20.100 Final Hydraulic Report FLAT.pdf

Wilson Campground Road

NV FTBL 1094(1)

Final Hydraulics Report

Federal Highway Administration, Central Federal Lands Highway Division

May 2025

AtkinsRéalis | NV FTBL 1094(1) Final Hydraulics Report Page i

Certification I hereby certify that this Final Hydraulics Report for Wilson Campground Road, NV FTBL 1094(1), was prepared by me (or under my direct supervision) in accordance with the provisions of the Federal Highway Administration, Office of Federal Lands Highway, Project Development and Design Manual.

Keira Trujillo, P.E.

Registered Professional Engineer

State of Nevada No. 032880

06/30/202606/30/2026

Date: 05/12/2025

AtkinsRéalis | NV FTBL 1094(1) Final Hydraulics Report Page ii

Contents Chapter Page Certification i

1. Introduction

2. Project Background

2.1. Project Location

2.2. Field Reviews

3. Design Discussion

3.1. Design Criteria

3.2. Future Land Use

3.3. Wetlands and Waters of the U.S

3.4. Water Quality

3.5. Cultural Resources

3.6. Existing Structures

4. Hydrology

4.1. Drainage Basins

4.2. Soils

4.3. Flood History

4.4. Hydrology Methodology

5. Recommended Design

5.1. Culverts

5.2. Ditches

6. Summary

7. References

Appendices Appendix A. Resources Appendix B. Hydrology Appendix C. Hydraulics

Tables Table 1: Wilson Campground Road Proposed Culvert Recommendations Table 2: Culvert Replacement Design Recommendations

AtkinsRéalis | NV FTBL 1094(1) Final Hydraulics Report Page iii

Figures Figure 1: Project Limits Figure 2: STA 475+52 Existing Culvert 26 Entrance Figure 3: STA 475+52 Existing Culvert 26 Outlet

AtkinsRéalis | NV FTBL 1094(1) Final Hydraulics Report Page iv

Acronyms BLM Bureau of Land Management CE Categorical Exclusion CFLHD Central Federal Lands Highway Division CLOMR Conditional Letter of Map Revision DEM Digital Elevation Model FEMA Federal Emergency Management Agency FHWA Federal Highway Administration FIRM Flood Insurance Rate Map FLH Federal Lands Highway HDS Hydraulic Design Series HEC Hydraulic Engineering Circular HSG Hydrologic Soil Group HW/D Headwater to Diameter Ratio LOMR Letter of Map Revision NDOT Nevada Department of Transportation NEPA National Environmental Policy Act NOAA National Oceanic and Atmospheric Administration NRCS Natural Resources Conservation Service NWI National Wetland Inventory OHWM Ordinary High Water Marks PDDM Project Development and Design Manual PDP Project Delivery Plan PS&E Plans, Specifications, and Estimates ROW Right-of-Way SOW Scope of Work STA Station USFWS U.S. Fish and Wildlife Service USGS U.S. Geological Survey WOUS Waters of the United States

AtkinsRéalis | NV FTBL 1094(1) Final Hydraulics Report Page 1

1. Introduction The Scope of Work (SOW) for the NV FTBL 1094(1) Wilson Campground Road Project is to perform final design, including roadway and hydraulics and hydrology design, and to provide project management services to deliver a final set of plans, specifications, and estimates (PS&E) to the Federal Highway Administration (FHWA), Central Federal Lands Highway Division (CFLHD) for proposed improvements to approximately nine miles of Wilson Campground Road in Elko County, Nevada.

The purpose of the project is to improve safety, increase visitor usage, and enhance the driving experience.

Reconstruction will include rehabilitation and resurfacing of the aggregate road, addition of pullouts, cleaning and resetting of cattleguards, minor bridge repairs, drainage improvements, and an alignment shift with grading to address existing sight distance deficiencies.

The purpose of this Final Hydraulics Report is to provide hydraulic recommendations for existing and proposed culverts (location and diameter), along with geometry for proposed roadway ditches through the realignment for Wilson Campground Road.

