BRIDGE FEASIBILITY STUDY

PEDESTRIAN CROSSING OF THE 

HENRY’S FORK OF THE SNAKE RIVER

St. Anthony, ID 

July 2019 

Prepared by: Western Federal Lands 

Highway Division (Vancouver, WA)
(page intentionally blank)
To: Project File, FHWA, WFLHD, 7/17/2019 

1. INTRODUCTION 

The City of St. Anthony, ID and Bureau of Land Management have a shared interest to improve 

access to recreational activities along the Henry’s Fork of the Salmon River near St. Anthony, ID. 

These activities include hiking, biking, birdwatching, hunting, fishing, and many more. 

The ultimate goals of the project are to improve public safety and provide better access and usage 

of the Henry’s Fork Greenway and adjacent public lands. Specifically, this report will focus on 

options to cross all or portions of the Henry’s Fork of the Snake River with a pedestrian bridge(s) 

downstream of St. Anthony, ID. 

2. BACKGROUND

The Henry’s Fork Greenway is located on the Henry’s Fork River just downstream (southwest) of 

St. Anthony, ID (see Figure 1). The Greenway is located on the north and the south side of the 

river, and there are pedestrian trails on both sides of the river. However, there is not a safe and 

legal way to cross the river. Some people use the railroad bridge at the southwest end of the 

planning area to cross the river, but it is owned by the Eastern Idaho Railroad (EIRR) and is not 

currently intended for pedestrian use. 

The City of St. Anthony and the BLM applied for funding for a planning study in the 2017 Idaho 

Federal Lands Access Program (FLAP) Call for Projects. The Henry’s Fork Greenway project was 

selected for funding with the purpose of completing a pedestrian bridge feasibility study to 

examine bridge crossing options and determine potential funding sources. 

Federal Highway Administration-Western Federal Lands Highway Division is providing project 

management and technical staff to produce this Bridge Feasibility Study and an associated 

Implementation/Funding Plan.

3. SUMMARY OF OPTIONS 

The project team, consisting of staff from City of St. Anthony, BLM and FHWA, performed a site 

visit of the St. Anthony Greenway Project area September 11th through 13th. The team reviewed 

both sides of the river from the city of St. Anthony to the area around the existing EIRR bridge (as 

shown in Figure 1) 

One initial project preference was the desire to complete a long loop trail (connecting both sides of 

the river with trail and a crossing near the existing railroad bridge). However, during the site visit 

it was noted that this would not likely be immediately feasible due to private land ownership along 

the southern banks of the Henry’s Fork. 

During the site visit three main options based on location of the crossing were considered to move 

forward for further development, these options are summarized below and documented in this 

report: 

• OPTION 1: “Railroad Bridge Option”- Cross the Henry’s Fork near the existing railroad 

bridge, two sub-options were developed for this location: 

o OPTION 1A: Construct a new pedestrian bridge just downstream of the existing 

railroad bridge. New bridge would consist of a two span, 352 foot long steel truss 

with concrete pier foundation in the river. 
To: Project File, FHWA, WFLHD, 7/17/2019 

o OPTION 1B: Acquire the existing railroad bridge and convert to only pedestrian & 

cyclist access.

• OPTION 2: “Island Hopping Option” – Construct a series of bridges and trails that connect 

through the braided portion of the Henry’s Fork (located approximately midway through 

the study area). Three bridges would be required: Bridge #1, 352 foot steel truss, Bridge 

#2, 150 foot steel truss, and Bridge #3, 175 foot steel truss along with two segments of trail 

or boardwalk on the islands totaling 800 foot in length

• Option 3: “Diversion Crossing Option” – Cross the Henry’s Fork near the beginning of the 

study area at the area adjacent to the existing water diversion weir and boat launch. A 667 

foot long, four span steel truss bridge consisting of 175 foot spans would be required to 

cross the river at this location. 

Summary of Advantages 

Option 

1A

Option 

1B Option 2 Option 3

Advantages

Initial cost of construction 4 5 2 1

Operation & Maintenance Costs 5 4 2 1

Fill and ground disturbance 3 5 1 2

Provides access to islands 1 1 5 1

Creates opportunity for loop trail 3 3 5 5

Discourages unsafe use of Rail Bridge 4 5 1 1

ROW acquisition (temp. and perm.) 3 1 3 5

Total Advantage Relative “Score” = 23 24 19 16

Note: the options were rated on a scale of 1-5 for each category. A score of “1” indicates that the option scored 

poorly in that category. A score of “5” indicates that the option scored favorably in that category.
To: Project File, FHWA, WFLHD, 7/17/2019 

Figure 1 – Study Area Map
To: Project File, FHWA, WFLHD, 7/17/2019 

4. DESIGN OPTIONS 

The following is a detailed narrative for each of the options. 

Option 1A- Construct a new pedestrian bridge on the downstream side of the existing railroad 

bridge. The proposed bridge would consist of a two span, 352 foot long steel truss with a single 

concrete pier foundation in the river. A minimum of 8 foot pedestrian walkway width is provided 

on the proposed bridge. Minimal trail work would be included, only constructing connections at 

the ends of the bridge. 

Design and Materials: 

It is recommended to construct the bridge superstructure from weathering steel. This steel does 

not require painting but rather an oxidized surface forms (patina) that coats and protects the steel 

from further deterioration or corrosion. The weathering steel produces a rustic and weathered 

aesthetic that would fit the character of the adjacent historic railroad truss. 

Foundation elements are recommended to be constructed with reinforced concrete on spread 

footings. 

The foundation elements and the steel truss superstructure would have an intended design life of 

100 years. 

A treated timber deck would be an appropriate deck surface and fit the aesthetics of the other 

boardwalks and trail bridges already constructed on the Henry’s Fork Greenway. The timber deck 

has an anticipated design life of about 50 years in the project’s climate and would have to be 

replaced at some point during the life of the structure (A $50,000 expense in current year dollars). 

Future design considerations should include accommodation of ice jams and hydraulic clearances 

during high water events. A minimum low chord (lowest part of steel truss) should be at 

approximately 3 to 5 feet higher than the 50 year flood event water surface elevation. 

Construction Techniques and Considerations: 

Construction access for heavy equipment and materials to the south bank of the Henry’s Fork at 

this crossing location will be simplified through the use of local/county roads that connect right to 

the south abutment location. There is also a large cleared informal parking area that could be 

utilized for staging and stockpiling material for the construction of the proposed bridge. 

This option proposes to place a single pier in the middle of the Henry’s Fork River. To access this 

pier a temporary bridge will need to be constructed. Cofferdams or other dewatering techniques 

will need to be utilized to divert the river water from the work area. Given the limited access to 

the north bank at this crossing location a temporary bridge that spans the entire channel may be 

required to provide access for materials and equipment to that side of the river. Large cranes will 

be required to place the steel trusses and the temporary bridge will need to accommodate these 

heavy loads. 
To: Project File, FHWA, WFLHD, 7/17/2019 

Operations and Pedestrian Movement: 

The existing railroad bridge is currently utilized for illegal and unsafe crossings of the Henry’s 

Fork. Placing a safe crossing directly adjacent to the railroad bridge will allow for safe crossing of 

the river eliminating conflicts with the active rail line. The location also allows for future 

expansion or connection to a larger loop (approximately 5 miles) than if the river was crossed 

closer to St. Anthony. 

To provide pedestrian and cyclist access to the north side of the Henry’s Fork Greenway Trail a 

trail connection would be constructed under the existing railroad bridge. This would eliminate or 

discourage the current practice of illegally crossing the railroad tracks at grade. 

Summary of Costs: 

Estimate of Construction items only = $1,275,000 

Estimate of Engineering Costs only = $380,000 

Estimate of total project cost = $1,655,000 

Estimated remaining service life = 100 years for the foundation and superstructure; 50 years for 

the timber deck

Summary of Advantages and Disadvantages: 

ADVANTAGES DISADVANTAGES

Only one pier in the river Does not (yet) create a loop trail

Discourages unsafe use of existing railroad 

bridge

Does not provide access to islands within Henry’s 

Fork

Opportunity for future larger loop from St.

Anthony 

Opportunity for future expansion and upgrades 

to the informal parking area on the south bank

Minimum new bridge structure constructed 

(limits future maintenance costs and needs)
HENRY'S FORK BRIDGE STUDY 11/26/2018

Item # Description Unit Quantity Unit price Amount

20801 - 0000 Structural Excavation CUYD 330 $ 25.0 $8,250.0

20815 - 0000 Cofferdams (Pier Construction) LPSM 1 $ 50,000.0 $50,000.0

55201 - 0200 Structural Concrete A(AE) CUYD 220 $ 1,000.0 $220,000.0

55401 - 1000 Reinforcing Steel LB 55000 $ 2.0 $110,000.0

55504 - 0000 Pre-fabricated Steel Bridge (2x175ft) LPSM 1 $ 400,000.0 $400,000.0

55601 - 0900 Rail, Steel Approach LNFT 60 $ 225.0 $13,500.0

55700 - 0000 Treated Timber Decking for Truss MFBM 8 $ 5,000.0 $40,000.0

56202 - 0000 Temporary Work Bridge LPSM 1 $ 125,000.0 $125,000.0

Trail and Approach work LPSM 1 $ 50,000.0 $50,000.0

$0.0

$0.0

$1,016,750.00

Description Amount

Preliminary Engineering (Design) - 15% $191,250.0

Construction Engineering - 15% $191,250.0

Construction Cost Estimate 

Rounded Estimated Cost of Proposed Bridge $1,275,000.00

B. Oltmann

Option #1A: New bridge crossing DS of existing railroad bridge

Total:

15% Contingency $152,500.00

10% Mobilization $101,675.00

Area of Bridge to be built SQFT 2816

Total Project Construction $1,655,000.00

Cost per SQFT of new bridge $ $452.77

Engineering Costs

Rounded Total Engineering Costs $380,000.00
LIVE LOAD SPECIAL LOADS

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STATE

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U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

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WESTERN FEDERAL LANDS HIGHWAY DIVISION

175'-0" 175'-0"

352'-0"

HENRY'S FORK PEDESTRIAN BRIDGE HENRY'S FORK OF THE SNAKE RIVER

IDAHO

B. OLTMANN

1:30

Ped. 90 PSF

8'-0"

4'-6"

11'-0"

Steeltruss

depth

WEATHERING STEEL TRUSS WITH TIMBER DECK

STEEL PEDESTRIAN RAIL

N/A N/A N/A

Henry's fork

groundline

Assumed 

on rock

Concrete pier

4900

4875

4925

4950

OPTION 1A - NEW BRIDGE D.S. RAILROAD BRIDGE

deck

Timber 

N

under bridge

Trail connection

to parking

Trail connection

352'-0"

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To: Project File, FHWA, WFLHD, 7/17/2019 

Option 1B- Acquire the existing railroad bridge and convert it to only pedestrian and cyclist 

access. Install new timber decking and pedestrian railing. This approach is similar to many other 

“rails to trails” projects that have been completed at many other historic railroad bridges (including 

nearby at the Ashton-Tetonia Trail). 

Existing Railroad Bridge: 

The existing St. Anthony Pegram Truss Railroad Bridge is listed on the National Register of 

Historic Places. The bridge was originally fabricated in 1896 and placed in its current location and 

foundations in 1914. Since that time there have been no major modifications to the structure that 

would alter its historic significance. The bridge is located on a spur of the old East Belt Branch 

and is still used periodically by the Eastern Idaho Railroad. 

There are some risks associated with converting an older structure for new use. Note that the 

existing bridge is currently 122 year old, and may have some defects. It is recommended that if 

this option is pursued that a detailed “hands-on” inspection of all members along with ultra-sonic 

testing of the pins be completed. The structural loading will be much less with pedestrian use 

compared to active railroad hauling, but a full structural analysis would also be appropriate. Given 

the construction date of the bridge it is likely that lead based paint was also used and should be 

verified if this option is carried forward.

A further evaluation of the existing bridge’s single pier in the river and abutments for scour issues 

would be warranted to ensure the long-term performance of the bridge.

A treated timber deck would be an appropriate deck surface and fit the aesthetics of the other 

boardwalks and trail bridges already constructed on the Henry’s Fork Greenway. The timber deck 

has an anticipated design life of about 50 years in the project’s climate. 

Construction Techniques and Considerations: 

Construction access for light equipment and materials to the south bank of the Henry’s Fork at this 

crossing location will be simplified through the use of local/county roads that connect right to the 

south abutment location. There is also a large cleared informal parking area that could be utilized 

for staging and stockpiling material for the conversion of the existing bridge. 

This option would not require any in-water work as all the work would occur on the existing 

bridge and approach way.

Operations and Pedestrian Movement: 

Similar to Option 1A: The existing railroad bridge is currently utilized for illegal and unsafe 

crossings of the Henry’s Fork. Placing a safe crossing on the railroad bridge itself will allow for 

safe crossing of the river eliminating conflicts with the rail line. The location also allows for 

future expansion or connection to a larger loop (approximately 5 miles) than if the river was 

crossed closer to St. Anthony. 
To: Project File, FHWA, WFLHD, 7/17/2019 

Summary of Costs: 

Estimate of Construction items only = $200,000 

Estimate of Engineering Costs only = $140,000 

Estimate of total project cost = $340,000 

Estimated remaining service life = 50 years

(Note that the costs assume existing bridge is acquired at no-cost) 

Summary of Advantages and Disadvantages: 

ADVANTAGES DISADVANTAGES

No in-water work or additional clearing Does not (yet) create a loop trail

Eliminates unsafe use of existing railroad bridge

– improves safety of railroad crossing

Risks associated with rehabilitating or changing 

use of historic steel bridge

Opportunity for future larger loop from St.

Anthony 

Shortest design life of options

Lowest total project cost Requires acquisition of railroad bridge, of which 

feasibility is unknown

Existing Henry’s Fork Pegram Truss Railroad Bridge 
HENRY'S FORK BRIDGE STUDY 11/26/2018

Item # Description Unit Quantity Unit price Amount

55700 - 0000 Treated Timber Decking for Truss MFBM 7 $ 5,000.0 $35,000.0

55700 - 0000 Pedestrian Rail LNFT 600 $ 125.0 $75,000.0

Trail and Approach work LPSM 1 $ 50,000.0 $50,000.0

$160,000.00

Description Amount

Detailed bridge inspection (climbing) $40,000.0

Preliminary Engineering (Design) - 25% $50,000.0

Construction Engineering - 25% $50,000.0

Total Project Construction $340,000.00

Cost per SQFT of new bridge $ $113.96

Engineering Costs

Rounded Total Engineering Costs $140,000.00

Rounded Estimated Cost of Proposed Bridge $200,000.00

B. Oltmann

Construction Cost Estimate 

Option #1B: Retrofit Existing Railroad Bridge

Total:

15% Contingency $24,000.00

10% Mobilization $16,000.00

Area of Bridge to be built SQFT 1755
LIVE LOAD SPECIAL LOADS

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DRAINS UTILITIES

 

 

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BRIDGE NAME

ROUTE NAME AND NUMBER

STATE

ACCOUNT NO.

PREPARED BY

SCALE: DATE:

ESTIMATED STRUCTURE COST

FOREST/PARK/OTHER

STREAM NAME

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

PRELIMINARY LAYOUT

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WESTERN FEDERAL LANDS HIGHWAY DIVISION

HENRY'S FORK PEDESTRIAN BRIDGE HENRY'S FORK OF THE SNAKE RIVER

IDAHO

B. OLTMANN

1:30

Ped. 90 PSF

WEATHERING STEEL TRUSS WITH TIMBER DECK

STEEL PEDESTRIAN RAIL

N/A N/A N/A

Henry's fork

groundline

Assumed 

4900

4875

4925

4950

135'-0" 135'-0"

270' +/-

truss

Existing Railroad

OPTION 1B - RETROFIT RAILROAD BRIDGE - NEW DECK/RAILS

6'-6"

Existing rail ties

New timber decking

New timber rails

Existing steel beams

N

bridge deck

Retrofit existing 

Trail connection

to parking

Trail connection

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To: Project File, FHWA, WFLHD, 7/17/2019 

Option 2- “Island Hopping Option” – Construct a series of bridges and trails that connect through 

the braided portion of the Henry’s Fork (located approximately midway through the study area). 

Three bridges would be required: Bridge #1, 352 foot steel truss, Bridge #2, 150 foot steel truss, 

and Bridge #3, 175 foot steel truss along with two segments of trail or boardwalk on the islands 

totaling 800 foot in length.

