Build a Log Bridge

Here is a minimally disruptive method of building a log bridge across a stream.

| February/March 1994

  • 142 log bridge - photo 5 - planks
    The finished log bridge looked like this. The 2 x 12 boards running the length of the bridge provide a track for car or tractor tires.
    PHOTO: MOTHER EARTH NEWS STAFF
  • 142 log bridge - photo 1- using a winch
    The author used a tractor and winch to haul logs for the log bridge without harming the stream bed. 
    MOTHER EARTH NEWS STAFF
  • 142 log bridge - diagram 4 - water level
    Diagram shows method of using a simple water level to determine if the bunker logs on each side of the stream are at the same height.
    SCOTT MACNEILL
  • 142 log bridge - diagram 3 - A-frame
    Diagram shows method of making an "A" frame or tripod to provide an anchor point for a pulley, as well securing a 12' bunker log.
    SCOTT MACNEILL
  • 142 log bridge - diagram 5 - placing span log
    Diagram shows method of using a forked stick to mark a curve on a span slog, which can then be cut to fit snugly against the bunker log. Position span logs with their curved side up, because logs will sag over time.
    SCOTT MACNEILL
  • 142 log bridge - photo 2 - putting logs in place
    A tripod provides a stable pulling point above the stream bed.
    MOTHER EARTH NEWS STAFF
  • 142 log bridge - diagram 1 - aparatus
    Diagram shows method of using truck winch, pulley, and bunker log to maneuver a span log across the stream.
    SCOTT MACNEILL
  • 142 log bridge - photo 3 - cutting saddle
    Rough-trim the log tops so that they fit the planks of the bridge.
    MOTHER EARTH NEWS STAFF
  • 142 log bridge - diagram 2 - crossing strings
    Run string diagonally across the bridge, forming an "X" in the middle, to determine if the span logs are more or less level.
    SCOTT MACNEILL
  • 142 log bridge - photo 4 - leveling2
    A string run from corner to corner will reveal whether your span logs are level. 
    MOTHER EARTH NEWS STAFF

  • 142 log bridge - photo 5 - planks
  • 142 log bridge - photo 1- using a winch
  • 142 log bridge - diagram 4 - water level
  • 142 log bridge - diagram 3 - A-frame
  • 142 log bridge - diagram 5 - placing span log
  • 142 log bridge - photo 2 - putting logs in place
  • 142 log bridge - diagram 1 - aparatus
  • 142 log bridge - photo 3 - cutting saddle
  • 142 log bridge - diagram 2 - crossing strings
  • 142 log bridge - photo 4 - leveling2

Outside of a drought or miracle similar to the crossing of the Red Sea, there is no way to make a dry crossing over a body of water without a bridge. I desperately needed one to cross the Class One stream on our property in the western Cascades of Oregon. So I decided to build a log bridge, one that would meet my needs without causing damage to the environment.

The first thing I did was take a trip to the area State Forest office and make a request for a bridge-building permit. That was followed by an on-site inspection by the local forester, who decided the stream banks were level enough so that water drainage from a road wouldn't flow down onto a bridge and into the stream.

The permit explained the two best methods of moving logs across a stream without harming the stream bed. The method I selected, explained below, involves an elevated-cable system, a truck winch, and an anchored-log tripod with a cable pulley. This allowed me to haul logs across the stream without touching the stream bed at all.

The other (more costly) method is to use a large backhoe to lift the logs across the stream. According to the permit, we were also responsible for reseeding those areas along the roadway and bridge that were disrupted by our machinery. The whole process was so simple and turned out so well that I drew up some plans and diagrams to share with you.



Bridge Construction

Begin by finding (or, if necessary, hiring) someone with a portable saw mill to saw planks for the bridge deck. We had a friend cut forty 3 x 12s, sixteen 2 x 12s, and seven 4 x 6s. Cut down and limb just enough cedar trees to make six 42' span logs (which run across the stream) and two 12' bunker logs (which hold up the span logs).

Place the larger of the two bunker logs in a shallow trench on the accessible side of the stream (the side you're standing on); you may have to dig a trench if a natural one doesn't exist. Level the top. Next, position long but narrow logs across the stream, allowing the top ends to rest on the bunker so that they form a ramp. Using the ramp, roll the second bunker log to the far bank.






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