WESTERN FEDERAL LANDS HIGHWAY DIVISION

610 East Fifth Street, Vancouver, WA 98661

HYDRAULICS DESIGN

MEMORANDUM

Defense Access Roads FY 2021, MT DAR 2021(1) IDIQ Contract No. DTFH7015D0007L Task Order No. 69056720F000002

February 2021

Prepared by:

ROBERT PECCIA &

ASSOCIATES

Helena, Montana

Robert Peccia and Associates Hydraulics Design Memorandum February 2021 i

TABLE OF CONTENTS

1.0 Introduction

2.0 This Memorandum

3.0 Drainage Characteristics

4.0 Existing Hydraulic Structures

5.0 Hydrology

5.1 Drainage Basin Delineation

5.2 Design Flood Frequency

5.3 Drainage Culvert Hydrologic Estimates

6.0 Hydraulics

7.0 Conclusion

Appendices

Appendix A: Project Map Appendix B: StreamStats Report Appendix C: G-05 Road M.P. 3.12 – Crossing Hydraulic Analyses

February 2021 ii

ABBREVIATIONS/ACRONYMS

ADT average daily traffic

CMP corrugated metal pipe

DAR Defense Access Roads

FEMA Federal Emergency Management Agency

FHWA Federal Highway Administration

M.P. mile post

PDDM Project Development and Design Manual

Q10 10-year design flow

Q25 25-year design flow

Q50 50-year design flow

RCPA Reinforced Concrete Pipe Arch

RPA Robert Peccia and Associates

SIR Scientific Investigations Report

T-E Transporter – Erector (vehicles)

USAF United States Air Force

USGS United States Geological Survey

WFLHD Western Federal Lands Highway Division

February 2021 1

1.0 INTRODUCTION

The Western Federal Lands Highway Division (WFLHD) of the Federal Highway Administration (FHWA), in cooperation with the US Air Force (USAF) Base at Malmstrom, Montana of the Department of Defense, Cascade County, Teton County, and Lewis and Clark County, is proposing to complete the design documentation for this Defense Access Roads FY 2021 project (MT DAR 2021(1)). The proposed project consists of drainage improvements and re-graveling of the existing Defense Access Roads (DAR) consistent with Transporter-Erector (T-E) Route Standards as agreed upon by the USAF, Counties, and FHWA. Robert Peccia and Associates (RPA) was selected by FHWA to assist in the development of the project.

2.0 THIS MEMORANDUM

The purpose of this memorandum is to investigate possible hydraulic improvement options at an unnamed tributary of Little Muddy Creek crossing on G-05 Road (St. Peter Mission Road) at mile post (M.P.) 3.12.

The memorandum intends to describe and document the hydraulic analysis and potential drainage improvements options.

3.0 DRAINAGE CHARACTERISTICS

The unnamed stream lies in the northwestern portion of Cascade County near the town of Cascade, Montana and is within the Missouri River watershed. St. Peter Mission Road crosses this stream three times before it eventually flows into Little Muddy Creek which empties into the Missouri River halfway between the towns of Cascade, Montana and Ulm, Montana. The DAR route within the drainage basin is as follows and a general vicinity of the project is depicted in Appendix A:

G-05 Road (St. Peter Mission Road)

The drainage characteristics for the project corridor are typical to most routes in central Montana. The area falls within the Northwest Foothills Region as described in the United States Geologic Survey (USGS) Scientific Investigation Report (SIR) 2015-5019-F. Un-forested buttes, open ridges, and rangeland dominate the area, with both gently-graded and relatively steep drainage basins contributing flow to the crossing on G-05 Road at M.P. 3.12.

The unnamed stream is crossed by G-05 Road in three locations. The proposed culvert replacement is in the upper third of the unnamed stream’s drainage basin. The proposed culvert replacement at M.P. 3.12 is the second of the three crossings. The upstream-most crossing on G-05 Road is at M.P. 3.66. The downstream-most crossing of G-05 Road is at M.P. 2.24. The unnamed stream further crosses route G- 03 at M.P. 0.70 before flowing into Little Muddy Creek. At its junction with Little Muddy Creek the unnamed stream flows through a large flat. Little Muddy Creek flows under Interstate 15 prior to emptying into the Missouri River. The entire project corridor is located within Federal Emergency Management Agency (FEMA) floodplain “Zone D” for unmapped areas.

4.0 EXISTING HYDRAULIC STRUCTURES

Existing culvert locations and characteristics were collected for this project in April of 2019 and May 2020 and are presented within the DAR 2020 Culvert Deficiency Report and DAR 2021 Culvert Deficiency Report, respectively. Additionally, a topographic survey was completed at the crossing on G-05 Road at M.P. 3.12 in July 2019. All hydraulic analyses are based off this project data.