Design and Materials: 

It is recommended to construct the bridge superstructures from weathering steel. This steel does 

not require painting but rather an oxidized surface forms (patina) that coats and protects the steel 

from further deterioration or corrosion. The weathering steel produces a rustic and weathered 

aesthetic that would fit the character of the adjacent historic railroad truss. 

Foundation elements are recommended to be constructed with reinforced concrete on spread 

footings. Only one pier is required in the Henry’s Fork with this option: at Bridge #1. 

The foundation elements and the steel truss superstructure would have an intended design life of 

100 years. 

A treated timber deck would be an appropriate deck surface and fit the aesthetics of the other 

boardwalks and trail bridges already constructed on the Henry’s Fork Greenway. The timber deck 

has an anticipated design life of about 50 years in the project’s climate, and would have to be 

replaced at some point during the life of the structure (A $75,000 expense in current year dollars). 

The new trail Segment #1 on the island is located in an area that has been previously designated as 

wetlands. This area may need to be crossed with simple boardwalks of the type already 

constructed on other portions of the Henry’s Fork Greenway. 

Future design considerations should include accommodation of ice jams and hydraulic clearances 

during these events during high water. A minimum low chord (lowest part of steel truss) should be 

at approximately 3 to 5 feet higher than the 50 year flood event water surface elevation.

Construction Techniques and Considerations: 

There is good construction access for heavy equipment and materials to the north bank of the 

Henry’s Fork near the cemetery parking area and can be accessed through the use of local/county 

roads that connect right to the north abutment location of Bridge #1. There is also medium sized 

paved parking area that could be utilized for staging and stockpiling material for the construction 

of the proposed bridges and trails. 

Access to the Bridge #3 location will be complicated by the distance along the narrow Greenway 

trail, private landowner easements and need for large heavy equipment to access both ends of the 

bridge during construction. A temporary bridge will be required to reach the far abutment of 

Bridge #3 that is located on an island. This temporary bridge would also be utilized to move 

material over to the island and then build another temporary bridge adjacent to Bridge #2. These 

bridges are required to erect the steel trusses and also to move equipment and materials needed to 

construct the concrete abutments and pier associated with the permanent structures. 
To: Project File, FHWA, WFLHD, 7/17/2019 

A total of three temporary bridge are anticipated to be constructed to facilitate the construction of 

the three permanent bridges. These temporary bridges will allow equipment and material to access 

the islands. The temporary bridges would be removed once the permanent bridges are installed. 

This option also proposes to place a single pier in the middle of the Henry’s Fork River. 

Cofferdams or other dewatering techniques will need to be utilized to divert the river water from 

the work area. Given the limited access to the southern abutment located on an in-channel island

at this crossing location a temporary bridge that spans the entire channel may be required. 

Operations and Pedestrian Movement: 

Option 2 would allow for a medium loop route to be completed from St. Anthony along both the 

north and south banks of the Henry’s Fork. This loop would be approximately 3 miles in length. 

This option does not address the concerns associated with the current use of the existing railroad 

bridge. It would still be utilized for illegal and unsafe crossings of the Henry’s Fork. The 

proposed crossing is too far away from the existing railroad bridge and it is unlikely that people 

who want to cross in the area of the existing bridge would walk to the new bridge to cross. 

Summary of Costs: 

Estimate of Construction items only = $2,910,000 

Estimate of Engineering Costs only = $900,000 

Estimate of total project cost = $3,810,000 

Estimated remaining service life = 100 years for the foundation and superstructures; 50 years for 

the timber decks

Summary of Advantages and Disadvantages: 

ADVANTAGES DISADVANTAGES

Only one pier in the river Does not discourage unsafe use of the existing 

railroad bridge

Creates a loop trail Constructs trail and bridges in areas previously 

designated/mapped as wetlands

Provides island viewing recreational 

opportunities 

Large quantity of new bridge constructed (higher 

maintenance costs)

Highest total project cost
HENRY'S FORK BRIDGE STUDY 11/26/2018

Item # Description Unit Quantity Unit price Amount

20801 - 0000 Structural Excavation CUYD 800 $ 25.0 $20,000.0

20815 - 0000 Cofferdams (Pier Construction) LPSM 1 $ 50,000.0 $50,000.0

55201 - 0200 Structural Concrete A(AE) CUYD 525 $ 1,000.0 $525,000.0

55401 - 1000 Reinforcing Steel LB 131250 $ 2.0 $262,500.0

55504 - 0000 Pre-fabricated Steel Bridge (3x175ft, 1x150ft) LPSM 1 $ 775,000.0 $775,000.0

55601 - 0900 Rail, Steel Approach LNFT 180 $ 225.0 $40,500.0

55700 - 0000 Treated Timber Decking for Truss MFBM 15 $ 5,000.0 $75,000.0

56202 - 0000 Temporary Work Bridges LPSM 1 $ 300,000.0 $300,000.0

Trail and Approach work LPSM 1 $ 275,000.0 $275,000.0

$2,323,000.00

Description Amount

Preliminary Engineering (Design) - 15% $450,000.0

Construction Engineering - 15% $450,000.0

Total Project Construction $3,810,000.00

Cost per SQFT of new bridge $ $538.89

Engineering Costs

Rounded Total Engineering Costs $900,000.00

Rounded Estimated Cost of Proposed Bridge $2,910,000.00

B. Oltmann

Construction Cost Estimate 

Option #2: New bridges crossing thru Islands

Total:

15% Contingency $348,400.00

10% Mobilization $232,300.00

Area of Bridge to be built SQFT 5400
 

ROUTE NAME AND NUMBER

STATE COUNTY

ACCOUNT NO.

PREPARED BY

 

 FOREST/PARK/OTHER

STREAM NAME

ESTIMATED STRUCTURE COST

SCALE: DATE:

 

BRIDGE NAME

PRELIMINARY LAYOUT

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

 

PLAN

WESTERN FEDERAL LANDS HIGHWAY DIVISION

OPTION 2 - ISLAND HOPPING

Henry's fork

Henry's fork

PAGE 1 OF 4

IDAHO

B. OLTMANN 1:50

HENRY'S FORK SNAKE RIVER

CITY OF ST. ANTHONY AND BLM

HENRY'S FORK BRIDGE #1, #2, #3

N

(350 ft)

Bridge #1

(550 LNFT)

Trail Segment #1

(175 ft)

Bridge #3

(250 LNFT)

Trail Segment #2

(150 ft)

Bridge #2

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STATE

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PREPARED BY

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FOREST/PARK/OTHER

STREAM NAME

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

PRELIMINARY LAYOUT

COUNTY 

 

 

 

 

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REMARKS

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BOTTOM EL.:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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DEPTH:

 

 

 

 

RECEIVED

RECEIVED

 

 

 

 

 

 

TYPICAL ROADWAY SECTION

SUPER ROTATED ABOUT

STA.

STA.

RATE

RATE

m/m

m/m

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PROFILE GRADE DIAGRAM

EL. ARE AT GRADE

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WESTERN FEDERAL LANDS HIGHWAY DIVISION

175'-0" 175'-0"

352'-0"

HENRY'S FORK OF THE SNAKE RIVER

IDAHO

B. OLTMANN

1:30

Ped. 90 PSF

8'-0"

4'-6"

11'-0"

Steeltruss

depth

WEATHERING STEEL TRUSS WITH TIMBER DECK

STEEL PEDESTRIAN RAIL

N/A N/A N/A

Henry's fork

groundline

Assumed 

4900

4950

4975

OPTION 2 - ISLAND HOPPING

4925

Concrete pier

HENRY'S FORK PEDESTRIAN BRIDGES

ELEVATION BRIDGE #1

PAGE 2 OF 4

deck

Timber 

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LIVE LOAD SPECIAL LOADS

SUPERSTRUCTURE

OVERLOAD

TYPICAL BRIDGE SECTION

SIDEWALKS

RAIL

 

REMARKS

TRANSITION

DRAINS UTILITIES

 

 

DESIGN DATA

BRIDGE NAME

ROUTE NAME AND NUMBER

STATE

ACCOUNT NO.

PREPARED BY

SCALE: DATE:

ESTIMATED STRUCTURE COST

FOREST/PARK/OTHER

STREAM NAME

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

PRELIMINARY LAYOUT

COUNTY 

 

 

 

 

PLAN

GEOMETRICS HYDRAULICS SCOUR

HYDRAULICS REPORT NO.

MATERIALS REPORT NO.

SCOUR

REMARKS

SLOPE PROTECTION

TOP EL.:

TYPE:

QQ100 Q50 Q2

Q Vm WS EL.

REMARKS

CLASS:

BOTTOM EL.:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SLOPE:

DEPTH:

 

 

 

 

RECEIVED

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TYPICAL ROADWAY SECTION

SUPER ROTATED ABOUT

STA.

STA.

RATE

RATE

m/m

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PROFILE GRADE DIAGRAM

EL. ARE AT GRADE

AT

 

 

 

 

 

 

 

WESTERN FEDERAL LANDS HIGHWAY DIVISION

HENRY'S FORK OF THE SNAKE RIVER

IDAHO

B. OLTMANN

1:20

Ped. 90 PSF

8'-0"

4'-6"

11'-0"

Steeltrussdepth

WEATHERING STEEL TRUSS WITH TIMBER DECK

STEEL PEDESTRIAN RAIL

N/A N/A N/A

N

Henry's fork

groundline

Assumed 

4900

4950

4975

OPTION 2 - ISLAND HOPPING

4925

HENRY'S FORK PEDESTRIAN BRIDGES

ELEVATION BRIDGE #2

PAGE 3 OF 4

150'-0"

abutment

Concrete 

deck

Timber 

Trail connection

Trail connection

NOVEMBER 2018

8:45 AM 27 Novem ber2018 ] Default [ c:\m yfiles\pw_production\d0385837\Option 2 -Henry'sFork -Island Hopping COLOR.dgn
LIVE LOAD SPECIAL LOADS

SUPERSTRUCTURE

OVERLOAD

TYPICAL BRIDGE SECTION

SIDEWALKS

RAIL

 

REMARKS

TRANSITION

DRAINS UTILITIES

 

 

DESIGN DATA

BRIDGE NAME

ROUTE NAME AND NUMBER

STATE

ACCOUNT NO.

PREPARED BY

SCALE: DATE:

ESTIMATED STRUCTURE COST

FOREST/PARK/OTHER

STREAM NAME

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

PRELIMINARY LAYOUT

COUNTY 

 

 

 

 

PLAN

GEOMETRICS HYDRAULICS SCOUR

HYDRAULICS REPORT NO.

MATERIALS REPORT NO.

SCOUR

REMARKS

SLOPE PROTECTION

TOP EL.:

TYPE:

QQ100 Q50 Q2

Q Vm WS EL.

REMARKS

CLASS:

BOTTOM EL.:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SLOPE:

DEPTH:

 

 

 

 

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TYPICAL ROADWAY SECTION

SUPER ROTATED ABOUT

STA.

STA.

RATE

RATE

m/m

m/m

CROWN m/m

PROFILE GRADE DIAGRAM

EL. ARE AT GRADE

AT

 

 

 

 

 

 

 

WESTERN FEDERAL LANDS HIGHWAY DIVISION

HENRY'S FORK OF THE SNAKE RIVER

IDAHO

B. OLTMANN

1:20

Ped. 90 PSF

8'-0"

4'-6"

11'-0"

Steeltrussdepth

WEATHERING STEEL TRUSS WITH TIMBER DECK

STEEL PEDESTRIAN RAIL

N/A N/A N/A

N

Henry's fork

groundline

Assumed 

4900

4950

4975

OPTION 2 - ISLAND HOPPING

4925

HENRY'S FORK PEDESTRIAN BRIDGES

ELEVATION BRIDGE #3

PAGE 4 OF 4

175'-0"

abutment

Concrete 

deck

Timber 

Trail connection

Trail connection

NOVEMBER 2018

8:45 AM 27 Novem ber2018 ] Default [ c:\m yfiles\pw_production\d0385837\Option 2 -Henry'sFork -Island Hopping COLOR.dgn
To: Project File, FHWA, WFLHD, 7/17/2019 

As an additional opportunity the Option 2, Bridge #3 could be added to other options as a way to 

improve access to the islands in the braided section of the Henry’s Fork. This crossing location is 

the only upland island (non-wetland) noted in previous wetland identifications. 

Cost of Option 2, Bridge #3 only: 

Estimate of Construction items only = $875,000 

Estimate of Engineering Costs only = $260,000 

Estimate of total project cost = $1,135,000 

Estimated remaining service life = 100 years for the foundation and superstructure; 50 years for 

the timber deck

Approximate crossing location of Bridge #3 
HENRY'S FORK BRIDGE STUDY 11/26/2018

Item # Description Unit Quantity Unit price Amount

20801 - 0000 Structural Excavation CUYD 220 $ 25.0 $5,500.0

20815 - 0000 Cofferdams (Pier Construction) LPSM 1 $ 50,000.0 $50,000.0

55201 - 0200 Structural Concrete A(AE) CUYD 155 $ 1,000.0 $155,000.0

55401 - 1000 Reinforcing Steel LB 38750 $ 2.0 $77,500.0

55504 - 0000 Pre-fabricated Steel Bridge (3x175ft, 1x150ft) LPSM 1 $ 200,000.0 $200,000.0

55601 - 0900 Rail, Steel Approach LNFT 60 $ 225.0 $13,500.0

55700 - 0000 Treated Timber Decking for Truss MFBM 5 $ 5,000.0 $25,000.0

56202 - 0000 Temporary Work Bridges LPSM 1 $ 125,000.0 $125,000.0

Trail and Approach work LPSM 1 $ 50,000.0 $50,000.0

$701,500.00

Description Amount

Preliminary Engineering (Design) - 15% $131,250.0

Construction Engineering - 15% $131,250.0

Rounded Estimated Cost of Proposed Bridge $875,000.00

B. Oltmann

Construction Cost Estimate 

Option #2, Bridge #3 ONLY: New bridge to one island

Total:

15% Contingency $105,200.00

10% Mobilization $70,150.00

Area of Bridge to be built SQFT 5400

Total Project Construction $1,135,000.00

Cost per SQFT of new bridge $ $162.04

Engineering Costs

Rounded Total Engineering Costs $260,000.00
To: Project File, FHWA, WFLHD, 7/17/2019 

Option 3- Construct a new pedestrian bridge on the upstream side of the existing irrigation 

diversion and weir at the northern end of the study area. The proposed bridge would consist of a 

four span, 667 foot long steel truss with three concrete pier foundations in the river. A minimum 

of 8 foot pedestrian walkway width would be provided on the proposed bridge. Minimal trail 

work would be included, only constructing connections at the ends of the bridge to existing trail on 

the south end and the existing boat launch on the north end. 

Design and Materials: 

It is recommended to construct the bridge superstructures from weathering steel. This steel does 

not require painting but rather an oxidized surface forms (patina) that coats and protects the steel 

from further deterioration or corrosion. The weathering steel produces a rustic and weathered 

aesthetic that would fit the character of the adjacent historic railroad truss. 

Foundation elements are recommended to be constructed with reinforced concrete on spread 

footings. 

The foundation elements and the steel truss superstructure would have an intended design life of 

100 years. 

A treated timber deck would be an appropriate deck surface and fit the aesthetics of the other 

boardwalks and trail bridges already constructed on the Henry’s Fork Greenway. The timber deck 

has an anticipated design life of about 50 years in the project’s climate, and would have to be 

replaced at some point during the life of the structure (A $150,000 estimated cost in current year 

dollars). 

Future design considerations should include accommodation of ice jams and hydraulic clearances 

during high water events. A minimum low chord (lowest part of steel truss) should be at 

approximately 3 to 5 feet higher than the 50 year flood event water surface elevation.

Construction Techniques and Considerations: 

Construction access for heavy equipment and materials to the north bank of the Henry’s Fork at 

this crossing location will be simplified through the use of local/county roads that connect to an 

area near the north abutment location. The south abutment location could be accessed with 

moderate difficulty down the existing Greenway trail corridor. A staging area would need to be 

cleared at the south abutment location. 

This option proposes to place three piers in the middle of the Henry’s Fork River. To access these 

piers a temporary bridge will need to be constructed. Cofferdams or other dewatering techniques 

will need to be utilized to divert the river water from the work areas. Given the limited access to 

the south bank at this crossing location a temporary bridge that spans the entire channel may be 

required to provide access for materials and equipment to that side of the river. Large cranes will 

be required to place the steel trusses and the temporary bridge will need to accommodate these 

heavy loads. 
To: Project File, FHWA, WFLHD, 7/17/2019 

Operations and Pedestrian Movement: 

Option 3 would allow for a medium loop route to be completed from St. Anthony along both the 

north and south banks of the Henry’s Fork. This loop would be approximately 2.5 miles in length. 

