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Extension > Environment > Trees and woodlands > Forest management practices fact sheet: Crossing options series > Timber bridges

Timber bridges

Best Management Practices (BMPs) can prevent or minimize the impact of forestry activities on rivers, lakes, streams, groundwater, wetlands, and visual quality.

Introduction

Timber bridges can help protect water quality and stream habitat during forestry operations.

There are three basic types of temporary timber bridges. Log stringer bridges are built from trees felled in the area. Solid-sawn stringer bridges are made from new lumber, railroad ties, or large timbers removed from buildings that are being torn down. Panel bridges are constructed from stress-laminated, glued-laminated, dowel-laminated, or nail-laminated lumber. A licensed engineer can help operators design a safe, appropriate timber bridge.

Where used

Timber bridges can be placed over small streams or channels with firm, stable banks.

Application

Check with the appropriate regulatory agency in your state to see if permits are required to build timber bridges.

When building and installing a log stringer bridge:

log-stinger-bridge

Log stringer bridge

When building and installing a solid-sawn stringer bridge:

When installing a panel bridge:

Advantages

Operators can find materials for timber bridges at the site or purchase them locally or through commercial outlets. Little site preparation is needed. Structural characteristics are known and engineering specifications may be available for lumber or panels. Operators can remove and reuse timber bridges several times. Local water regulators generally favor timber bridges.

Disadvantages

Timber bridges may pose a safety hazard if operators don't get help from a licensed engineer or accurately assess the strength of logs and other construction materials. Logs, railroad ties, and demolition materials can have rot, knots, and other problems that affect strength. If operators don't use proper abutments, timber bridges may freeze into the ground during the winter. Surfaces may wear quickly during skidding operations.

Maintenance

Inspect timber bridges during and between uses to check for signs of wear or weakness.

Cooperators
University of Minnesota Extension, Minnesota Department of Natural Resources, Minnesota Logger Education Program, Michigan Department of Natural Resources, Michigan State University Extension, USDA Forest Service, and Wisconsin Department of Natural Resources.

WW-07005 1998


 

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