Building Bridge Crossings

Time Required
1-2 Days for Anchor-Post Bridge crossing
2-4 Hours for tree-to-tree crossings

Materials List

Qty	Item	Notes
n/a *	3/8” Turnbuckle Hardware	For adding tension in cable. Truner brand recommended if available. Try to avoid cheap pot metal variety found in most hardware stores.
n/a *	3/8” steel cable	For elevating tube
n/a *	5/16” Hardware clips	For clipping cable to trees, other hardware
n/a *	Nylon string, wire, or thin PVC rings from larger piece of PVC	For attaching tube to cable
1	Hacksaw	For cutting cable, rebar for anchor-post crossing, PVC tube, galvanized pipe. Wire cutters also work well to cut cable
1	Pliers	For tightening nuts on hardware clips, bending wire when attaching tube to cable, tying rebar
n/a *	3/8” thimbles	For looping cable around rebar on anchor-post crossings
n/a *	3/8” rebar	For protection against UV rays
n/a *	Exterior paint	For protection against UV rays
n/a *	sack of cement
1	20’ length of 3/8” rebar	Will only use about 15’. Usually comes in 20’ lengths
1	5’ length of 16ga wire	For attaching tube to cable, tying rebar. Sold by the pound
n/a *	1-1/2” Galvanized pipe	For anchor-post bridge crossings. Usually comes in 20' lengths. Can sometimes be cut to length at store.
2	level	For plumbing post in anchor-post bridge
1	Duct tape	For attaching level to post
1	Large stick	For stirring concrete during pour to remove air pockets
n/a *	5-gallon buckets of sand	For concrete mix 1:2:4, For anchor and posts
n/a *	5-gallon buckets of gravel	For concrete mix 1:2:4, For anchor and posts
2	shovels	For mixing concrete for anchor-post bridge
1	can PVC cement	For any tube work
1	metal trowel	For concrete work on anchor-post bridge
2	5-gallon bucket	For measuring, storing water for concrete mix

* Quantity dependent on final design

Construction
Because maintaining a crossing can be a lot of work after the fact, initial construction is important. Be sure that anchor points will last the life of the system, that the tree, boulder, or post location makes sense.

Make sure that the tube is elevated high enough above any water crossings to avoid debris in a flood. Ask community members about flood conditions to determine how robust the bridge crossing should be. Be careful of future erosion. Make sure that the anchors and posts are setback enough from the ravine.

Make sure that tubes are painted or in a larger tube sheath to protect against UV rays.

If the tube leaves the ground or enters the ground as part of the bridge crossing, encase the tube in a larger tube sheath to protect against potential machete cuts in the future undergrowth or livestock knocking against the tubes.

Anchor and Post Bridges

	This is the finished rebar for an anchor. The cage will be placed in the upper portion of the concrete anchor so that the U-shaped piece sticks out of the finished anchor. The bridge cable will connect to the U piece.
	Pour concrete into the formed hole. Use a level to make sure the post stays straight during construction. Tamp down concrete while pouring the form. See working with concrete section of the website
	Earth is mounded around the post. Sticks are placed on the elevated mound so that a cover can be placed over the whole post structure during curing.
	Use a level to make sure the post is level in the concrete. Cover the concrete during curing. See working with concrete section at the end of this manual.

Using Trees to Elevate Tubes

	Note: There are several ways of attaching to trees. The method shown in the following photos shows hardware clips. Volunteers have encountered problems with these clips cutting the plastic sheathing on cables when put under tension. If this is the case, in lieu of clips, the cable can be tied in a knot around the tree by making a loop and running around the tree and back through the loop.
	Loop cable around the tree and slide on hardware clip. Tighten nuts extremely well using pliers.
	Leave about 12” of cable from the hardware clip around the tree to the end of the cable. Run cable through turnbuckle hardware. Create loop at end of cable by doubling back. The eye of the turnbuckle should be in this loop. Tighten loop with hardware clip.
	Loosen bolts on turnbuckle as shown in the picture. Create loop in new piece of cable using hardware clip. Attach new cable to hook on turnbuckle hardware.
	Repeat above attachment method on other side of bridge if attaching to another tree. For smaller crossings (< 20 feet), one turnbuckle should be sufficient. For larger crossings, the extra turnbuckle will help add more tension in the cable. For crossings with two turnbuckles, measure out distance of cable to connect to other side of bridge. Pull on cable to add tension before deciding where to cut the cable.
	Paint any tubes that will be exposed to UV rays.
	Attach tube to cable using nylon string or wire. This solution could use some work. Nylon string tends to degrade in the sun. Wire will rust. If you're able to find plastic coated metal or can make thin PVC rings from a larger diameter PVC tube, this is the preferred choice for attachment. Make sure attachments are located about every three feet and are have some slack since the cable will move when put under tension.
	Elevate cable and tube. Attach cable as needed using hooks of turnbuckle hardware. Tighten bolts in turnbuckle hardware as needed. The tube should be straight with very little sag in the middle of the crossing.

Using Rocks to Anchor

To the left is a picture of a potential rock anchor. This was taken from an existing system, so there are no installation instructions at this time.

Other Considerations

	If your bridge crossing involves a transition from the ground to being elevated, sheath the transition point in about 4' of larger tubing. This will help protect the inner tube from machetes or animals that may come in contact with where the tube enters the ground.
	Since you'll be shutting off the water for bridge maintenance or construction, the bridge may also be a location to install a shutoff valve and/or cleanout valve as shown in the picture to the left.