This option does not address the concerns associated with the current use of the existing railroad 

bridge. It would still be utilized for illegal and unsafe crossings of the Henry’s Fork. The 

proposed crossing is too far away from the existing railroad bridge and it is unlikely that people 

who want to cross in the area of the existing bridge would walk to the new bridge to cross. 

Summary of Costs: 

Estimate of Construction items only = $2,665,000 

Estimate of Engineering Costs only = $800,000 

Estimate of total project cost = $3,465,000 

Estimated remaining service life = 100 years for the foundation and superstructure; 50 years for 

the timber deck

Summary of Advantages and Disadvantages: 

ADVANTAGES DISADVANTAGES

Creates a loop trail Three piers in the river creates additional in-water 

work and impacts to environment

Crosses the Henry’s Fork at a location where

there is already infrastructure in the channel (at 

the diversion weir)

Does not discourage unsafe use of the existing 

railroad bridge

Least Right of Way acquisition Does not provide opportunity for future long loop 

route around the railroad bridge 

Does not provide “island hopping” experience or 

access to islands within the braided section of the 

Henry’s Fork

Large amount of new bridge constructed (highest 

maintenance costs)

High total project cost
HENRY'S FORK BRIDGE STUDY 11/26/2018

Item # Description Unit Quantity Unit price Amount

20801 - 0000 Structural Excavation CUYD 375 $ 25.0 $9,375.0

20815 - 0000 Cofferdams (Pier Construction) LPSM 1 $ 125,000.0 $125,000.0

55201 - 0200 Structural Concrete A(AE) CUYD 360 $ 1,000.0 $360,000.0

55401 - 1000 Reinforcing Steel LB 90000 $ 2.0 $180,000.0

55504 - 0000 Pre-fabricated Steel Bridge (4x175ft) LPSM 1 $ 800,000.0 $800,000.0

55601 - 0900 Rail, Steel Approach LNFT 60 $ 225.0 $13,500.0

55700 - 0000 Treated Timber Decking for Truss MFBM 28 $ 5,000.0 $140,000.0

56202 - 0000 Temporary Work Bridges LPSM 1 $ 350,000.0 $350,000.0

Trail and Approach work LPSM 1 $ 150,000.0 $150,000.0

$0.0

$0.0

$2,127,875.00

Description Amount

Preliminary Engineering (Design) - 15% $400,000.0

Construction Engineering - 15% $400,000.0

Total Project Construction $3,465,000.00

Cost per SQFT of new bridge $ $499.44

Engineering Costs

Rounded Total Engineering Costs $800,000.00

Rounded Estimated Cost of Proposed Bridge $2,665,000.00

B. Oltmann

Construction Cost Estimate 

Option #3: New bridge crossing US of existing diversion/wier

Total:

15% Contingency $319,100.00

10% Mobilization $212,787.50

Area of Bridge to be built SQFT 5336
LIVE LOAD SPECIAL LOADS

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D

ES

IGN DATA

BRIDGE NAME

ROUTE NAME AND NUMBER

STATE

ACCOUNT NO.

PREPARED BY

SCALE: DATE:

ESTIMATED STRUCTURE COST

FOREST/PARK/OTHER

STREAM NAME

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

PRELIMINARY LAYOUT

COUNTY 

 

 

 

 

PLAN

G

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METR

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HYDRAULICS REPORT NO.

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SCOUR

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TOP EL.:

TYPE:

Q

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REMARKS

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BOTTOM EL.:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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SUPER ROTATED ABOUT

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PROFILE GRADE DIAGRAM

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AT

 

 

 

 

 

 

 

WESTERN FEDERAL LANDS HIGHWAY DIVISION

HENRY'S FORK OF THE SNAKE RIVER

IDAHO

B. OLTMANN

1:30

Ped. 90 PSF

8'-0"

4'-6"

11'-0"

Steeltruss

depth

WEATHERING STEEL TRUSS WITH TIMBER DECK

STEEL PEDESTRIAN RAIL

N/A N/A N/A

Henry's fork

groundline

Assumed 

4900

4950

4975

4925

Concrete pier

HENRY'S FORK PEDESTRIAN BRIDGES

OPTION 3 - DIVERSION CROSSING

165'-0" 165'-0" 165'-0" 165'-0"

667'-0"

ELEVATION

deck

Timber 

Trail connection

N

166'-0"

667'-0"

166'-0" 167'-0" 167'-0"

(325 LNFT)

Trail connection

Truss Length Truss Length Truss Length Truss Length

Total Bridge Length

boat launch

Existing 

Diversion/Weir

55'-0"

NOVEMBER 2018

8:47

AM 27

Novem

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efault [ c:\m

yfiles\pw_production\d0385837\O

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enry'sFork -Diversion

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To: Project File, FHWA, WFLHD, 7/17/2019 

Approximate location of Option 3 Crossing 

Appendix A through C of this report contain additional information on Environmental, 

Geotechnical and Hydraulic information regarding the various options. 
(page intentionally blank)
To: Project File, FHWA, WFLHD, 7/17/2019 

APPENDIX A

ENVIRONMENTAL
(page intentionally blank)
Memorandum 

Western Federal Lands Highway Division

610 E. Fifth Street 

Vancouver, WA 98661-3801 

 

TO: Project Files 

FROM: Seth English-Young, WFLHD 

DATE: June 27, 2019 

SUBJECT: 

Environmental Considerations for the Henry’s 

Fork Bridge Feasibility Study – ID STANTH T 

2017(1) 

Summary 

The purpose of this memo is to present a preliminary environmental overview of the Henry’s Fork 

Bridge Feasibility Study project – ID STANTH T 2017(1). This document outlines environmental 

considerations for possible future construction projects based on the proposed options described in 

the Henry’s Fork Bridge Feasibility Study document. The options presented in the Study vary in level 

of impact to the environment, and any future construction project would need a NEPA analysis to be 

completed that will fully describe impacts from the range of options and mitigation measures to 

minimize those impacts. The two issues in this memo that pose the greatest risk to the scope, schedule 

or budget of a future construction project are: 

 For any option that requires property acquisition, there is the potential that the inability to gain 

access would make that option a nonstarter. 

 If part of the project area becomes critical habitat for the ESA threatened yellow-billed 

cuckoo, that could increase the ESA consultation required to build in the protected area. 

Below is an overview and summary of relevant environmental categories: 

NEPA 

The NEPA analysis and documentation depends on the scope, funding source, and lead federal 

agency of the future construction project. It is likely that the NEPA document would be a Categorical 

Exclusion or Environmental Assessment, which have shorter timelines than Environmental Impact 

Statements. Since the project would likely occur at least partially on BLM land, they would determine 

which type of NEPA document would meet their needs. BLM often produces Environmental 

Assessments on construction projects. However, if FHWA is involved, the project could potentially 

fall under the FHWA categorical exclusions described in 23.CFR.771.117. BLM would need to 

determine if they could use FHWA’s categorical exclusion to satisfy their NEPA requirements. 

Attached is a template of the FHWA categorical exclusion document (see Attachment A). 

Land Use 

The land in the study area is designated as Open Space in the City of St. Anthony Comprehensive 

Plan. Per the City Zoning Ordinance, the Open Space Zone is for lands “that are desired to be 

maintained as natural, undeveloped open space or used for recreational uses.” Public Parks, and 

“other uses approved by the planning and zoning commission which are similar to the above‐listed 
 

Page 2 of 6 

uses and in harmony with the objectives and characteristics of this zone” such as public trails and 

structures, are allowed or conditionally allowed in the Open Space Zone. 

According to BLM’s 2008 Snake River Activity/Operations Plan Revision, the area near the railroad 

bridge is designated as land that can be used for recreational purposes. 

 

Traffic 

Since the proposal is for a pedestrian bridge, substantial permanent traffic impacts are unlikely. There 

may be some induced traffic on adjoining roads if the bridge and paths draw more users than they do 

today. Depending on which construction option is chosen, parking facilities may be needed to be built 

or expanded. There would be some temporary traffic impacts on adjacent roads during construction. 

Visual Quality 

There is potential for visual impacts, varying depending on the option chosen. The option near the 

existing railroad bridge would have less visual impact than one located in a more remote area of the 

study area. Since the project would be a pedestrian bridge and have a relatively small footprint, major 

visual quality impacts are not expected. 

Air Quality 

The study area is not in a non-attainment air quality area and the project is not expected to have more 

than marginal air quality impacts. 

Environmental Justice 

The project would be open to all and would likely not impact any environmental justice communities 

disproportionately. Any ROW acquisitions required from private owners would not likely 

disproportionately impact low-income or other protected classes. 

Floodplains 

The area was mapped by FEMA in 1991 and the project area is within a Zone A flood hazard area 

inundated by the 100-year flood (see Attachment B). Either a “no-rise” certification will be required 

(information here: https://www.fema.gov/no-rise-certification-floodways), or a Conditional Letter of 

Map Revision (CLOMR information here: https://www.fema.gov/conditional-letter-map-revision). 

One of the options proposes “island-hopping” with a series of bridges and trails on islands within the 

braided section of the river. The islands within the river may shift, increasing the risk of damage to 

the bridges and trails. This issue is described in further detail in the Hydraulic Memo. 

Hazardous Materials 

The Idaho DEQ Waste Remediation Facilities Mapper (http://www.deq.idaho.gov/waste-mgmtremediation/remediation-activities/facility-mapper/) shows some sites near the project area that 

generate or manage wastes or have released wastes into the environment and require remediation (see 

Attachment C). 

As noted in the Water Quality section below, the Henry’s Fork River is not on the state 303(d) list of 

impaired waters, so it is unlikely that any hazardous materials sites are causing substantial pollution 

to the river. 
 

Page 3 of 6 

Noise 

Since the proposed project is a pedestrian bridge and there are not noise-sensitive receivers nearby, 

noise impacts are not expected to be noteworthy. There will be some temporary construction noise. 

Cultural, Historic and Recreational Resources 

During the planning and design phase of the construction project, project partners should complete a 

database search and pedestrian survey for cultural resources. The federal project lead will coordinate 

with the State Historic Preservation Office to ensure that the project complies with Section 106 of the 

National Historic Preservation Act. Preliminary information from BLM indicates that there are not 

known cultural resources in the project area. Prior to construction, additional cultural resource 

investigation and consultation will be required. 

Biological Resources 

Two species on the Endangered Species List have potential to occur within the project area: yellowbilled cuckoo, and Ute ladies’-tresses, a flowering plant, both listed as Threatened. Additionally, 

yellow-billed cuckoo critical habitat is proposed near the project area. The existing proposed critical 

habitat does not overlap with the project area, however BLM indicates that the proposed critical 

habitat may be expanded to include the project area. The yellow-billed cuckoo is a BLM-Designated 

Sensitive Species and may occur is very low densities in the project area. 

The project partners will need to go through consultation with the USFWS regarding impacts to listed 

species and critical habitats. The consultation will probably require completing a biological survey 

and producing a Biological Assessment (BA) which indicates the effects that the project will have on 

listed species/critical habitats and mitigation measures to reduce the impacts. USFWS will use the BA 

to produce a Biological Opinion or concurrence with the BLM effect determination. 

The Henry’s Fork is a popular recreational sport fishery, largely comprised of non-native rainbow 

trout and brown trout. Within the project area, fish populations are dominated by brown trout, 

rainbow trout and mountain whitefish. The Henry’s Fork is occupied habitat for the Yellowstone 

Cutthroat Trout, a BLM-Designated Sensitive Species. Yellowstone Cutthroat Trout occur in very 

low densities in the mainstream Henry’s Fork, mostly occupying tributaries. The IDFG has 

established recommended in-stream work windows for the lower Henrys Fork to limit potential 

impacts to sensitive life stages of fish or habitat use, such as spawning. The recommended in-stream 

work window for the lower Henry’s Fork is July 15 - September 15 (BMP Handbook, Best 

Management Practices for Idaho Rural Road Maintenance, August 2005). Flows during this time 

frame may not be feasible for equipment access or construction. Exemptions may be granted but 

coordination with IDFG regarding the work window and project construction timing would need to 

be conducted. 

Vegetation removal would be required for the any of the options, to varying degrees, and should be 

minimized to the extent possible. Vegetation removal would be described in the NEPA and ESAconsultation process to determine impacts to biological resources and potential measures to mitigate 

impacts. 

Wild and Scenic Rivers 

The Henry’s Fork is not a designated Wild and Scenic River. 
 

Page 4 of 6 

Wetlands and Waters of the US 

According to National Wetland Inventory mapping (see Attachment E), there are wetlands and waters 

of the US in the project area. Preliminary visual assessment from the site visit corroborates that there 

are wetlands in the area. Any construction of a new bridge will likely have permanent and temporary 

wetland/waters impacts and will need to be permitted through the US Army Corps of Engineers 

(USACE) 404 permitting process. Project partners would need to complete a wetland/waters 

delineation according to USACE requirements and advance design far enough to calculate impacts to 

wetlands/waters in order to apply for the permits. 

The type and effect of 404 permit process depends on the amount of permanent impacts to 

wetlands/waters. Generally, if the project has less than 0.1 acre of permanent impacts, the project will 

fall under a nationwide permit and compensatory mitigation is not required. If the project has 

between 0.1 and 0.5 acres of permanent impact, the project will fall under a nationwide permit and 

compensatory mitigation is required. According to USACE regulations, there are three mechanisms 

for providing compensatory mitigation (listed in order of preference as established by the 

regulations): mitigation banks, in-lieu fee programs, and permittee-responsible mitigation 

(https://www.epa.gov/cwa-404/compensatory-mitigation). If the project has over 0.5 acres of 

permanent wetland impacts a 404 Individual Permit is necessary. An Individual Permit has a longer 

timeframe, more in-depth permit analysis, and greater mitigation requirements. 

The project lead will likely submit a Joint Application for Permit, which covers the USACE 404 

permit, Idaho Department of Water Resources Stream Alteration Permit, and the 401 water quality 

certification or waiver for impacts to waters within the State of Idaho. 

(http://www.nww.usace.army.mil/Business-With-Us/Regulatory-Division/Joint-Application-forPermit/) 

Water Quality 

The stretch of the Henry’s Fork River in the project area is not on the state 303(d) list of impaired 

waters (http://www.deq.idaho.gov/water-quality/surface-water/monitoring-assessment/integratedreport.aspx). The project is not expected to permanently impact water quality. 

Contract requirements in the construction contract will minimize temporary water quality impacts. 

The project lead will likely need to get permits for temporary turbidity increases due to construction. 

The Idaho Department of Environmental Quality (DEQ) administers the 401 Certification process to 

comply with Section 401 of the Clean Water Act (http://www.deq.idaho.gov/water-quality/surfacewater/standards/401-certification/). The construction project will need to obtain a 401 Certification, 

which is usually applied for in conjunction with the USACE 404 permit with the Joint Application. 

Navigable Waterways 

All of the Henry’s Fork is considered navigable under the authority of the state 

(https://www.idl.idaho.gov/lakes-rivers/list-navigable-lakes-rivers.pdf). The USCG has made a 

determination that the Snake River is navigable to the Guffy Dam Site between Murphy and Melba, 

Idaho(https://www.pacificarea.uscg.mil/Portals/8/District_13/dpw/docs/Navigability_Determination_

for_the_13th_Coast_Guard_District.pdf?ver=2017-06-20-135946-777). Because of the location of 

the dam far downstream from the project area, and that determination, it is unlikely that the stretch of 

the Henry’s Fork in the project area is under USCG jurisdiction with regard to bridge permitting. 
 

Page 5 of 6 

Regardless, due to usage of the river by boats it is advisable to accommodate the existing and 

potential users of the river when determining the height of any proposed bridges. The proposed 

bridge would likely accommodate all users if it matches the clearance provided by the downstream 

railroad bridge. 

Property Acquisition 

Some construction options would require acquisition of property or easements, but would not require 

obtaining structures or displacing residents. Any property acquisitions would need to comply with the 

Uniform Act of 1970. Property or easement acquisitions could increase the pre-construction timeline. 

Some of the options require property acquisition from the Eastern Idaho Railroad. If property cannot 

be acquired from the railroad, it would cause those options to not be feasible. 

