Livestock pasture fences sometimes require closing off a stream or gully. The project poses the challenge of creating a fence that is solid enough to keep the animals contained while being flexible enough to prevent washouts during high water flows. The portion of the fence that extends into the stream bed will encounter not only water but the debris moving in the stream. The project is among the most advanced for do-it-yourself fence builders but they can do it with the proper tools and skills.
Set fence posts on the banks of the stream. Dig 3-foot deep fence post holes as close to the bank as possible where the ground is stable. Set the posts in the hole and tamp dirt around the post. Stretch along the fence line and fasten to the posts set at the bank in the normal manner.
Wrap a 1/4-inch steel cable around one of the posts and fasten it to itself with a cable clamp. Stretch the cable to the other post. Use a fence stretcher to pull it tight and fasten it around the second post securing it with a cable clamp.
Build a framework that is tailored to fit the streambed gap below the cable and fence. Measure the distance between the cable and stream and the width of the stream bed. The bottom portion of the framework may be narrower than the top with the sides angled to accommodate the slope of the stream banks. Cut the frame to fit the measurements out of treated 2-by-4 lumber. Bolt the corners together with 1/4-inch carriage bolts.
Wrap barbed wire around the side support of one side of the frame. Pull the barbed wire tight to the other side and wrap it around the side support. Attach the wire to the side supports using fencing staples. Repeat the process adding a barbed wire strand every 12 inches from the bottom to the top of the framework.
Hang the framework from the cable placed in step 2. Use a heavy bendable wire to create a loop that includes the upper support of the framework and the cable in a loose connection. Place a loop every 3 feet along the cable. The framework should swing loosely under the cable allowing debris floating in the stream to pass under the fence.
You can also swing the framework clear of the stream by hand and fastene it in place along the fence. This is commonly done when the pasture is not in use to prevent damage to the hanging fence assembly. Check the regulations concerning fencing waterways or streams. Some states prohibit permanent fences over meandered streams. Meandered streams are public waterways where canoe or other boat traffic is allowed.