Trail Bridges – A Common Sense Approach to Selecting Bridge Sites

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

Introduction • Site Reconnaissance • Geomorphology Concerns • Hydrology and Hydraulics • Alignment • Environmental Concerns • Design Loads • Trail Bridge Website • Summary

Site Reconnaissance • Site Investigation - simple

Site Reconnaissance • Site Investigation - Complex Streambed strata Floodplain widths Soil types Logs in stream Ice Damage Drift locations Etc

Site Reconnaissance • Site Survey Center of Stream Edge of water Bottom of Bank Top of Bank Floodplains Trail Utilities Roads Drift / Ice damage Etc Survey upstream and downstream for 300 ft Survey approaches on both sides 150 ft Survey top of banks for 30 ft

Site Reconnaissance • Geotechnical Investigation Bedrock Loam

Geomorphology Concerns From Rosgen’s “Field Guide for Stream Classification”

Geomorphology Concerns • Stream Stability Deposition Area – Type C Channel Bedrock - Type A Channel Stable Banks – Type B Channel

Geomorphology Concerns • Bank Stability

Hydrology and Hydraulics + Regression Equations from USGS Reports on Estimating Frequency and Magnitude of Floods = Flow (CFS) • Waterway Adequacy • Hydrology

Hydrology and Hydraulics • Waterway Adequacy • Hydraulics 1) Take CFS from Hydrology 2) Take Site Investigation info 3) Take Site Survey And Use a computer model such as HEC-RAS (River Analysis System) Or WinXSPRO And you get this….. HEC-RAS Example

Hydrology and Hydraulics • Flooding –Spring, Fall or rain on snow Good or Bad Location?

Hydrology and Hydraulics • Scour

Hydrology and Hydraulics • Navigational Clearance 5 ft Minimum Required

Alignment • Horizontal 90 degree Bend Straight

Alignment • Vertical Bottom of Sag Curve Slight Grade

Environmental Concerns • Fisheries • Spawning Areas, Fish passage • TES - Closures • Salmon • Bull Trout • Cutthroat Trout • etc • Wildlife • Nesting Trees, Rearing areas, etc • TES - Closures • Indiana Bat • Bald Eagles • Northern Goshawk • etc

Environmental Concerns • Ice Flow • Floating Debris • Falling Trees • Falling Rocks • Excessive Snow Loads • Avalanche Chutes • Springs/Seeps • Wetlands • Others

Design Loads • Dead Loads • Superstructure • Decking • Railing • Wearing Surface • Miscellaneous • Utility Lines • Covers

Design Loads • Live Load • Pedestrian – 85 psf • Equestrian • OHV’s • Snowmobiles • Mountain Bikes • Vehicles • 5,000 width <6 ft • 10,000 6 ft<width<10 ft

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#

Bridge Types • 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/

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

Summary • Site Reconnaissance • Geomorphology Concerns • Hydrology and Hydraulics • Alignment • Environmental Concerns • Design Loads • Trail Bridge Website • Questions?

Trail Bridges – A Common Sense Approach to Selecting Bridge Sites