Section 4(f) of the Department of Transportation Act 

If FHWA is involved in the construction project, it will need to comply with Section 4(f) of the 

Department of Transportation Act, which “stipulates that FHWA and other DOT agencies cannot 

approve the use of land from publicly owned parks, recreational areas, wildlife and waterfowl 

refuges, or public and private historical sites unless the following conditions apply: 

 There is no feasible and prudent avoidance alternative to the use of land; and the action 

includes all possible planning to minimize harm to the property resulting from such use; 

OR 

 The Administration determines that the use of the property will have a de minimis impact.” 

(https://www.environment.fhwa.dot.gov/legislation/section4f.aspx) 

FHWA will need to determine if 4(f) properties exist in the project area, then determine if the project 

will “use” those 4(f) properties. If the “4(f) use” is de minimis, meaning “for parks, recreation areas, 

and wildlife and waterfowl refuges, a de minimis impact is one that will not adversely affect the 

features, attributes, or activities qualifying the property for protection under Section 4(f)” then it will 

be noted in the file and project can proceed. If the “4(f) use” is determined to be greater than de 

minimis, then a written evaluation must be prepared that describes the use and evaluates the 

alternatives, and proposes mitigation and minimization measures. 

While it is likely that the project will use 4(f) resources, it is also likely that the impact will be de 

minimis or that one of the designated exceptions to the law will apply, making it unlikely that the 4(f) 

process will delay the project. 

Section 6(f) of the Land and Water Conservation Act 

Section 6(f) applies when a project is converting lands or facilities acquired with Land and Water 

Conservation Funds (LWCF) Act. BLM acquired a parcel of land on the south side of the river with 

LWCF monies in 2001. Once an option is chosen, project partners would be advised to avoid 6(f) 

lands. However, if it is necessary to impact Section 6(f) land, then the project lead will need to 

determine if the project would convert Section 6(f) lands to a use other than public outdoor recreation 

use. If it is determined that the project converts Section 6(f) lands, then a replacement property will 

need to be found that is of reasonably equivalent usefulness and location as that being converted. 

(https://www.environment.fhwa.dot.gov/env_topics/other.aspx#6f). 
 

Page 6 of 6 

Tribal Coordination 

BLM will discuss this planning project in their quarterly meetings with the Shoshone-Bannock Tribe. 

Government-to-government coordination will be undertaken during the planning process for the 

construction project. 

Public Involvement 

There will be a public comment period and public meeting after release of the draft Bridge Feasibility 

Report. The public, and tribes, landowners, land management agencies, resource agencies, and other 

stakeholders will be invited to comment on the proposed construction options. It is likely that another 

public meeting and comment period will be held during the NEPA process. 

Federal Land Management Agency Consistency Determination 

Since the project will likely be on federal land, BLM will need to provide a determination that the 

project is consistent with its policies and plans. The determination may be in the form of a BLM 

NEPA document, or it could be a separate document. 

Cumulative and Indirect Impacts 

If an environmental assessment is prepared, cumulative and indirect impacts will need to be 

addressed. Cumulative impacts are defined as: 

“...impact on the environment, which results from the incremental impact of the action when added 

to other past, present, and reasonably foreseeable future actions regardless of what agency (Federal 

or non-Federal) or person undertakes such other actions. Cumulative impacts can result from 

individually minor but collectively significant actions taking place over a period of time. (40 CFR § 

1508.7)” 

Other “past, present, and reasonably foreseeable future actions” that could be included in the 

cumulative impacts analysis are: the railroad bridge, the weir and diversion for irrigation, the existing 

and future trail system, and future improvements to nearby parking lots. 

Indirect impacts are defined as: 

...caused by the action and are later in time or farther removed in distance, but are still reasonably 

foreseeable. Indirect effects may include growth inducing effects and other effects related to induced 

changes in the pattern of land use, population density or growth rate, and related effects on air and 

water and other natural systems, including ecosystems. (40 CFR § 1508.8)” 

(https://www.environment.fhwa.dot.gov/nepa/QAimpact.aspx) 

Indirect impacts that could be “reasonably foreseeable” are: an increase in usage of the trail system 

and in adjacent natural areas, increased parking demand, and increased usage of the Henry’s Fork by 

recreationists and guides. 

Construction Impacts 

During construction there are possible temporary impacts to: traffic in the project area, water quality, 

biological resources, and recreational usage. Materials, staging, and disposal sites, if known, will 

need to be included in the NEPA analysis. 
List “D” (documented) Categorical Exclusion (23 CFR 117[d])

August 22, 2018

Project Name

Project Number (FLH Accounts Table) Project Manager

Project Description (Briefly describe the project including need, purpose, location (Township Range and Section; Latitude and Longitude for beginning and end), 

limits, right-of-way requirements, and activities involved in this box. Attach map.)

Attachment A: Example FHWA Categorical Exclusion Template
List “D” (documented) Categorical Exclusion (23 CFR 117[d])

August 22, 2018

 Section 1: Type of List "D" (documented) Categorical Exclusion (23 CFR 117[d]): 

 A. Use the information in this section to determine the applicable "D" list activity for this project.

 B. Independent Utility and Logical Termini

The project complies with NEPA requirements related to connected actions and segmentation (i.e. the project must have independent utility, connect 

logical termini when applicable, be usable and be a reasonable expenditure even if no additional transportation improvements in the area are made and 

not restrict further consideration of alternatives for other reasonably foreseeable transportation improvements). (FHWA Final Rule, "Background," Federal 

Register Vol. 79, No. 8, January 13, 2014.) 

 C. Categorical Exclusions Defined (23 CFR 771.117[a])

FHWA regulation 23 CFR 771.117(a) defines categorical exclusions as actions which: 

 - do not induce significant impacts to planned growth or land use for the area; 

 - do not require the relocation of significant numbers of people; 

 - do not have a significant impact on any natural, cultural, recreational, historic or other resources; 

 - do not involve significant air, noise, or water quality impacts; 

 - do not have significant impacts on travel patterns; or 

 - do not otherwise, either individually or cumulatively, have any significant environmental impacts. 

Checking this box certifies that the project meets the above definition for a Categorical Exclusion. 

 D. Exceptions to Categorical Exclusions/Unusual Circumstances (23 CFR 771.117[b])

FHWA regulation 23 CFR 771.117(b) provides that any action which normally would be classified as a CE but could involve unusual circumstances requires the 

Department to conduct appropriate environmental studies to determine if the CE classification is proper. Unusual circumstances include actions that involve: 

 - Significant environmental impacts; 

 - Substantial controversy on environmental grounds; 

 - Significant impact on properties protected by section 4(f) of the DOT Act or section 106 of the National Historic Preservation Act; or 

 - Inconsistencies with any Federal, State, or local law, requirement or administrative determination relating to the environmental aspects of the action. 

 

All of the above unusual circumstances have been considered in conjunction with this project. (Please select one.) 

Checking this box certifies that none of the above conditions apply and that the project qualifies for a Categorical Exclusion. 

Checking this box certifies that unusual circumstances are involved. However, the appropriate studies/analysis have been completed, 

and it has been determined that the CE classification is still appropriate. 

 E. Required Federal Agency Consultation Processes

Proceed to Section F if all federal processes are complete. 

Please provide the anticipated results of the required federal consultation processes below if this project is determined to be a Categorical Exclusion prior to completing 

these processes. Confirmation of the results will be documented in Section 2 of this form. 

a.) Cultural Resources 

 Anticipated Section 106 finding:

Screened Undertaking

No Historic Properties Affected

No Adverse Effect

Adverse Effect

Programmatic Agreement; PA date and stipulation

b.) Endangered Species Act 

 Anticipated Endangered Species Act finding (effect determination):

No section 7 Needed

No Effect Not Likely to Adversely Affect Likely to Adversely Affect

Programmatic BO held by Partner Agency:

c.) Section 4(f) Transportation Act (23 CFR 774)

Section 4(f) does not apply

Section 4(f) exception:
List “D” (documented) Categorical Exclusion (23 CFR 117[d])

August 22, 2018

De Minimis

Individual

Programmatic:

F. Required Environmental Analysis for Documented Exclusions: These projects may be categorical exclusions under 23 CFR § 771.177(d), but require additional

documentation demonstrating that the specific conditions or criteria for the CEs are satisfied and that significant effects will not result. These questions need to be 

answered in order to categorize a project as a CE under list D.

Not Applicable - project is located wholly within federally owned lands

1.) Land Use

If applicable, attach a map or describe project location and surrounding land uses. Briefly describe the existing zoning of the project area and indicate 

whether the proposed project is consistent. Describe the community (geographic, demographic, economic, and population characteristics) in the vicinity of the project.

Low volume road with little to no traffic impacts resulting from the transportation improvements.

2.) Traffic

If applicable, describe potential traffic and parking impacts, including whether the existing roadways have adequate capacity to handle increased vehicular 

traffic. Include a map or diagram if the project will modify existing roadway configurations. Describe connectivity to other transportation facilities and modes.

3.) Temporary Traffic

Is there construction of temporary access, or the closure of existing road, bridge, or ramps, that would result in major traffic disruptions? No Yes

 If yes, describe.

4.) Visual Quality

a) Will the project have an adverse effect on a designated scenic area or scenic byway? No Yes

If yes, describe.

b) Will the project substantially degrade the existing visual character or quality of the site or its surrounding? No Yes

If yes, describe.

5.) Air Quality

a) Does the project have the potential to adversely impact air quality? No Yes

If yes, describe.

b) Is the project located in an Environmental Protection Agency (EPA) - designated non-attainment or maintenance area? No Yes

If yes, indicate the criteria pollutant (example: carbon monoxide, ozone, particulate matter (PM))
List “D” (documented) Categorical Exclusion (23 CFR 117[d])

August 22, 2018

c) If the non-attainment area is also in a metropolitan area, is the project included in the MPO's Transportation Improvement Program (TIP) air quality conformity 

analysis? No Yes

If yes, date of USDOT conformity finding

6.) Coastal Zone

Is the proposed project located in a designated coastal zone management area? No Yes

 If yes, describe coordination with the State regarding consistency with the coastal zone management plan and attach the State finding, if available.

No Environmental Justice populations are affected by the project

7.) Environmental Justice

Environmental Justice populations are potentially affected by the project.

 Indicate whether the project will have disproportionately high or adverse impacts on minority or low-income populations. Describe any potential adverse effects. 

 Describe outreach efforts specifically at minority or low-income populations.

8.) Floodplains 

Is the proposed project located within the Federal Emergency Management Agency (FEMA) 100-year floodplain? No Yes

 If yes, describe potential impacts and include the FEMA map with project location identified.

9.) Hazardous Materials

Is there any known or potential contamination at the project site? No Yes

 If NO, describe steps taken to determine whether hazardous materials are present on the site.

 If YES, note mitigation and clean-up measures that will be taken to remove hazardous materials from the project site.

10.) Navigable Waterways

Does the proposed project cross or have the potential to impact a navigable waterway? No Yes

 If yes, describe potential impacts and any coordination with the US Coast Guard.

11.) Noise

Does the project have the potential to increase noise? Does the project increase number of lanes, change the vertical or horizontal alignment, etc? 

(Reference: http://www.fhwa.dot.gov/environment/noise/regulations_and_guidance/)

No Yes

 If yes, describe resource and impacts and any noise studies that were completed.

Does the project have the potential to impact any cultural resources? No Yes

12.) Cultural, Historic and Recreational Resources
List “D” (documented) Categorical Exclusion (23 CFR 117[d])

August 22, 2018

 If yes, describe resource and impacts, including any coordination with Tribes and state SHPO offices.

Does the project have the potential to impact historic resources? No Yes

 If yes, describe.

Does the project have the potential to impact 4(f) recreational or wildlife refuge resources? 

(Reference: http://www.environment.fhwa.dot.gov/4f/index.asp)

No Yes

 If yes, describe the recreational resource and potential impacts.

13.) Biological Resources: Obtain a list of threatened and endangered species in the project area from the US Fish and Wildlife Service (USFWS) and the National Oceanic and

 Atmospheric Administration-Fisheries (NOAA-Fisheries). Attach a current species map (within six (6) months).

Are there listed species in the project area? No Yes

 If yes, describe potential impacts, including any critical habitat, essential fish habitat or other ecologically sensitive areas.

14.) Water Quality

Does the project have the potential to impact water quality, including during construction? No Yes

 If yes, describe potential impacts.

Will there be an increase in impervious surface? No Yes

 If yes, describe potential impacts and proposed treatment for storm water runoff.

Is the project located in the vicinity of an EPA-designated sole source aquifer? No Yes

 If yes, describe potential impacts and include a map of the sole source aquifer with project location identified.

15.) Wetlands and Waters

Does the proposal temporarily or permanently impact wetlands or require alterations to streams or waterways? No Yes

 If yes, describe potential impacts

16.) Cumulative and Indirect Impacts

Are cumulative and/or indirect impacts likely? No Yes
List “D” (documented) Categorical Exclusion (23 CFR 117[d])

August 22, 2018

 If yes, describe the reasonably foreseeable:

a) Cumulative impacts: Result from the incremental impact of the action when added to other past, present, and reasonably foreseeable future actions regardless of 

what agency (Federal or non-Federal) or person undertakes such other actions. Cumulative impacts can result from individually minor but collectively significant 

actions taking place over a period of time. 

b) Indirect Impacts: Caused by the action and are later in time or farther removed in distance, but are still reasonably foreseeable. Indirect impacts may include 

growth inducing effects and other effects related to induced changes in the pattern of land use, population density rate, and related effects on air, water and other 

natural systems, including ecosystems.

17.) Property Acquisition

Will there be property acquired for this project? No Yes

 If yes, please describe property acquisitions and indicate whether acquisition will result in relocation of businesses or individuals.

18.) Public Notification - Public outreach activities are not required for all projects. However, there may be specific conditions that require public outreach.

No public outreach activities were conducted for this project.

Public activities were or will be conducted for this project. 

 Describe public outreach efforts undertaken on behalf of the project. Indicate opportunities for public hearings, (board meetings, open houses, special hearings, etc.).

 Indicate any significant concerns expressed by agencies or the public regarding the project.

19.) Federal Land Management Agency (FLMA) Consistency Determination.

Yes - if applicable, attach the consistency statement from the FLMA (letter or email)

No - Describe the coordination and any information from the FLMA that allows the project to move forward.

Is the project consistent with applicable federal land management policies and/or plans?

Not Applicable

20.) Construction Impacts

Are there additional construction impacts not described in this document? No Yes

 If yes, please describe any potential impacts not described elsewhere.

G. Certification Based on project proposal and known information, the project is determined to be a Categorical Exclusion pursuant to the National 

Environmental Act listed in 23 CFR 771.117(d)

Title: Environmental Manager

Print Name

Approved By:

Signature:

Signature:

Print Name

Prepared By:
Attachment B: FEMA Floodplain Firmette


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IPaC resource list

This report is an automatically generated list of species and other resources such as critical habitat

(collectively referred to as trust resources) under the U.S. Fish and Wildlife Service's (USFWS)

jurisdiction that are known or expected to be on or near the project area referenced below. The list

may also include trust resources that occur outside of the project area, but that could potentially be

directly or indirectly aected by activities in the project area. However, determining the likelihood

and extent of eects a project may have on trust resources typically requires gathering additional

site-specic (e.g., vegetation/species surveys) and project-specic (e.g., magnitude and timing of

proposed activities) information.

Below is a summary of the project information you provided and contact information for the USFWS

oce(s) with jurisdiction in the dened project area. Please read the introduction to each section

that follows (Endangered Species, Migratory Birds, USFWS Facilities, and NWI Wetlands) for

additional information applicable to the trust resources addressed in that section.

Location

Fremont County, Idaho

Local oce

Idaho Fish And Wildlife Oce

 (208) 378-5243

 (208) 378-5262

1387 South Vinnell Way, Suite 368

Boise, ID 83709-1657

IPaC U.S. Fish & Wildlife Service

Attachment D: USFWS Environmental Resource List
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Endangered species

This resource list is for informational purposes only and does not constitute an analysis of

project level impacts.

The primary information used to generate this list is the known or expected range of each species.

Additional areas of inuence (AOI) for species are also considered. An AOI includes areas outside of

the species range if the species could be indirectly aected by activities in that area (e.g., placing a

dam upstream of a sh population, even if that sh does not occur at the dam site, may indirectly

impact the species by reducing or eliminating water ow downstream). Because species can move,

and site conditions can change, the species on this list are not guaranteed to be found on or near

the project area. To fully determine any potential eects to species, additional site-specic and

project-specic information is often required.