February 2021 2

The existing crossing at M.P. 3.12 consists of one 36-inch diameter corrugated metal pipe (CMP). The outlet of the 36-inch CMP is severely corroded. Furthermore, a rock retaining wall constructed above the outlet appears to be deforming the corrosion-weakened pipe barrel.

The upstream-most crossing on G-05 Road is at M.P. 3.66 and is a 48-inch x 80-inch reinforced concrete pipe arch (RCPA) stock pass. This pipe is in fair condition and no actions have been recommended for this pipe. The proposed culvert replacement is at the central crossing at M.P 3.12. The unnamed stream crosses G-05 Road downstream of the proposed pipe replacement at M.P. 2.24 through a 36-inch diameter CMP. This pipe exhibits severe head cutting at the inlet and pipe barrel segments are separating. Repairing and installing an inlet headwall has been proposed for this crossing. Further downstream, the unnamed stream crosses G-03 Road at M.P. 0.70 through two 48-inch diameter CMP’s before flowing into Little Muddy Creek and then the Missouri River. The double 48-inch diameter pipes are too short and are causing fill slope erosion. Both pipes were extended in the MT Defense Access Roads FY 2020 Project (MT DAR 2020(1)).

5.0 HYDROLOGY

5.1 DRAINAGE BASIN DELINEATION

USGS StreamStats v4 was used to identify and delineate drainage areas contributing flow to the crossing location on G-05 Road at M.P. 3.12. The basin delineation resulted in flows that would overtop the crossing at M.P. 3.12 during the 10-year event. An agricultural stock pond exists directly upstream of the M.P. 3.12 crossing. This pond undoubtably truncates peak flows through the delineated basin. Hydrologic analysis conducted on the drainage basin did not factor the presence of the stock pond in flow rate calculations.

Results of the hydrologic calculations and drainage basin delineation maps for M.P. 3.12 are included in Appendix B.

5.2 DESIGN FLOOD FREQUENCY

The project roadway has a design speed lower than 45 miles per hour and an Average Daily Traffic (ADT) lower than 1,500 vehicles per day. From this data, the corridor would generally be classified as a low standard road. However, this section of road is classified as a critical access for the missile launch facilities located along the missile base routes. Therefore, per chapter 7.1.6.1 of the FHWA Project Development and Design Manual (PDDM), the roadway can be classified as a High-Standard Road, and the resulting design flood frequency is the 50-year event.

5.3 DRAINAGE CULVERT HYDROLOGIC ESTIMATES

Peak discharges for the drainage basins associated with M.P. 3.12 were determined by using the USGS Rural Regression Equations (Basin and Climatic Characteristics) as described in the USGS SIR 2015- 5019-F. These equations are the most commonly accepted method for estimating peak flows for large watersheds without gages. The project area is in the Northwest Foothills Region of Montana and the variables used in the USGS equations include the drainage basin area and the mean annual precipitation.

Results of the USGS Rural Regression Equations are summarized in Appendix B.

6.0 HYDRAULICS

The existing structure at the unnamed stream crossing at M.P. 3.12 includes one 36-inch diameter CMP.

The low spot of the existing roadway is located roughly 100 feet prior to the 36-inch diameter CMP. At an

February 2021 3 inlet headwater depth of 3.2 feet, water begins to spread out from the main channel to the east along the route. At an inlet headwater depth of 10.9 feet, corresponding to about a 10-year flood event for the existing 36-inch diameter CMP, G-05 Road is overtopped at the low spot.

Hydraulic design calculations for proposed drainage were completed using the HY-8 Culvert Analysis Program and all proposed culverts are designed in accordance with Chapter 7 of the PDDM. Due to the corrosion and alkali soils noted during the initial field inventory work in April 2019 and May 2020, galvanized steel culverts are not recommended.

During the DAR 2020 Preliminary Field Review in May of 2019, it was proposed to replace the severely corroded and collapsing 36-inch diameter CMP. Hydraulic analysis at the proposed crossing were calculated using the Q10, Q25, and Q50 flow rates. The analysis of the crossing indicated that a 72-inch diameter CMP would pass the Q50 design flow rate and meet WFLHD requirements. Given the height of the fill slopes in this area, meeting minimum cover criteria will not be an issue. Hydraulic analyses are summarized in Appendix C.

7.0 CONCLUSION

Hydrologic analysis was performed for the culvert replacement at M.P. 3.12 on G-05 Road. USGS StreamStats v4 was used to identify and delineate drainage areas contributing flow to the crossing. The hydrologic calculations did not account for a stock pond directly upstream on the crossing and therefore, flow rates are likely conservative.

Hydraulic analysis preformed with the HY-8 Culvert Analysis Program indicate that the existing structure is unable to pass the developed Q50 design flow. Analyses indicated that a single 72-inch CMP would pass the Q50 design flow without alteration of the existing route profile and fit the existing stream channel.