2. Project Background

2.1. Project Location

The Wilson Campground Project is located in north-central Nevada, approximately 83 miles northwest of Elko, Nevada within Elko County as seen in Figure 1, next page. The project is comprised of approximately 7.23 miles of two-lane aggregate surfaced road and 1.89 miles of single lane aggregate surfaced site roads which provide access into and around the Wilson Campground Recreation Area.

2.2. Field Reviews

A Scoping Trip was conducted in Fall of 2021 to assist in the development of the Project Delivery Plan (PDP) for this rehabilitation work. A 30% Field Review occurred in November of 2023.

AtkinsRéalis | NV FTBL 1094(1) Final Hydraulics Report Page 2

Figure 1: Project Limits

Source: Google Earth Imagery (2015)

Wilson Reservoir

NV FTBL 1094(1) End

NV FTBL 1094(1) Begin

Not to Scale

AtkinsRéalis | NV FTBL 1094(1) Final Hydraulics Report Page 3

3. Design Discussion

3.1. Design Criteria

In August 2023, AtkinsRéalis submitted the NV FTBL 1094(1) Wilson Campground Road Hydrologic and Hydraulic Criteria and Computational Methods Memorandum. This memorandum outlined the proposed design criteria and methodologies to be used for the project. Drainage criteria were developed using methods, guidelines, and standards set forth in the Federal Lands Highway (FLH) Project Development and Design Manual (PDDM), FHWA Hydraulic Engineering Circulars (HEC) and Hydraulic Design Series (HDS) publications, and the Nevada Department of Transportation (NDOT) Road Design Guide. For reference, the memorandum is attached in Appendix A.

3.2. Future Land Use

The project scope assumes that no land use analysis or documentation will be required as the proposed project will stay within the existing right-of-way (ROW) and will not increase roadway capacity. The land use designation is not anticipated to change.

3.3. Wetlands and Waters of the U.S.

Waters of the United States (WOUS) are located adjacent to or within the project area. Included is Wilson Reservoir, Sulphur Creek, Wilson Creek Tributaries, and Deep Creek Tributary. Expected impacts are estimated to be 0.005 acres from riprap placed in Sulphur Creek but are considered de minimis. The project is anticipated to qualify under the Clean Water Act Section 4-4 Nationwide Permit 3a-Maintenance (non-notify).

An aquatic resources delineation was conducted on May 23 and 24, 2024 to determine WOUS in the project area.

Two intermittent streams were identified and delineated at their Ordinary High Water Marks (OHWM): Sulphur Creek and Wilson Reservoir Outfall. The field delineation confirmed that there are no other WOUS, including wetlands, in the project area. There are no wetland impacts. Therefore, wetland mitigation is not proposed or anticipated.

CFLHD is the lead federal agency for NEPA. The project is anticipated to qualify as a Categorical Exclusion (CE) under 23 CFR 771.117(c) 22 and 26. BLM will address their own NEPA documentation requirements as needed.

3.4. Water Quality

Notice of Intent for inclusion under the State of Nevada’s Construction Stormwater General Permit (CSGP) NVR1000000 and a Stormwater Pollution Prevention Plan (SWPPP) is required for all soil disturbing activities where one or more acres will be disturbed.

Anticipated approximate disturbance area of Schedule A is 20 acres with an additional 4 acres for Option X;

therefore, the contractor will be required to obtain a CSGP and submit a SWPPP using the NDOT SWPPP Template for Construction Activities.

3.5. Cultural Resources

A cultural resources survey that encompasses the project area has been conducted by BLM. Coordination between BLM and CFLHD will occur to include cultural resources information in the CE.

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3.6. Existing Structures

Minor hydraulics work is anticipated. There are believed to be 36 existing minor culverts (less than 48-inches), filled with sediment and debris. Neither Elko County nor the Bureau of Land Management (BLM) noted history of flooding or request culvert replacement; therefore, it is recommended that existing culverts be replaced in kind with minimum 24” equivalent CMP or cleared of debris and flared end sections be added upstream and downstream.