Section 7 of the Endangered Species Act requires Federal agencies to "request of the Secretary

information whether any species which is listed or proposed to be listed may be present in the area

of such proposed action" for any project that is conducted, permitted, funded, or licensed by any

Federal agency. A letter from the local oce and a species list which fullls this requirement can

only be obtained by requesting an ocial species list from either the Regulatory Review section in

IPaC (see directions below) or from the local eld oce directly.

For project evaluations that require USFWS concurrence/review, please return to the IPaC website

and request an ocial species list by doing the following:

1. Draw the project location and click CONTINUE.

2. Click DEFINE PROJECT.

3. Log in (if directed to do so).

4. Provide a name and description for your project.

5. Click REQUEST SPECIES LIST.

Listed species and their critical habitats are managed by the Ecological Services Program of the U.S.

Fish and Wildlife Service (USFWS) and the sheries division of the National Oceanic and Atmospheric

Administration (NOAA Fisheries ).

Species and critical habitats under the sole responsibility of NOAA Fisheries are not shown on this

list. Please contact NOAA Fisheries for species under their jurisdiction.

1. Species listed under the Endangered Species Act are threatened or endangered; IPaC also shows

species that are candidates, or proposed, for listing. See the listing status page for more

information.

2. NOAA Fisheries, also known as the National Marine Fisheries Service (NMFS), is an oce of the

National Oceanic and Atmospheric Administration within the Department of Commerce.

The following species are potentially aected by activities in this location:

Mammals

1

2

NAME STATUS
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Flowering Plants

Critical habitats

Potential eects to critical habitat(s) in this location must be analyzed along with the endangered

species themselves.

THERE ARE NO CRITICAL HABITATS AT THIS LOCATION.

Migratory birds

The birds listed below are birds of particular concern either because they occur on the USFWS Birds

of Conservation Concern (BCC) list or warrant special attention in your project location. To learn

more about the levels of concern for birds on your list and how this list is generated, see the FAQ

below. This is not a list of every bird you may nd in this location, nor a guarantee that every bird on

this list will be found in your project area. To see exact locations of where birders and the general

Grizzly Bear Ursus arctos horribilis

No critical habitat has been designated for this species.

https://ecos.fws.gov/ecp/species/7642

Threatened

NAME STATUS

Ute Ladies'-tresses Spiranthes diluvialis

No critical habitat has been designated for this species.

https://ecos.fws.gov/ecp/species/2159

Threatened

Certain birds are protected under the Migratory Bird Treaty Act and the Bald and Golden Eagle

Protection Act .

Any person or organization who plans or conducts activities that may result in impacts to migratory

birds, eagles, and their habitats should follow appropriate regulations and consider implementing

appropriate conservation measures, as described below.

1. The Migratory Birds Treaty Act of 1918.

2. The Bald and Golden Eagle Protection Act of 1940.

Additional information can be found using the following links:

Birds of Conservation Concern http://www.fws.gov/birds/management/managed-species/

birds-of-conservation-concern.php

Measures for avoiding and minimizing impacts to birds

http://www.fws.gov/birds/management/project-assessment-tools-and-guidance/

conservation-measures.php

Nationwide conservation measures for birds

http://www.fws.gov/migratorybirds/pdf/management/nationwidestandardconservationmeasures.pdf

1

2
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public have sighted birds in and around your project area, visit the E-bird data mapping tool (Tip:

enter your location, desired date range and a species on your list). For projects that occur o the

Atlantic Coast, additional maps and models detailing the relative occurrence and abundance of bird

species on your list are available. Links to additional information about Atlantic Coast birds, and

other important information about your migratory bird list, including how to properly interpret and

use your migratory bird report, can be found below.

For guidance on when to schedule activities or implement avoidance and minimization measures to

reduce impacts to migratory birds on your list, click on the PROBABILITY OF PRESENCE SUMMARY at

the top of your list to see when these birds are most likely to be present and breeding in your

project area.

Probability of Presence Summary

The graphs below provide our best understanding of when birds of concern are most likely to be

present in your project area. This information can be used to tailor and schedule your project

activities to avoid or minimize impacts to birds. Please make sure you read and understand the FAQ

“Proper Interpretation and Use of Your Migratory Bird Report” before using or attempting to

interpret this report.

Probability of Presence ( )

NAME BREEDING SEASON (IF A

BREEDING SEASON IS INDICATED

FOR A BIRD ON YOUR LIST, THE

BIRD MAY BREED IN YOUR

PROJECT AREA SOMETIME WITHIN

THE TIMEFRAME SPECIFIED,

WHICH IS A VERY LIBERAL

ESTIMATE OF THE DATES INSIDE

WHICH THE BIRD BREEDS

ACROSS ITS ENTIRE RANGE.

"BREEDS ELSEWHERE" INDICATES

THAT THE BIRD DOES NOT LIKELY

BREED IN YOUR PROJECT AREA.)

Bald Eagle Haliaeetus leucocephalus

This is not a Bird of Conservation Concern (BCC) in this area, but

warrants attention because of the Eagle Act or for potential

susceptibilities in oshore areas from certain types of development

or activities.

https://ecos.fws.gov/ecp/species/1626

Breeds Dec 1 to Aug 31

Golden Eagle Aquila chrysaetos

This is a Bird of Conservation Concern (BCC) only in particular Bird

Conservation Regions (BCRs) in the continental USA

https://ecos.fws.gov/ecp/species/1680

Breeds Dec 1 to Aug 31
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 probability of presence  breeding season  survey eort  no data

Each green bar represents the bird's relative probability of presence in the 10km grid cell(s) your

project overlaps during a particular week of the year. (A year is represented as 12 4-week months.)

A taller bar indicates a higher probability of species presence. The survey eort (see below) can be

used to establish a level of condence in the presence score. One can have higher condence in the

presence score if the corresponding survey eort is also high.

How is the probability of presence score calculated? The calculation is done in three steps:

1. The probability of presence for each week is calculated as the number of survey events in the

week where the species was detected divided by the total number of survey events for that

week. For example, if in week 12 there were 20 survey events and the Spotted Towhee was

found in 5 of them, the probability of presence of the Spotted Towhee in week 12 is 0.25.

2. To properly present the pattern of presence across the year, the relative probability of presence

is calculated. This is the probability of presence divided by the maximum probability of presence

across all weeks. For example, imagine the probability of presence in week 20 for the Spotted

Towhee is 0.05, and that the probability of presence at week 12 (0.25) is the maximum of any

week of the year. The relative probability of presence on week 12 is 0.25/0.25 = 1; at week 20 it is

0.05/0.25 = 0.2.

3. The relative probability of presence calculated in the previous step undergoes a statistical

conversion so that all possible values fall between 0 and 10, inclusive. This is the probability of

presence score.

To see a bar's probability of presence score, simply hover your mouse cursor over the bar.

Breeding Season ( )

Yellow bars denote a very liberal estimate of the time-frame inside which the bird breeds across its

entire range. If there are no yellow bars shown for a bird, it does not breed in your project area.

Survey Eort ( )

Vertical black lines superimposed on probability of presence bars indicate the number of surveys

performed for that species in the 10km grid cell(s) your project area overlaps. The number of

surveys is expressed as a range, for example, 33 to 64 surveys.

To see a bar's survey eort range, simply hover your mouse cursor over the bar.

No Data ( )

A week is marked as having no data if there were no survey events for that week.

Survey Timeframe

Surveys from only the last 10 years are used in order to ensure delivery of currently relevant

information. The exception to this is areas o the Atlantic coast, where bird returns are based on all

years of available data, since data in these areas is currently much more sparse.

SPECIES JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
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Bald Eagle

Non-BCC Vulnerable

(This is not a Bird of

Conservation

Concern (BCC) in this

area, but warrants

attention because of

the Eagle Act or for

potential

susceptibilities in

oshore areas from

certain types of

development or

activities.)

Golden Eagle

BCC - BCR (This is a

Bird of Conservation

Concern (BCC) only in

particular Bird

Conservation Regions

(BCRs) in the

continental USA)

Tell me more about conservation measures I can implement to avoid or minimize impacts to migratory birds.

Nationwide Conservation Measures describes measures that can help avoid and minimize impacts to all birds at

any location year round. Implementation of these measures is particularly important when birds are most likely to

occur in the project area. When birds may be breeding in the area, identifying the locations of any active nests and

avoiding their destruction is a very helpful impact minimization measure. To see when birds are most likely to

occur and be breeding in your project area, view the Probability of Presence Summary. Additional measures and/or

permits may be advisable depending on the type of activity you are conducting and the type of infrastructure or

bird species present on your project site.

What does IPaC use to generate the migratory birds potentially occurring in my specied location?

The Migratory Bird Resource List is comprised of USFWS Birds of Conservation Concern (BCC) and other species

that may warrant special attention in your project location.

The migratory bird list generated for your project is derived from data provided by the Avian Knowledge Network

(AKN). The AKN data is based on a growing collection of survey, banding, and citizen science datasets and is

queried and ltered to return a list of those birds reported as occurring in the 10km grid cell(s) which your project

intersects, and that have been identied as warranting special attention because they are a BCC species in that

area, an eagle (Eagle Act requirements may apply), or a species that has a particular vulnerability to oshore

activities or development.

Again, the Migratory Bird Resource list includes only a subset of birds that may occur in your project area. It is not

representative of all birds that may occur in your project area. To get a list of all birds potentially present in your

project area, please visit the E-bird Explore Data Tool.

What does IPaC use to generate the probability of presence graphs for the migratory birds potentially

occurring in my specied location?

The probability of presence graphs associated with your migratory bird list are based on data provided by the

Avian Knowledge Network (AKN). This data is derived from a growing collection of survey, banding, and citizen

science datasets .

Probability of presence data is continuously being updated as new and better information becomes available. To

learn more about how the probability of presence graphs are produced and how to interpret them, go the

Probability of Presence Summary and then click on the "Tell me about these graphs" link.
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How do I know if a bird is breeding, wintering, migrating or present year-round in my project area?

To see what part of a particular bird's range your project area falls within (i.e. breeding, wintering, migrating or

year-round), you may refer to the following resources: The Cornell Lab of Ornithology All About Birds Bird Guide, or

(if you are unsuccessful in locating the bird of interest there), the Cornell Lab of Ornithology Neotropical Birds

guide. If a bird on your migratory bird species list has a breeding season associated with it, if that bird does occur

in your project area, there may be nests present at some point within the timeframe specied. If "Breeds

elsewhere" is indicated, then the bird likely does not breed in your project area.

What are the levels of concern for migratory birds?

Migratory birds delivered through IPaC fall into the following distinct categories of concern:

1. "BCC Rangewide" birds are Birds of Conservation Concern (BCC) that are of concern throughout their range

anywhere within the USA (including Hawaii, the Pacic Islands, Puerto Rico, and the Virgin Islands);

2. "BCC - BCR" birds are BCCs that are of concern only in particular Bird Conservation Regions (BCRs) in the

continental USA; and

3. "Non-BCC - Vulnerable" birds are not BCC species in your project area, but appear on your list either because of

the Eagle Act requirements (for eagles) or (for non-eagles) potential susceptibilities in oshore areas from

certain types of development or activities (e.g. oshore energy development or longline shing).

Although it is important to try to avoid and minimize impacts to all birds, eorts should be made, in particular, to

avoid and minimize impacts to the birds on this list, especially eagles and BCC species of rangewide concern. For

more information on conservation measures you can implement to help avoid and minimize migratory bird

impacts and requirements for eagles, please see the FAQs for these topics.

Details about birds that are potentially aected by oshore projects

For additional details about the relative occurrence and abundance of both individual bird species and groups of

bird species within your project area o the Atlantic Coast, please visit the Northeast Ocean Data Portal. The Portal

also oers data and information about other taxa besides birds that may be helpful to you in your project review.

Alternately, you may download the bird model results les underlying the portal maps through the NOAA NCCOS

Integrative Statistical Modeling and Predictive Mapping of Marine Bird Distributions and Abundance on the Atlantic

Outer Continental Shelf project webpage.

Bird tracking data can also provide additional details about occurrence and habitat use throughout the year,

including migration. Models relying on survey data may not include this information. For additional information on

marine bird tracking data, see the Diving Bird Study and the nanotag studies or contact Caleb Spiegel or Pam

Loring.

What if I have eagles on my list?

If your project has the potential to disturb or kill eagles, you may need to obtain a permit to avoid violating the

Eagle Act should such impacts occur.

Proper Interpretation and Use of Your Migratory Bird Report

The migratory bird list generated is not a list of all birds in your project area, only a subset of birds of priority

concern. To learn more about how your list is generated, and see options for identifying what other birds may be

in your project area, please see the FAQ “What does IPaC use to generate the migratory birds potentially occurring

in my specied location”. Please be aware this report provides the “probability of presence” of birds within the 10

km grid cell(s) that overlap your project; not your exact project footprint. On the graphs provided, please also look

carefully at the survey eort (indicated by the black vertical bar) and for the existence of the “no data” indicator (a

red horizontal bar). A high survey eort is the key component. If the survey eort is high, then the probability of

presence score can be viewed as more dependable. In contrast, a low survey eort bar or no data bar means a lack

of data and, therefore, a lack of certainty about presence of the species. This list is not perfect; it is simply a starting
10/18/2018 IPaC: Explore Location

https://ecos.fws.gov/ipac/location/J5X7UESVAFBTXNLBRUEKVIVZC4/resources 8/9

point for identifying what birds of concern have the potential to be in your project area, when they might be there,

and if they might be breeding (which means nests might be present). The list helps you know what to look for to

conrm presence, and helps guide you in knowing when to implement conservation measures to avoid or

minimize potential impacts from your project activities, should presence be conrmed. To learn more about

conservation measures, visit the FAQ “Tell me about conservation measures I can implement to avoid or minimize

impacts to migratory birds” at the bottom of your migratory bird trust resources page.

Facilities

Wildlife refuges and sh hatcheries

REFUGE AND FISH HATCHERY INFORMATION IS NOT AVAILABLE AT THIS TIME

Wetlands in the National Wetlands Inventory

Impacts to NWI wetlands and other aquatic habitats may be subject to regulation under Section 404

of the Clean Water Act, or other State/Federal statutes.

For more information please contact the Regulatory Program of the local U.S. Army Corps of

Engineers District.

Please note that the NWI data being shown may be out of date. We are currently working to update

our NWI data set. We recommend you verify these results with a site visit to determine the actual

extent of wetlands on site.

This location overlaps the following wetlands:

FRESHWATER EMERGENT WETLAND

PEM1C

FRESHWATER FORESTED/SHRUB WETLAND

PFO1C

PSS1/FO1C

FRESHWATER POND

PUBK

PUBFx

RIVERINE

R3UBH

R2UBHx

R5UBFx

R5UBH

A full description for each wetland code can be found at the National Wetlands Inventory website
10/18/2018 IPaC: Explore Location

https://ecos.fws.gov/ipac/location/J5X7UESVAFBTXNLBRUEKVIVZC4/resources 9/9

Data limitations

The Service's objective of mapping wetlands and deepwater habitats is to produce reconnaissance level

information on the location, type and size of these resources. The maps are prepared from the analysis of high

altitude imagery. Wetlands are identied based on vegetation, visible hydrology and geography. A margin of error

is inherent in the use of imagery; thus, detailed on-the-ground inspection of any particular site may result in

revision of the wetland boundaries or classication established through image analysis.

The accuracy of image interpretation depends on the quality of the imagery, the experience of the image analysts,

the amount and quality of the collateral data and the amount of ground truth verication work conducted.

Metadata should be consulted to determine the date of the source imagery used and any mapping problems.

Wetlands or other mapped features may have changed since the date of the imagery or eld work. There may be

occasional dierences in polygon boundaries or classications between the information depicted on the map and

the actual conditions on site.

Data exclusions

Certain wetland habitats are excluded from the National mapping program because of the limitations of aerial

imagery as the primary data source used to detect wetlands. These habitats include seagrasses or submerged

aquatic vegetation that are found in the intertidal and subtidal zones of estuaries and nearshore coastal waters.

Some deepwater reef communities (coral or tubercid worm reefs) have also been excluded from the inventory.

These habitats, because of their depth, go undetected by aerial imagery.

