Trail Bridges –
A Common Sense Approach to
Selecting Bridge Sites
Presenter:
James “Scott” Groenier, P.E.
Project Leader, MTDC, WIT
Prepared for: NOHVCC Conference
Ontario, CA
March 17, 2005
Technology & Development
Introduction
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Site Reconnaissance
Geomorphology Concerns
Hydrology and Hydraulics
Alignment
Environmental Concerns
Design Loads
Trail Bridge Website
Summary
2
Technology & Development
Site Reconnaissance
 Site Investigation - simple
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Technology & Development
Site Reconnaissance
 Site Investigation - Complex
Streambed strata
Floodplain widths
Soil types
Logs in stream
Ice Damage
Drift locations
Etc
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Technology & Development
Site Reconnaissance
 Site Survey
Center of Stream
Edge of water
Bottom of Bank
Top of Bank
Floodplains
Trail
Survey upstream
and downstream for
300 ft
Survey approaches
on both sides 150 ft
Survey top of banks
for 30 ft
Utilities
Roads
Drift / Ice damage
Etc
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Technology & Development
Site Reconnaissance
 Geotechnical Investigation
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Bedrock
Loam
Geomorphology Concerns
Technology & Development
From Rosgen’s
“Field Guide for
Stream Classification”
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Technology & Development
Geomorphology Concerns
 Stream Stability
Deposition Area – Type C Channel
Bedrock - Type A Channel
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Stable Banks – Type B Channel
Technology & Development
Geomorphology Concerns
 Bank Stability
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Technology & Development
Hydrology and Hydraulics
 Waterway Adequacy
 Hydrology
+
Regression Equations
from USGS Reports on
Estimating Frequency
and Magnitude of
Floods
=
Flow (CFS)
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Technology & Development
Hydrology and Hydraulics
 Waterway Adequacy
 Hydraulics
1) Take CFS from Hydrology
2) Take Site Investigation info
3) Take Site Survey
HEC-RAS Example
And
Use a computer model such as
HEC-RAS (River Analysis System)
Or
WinXSPRO
And you get this…..
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Technology & Development
Hydrology and Hydraulics
 Flooding –Spring, Fall or rain on snow
Good or Bad Location?
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Technology & Development
Hydrology and Hydraulics
 Scour
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Technology & Development
Hydrology and Hydraulics
 Navigational
Clearance
5 ft Minimum
Required
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Technology & Development
Alignment
 Horizontal
90 degree Bend
Straight
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Technology & Development
Alignment
 Vertical
Bottom of Sag Curve
Slight Grade
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Technology & Development
Environmental Concerns
 Fisheries
 Spawning Areas, Fish passage
 TES - Closures
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Salmon
Bull Trout
Cutthroat Trout
etc
 Wildlife
 Nesting Trees, Rearing areas, etc
 TES - Closures
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Indiana Bat
Bald Eagles
Northern Goshawk
etc
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Technology & Development
Environmental Concerns
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Ice Flow
Floating Debris
Falling Trees
Falling Rocks
Excessive Snow Loads
Avalanche Chutes
Springs/Seeps
Wetlands
Others
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Technology & Development
Design Loads
 Dead Loads
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Superstructure
Decking
Railing
Wearing Surface
Miscellaneous
 Utility Lines
 Covers
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Technology & Development
Design Loads
 Live Load
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Pedestrian – 85 psf
Equestrian
OHV’s
Snowmobiles
Mountain Bikes
Vehicles
 5,000 width <6 ft
 10,000 6 ft<width<10 ft
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Technology & Development
Design Loads
 Snow Loads – 0 psf to over 350 psf
 SNOTEL sites – 550 to 600 in the West
 Local Building Officials
 http://fsweb.mtdc.wo.fs.fed.us/snow_load/
 Wind Loads
 Overloads
 Groomers
 7600# - 18,000#
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Bridge Types
Technology & Development
 Trail Bridge Catalog
 Forest Service Intranet http://fsweb.mtdc.wo.fs.fed.us/bridges/
 Forest Service Internet http://www.fs.fed.us/na/wit/WITPages/bridgecatalog/
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Technology & Development
Bridge Fabrication/Supply
 Structure produced by a certified Manufacturer
for the type of material being used.
- See “Contact Information For Wood and Steel Pedestrian and
Trail Bridges” at National Wood In Transportation Website
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Technology & Development
Summary
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Site Reconnaissance
Geomorphology Concerns
Hydrology and Hydraulics
Alignment
Environmental Concerns
Design Loads
Trail Bridge Website
Questions?
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