The sedimented Culvert 26 entrance and damaged outlet near STA 475+52 are shown in Figure 2 and Figure 3, which provide examples of conditions requiring improvements based on field investigations. See Appendix A for a surveyed culvert inventory with locations and pictures, along with pictures from the Fall 2021 Scoping Trip.

Figure 2: STA 475+52 Existing Culvert 26 Entrance

Figure 3: STA 475+52 Existing Culvert 26 Outlet

There are no known storm drains within the project area. It is anticipated that local drainage conveyance will be through existing roadside swales.

4. Hydrology

4.1. Drainage Basins

Using 20-foot contours from the U.S. Geological Survey (USGS) quad maps, Light Detection and Ranging (LiDAR) Data provided by BLM, Google Earth software, and field survey conducted in June 2023, eight watershed basin delineations were prepared. Basin elevations varied from approximately 5,337 feet to 5,590 feet. Basin sizes ranged from 0.96 acres to 1907 acres. Basin flow lengths, discharge points, and slopes were estimated from survey and USGS topographic mapping. Estimates of land use were determined from aerial photos in Google Earth and the Fall 2021 field review. Areas not delineated drain to existing ditches or culverts that are not expected to require improvements; therefore, not analyzed as part of this project. A basin map is provided in Appendix B.

AtkinsRéalis | NV FTBL 1094(1) Final Hydraulics Report Page 5

4.2. Soils

Soil types for the project area have been determined using the Natural Resources Conservation Service (NRCS) Soil Survey. Based on NRCS, the project area contains soils of hydrologic soil group (HSG) Type C and D, primarily silty and cobbly loam. This indicates soil type varying by location in the project area and will be considered basin by basin. Soils will range from low infiltration rate and high runoff potential to high infiltration rate and low runoff potential (NRCS, 2020).

Type C sandy clay loam soils have low infiltration rates when thoroughly wetted and impede downward movement of water. Type D soil type includes clay loam, silty clay loam, sandy clay, silty clay, or clay. This type of soil has very low infiltration rates and high runoff potential (NRCS).

4.3. Flood History

Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM) Panels 32007C1475E (effective 9/4/2013) and 32007C2100E (effective 9/4/2013) encompass the Wilson Campground Road Project. The project area is located within Zone X as shown on the attached FIRM Panels. Zone X indicate areas determined to be outside the 0.2% annual chance floodplain. FEMA permitting and the associated coordination with a local floodplain administrator are not needed. The FEMA documentation is in Appendix A, in the NV FTBL 1094(1) Wilson Campground Road Hydrologic and Hydraulic Criteria and Computational Methods Memorandum.

4.4. Hydrology Methodology

Peak flows were calculated only for proposed ditches, the proposed culvert near STA 497+00, and the 48” culvert replacement near STA 179+00. All other existing features were not analyzed and are expected to continue to perform as in existing conditions.

Peak flows for offsite areas greater than 200 acres in size were calculated using regression equations with guidance from USGS publications for estimating rural and urban flood-frequency statistics, such as the 100-year flood. The Rational Method was used to determine all local runoff and onsite peak flows less than 200 acres in size. Regression and rational method calculations are provided in Appendix B.

Rainfall data from National Oceanic and Atmospheric Administration Atlas 14 was used when determining peak runoff flows. A copy of the point precipitation depths and intensities used for this project are provided in Appendix A.

Basins were analyzed for the 10-, 25-, and 100-year storm events. Proposed roadside ditches were designed to the 10-year storm event, and cross culverts were designed to the 25-year storm events. Both drainage features were checked for the 100-year storm event.

Calculations represent existing and proposed flows as proposed improvements do not alter hydrologic conditions.

Basin characteristic input values required for intensity and peak flow calculation methodology presented in HDS 2 include Manning’s Roughness Coefficient (n), Intercept Coefficient (k), and Runoff Coefficient (C). Values were determined using Table 2.1 and Table 2.2 from HDS 2, as shown in Appendix B. The project area soil data indicate sandy/heavy soils of flat to steep slope resulting in a C value range of 0.25-0.35. The project area contains primarily short grass pasture, indicating a k value of 0.213 and an n value range of 0.15 for sheetflow and 0.025 for channelized flow. Drainage areas delineated correlate to potential proposed culverts or ditches. Drainage basin maps are presented in Appendix B, along with peak flow calculations. Peak flows are displayed in Table 1.