Data precautions

Federal, state, and local regulatory agencies with jurisdiction over wetlands may dene and describe wetlands in a

dierent manner than that used in this inventory. There is no attempt, in either the design or products of this

inventory, to dene the limits of proprietary jurisdiction of any Federal, state, or local government or to establish

the geographical scope of the regulatory programs of government agencies. Persons intending to engage in

activities involving modications within or adjacent to wetland areas should seek the advice of appropriate federal,

state, or local agencies concerning specied agency regulatory programs and proprietary jurisdictions that may

aect such activities.
Henry's Fork Wetlands

U.S. Fish and Wildlife Service, National Standards and Support Team,

wetlands_team@fws.gov

Wetlands

Estuarine and Marine Deepwater

Estuarine and Marine Wetland

Freshwater Emergent Wetland

Freshwater Forested/Shrub Wetland

Freshwater Pond

Lake

Other

Riverine

October 18, 2018

0 0.25 0.5 1 mi

0 0.375 0.75 1.5 km

1:28,871

This page was produced by the NWI mapper

National Wetlands Inventory (NWI)

This map is for general reference only. The US Fish and Wildlife 

Service is not responsible for the accuracy or currentness of the 

base data shown on this map. All wetlands related data should 

be used in accordance with the layer metadata found on the 

Wetlands Mapper web site.

Attachment E: NWI Map
(page intentionally blank)
To: Project File, FHWA, WFLHD, 7/17/2019 

APPENDIX B

HYDRAULICS
(page intentionally blank)
Memorandum 

Western Federal Lands Highway Division

610 E. Fifth Street 

Vancouver, WA 98661-3801 

Draft Hydraulic Bridge Feasibility Study 

To: Seth English-Young, WFLHD Project Manager 

From: James Neighorn, P.E., WFLHD Hydraulics Engineer 

Date: November 15, 2018 

Project: Henry’s Fork Pedestrian Bridge Crossing Feasibility Study 

 

Introduction 

The City of St. Anthony and Bureau of Land Management, in Fremont County, Idaho, are studying the 

feasibility of constructing a trail bridge to improve greenway access and connectivity of trail segments 

within the Henry’s Fork Greenway. Proposed improvements begin approximately 1.5 miles west of US 

20 milepost 344 and ends approximately 0.25 miles north of the US 20 milepost 346. Western Federal 

Lands Highway Division (WFLHD) has developed three river crossing alternatives (See Vicinity Map, 

Figure 1). 

Summary of Options 

The project team conducted a site reconnaissance of the project area in October. The team developed three 

bridge crossing options for consideration which are summarized below and illustrated in Figure 2: 

Option 1: “Railroad Bridge Option” – Cross the Henry’s Fork near the existing railroad bridge. Two suboptions were developed for this location: 

Option 1A: Construct a new pedestrian bridge immediately downstream of the existing railroad 

bridge. The new bridge would consist of a two-span, 352-foot long steel truss with concrete pier 

foundation in the river. The pier foundation would be placed in-line with the existing railroad 

bridge pier. 

Option 1B: Acquire the existing railroad bridge from Eastern Idaho Railroad and convert it for 

pedestrian and bicycle use. 

Option 2: Island Hopping Option” – Construct a series of three bridges, with connecting trail segments, that 

cross the braided portion of the Henry’s Fork. The bridges would consist of a 352-foot, 150-foot, and 175-

foot steel truss bridges which would connect the islands across the braided river. Approximately 800-feet 

of boardwalk would be constructed on the islands to connect the bridges. 

Option 3: “Diversion Crossing Option” – Construct a 667-foot long four span steel truss bridge upstream 

of the diversion weir and boat launch. 

 
2 

Draft Hydraulic Bridge Feasibility Study 

November 15, 2018 

Table 1. Summary of Hydraulic Advantages 

 

Option 

1A 

Option 

1B 

Option 

2 

Option 

3 

Advantages 

Reduces risk of scour High Highest Lowest Low 

Reduce ice jam potential Higher Highest Lower Lowest 

Minimize fill within flood zone Higher Highest Lowest Low 

Allows for natural channel migration Highest Highest Lowest High 

Reduce post-flood maintenance Higher Highest Lowest High 

General Basin and Site Conditions 

Drainage in Fremont County flows south and west beginning at the Continental Divide. Fremont County 

is drained by the Henry's Fork of the Snake River and its tributaries. Henry's Fork begins at Henry's Lake 

and flows from north to south, dividing Fremont County. The Henrys Fork watershed is supplied by four 

major subbasins: upper Henrys Fork, lower Henrys Fork, Fall River, and Teton River. The basin flows 

are dominated by groundwater that originates as snowmelt from the Yellowstone Plateau. This snowmelt 

moves through geologic rhyolite layers and emerge as springs in the lower watershed reaches. Residence 

times and attenuation in these rhyolite aquifers are great, resulting in very stable and high baseflows in the 

Henry’s Fork. 

Flows within the Henry’s Fork are altered by the operation of Henrys Lake Dam, Grassy Lake Dam, and 

Island Park Dam which provide water storage for irrigation. In general, Henrys Lake Dam and Island 

Park Dam are operated so that winter flows are captured and the reservoirs are close to full during the 

spring. This results in low outflows from the dams during the winter. Irrigation has been heavily 

developed within the basin and the Henry’s Fork supplies water to approximately 15,000 acres in small 

blocks of land. Additionally, several large land areas are sub-irrigated within the basin. 

Within the study area, the Henry’s Fork is braided with multiple channels and islands. For much of the 

study area, the wetlands and the floodplain extend several hundred feet beyond the river channels. The 

topography of the vicinity is relatively flat with terraces immediately beyond the floodplain. These 

terraces are approximately 15 to 20 feet higher than the river level. Bedrock is exposed along the banks 

and river bed. Where bedrock is not exposed, it is expected that it can be found near the surface or within 

15 feet below the cover layer of cobbly gravel and sand alluvium. 

A weir extends across the Henry’s Fork at the northeast end of the study area. This weir diverts flow into 

the Independent Canal. A boat launch is located at the Independent Canal diversion on the north river 

bank. A two-span Pegram through truss bridge crosses over Henry's Fork on the west end of the study 

area. The bridge is owned by the Eastern Idaho Railroad and crosses at a narrow point in the river channel 

where bedrock formations constrict flow. 

Hydrology 

Peak discharges for Henry’s Fork are taken from a USGS streamgage located upstream from the bridge on 

Main Street of St. Anthony. The basin area consists of 1770 square miles with a mean basin elevation of 
3 

Draft Hydraulic Bridge Feasibility Study 

November 15, 2018 

6670 feet and mean annual precipitation of 33-inches. St. Anthony receives an average of 43-inches annual 

snowfall. Peak discharges estimates are presented in Table 2. 

Table 2. 

Peak Flood (cfs) 

2-yr 10-yr 25-yr 50-yr 100-yr 500-yr 

5,930 9,210 10,600 11,600 12,500 14,300 

The diversion intakes of the Egin, Saint Anthony Union, and Independent Canals area located between 

the streamgage station and the study area. These canals divert flows away from the river. Therefore, 

flows listed in Table 1 are conservatively higher since the canals likely act to reduce flows within the 

river channel. 

Floodplain and Flood-rise 

Federal Emergency Management Agency (FEMA) flood inundation map 160061 0530B (See Figure 3) was 

reviewed to determine what mapped floodplains occur within the project study area. Each of the three 

crossing alternatives are mapped within a Zone A floodplain designation. Zone A are areas of 100-year 

flood with base flood elevations and flood hazards factors not determined. Detailed mapping and study has 

not been completed in this zone. 

Bridge and trail alternatives that are constructed within the flood zone will require a detailed flood study to 

determine the 100-year flood elevations and any impacts to flooding. Alternatives will need to be designed 

to cause no rise in the 100-year flood profile. This will be particularly important since private properties 

with insurable buildings are found in the low-lying floodplain area immediately south of the study area. 

A no-rise certification (https://www.fema.gov/no-rise-certification-floodways), or a Conditional Letter of 

Map Revision (CLOMR https://www.fema.gov/conditional-letter-map-revision) will need to be submitted 

to the local floodplain manager. If a flood-rise results from a proposed improvement, further site 

investigation may need to be conducted to determine upstream impacts and necessary mitigation. 

Water Quality 

The primary potential pollutant in stormwater runoff, caused by bridge and trail improvements is 

sediment/total suspended solids originating from soils exposed onsite during the construction process. 

Sediment may be entrained in stormwater runoff from cut/fill slope areas that are excavated and graded 

for the trail and bridge approaches. Concentrations of petroleum products, suspended and dissolved metals, 

and other pollutants normally found in runoff from roadways will not be a concern since trail use will be 

limited to pedestrian and bicycle use. 

Stormwater best management practices (BMPs) will need to be implemented during construction to prevent 

soil erosion and sediment transport. These should be sufficient at preventing sediment from entering the 

Henry’s Fork and adjacent wetlands. 

Navigable Waterway 

Henry’s Fork River is listed as a navigable river under the authority of Idaho State, with a 15-horsepower 

maximum from the Fun Farm diversion dams to the Independent Canal Diversion Dam, east of the St. 

Anthony Cemetery. A boat put-in is located along the north bank of the Henry’s Fork near the beginning 

(east side) of the study area. Bridge crossing alternatives will need to consider providing sufficient 

clearance to accommodate river traffic. Matching the clearance provided by the existing railroad bridge, at 

the downstream (west side) of the study area will likely provide sufficient height for current river users. 
4 

Draft Hydraulic Bridge Feasibility Study 

November 15, 2018 

Flooding History 

Flooding in Fremont County has been mostly due to a rain-on-snow condition or a very warm temperature 

snowmelt. Major flooding on Henry's Fork has generally been due to warm temperature snowmelt 

conditions. The largest recorded flood to hit the Henry's Fork drainage (excluding the Teton Dam failure) 

occurred in May 1984. Very warm temperatures combined with above average snowpack at low elevations 

caused overbank flooding on Henry's Fork. The Henry's Fork gage at St. Anthony recorded a flow of 13,200 

cfs, which is just above a 100- year event. 

Three reservoirs in the Henry's Fork Basin provide some 221,800 acre-feet of storage. They are Henry's 

Lake and Island Park on upper Henry's Fork and Grassy Lake on the headwaters of Falls River. There is 

also a run-of-river power dam on Henry's Fork near Ashton but its usable storage is negligible. All three 

reservoirs are used for irrigation, with flood control being only incidental. Even though they were not 

constructed as flood protection measures, and formal agreements do not exist for their use as such, the 

numerous irrigation canals do provide some limited flood protection by diverting river flows, primarily 

from Henry's Fork, generally during peak flow times. Without the canals, natural peak flows would be 

higher. 

Ice is a major problem on Henry's Fork, downstream of St. Anthony. Ice jam flooding has historically 

exceeded free-flow flooding conditions. Ice jams are caused by the accumulation of frazil ice beneath and 

upstream of the sheet ice cover which forms on the river. As more frazil arrives, ice jams grow and cause 

the river just upstream to rise in stage and slow in velocity. Flooding caused by ice jams is similar to flash 

flooding. Ice jam formation causes a rapid rise of water at the jam and extends upstream. Failure or release 

of the jam causes sudden flooding downstream. The formation of ice jams depends on the weather and 

physical conditions in river channels. Ice jams are most likely to occur where the channel slope naturally 

decreases, where culverts freeze solid, at headwaters of reservoirs, at natural channel constrictions such as 

bends and bridges, and along shallows where channels may freeze solid. Ice jam floods can occur during 

fall freeze-up, during midwinter periods when stream channels freeze solid to form anchor ice, and during 

spring break-up when rising water levels from snowmelt or rainfall break the existing ice cover into large 

floating masses that lodge at bridges and other constrictions. Damage from ice jam flooding usually exceeds 

that caused by open water flooding. Flood elevations are usually higher than predicted for free-flow 

conditions (1 to 4 feet higher than the 100-year), and water levels may change rapidly. Additional physical 

damage may also be caused by the force of ice striking buildings and other structures. 

Ice jam flooding is a chronic problem for the lower 4 miles of the Henry's Fork in Fremont County. In the 

early 2000’s, an ice jam severely damaged the Salem Road bridge over the Henry’s Fork approximately 3.5 

miles west of the study area. According to the Fremont County Multi-Jurisdiction All Hazard Mitigation 

Plan, there is a high probability of annual flooding along the Henry’s Fork. Significant flooding occurs 

annually between St. Anthony and Parker in the riparian areas within the FEMA FIRM designated 

floodplain. 

Proposed bridge structures need to be designed to accommodate ice jam conditions and meet requirements 

by the Fremont County Emergency Management coordinator and the Floodplain Administrator. The 

bridges and associated trails must also demonstrate that they will not aggravate ice jam formation and 

flooding conditions. 
5 

Draft Hydraulic Bridge Feasibility Study 

November 15, 2018 

Scour 

A scour analysis has not been performed as part of this initial feasibility study. Final foundation types still 

need to be determined following a geotechnical investigation as project development continues. Due to the 

expected near surface bedrock within the area, shallow foundations are considered feasible for the bridge 

site alternatives. Once foundation types have been identified, a scour analysis will need to be performed for 

each bridge. Where practical, bridge foundations will need to be extended to sound bedrock to eliminate 

potential undermining due to scour. 

Hydraulic Design Considerations 

The following discusses key hydraulic design considerations for each of the options: 

Option 1A - Construct a new pedestrian bridge on the downstream side of the existing railroad bridge. The 

proposed bridge would consist of a two span, 352-foot long steel truss with a single concrete pier foundation 

in the river. A minimum of 8-foot pedestrian walkway width is provided on the proposed bridge. Minimal 

trail work would be included, only constructing connections at the ends of the bridge. 

This option takes advantage of the natural river constriction at the existing railroad bridge. Bridge 

abutments would extend outside of the floodplain and would likely be founded in the bedrock which is 

visible along the channel banks. This would likely eliminate scour concerns for the abutments. However, 

the single concrete pier foundation will need to be analyzed for scour unless the foundation can be extended 

into bedrock. 

Extending the abutments outside the floodplain will avoid impacting the flood zone, will not restrict river 

migration, and prevent ice jams from impacting the abutments. The single concrete pier should be located 

so that it aligns with the existing railroad bridge’s pier. This will ensure that the new pier will not further 

constrict the channel and will likely not cause a rise in flood levels. The existing pier will also act to 

protected the new pier from debris and ice jams. A hydraulic analysis will need to be performed to verify 

that the pier does not cause a flood rise. 

The new bridge structure should be elevated to match the clearance provided by the existing railroad bridge. 

The existing railroad bridge has not historically been affected by ice jams or debris and provides sufficient 

clearance for river boat users. Providing similar clearance will eliminate concerns for ice jam and debris 

damage, and will avoid restricting current boat use. Maintenance of the new structure would be limited, 

with little to no additional maintenance resulting from hydraulic conditions. 

Option 1B - Acquire the existing railroad bridge and convert it to only pedestrian and cyclist access. Install 

new timber decking and pedestrian railing. This approach is similar to many other “rails to trails” projects 

that have been completed at many other historic railroad bridges. 

A full review of the existing bridge structure and foundation conditions will need to be conducted to ensure 

that the abutments and the pier are founded in sound bedrock and are not susceptible to undermining due 

to scour. 

No work would be required within the waterway or floodplain. This avoids impacts to flood levels, 

restriction of natural channel migration, and ice jam concerns. 

Option 2 - “Island Hopping Option” – Construct a series of three bridges, with connecting trail segments, 

that cross the braided portion of the Henry’s Fork. The bridges would consist of a 352-foot, 150-foot, and 
6 

Draft Hydraulic Bridge Feasibility Study 

November 15, 2018 

175-foot steel truss bridges which would connect the islands across the braided river. Approximately 

800-feet of boardwalk would be constructed on the islands to connect the bridges.

The abutment and pier foundations will need to be analyzed for scour. Foundation designs will need to be 

adjusted to account for scour or will need to extend into competent bedrock. 

Bridge structures will need to be elevated to allow for flood, debris, ice jam, and boat access. This will 

likely require elevating the bridges well above the normal water surface level to a similar clearance as the 

existing downstream railroad bridge. The elevated bridges will require construction of significant approach 

embankments if they are designed to meet ADA access requirements. Trail approach embankments within 

the flood zone will likely need to have countermeasures, such as riprap, installed to prevent scour and 

erosion. The ability to construct boardwalks along the natural floodplain elevation within the islands will 

be significantly reduced due to the need to construct the approach embankments for ADA access. 

A flood rise analysis will need to be performed. Due to the extensive amount of abutment and embankment 

construction within the floodway, this option has a high probability of increasing flood levels within the 

flood zone and of being impacted by ice jams. The fixed abutments and approach trail embankments within 

the floodplain will also limit natural channel migration within this braided segment of the Henry’s Fork. 