Given the size of this structure and the significant alteration to the existing flow patterns, additional discussion and/or analyses may be needed to address the following concern:

Downstream impacts: The existing crossing may act as a detention device, storing water in the upstream flood plain while metering out flow through the existing pipes. Major drainage improvements will reduce the detention capacity which may impact the downstream crossing at M.P. 2.24 which will remain a 36-inch diameter CMP.

APPENDIX A: PROJECT MAP

APPENDIX B: STREAMSTATS REPORT

8/13/2019 StreamStats https://streamstats.usgs.gov/ss/ 1/3

StreamStats Report

Unedited Watershed

Basin Characteristics

Parameter Code Parameter Description Value Unit

CONTDA Area that contributes flow to a point on a stream 0.6 square miles

PRECIP Mean Annual Precipitation 15.18 inches

General Disclaimers

Upstream regulation was checked for this watershed.

Region ID: MT Workspace ID: MT20190813183647121000 Clicked Point (Latitude, Longitude): 47.32401, -111.85109 Time: 2019-08-13 12:36:36 -0600 https://streamstats.usgs.gov/ss/ 2/3

Peak-Flow Statistics Parameters[NW Foothills Region BasinC 2015 5019F]

Parameter Code Parameter Name Value Units Min Limit Max Limit

CONTDA Contributing Drainage Area 0.6 square miles 0.19 1240

PRECIP Mean Annual Precipitation 15.18 inches 10.1 23.4

Peak-Flow Statistics Flow Report[NW Foothills Region BasinC 2015 5019F]

PIl: Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE:

Standard Error (other -- see report)

Statistic Value Unit PIl PIu SEp

1.5 Year Peak Flood 8.97 ft^3/s 1.66 48.4 123

2 Year Peak Flood 18 ft^3/s 4.57 70.9 92.7

2 33 Year Peak Flood 23.5 ft^3/s 6.5 85 85

5 Year Peak Flood 60.8 ft^3/s 21.8 170 63.8

10 Year Peak Flood 107 ft^3/s 42.4 268 56.4

25 Year Peak Flood 184 ft^3/s 74.3 457 55.2

50 Year Peak Flood 255 ft^3/s 96.9 673 59.1

100 Year Peak Flood 332 ft^3/s 115 962 65.8

200 Year Peak Flood 433 ft^3/s 134 1400 74.8

500 Year Peak Flood 580 ft^3/s 150 2250 89.5

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.

(http://dx.doi.org/10.3133/sir20155019F)

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.

http://dx.doi.org/10.3133/sir20155019F https://streamstats.usgs.gov/ss/ 3/3

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: 4.3.8

APPENDIX C: G-05 ROAD M.P. 3.12 - CROSSING

HYDRAULIC ANALYSES

Project: Defense Access Roads FY 2020 Project Number: DAR 2020(1) By: S. Markwardt Date: September, 2019

EXISTING CULVERT HYDRAULIC ANALYSIS

DESIGN FLOWS

Q10 107.0 cfs Q50 255.0 cfs Q100 332.0 cfs

PROPOSED CONDITIONS

Sta. G-05 Road: M.P. 3.11 Area Name Unnamed tributary of Little Muddy Creek Existing Pipe Rise (in.) 36 (36" dia. CMP)

PIPE DATA

Inv. In (ft) 3828.40 Inv. Out (ft) 3826.06 Length (ft) 56.00 Slope % 4.17 Skew (deg) 0

ROADWAY DATA / SITE DATA

Overtopping Sta. G-05 Road: M.P. 3.00 Overtop elevation (ft) 3839.51 Crest Width (ft) 22 Crest Length (ft) 100 Type Roadway at Sag

OUTLET CHANNEL GEOMETRY

Bottom Width (ft) Channel Slope % 2.7900 Lt. Side Slope (_:1) irregular Rt. Side Slope (_:1) irregular Manning's (n) 0.035

Existing Culvert Capacity per Hy8 Run 91.77 cfs Ex. CMP

Q25 HW Elev. = Q50 HW Elev. = Q25 HW Depth = Q50 HW Depth = D D 1.5D 1.5D Meets Requirements Meets Requirements Notes:

No No

11.22 11.80 3.0' 0.0' 4.5' 0.0'