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Table 1. Basin Peak Flows

Basin ID Methodology Basin Area

(ac) 10-Year (cfs) 25-Year (cfs) 100-Year (cfs)

DA-D-178 Rational 0.96 0.50 0.60 1.00

DA-C-179 Regression 1907.00 66.57 88.24 121.49

DA-D-182 Rational 23.08 8.30 11.00 16.40

DA-D-294 Rational 1.55 0.50 0.60 0.90

DA-D-393 Rational 21.35 4.50 6.00 9.00

DA-D-410 Rational 12.78 4.40 5.90 8.80

DA-D-428 Rational 32.80 9.90 13.20 19.60

DA-C-497 Rational 21.93 7.60 10.20 15.20

5. Recommended Design Within the limits of Wilson Campground Road, recommendations consist of one proposed cross culvert, 19 culvert replacements, one approach culvert, cleaning and installation of flared end sections to existing culverts as called out in the plans, and ditch reconditioning. Areas within the campground experience sheet or shallow flow crossing the existing road. Formalized crossings were not deemed appropriate to the project goals by the project team due to flat grade and minimal existing erosion. Proposed roadway grading will ensure a cross slope to encourage drainage toward the reservoir and reduce ponding within the campground area, improving overall drainage conditions. These recommendations are based on field observation, photographs, and survey.

5.1. Culverts

Aquaveo’s HY-8 culvert hydraulic analysis software was used to analyze the proposed culvert and one culvert replacement. All other replacements were not analyzed as they had significantly smaller contribution areas, and there is no known history of drainage issues or overtopping at these locations. Culvert replacements will be upsized to 24” or 24” equivalent CMP at a minimum and include flared end sections. Headwater to Diameter Ratio (HW/D) of <1.5 is used as a design consideration to ensure the water depth does not exceed the height of the culvert by more than is allowed by Hydraulic Criteria in Appendix A.2.

Culvert recommendations are presented in Table 1 and Table 2. HY-8 results can be found in Appendix C.

Culvert C-10 is a culvert replacement but was treated as proposed due to the larger pipe size. Culvert C-10 includes flared end sections and outlet protection designed to FLH Detail C251-50, at a minimum as designated on the plans. Culvert C-27 includes flared end sections and outlet protection in the form of typical riprap designed to FLH Detail C251-50, at a minimum as designated on the plans.

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Table 1: Wilson Campground Road Proposed Culvert Recommendations

ID STA Q25

(cfs)

Size (in)

Length (ft)

Slope

Inv In (ft)

Inv out (ft)

HW

(ft)

HW/D

(ft/ft)

Velocity (fps)

C-10 179+72 88.24 48 34 3.82 5389.57 5388.29 5.02 1.26 11.90 C-27A 497+45 10.20 28x20 30 1.96 5314.43 5313.84 1.53 0.92 5.41

All culvert replacements shall be installed with flared end sections and riprap as shown on the plans. All culverts must be placed with a positive slope of at least 0.30% and cover of 1-ft to adhere to criteria. Various existing culvert conditions could not be field verified due to sediment build-up within the culvert. These locations have been assumed to need the existing culvert replaced. The CO can work with the contractor to decide if cleaning the existing culvert is a potential option instead of replacing the culvert.