With the increased number of piers, abutments, and trail constructed within the floodway, there will be a 

greater amount of maintenance required to address scour, debris, ice damage, and embankment erosion. 

Regular flooding over the proposed boardwalk may require increased debris removal and possible 

boardwalk repair. 

Option 3 - Construct a new pedestrian bridge on the upstream side of the existing irrigation diversion and 

weir at the northern end of the study area. The proposed bridge would consist of a four span, 667-foot long 

steel truss with three concrete pier foundations in the river. A minimum of 8-foot pedestrian walkway 

width is provided on the proposed bridge. 

The abutment and pier foundations will need to be analyzed for scour. Foundation designs will need to be 

adjusted to account for scour or will need to extend into competent bedrock. 

The bridge will need to be elevated to allow for flood, debris, ice jam, and boat access. This will likely 

require elevating the bridge above the normal water surface level to a similar clearance as the existing 

downstream railroad bridge. Some trail work, needed for ADA grade requirements, would be included to 

connect the bridge to the existing trail on the south end and the existing boat launch on the north end. 

A flood rise analysis will need to be performed to verify that the added piers within the floodway do not 

result in a flood rise. Construction of the abutments outside of the flood zone significantly reduces the 

potential for a flood rise and allows for natural channel migration. Impacts due to ice jams will still be a 

concern for this option due to the number of piers located in the channel and the bridge location upstream 

of the weir. 

With the longer bridge and increased number of piers within the waterway there may be an increase in the 

amount of maintenance required to address scour, debris, and ice damage. 

Attachments: Figure 1 – Study Area Map; Figure 2 – Bridge Options; Figure 3 – FEMA Flood Map 

 Photos 
Figure 1 – Study Area Map 

Figure 3
Historic Pegram Two-Span Truss Railroad Bridge 

Braided River Channel and Islands 

 
Braided River Channel and Islands 

Diversion Weir at Northeast End of Study Area 
(page intentionally blank)
To: Project File, FHWA, WFLHD, 7/17/2019 

APPENDIX C

GEOTECHNICAL
(page intentionally blank)
158377846 

 

M E M O R A N D U M

Western Federal Lands Highway Division 

610 E. Fifth Street 

Vancouver, WA 98661 

DATE: December 17, 2018 

TO: Seth English-Young, Project Manager 

Benn Oltmann, Structures Functional Manager 

FROM: Evan Garich, PE 

Geotechnical Engineer 

SUBJECT: Geotechnical Memo 39-18 

Henry’s Fork Bridge Geotechnical Feasibility Memo 

ID STANTH T 2017(1) – Henry’s Fork Greenway 

Bridge Feasibility Study 

St. Anthony, ID 

EXECUTIVE SUMMARY 

Shallow foundations are considered feasible for the bridge site alternatives being considered 

under the current study. Final foundation types should be determined following a geotechnical 

investigation as project development continues. A geotechnical investigation should be 

performed during the preliminary engineering phase at the selected crossing location. A 

geotechnical investigation may not be required if the crossing occurs on an existing structure. 

Final recommended foundation types will be based on project requirements including bridge 

loading, soil/rock properties, scour requirements, and other geotechnical considerations. 

INTRODUCTION 

This memo has been developed to provide general geotechnical considerations to support the 

Henry’s Fork Greenway Bridge Feasibility Study (Project). The information presented in this 

memo was developed from a site visit performed on September 11 and 12, 2018 as well as 

desktop studies. Geotechnical investigations have not been performed for this project. 

PROJECT DESCRIPTION 

The project is in the Henry’s Fork Greenway, near the city of St. Anthony, ID along the Henry’s 

Fork of the Snake River. The project begins approximately 1.5 miles west of US 20 milepost 

(MP) 344 and ends at approximately 0.25 miles north of US 20 MP 346.The project involves 

developing up to three river crossing alternatives within the Henry’s Fork Greenway. The site 

vicinity is shown in Figure 1. 
 

Page 2 of 13 

Figure 1. Project site area. 

SITE CONDITIONS 

The project site is located along the Henry’s Fork of the Snake River. The river is confined to 

one channel at each end of the project area. However, the river splits into several channels, 

separated by low lying islands through most of the project area. The Henry’s Fork ranges from 

approximately 225 feet to 1,350 feet wide in the project area. At several locations along the 

Henry’s Fork wetlands and the floodplain extend several hundred feet beyond the river 

channels. The topography of the vicinity is relatively flat. Terraces immediately beyond the 

floodplain are up to approximately 20 feet higher than the river level. Attachment 1 contains 

photographs taken during the site visit. 

GEOLOGY AND SEISMICITY 

The project site is located within the Snake River Plain physiographic province. The province 

consists of large volumes of rhyolite overlain with basalt (Alt and Hyndman, 1989). Alluvium 

(Qa) is found along the Henry’s Fork River in the project area. The alluvium is mapped as 

sandy gravel with cobbles and rare basalt boulders with localized humic silt present in some 

sloughs (Phillips, 2012). The alluvium is mapped as generally less than 10 to 15 feet thick. 

The mapped geology appears consistent with observations during the field visit. Unless 

manmade fill, the soil within the floodplain, on the low islands, and low terrace is alluvium. 

Approximately 15 to 20 feet above the existing river level and flood plain is terrace alluvium 

(Qt1, Qt2) consisting of cobbley gravel and sand which is similar to the alluvium (Phillips, 

2012). 
 

Page 3 of 13 

Basalt of St. Anthony (Qbsa) is exposed along much of the Henry’s Fork in the project area. In 

locations where the bedrock is not exposed, it is expected to be located beneath 0 to 

approximately 15 feet of alluvium. The depth to rock may be more in locations where 

manmade fill and embankments have been placed. Figure 2 displays the mapped geology of 

the project vicinity. 

Figure 2. Geologic Map of project area. (Phillips, 2012) 

The project site is located within a seismically active area vulnerable to shallow crustal 

earthquakes. The closest known major earthquake is the magnitude 7.3 Hebgen Lake, 

Montana earthquake which occurred in 1959, approximately 80 miles from the project site. 

There are no known active faults within the project area. Three potentially active faults have 

been mapped within 50 miles of the project site. These include the Centennial, Teton, and 

Madison faults (USGS, 2014). 

 Centennial Fault: A east-west trending fault located approximately 40 miles north of 

the project site. The total length of the fault is estimated to be 40 miles. Portions of the 

fault may have displaced in the last 15,000 years. 

Project Area 

N 
 

Page 4 of 13 

 Teton Fault: A north-south trending fault located approximately 45 miles east of the 

project site. The total length of the fault is estimated to be 40 miles. Portions of the 

fault may have displaced in the last 2,000 years. 

 Madison Fault: A north-south trending fault located approximately 50 miles north of the 

project site. The total length of the fault is estimated to be 70 miles. Portions of the 

fault may have displaced in the last 5,000 years. 

Preliminary Seismic Parameters 

Earthquakes from unmapped faults and the above faults could result in ground shaking. 

Ground shaking is responsible for generating high inertial forces and excessive dynamic 

movements that can impart unacceptable damage to structures. Design ground motions at the 

site have been developed following AASHTO Load and Resistance Factor Design (LRFD) 

guidelines and United States Geologic Survey (USGS) seismic mapping. Table 1 presents 

ground motion parameters that have been developed based on a preliminary assessment of 

the site (USGS, 2018). 

Table 1. Summary of Seismic Parameters (7% PE in 75 years) - General Procedure.

Site Class (by Soil Type and Profile) B 

Horizontal Peak Ground Acceleration (PGA) 0.14g 

Horizontal Response Spectral Acceleration at Period of 0.2 sec (Ss) 0.33g 

Horizontal Response Spectral Acceleration at Period of 1.0 sec (S1) 0.12g 

Site Factor for Zero-Period on Acceleration Spectrum (Fpga) 1.00 

Site Factor for Short-Period Spectral Acceleration (Fa) 1.00 

Site Factor for Long-Period Spectral Acceleration (Fv) 1.00 

Modified Horizontal Peak Ground Acceleration (As) 0.14g 

Modified Horizontal Response Spectral Acceleration at Period of 0.2 sec (SDS) 0.33g 

Modified Horizontal Response Spectral Acceleration at Period of 1.0 sec (SD1) 0.12g 

Seismic Zone 1 

Site Class B was selected based on the expected shallow depth to and outcropping of 

bedrock in the project vicinity. Recommended seismic design parameters may change during 

subsequent project phases based on site conditions. Performing geotechnical borings and 

obtaining soil samples via the Standard Penetration Test method at the bridge pier locations 

will provide the necessary information required for the seismic characterization during the 

design phase. Geophysical measurement of the soil shear wave velocity may be used to 

supplement information gathered from the borings. 
 

Page 5 of 13 

PRELIMINARY FOUNDATION CONCEPTS 

Due to the shallow and outcropping bedrock in the project area, shallow foundations are 

considered feasible for bridges at the site. However, deep foundations may be required if 

bedrock is deeper than anticipated, lateral sliding forces cannot be resisted by footings, or if 

overturning moments exceed footing capacities. 

Shallow foundation systems, such as spread footings, are likely acceptable for bridge 

locations being considered for this study. Shallow foundation systems will need to be 

designed for appropriate bearing capacity, settlement, overturning, and sliding capacity. 

Foundations placed near the river level or on islands will require dewatering. Scour protection 

must be provided as determined by the hydraulic requirements. 

In additional to spread footings, a type of shallow foundation system that could be appropriate 

at an abutment is a Geosynthetic Reinforced Soil – Integrated Bridge System (GRS-IBS). 

GRS-IBS abutments consist of closely spaced layers of geosynthetic reinforcement and 

compacted granular fill with a segmental retaining wall facing unit (SRWU) to create an 

abutment and integrated approach for the bridge. A reinforced soil foundation is typically 

constructed as a base, the geosynthetic reinforced soil and block facing is constructed on the 

reinforce soil foundation, and the bridge deck is supported directly on a bearing bed atop the 

GRS structure. A typical cross-section through a GRS-IBS abutment is shown in Figure 3. The 

system is easy to design and inexpensive to construct. It can be quickly built in variable 

weather conditions with semi-skilled labor and equipment and can easily be modified in the 

field. GRS-IBS is more flexible compared to other foundation alternatives during seismic 

events. It may be determined that GRS-IBS abutments are not appropriate during subsequent 

phases of the project. 

Figure 3. Typical GRS-IBS Cross Section (Adams and Nicks, 2018). 
 

Page 6 of 13 

If shallow foundations are not suitable a deep foundation will be required. Due to the shallow 

bedrock observed in the project area, rock socketed piles are considered feasible. It is 

expected the relatively modest loading will not warrant traditional drilled shafts. It is unlikely 

driven piles will penetrate into rock enough to provide the required lateral and scour resistance 

without drilling a rock socket. A concrete filled rock socket of ten feet depth or less should 

allow for the piles to be loaded to the structural capacity of the section. Steel H piles or pipe 

piles are considered feasible. Foundation types will be based on the results of a future 

geotechnical investigation. 

REFERENCES 

Adams, M. and Nicks, J., 2018, Design and Construction Guidelines for Geosynthetic 

Reinforced Soil Abutments and Integrated Bridge Systems, Federal Highway Administration, 

Report No. FHWA-HRT-17-080, June 2018. 

Alt, D. and Hyndman, D.W., 1989, Roadside Geology of Idaho. 

Phillips, W.M., 2012, Geologic Map of the St. Anthony Quadrangle, Fremont and Madison 

Counties, Idaho, Idaho Geologic Survey, Digital Web Map 145. 

USGS, 2014, 2014 National Seismic Hazard Maps – Source Parameters, 

https://earthquake.usgs.gov/cfusion/hazfaults_2014_search/query_results.cfm (accessed 

10/25/2018). 

USGS, 2018, U.S. Seismic Design Maps application, 

https://earthquake.usgs.gov/designmaps/us/application.php (accessed 10/25/2018) 

CLOSING 

Please contact Evan Garich at (360) 619-7224 or Evan.Garich@dot.gov with any questions 

regarding this memorandum. 

INITIALS 

CC: Geotechnical File 

Attachments: 

Attachment 1 – Site Photographs 
 

Picture 1. Looking across river at weir location from south bank. 

Picture 2. Looking across river at weir locations from north bank. 
 

Page 8 of 13 

Picture 3. Bedrock outcropping and river along south bank. 

Picture 4. Facing downstream from south bank, several islands present in background. 
 

Page 9 of 13 

Picture 5. Gravel and cobbley alluvium. 

Picture 6. Typical channel and islands in project area. 
 

Page 10 of 13 

Picture 7. Bank stabilization performed ~10 years ago consisting of riprap placement and 

revegetation. 

Picture 8. Looking south across river channel toward islands from north bank near sewer 

lagoons. 
 

Page 11 of 13 

Picture 9. View of existing rail bridge from north bank. 

Picture 10. Facing upstream from north bank near existing rail bridge. 
 

Page 12 of 13 

Picture 11. Facing south bank from downstream of existing rail bridge. 

Picture 12. View of existing rail bridge from south bank. 
 

Page 13 of 13 

Picture 13. Basalt outcrop, upstream of existing rail bridge on south bank. 
(page intentionally blank)
To: Project File, FHWA, WFLHD, 7/17/2019 

APPENDIX D

PUBLIC INVOLVEMENT 
(page intentionally blank)
Memorandum 

Western Federal Lands Highway Division

610 E. Fifth Street 

Vancouver, WA 98661-3801 

TO: 

FROM: 

DATE: 

SUBJECT: 

Project Files 

Seth English-Young, WFLHD 

July 1, 2019 

Public Involvement Summary for the Henry’s 

Fork Bridge Feasibility Study – ID STANTH T 

2017(1) 

The purpose of this memo is to describe the public involvement for the Henry’s Fork Bridge 

Feasibility Study project – ID STANTH T 2017(1). 

FHWA completed the draft Bridge Feasibility Study and Implementation and Funding Plan in March 

2019 and the public comment period was March 21 to May 6, 2019. 

Project partners held an open house on April 16, 2019. The City advertised the meeting by placing a 

public notice in the Rexburg Standard-Journal newspaper, sending emails to interested parties, 

posting signs in town and at the project site, sending an informational flyer out with a utility bill, and 

placing information on the City marquee. The FS sent out an email to their interested party list as 

well. FHWA place the documents on a website (https://flh.fhwa.dot.gov/projects/id/henrys-fork/). 

FHWA, City, and BLM staff attended the meeting and gave information and answered questions. 

Open house materials are attached to this memo and included six large information boards, an 

informational handout, a comment sheet with a questionnaire, and a slideshow of computer-generated 

images of the bridge options. On April 23, 2019, the Rexburg Standard Journal ran an article about 

the project and open house (attached). 

Sixteen people signed into the open house. The project partners received 17 written comments, either 

in person at the meeting, by mail, or by email. The comments are attached to this memo. Ten people 

provided comments on the questionnaire handed out at the meeting and six people provided 

comments in another form. The questionnaire asked the following questions, with summarized 

results. 
 

Page 2 of 2 

1. What is your relationship to the Henry’s Fork Greenway? 

Visitor: 1 

Adjacent property owner/resident: 0 

Fremont County resident: 10 

Other: (multiple answers) 

2. On average, how many times a year do you visit the Henry’s Fork Greenway? 

0: 0 

1-2: 1 

3-5: 1 

6-12: 2 

More than 12: 6 

3. What type of activities do you do when visiting the Henry’s Fork Greenway? 

Hiking/walking: 10 

Biking: 5 

Fishing: 4 

Hunting: 1 

Other: (multiple answers) 

4. Which option presented do you prefer? 

(The totals in this section include all comments (both in the questionnaire or other form of 

written comment) indicating a preferred option, including some people who checked multiple 

preferred options.)

Option 1A: 7 

Option 1B: 9 

Option 2: 5 

Option 3: 0 

I prefer none of these: 1 

General Comments 

(Summarized from all 17 written comments) 

 Wants any option to provide a loop (7) 

 Cost of bridges excessive (7) 

 Certain options don’t create loop (4) 

 Concern about disturbing wildlife (3) 

 Loop would be too long (2) 

 Concern about overlap of hunting and hiking/bird watching (2) 

 Concern about high and low-water (2) 

 Concern about maintenance costs for Option 1B 

 Prefers Option 2 because it is at a parking area 

 Would like partners to consider moving Henry's Fork Pratt Truss Bridge (AKA Fun Farm 

Bridge) to the study area 

 Concern about the visual impact of new bridges (Option 2 and 3)
4/23/2019 The Henry's Fork Greenway Pedestrian Bridge Feasibility Study is open for public comment. | | rexburgstandardjournal.com

https://www.rexburgstandardjournal.com/the-henry-s-fork-greenway-pedestrian-bridge-feasibility-study-is/article_da4ab642-a606-58fd-a072-ce3baf582037.html 1/2

https://www.rexburgstandardjournal.com/the-henry-s-fork-greenway-pedestrian-bridge-feasibility-studyis/article_da4ab642-a606-58fd-a072-ce3baf582037.html

The Henry's Fork Greenway Pedestrian Bridge Feasibility

Study is open for public comment.