Q25 HW Check Q50 HW Check Ex. CMP Ex. CMP

3839.62 3840.20

HY-8 Culvert Analysis Report

Table 1 - Summary of Culvert Flows at Crossing: Ex. G-05; M.P. 3.12

Headwater Elevation

(ft) Total Discharge (cfs) Ex. 36 CMP

Discharge (cfs) Roadway Discharge

(cfs) Iterations

3839.62 107.00 92.30 14.35 22

3839.72 129.50 92.74 36.44 6

3839.79 152.00 93.10 58.60 5

3839.86 174.50 93.41 80.96 5

3839.92 197.00 93.68 103.05 4

3839.97 219.50 93.94 125.40 4

3840.02 242.00 94.17 147.74 4

3840.05 255.00 94.30 160.42 3

3840.11 287.00 94.61 191.98 3

3840.16 309.50 94.81 214.48 3

3840.20 332.00 95.01 236.88 3

3839.51 91.77 91.77 0.00 Overtopping

Site Data - Ex. 36 CMP

Site Data Option: Culvert Invert Data

Inlet Station: 0.00 ft

Inlet Elevation: 3828.40 ft

Outlet Station: 55.23 ft

Outlet Elevation: 3826.06 ft

Number of Barrels: 1

Culvert Data Summary - Ex. 36 CMP

Barrel Shape: Circular

Barrel Diameter: 3.00 ft

Barrel Material: Corrugated Steel

Embedment: 0.00 in

Barrel Manning's n: 0.0240

Culvert Type: Straight

Inlet Configuration: Thin Edge Projecting

Inlet Depression: None

Roadway Data for Crossing: Ex. G-05; M.P. 3.12

Roadway Profile Shape: Constant Roadway Elevation

Crest Length: 150.00 ft

Crest Elevation: 3839.51 ft

Roadway Surface: Gravel

Roadway Top Width: 22.00 ft

Project: Defense Access Roads FY 2020 Project Number: DAR 2020(1) By: S. Markwardt Date: September, 2019

PROPOSED CULVERT HYDRAULIC ANALYSIS

DESIGN FLOWS

Q10 107.0 cfs Q50 255.0 cfs Q100 332.0 cfs

PROPOSED CONDITIONS

Sta. G-05 Road: M.P. 3.11 Area Name Unnamed tributary of Little Muddy Creek Proposed Pipe Rise (in) 72 72" CMP

PIPE DATA

Inv. In (ft) 3828.31 Inv. Out (ft) 3824.44 Length (ft) 68.00 Slope % 5.69 Skew (deg) 0

ROADWAY DATA / SITE DATA

Overtopping Sta. G-05 Road: M.P. 3.00 Overtop elevation (ft) 3839.51 Crest Width (ft) 22 Crest Length (ft) 100 Type Roadway at Sag

OUTLET CHANNEL GEOMETRY

Bottom Width (ft) Channel Slope % 2.7900 Lt. Side Slope (_:1) irregular Rt. Side Slope (_:1) irregular Manning's (n) 0.035

Proposed Culvert Capacity per Hy8 Run 339.30 cfs

CMP

Q25 HW Elev. = Q50 HW Elev. = Q25 HW Depth = Q50 HW Depth = D D 1.2D 1.2D Meets Requirements Meets Requirements Notes:

Q25 HW Check Q50 HW Check

CMP CMP

3834.32 3835.38

Yes Yes

6.01 7.07 6.0' 6.0' 7.2' 7.2'

HY-8 Culvert Analysis Report

Table 1 - Summary of Culvert Flows at Crossing: G-05; M.P. 3.12

Site Data - 72-in CMP

Site Data Option: Culvert Invert Data

Inlet Station: 0.00 ft

Inlet Elevation: 3828.31 ft

Outlet Station: 68.00 ft

Outlet Elevation: 3824.44 ft

Number of Barrels: 1

Culvert Data Summary - 72-in CMP

Barrel Shape: Circular

Barrel Diameter: 6.00 ft

Barrel Material: Corrugated Steel

Embedment: 0.00 in

Barrel Manning's n: 0.0240

Culvert Type: Straight

Inlet Configuration: Mitered to Conform to Slope

Inlet Depression: None

Headwater Elevation

(ft) Total Discharge (cfs) 72-in CMP Discharge

(cfs) Roadway Discharge

(cfs) Iterations

3832.64 107.00 107.00 0.00 1

3832.89 118.80 118.80 0.00 1

3833.14 130.60 130.60 0.00 1

3833.39 142.40 142.40 0.00 1

3833.64 154.20 154.20 0.00 1

3833.90 166.00 166.00 0.00 1

3834.17 177.80 177.80 0.00 1

3834.32 184.00 184.00 0.00 1

3834.75 201.40 201.40 0.00 1

3835.06 213.20 213.20 0.00 1

3835.38 225.00 225.00 0.00 1

3839.51 339.30 339.30 0.00 Overtopping

Roadway Data for Crossing: G-05; M.P. 3.12

Roadway Profile Shape: Constant Roadway Elevation

Crest Length: 150.00 ft

Crest Elevation: 3839.51 ft

Roadway Surface: Gravel

Roadway Top Width: 22.00 ft