Table 2: Culvert Replacement Design Recommendations

ID STA Size (Inch)

C-1 110+95 28x20 C-5 141+56 28x20 C-6 150+51 28x20

C-11A 190+63 28x20 C-13 342+27 28x20 C-14 348+62 24

C-14A 358+54 28x20 C-15 365+12 24 C-16 372+94 28x20 C-17 377+54 28x20 C-18 383+52 28x20 C-19 396+55 28x20 C-20 402+54 28x20 C-21 412+43 24 C-22 428+84 28x20 C-25 455+18 24 C-26 475+52 28x20 C-28 513+28 28x20

One approach culvert is proposed at STA 497+75 as shown in the plans. At a minimum, all existing culverts within project limits that are not being recommended for replacement shall be cleaned, removing all sediment and adding flared end sections to both the upstream and downstream ends. Riprap is recommended on existing culvert exits only where there is current evidence of erosion as designated on the plans. Locations of riprap recommendations were based on field observations during the 30% Field Review. Existing culverts were assumed to be functioning and sized appropriately as there is no history of overtopping or drainage related issues in areas not discussed in this report; therefore, existing culverts were not analyzed. Overall drainage recommendations will maintain existing drainage patterns.

AtkinsRéalis | NV FTBL 1094(1) Final Hydraulics Report Page 8

5.2. Ditches

There are two proposed ditches and four existing ditches recommended for ditch reconditioning. All other existing ditches were not analyzed as there is no known history of flooding or overtopping, and survey suggests successful positive drainage.

Hydraulic Toolbox was used to analyze proposed ditch geometries. Proposed ditch reconditioning was designed as 1.8-ft deep triangular ditches with 1:3 (V:H) foreslope and 1:2 backslope at the steepest, and longitudinal slope matching the roadway profile. Proposed ditches will adjust grade near proposed culvert inlets to match invert elevations. Ditch reconditioning will consist of cleaning debris and grading existing ditches for positive drainage.

The proposed ditch at approximately STA 182+95 was calculated to experience higher shear stresses that may warrant channel lining. However, the existing ditch at this location has near identical contributing basin and ditch geometry to proposed and there was no evidence of erosion in this area during the 30% Field Visit. BLM indicated that they do not desire permanent ditch lining in the area to maintain natural landscape and prevent obstructions within clearzone. For these reasons, AtkinsRéalis and partners have decided biodegradable temporary ditch stabilization as called out on the plans will be sufficient to allow vegetation to re-establish and return to existing conditions, to be maintained in the future as necessary.

A proposed ditch summary and calculations are in Appendix C.

6. Summary Within the limits of Wilson Campground Road, recommendations consist of one proposed cross culvert, 19 culvert replacements, one approach culvert, two proposed ditches, and ditch reconditioning. These recommendations are based on field observation, photographs, and survey.

Additional drainage recommendations include adding flared end sections and riprap aprons to existing minor culverts (equal to or less than 48 inches) as shown in the plans.

This Final Hydraulics Report was prepared in accordance with the methods, guidelines, and criteria set forth in the Federal Lands Highway PDDM, FHWA HEC and HDS publications, and the NDOT Road Design Guide.

AtkinsRéalis | NV FTBL 1094(1) Final Hydraulics Report Page 9

7. References Atkins North America, Inc. (AtkinsRéalis, formerly Atkins). (2023). NV FTBL 1094(1) Wilson Campground Road

Hydrologic and Hydraulic Criteria and Computational Methods Memorandum. Denver, CO: AtkinsRéalis.

Atkins North America, Inc. (AtkinsRéalis, formerly Atkins). (2022). NV FTBL 1094(1) Wilson Campground Road Scoping Report. Denver, CO: AtkinsRéalis.

Federal Highway Administration (FHWA). (2002). HDS 2: Highway Hydrology. Washington, DC: FHWA.

FHWA. (2015). Aquaveo Hydraulic Toolbox 4.4. Washington, DC: FHWA.

FHWA. (2019). Aquaveo HY-8 Version 7.60. Washington, DC: FHWA.

FHWA. (2014). Standard Detail C251-50. Washington, DC: FHWA.

FHWA. (2014). Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects (FP-

14). Washington, DC: FHWA.

Federal Highway Administration, Office of Federal Lands Highway. (2012). Project Development and Design

Manual. Washington, DC: FHWA.