By Victoria Varnedoe vvarnedoe@uvsj.com 21 hrs ago

ST. ANTHONY − The Federal Highway Administration (FHA) held an open house on April 16, to

inform the public about a bridge feasibility study. They are currently accepting public comment and

will do so until May 6.

“We’re looking at a few options on how to cross the henry’s fork within the greenway and getting

feedback from the public on what they like and answering any questions [they have],” said Seth

English-Young, with the Federal Highway Administration.

The map depicted at the top shows the crossing feasibility area. The bottom map shows where Option 1A & 1B would be loca

as well Option 2 and Option 3.

Courtesy Photo/The Federal Highway Administration

Attachment A: Article in Rexburg Standard-Journal
4/23/2019 The Henry's Fork Greenway Pedestrian Bridge Feasibility Study is open for public comment. | | rexburgstandardjournal.com

https://www.rexburgstandardjournal.com/the-henry-s-fork-greenway-pedestrian-bridge-feasibility-study-is/article_da4ab642-a606-58fd-a072-ce3baf582037.html 2/2

The open house was an opportunity to inform the public and for the FHA to take comments and

address questions.

“The city of St. Anthony and BLM applied for funding for this study and were awarded funding under

the Federal Lands Access Program and that paid for this study,” English-Young said. “We work to

gather information from locals and from existing conditions and determine what are feasible options

for crossing the river.”

The study is currently in draft form and includes four different project options.

“We’ll take any comments and make revisions as necessary and once we have a final draft then that’s

where the project ends for the time being,” English-Young said. “Then BLM and the City will

determine how they want to move forward [and obtain funding].”

Those looking to submit public comment have several venues to do so.

They can call in at 360-619-7803.

They can send an email with their public comment to seth.english-young@dot.gov

Or send their public comment by postal mail to:

Western Federal Lands Highway Division

Attn: Seth English-Young

610 east 5th Street Vancouver, WA, 98661

For more information, visit the FHA website at flh.fhwa.dot.gov/projects/ID/henrys-fork











April 24, 2019  

Henry’s Fork Greenway Pedestrian Bridges 

Western Federal Lands Highway Division  

Atten:  Seth English‐Young 

To Whom It May Concern:   

I would like to submit the following thoughts about possible river crossings for the St. Anthony Henry’s 

Fork Pedestrian Bridges Feasibility Study:   

1. The option for ‘island hopping’ along and within the river channel is a romantic and exciting

idea and would be a first‐choice if the cost of this option was feasible.  It seems this would be a

very expensive option and is likely to prevent a move forward to any option, because of it’s

expense.

2. Creating a new bridge lower to the surface of the river is a good option as it is one structure for

which to seeking funding.

3. Using the existing Eastern Idaho Railroad Bridge currently in place seems to be to be the best

and most affordable option.  Even if there was some monetary exchange with EIRR to obtain the

bridge, it seems it would be much less than building new.  And, perhaps the bridge would be

gifted from EIRR.  This bridge is on the national historical register and should be preserved and

improved.  The bridge very nearly connects to the existing Greenway Path; making is yet a more

affordable option.

Thank you for your time and expertise in conducting this Study and helping the St. Anthony Greenway 

expand.   

Respectfully submitted  

James C. Hobbs 

James C. Hobbs  

PO Box 34  

St. Anthony, ID 834345  

208.390.3801  
May 1, 2019  

Henry’s Fork Greenway Pedestrian Bridges 

Western Federal Lands Highway Division  

Atten:  Seth English‐Young 

To Whom It May Concern:   

I would like to submit the following thoughts about possible river crossings for the St. Anthony Henry’s 

Fork Pedestrian Bridges Feasibility Study:   

1. The option for ‘island hopping’ along and within the river channel is a romantic and exciting

idea and would be a first‐choice if the cost of this option was feasible.  It seems this would be a

very expensive option and is likely to prevent a move forward to any option, because of it’s

expense.

2. Creating a new bridge lower to the surface of the river is a good option as it is one structure for

which to seeking funding.

3. Using the existing Eastern Idaho Railroad Bridge currently in place seems to be to be the best

and most affordable option.  Even if there was some monetary exchange with EIRR to obtain the

bridge, it seems it would be much less than building new.  And, perhaps the bridge would be

gifted from EIRR.  This bridge is on the national historical register and should be preserved and

improved.  The bridge very nearly connects to the existing Greenway Path; making is yet a more

affordable option.

Thank you for your time and expertise in conducting this Study and helping the St. Anthony Greenway 

expand.   

Respectfully submitted  

Judith L. Hobbs 

Judith L. Hobbs 

PO Box 34 

St. Anthony, ID 834345  

208.390.8787  
From: Lisa O. Kyser

To: English-Young, Seth (FHWA)

Subject: Option 2, "The Island Hop Trail"

Date: Saturday, May 4, 2019 5:14:45 PM

Good afternoon,

My name is Lisa Kyser O'Shaughnessy and I live at 7 S. 3rd E. St.

Anthony, and I would love to talk about the feasibility choices for

bridges to get constructed for linking both sides of the river as one

large loop. I have your material in front of me and looking at the

choices and studying the paperwork, I can tell you will not to many

people here in St Anthony who will fill them out, but we are now growing

and growing fast, and the idea of a linking walking paths is something no

one else has within their local cities and would give us a big jump on a

wonderful place to live.

I have lived here for 4 years now, and own a home, and love it. I also

run a dear Abnb just up from the Sandbar Park. This little town caught

my attention because of the ''river.'' I am an avid on top kayaker and

love this area to do this in. And have many that would like to see more

entrances for this reason, including a path to the river through the

Boys Park. Yet when this new idea came up it sounded even better and I

am excited to see something of this type here connecting the islands

together. 

"And that is where I make my choice." I would go with the trail to the

railroad bridge, but with private property in the way, and I know just by

human nature owners will not deal for a public trail on private land. SO I

CHOOSE OPTION 2. The idea of having islands to explore and fish

off, is just a win-win situation the rest can wait for another time. I love

to fish as well, and if you notice people that love to fish need space. So

having connections from island to island is a great answer! 

Everything these days is expensive, but if you have a tourist trade, and

you have a wonderful lifestyle to enjoy the rivers for swimming and

recreation, growth will come, and done right we could out do Rexburg

for the place to live as a bedroom community! I don't mind growth, I

know many people fight growth with all their might, but once the growth

starts, they all of a sudden realize it's not as bad as it sounds. 

We are on the gateway to Yellowstone, and not even Yellowstone has
what we have, and that is 'No grizzly Bears'. Our trails can be used

year around even for cross country skiers on an afternoon. Their will

always be hazards like Moose, snow, and water, but we all live around

them, and learn they have their place and respect. 

Please put me down for 'Option 2', 'THE ISLAND HOP TRAIL.' And

thanks for asking and trying to get us to participate. I am hoping to

make it to this next meeting. Please continue to keep us informed

through Facebook. And, I would still like to take a tour of entry and

exit of bridges for 'Island Hop Trail' and get a feel for them and their

options. Thanks so much. Lisa Kyser

Any question for me, my number is 208-403-6154
From: Randall Marrett

To: English-Young, Seth (FHWA)

Subject: St Anthony bridge

Date: Thursday, April 25, 2019 7:29:50 PM

I prefer option 2, because it is at one of the parking areas.
1

English-Young, Seth (FHWA)

From: Mike Webster <webstermikeandsally@gmail.com>

Sent: Tuesday, April 23, 2019 7:12 AM

To: English-Young, Seth (FHWA)

Subject: Fwd: Delivery Status Notification (Failure)

‐‐‐‐‐‐‐‐‐‐ Forwarded message ‐‐‐‐‐‐‐‐‐ 

From: Mail Delivery Subsystem <mailer‐daemon@googlemail.com> 

Date: Tue, Apr 23, 2019 at 8:10 AM 

Subject: Delivery Status Notification (Failure) 

To: <webstermikeandsally@gmail.com> 

Address not found  

Your message wasn't delivered to english‐young@dot.gov because the address couldn't be found, or 

is unable to receive mail.  

The response from the remote server was: 

550 #5.1.0 Address rejected. 

‐‐‐‐‐‐‐‐‐‐ Forwarded message ‐‐‐‐‐‐‐‐‐‐ 

From: Mike Webster <webstermikeandsally@gmail.com> 

To: "english‐young@dot.gov" <english‐young@dot.gov> 

Cc:  

Bcc:  
2

Date: Tue, 23 Apr 2019 08:09:45 ‐0600 

Subject: Bridge for St. Anthony Henry's Fork Greenway 

Plans are currently underway to replace the old Fun Farm bridge that is located approximately 3 miles east of St. 

Anthony.  This is a historic bridge that is over 100 years old and efforts need to be made to preserve the bridge.  It is a 

Pratt Truss Bridge and would easily accommodate foot traffic as well as preserve a piece of history. 

A study was done for the I.D.O.T in 2018 by Preservation Solutions LLC that cataloged the few remaining steel bridges in 

the State of Idaho.  The Henry's Fork Pratt Truss Bridge (AKA Fun Farm Bridge) was part of that study.  The loss of these 

historic bridges has already begun in this area with the destruction of the old Del Rio Bridge.  Efforts need to be put in 

place for their preservation. 

If this bridge would be suitable for the area in question, we would encourage that option be explored further. 

Thank you. 

Michael and Sally Webster 

webstermikeandsally@gmail.com
1

English-Young, Seth (FHWA)

From: kim ragotzkie <kragotzkie@gmail.com>

Sent: Monday, May 6, 2019 4:39 PM

To: English-Young, Seth (FHWA)

Subject: Henrys Fork Greenway Pedestrian Feasibility Study

Follow Up Flag: Follow up

Flag Status: Flagged

Seth, I missed the open house for this potential project but wish to add my comments if it isn't too late. 

I'm a Fremont County resident, and visit the HF Greenway on a regular basis to walk, enjoy the sounds of the river, and 

watch birds and other wildlife.  I also occasionally fly‐fish in this area, using the pedestrian trail to gain access.  Although 

I am a hunter, I do not hunt in this area as there are too many people and homes near the river for me to feel 

comfortable hunting in this area.   

I most strongly support Alt. 1B if you could gain rights to the existing railroad bridge and convert it to a pedestrian 

trail.  However, if that is not possible, I also support Alt. 1A.  Both of these offer the potential for a loop trail if the trail 

on the southside can somehow be connected between the Carter property and the RR ROW.   

I am very much opposed to Alt. 2 and Alt. 3 for these reasons:   

1).  The cost is ridiculous and in no way could be justified when so many more pressing trail and recreational facilities go 

unfunded.   

2).  The bridges will significantly mess up the visual aesthetic of this area. 

3).  The islands are currently havens for wildlife, with few human disturbances other than the occasional fisherman or 

possibly duck or deer  hunter when the water is low and the river can be waded.  Constructing a bridge to two islands 

will pretty much destroy the value of these islands for wildlife.  

4).  There is a Great Blue Heron rookery in the vicinity, additional construction and human disturbance could negatively 

impact this rookery.  There are really no other places for this nesting area to move to due to the widespread human 

activity in the lower Henry's Fork area.   

5).  The bridges really don't create a loop trail.  The bridge proposed in Alt. 3 doesn't even connect to the trail on the 

north side of the river.  The 'loop' is mostly St. Anthony city streets, not the reason most people use the greenway 

trail.  The bridge proposed in Alt. 2 connects to the north side trail where it has barely gone past the cemetery and is still

adjacent to the sewer ponds.  It may make a loop, but again completely misses the nicest part of the trail on both sides, 

but especially on the north side.   

Thank you for considering my comments. 

Kim E. Ragotzkie 

P.O. Box 325 

Ashton, ID  83420 






For more information: https://flh.fhwa.dot.gov/projects/id/henrys‐fork/

Contact: Seth English‐Young, FHWA, 360‐619‐7803, seth.english‐young@dot.gov

HENRY’S FORK GREENWAY PEDESTRIAN BRIDGE FEASIBILITY STUDY 

Project Information Sheet 

Open House  Tuesday, April 16, 2019  4:30 pm to 7:00 pm  St. Anthony, Idaho 

Introduction

The Federal Highway Administration, in partnership with the City of St. Anthony and Bureau of Land Management, is 

conducting a feasibility study for a pedestrian bridge crossing of the Henry’s Fork River, in the Henry’s Fork Greenway. 

The ultimate goals of the project are to improve public safety and provide better access to the Henry’s Fork Greenway 

and adjacent public lands. Specifically, this project focuses on options to cross the Henry’s Fork River with a pedestrian 

bridge downstream of St. Anthony, ID. 

Attachment D: Open House Materials
Option 1A  

Construct a new pedestrian bridge just downstream of the 

existing railroad bridge. New bridge would consist of a twospan, 352-foot long steel truss with concrete pier foundation 

in the river. 

Option 1B 

Acquire the existing railroad bridge and convert to only 

pedestrian & cyclist access.

Option 2 

“Island Hopping Option” – Construct a series of 

bridges and trails that connect through the 

braided portion of the Henry’s Fork. Three 

bridges would be required: a 352-foot steel truss, 

a 150-foot steel truss, and a 175-foot steel truss 

along with two segments of trail or boardwalk 

on the islands totaling 800 feet in length 

Option 3 

Cross the Henry’s Fork 

adjacent to the existing 

water diversion weir and 

boat launch. A 667-foot 

long, four-span steel truss 

bridge consisting of 175-

foot spans would be 

required to cross the river at 

this location.
For more information: https://flh.fhwa.dot.gov/projects/id/henrys‐fork/

Contact: Seth English‐Young, FHWA, 360‐619‐7803, seth.english‐young@dot.gov

HENRY’S FORK PEDESTRIAN BRIDGE FEASIBILITY STUDY 

APRIL 16, 2019 OPEN HOUSE PUBLIC QUESTIONNAIRE 

1. What is your relationship to the Henry’s Fork Greenway? (Mark all that apply)

 Visitor  Adjacent property owner/resident  Fremont County resident

 Other: __________________________________________________

2. On average, how many times a year do you visit the Henry’s Fork Greenway?

 0  1-2  3-5  6-12  More than 12

3. What type of activities do you do when visiting the Henry’s Fork Greenway?

(Mark all that apply)

 Hiking/walking  Biking  Fishing  Hunting

 Other: __________________________________________________

4. Which option presented do you prefer?

 Option 1A  Option 1B  Option 2  Option 3  I prefer none of these

5. Are there any problems that you feel this project does not address?

___________________________________________________________________________

___________________________________________________________________________

___________________________________________________________________________

GENERAL COMMENTS

___________________________________________________________________________ 

___________________________________________________________________________ 

___________________________________________________________________________ 

___________________________________________________________________________ 

___________________________________________________________________________ 

___________________________________________________________________________ 

___________________________________________________________________________ 

Contact Information - OPTIONAL 

Name: ___________________________________________________________________ 

Street address: ____________________________________________________________ 

City: ___________________________________ State: ____________ ZIP: ____________ 

Telephone number: _________________________________________________________ 

Email: ___________________________________________________________________ 
Purpose of project

Provide options for a pedestrian bridge to cross the Henry’s Fork 

River to improve public safety and access to the Henry’s Fork 

Greenway and adjacent public lands.

Considerations

Henry’s Fork Pedestrian Bridge

Feasibility Study

• Construction and Operating Costs

• Usage and Access

• Public Safety

• Ownership and Right‐of‐Way

• Environmental Impacts
Existing Conditions Photos

Henry’s Fork Railroad Bridge

Diversion Weir

Path on South Side of River 

near Highway 20

Boardwalk on North Side of River

Pedestrians on Railroad 

Islands in Braided Portion of River
PEDESTRIAN CROSSING 

THE HENRY’S FORK OF 

SNAKE RIVER
;lkj

OPTION 1A & 1B

OPTION 2
;lkj

OPTION 1A & 1B

OPTION 2
;lkj

OPTION 1A & 1B

OPTION 2
;lkj

OPTION 1A & 1B

OPTION 2