Federal Emergency Management Agency (FEMA). (2013). Flood Insurance Rate Map Elko County, Nevada FIRM 32007C2100E. Washington, DC: FEMA

Federal Emergency Management Agency (FEMA). (2013). Flood Insurance Rate Map Elko County, Nevada FIRM 32007C1475E. Washington, DC: FEMA

U.S. Department of the Interior. (1997). Methods for Estimating Magnitude and Frequency of Floods in the Southwestern United States. Prepared by the U.S. Geological Survey.

National Oceanic and Atmospheric Administration. (2023). NOAA Atlas 14, Volume I, Version 5, Nevada, Precipitation-Frequency Estimates. Washington, DC: NOAA.

Natural Resources Conservation Service. (2022). Web Soil Survey. Washington, DC: NRCS.

Nevada Department of Transportation. (2006). Drainage Manual. Nevada: NDOT.

Nevada Department of Transportation. (2019). Road Design Guide. Nevada: NDOT.

Appendices

AtkinsRéalis | NV FTBL 1094(1) Final Hydraulics Report

Appendix A. Resources

A.1. Culvert Inventory

A.2. Hydrologic and Hydraulic Criteria and Computational Methods Memorandum

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*'�� D �+ D

W ils on C am pg ro un d R oa d

En d

Pr oj ec t

Sc he du le

A

W ils on C am pg ro un d R oa d

Be gi n Pr oj ec t Sc he du le A

W ils on C am pg ro un d R oa d

Appendix B. Hydrology

B.1. Drainage Maps

So ur ce s:

D _W

G S_

, 1 5m

T er ra C ol or

W or ld Im ag er y

7/

/2

T

R U

J4

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:\K ei ra T ru jil lo \C

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4( 1)

Le ge nd Ex is tin g C ul ve rt M od ify

E xi st in g C ul ve rt Pr op os ed C ul ve rt R ep la ce E xi st in g

C ul ve rt

D ra in ag e A re a

Fl ow

A rro w

W ils on C am pg ro un d R oa d

D ra in ag e Ar ea s

CE

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RA

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DA

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DA

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DA

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.9 ce s:

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8/ 1/

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4( 1)

Le ge nd Ex is tin g C ul ve rt M od ify

E xi st in g C ul ve rt Pr op os ed C ul ve rt R ep la ce E xi st in g

C ul ve rt

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Fl ow

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W ils on C am pg ro un d R oa d

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CE

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(a c)

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1.

ce s:

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, 1 5m

T er ra C ol or

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8/ 1/

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4( 1)

Le ge nd Ex is tin g C ul ve rt M od ify

E xi st in g C ul ve rt Pr op os ed C ul ve rt R ep la ce E xi st in g

C ul ve rt

D ra in ag e A re a

Fl ow

A rro w

W ils on C am pg ro un d R oa d

D ra in ag e Ar ea s

CE

NT

RA

L

FE

DE

RA

L

LA

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HI

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AY

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-D

-4

ID

A re a

(a c)

DA

-D -3

.3

DA

-D -4

.7

DA

-D -4

.8 ce s:

D _W

G S_

, 1 5m

T er ra C ol or

W or ld Im ag er y

8/ 1/

T R

U J4

Y :\K ei ra

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G

IS

\D A

_E xh ib it0

4.

m xd

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1, Fe et

N V

FT

BL

4( 1)

Le ge nd Ex is tin g C ul ve rt M od ify

E xi st in g C ul ve rt Pr op os ed C ul ve rt R ep la ce E xi st in g

C ul ve rt

D ra in ag e A re a

Fl ow

A rro w

W ils on C am pg ro un d R oa d

D ra in ag e Ar ea s

CE

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L

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L

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D

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N

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-4

ID

A re a

(a c)

DA

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B.2. Rational Method

- 1 0Y

R

YR

0Y R

B.3. Regression Method

Re gr es sio n Ca lcu la tio n

Ba si n

ID

Ar ea

(a c)

Ar ea

(s q.

m i.)

M ea n El ev at io n

(ft

-y r

-y r

0-yr

DA

-C

-1

2.

.5

.2

1.

Pe ak

F lo w s

(c fs

Appendix C. Hydraulics

C.1. Culvert Analysis

C.2. Ditch Analysis yr