What a water gap is and when a draw needs one

The short answer

A water gap is the stretch of fence where the line crosses a creek, a draw, or any low spot that runs water after a rain. It has two jobs: keep livestock from walking out down the creek bed, and let floodwater and the brush it carries pass without tearing out the fence. If your fence line crosses anything that runs after a hard rain, it needs a water gap. Creek crossings are a weak spot in any fence line because water and debris push on them. We lay out and build water gaps as part of the fence line, not as an afterthought.

Why a regular fence fails at a creek

Run a tight wire fence straight across a draw and it works fine until the first big rain. Then the water rises, brush and logs pile against the wire, pressure builds, and the fence either tears loose or pulls the corner posts out on both banks. When the water goes down, you've got a hole in your fence and stock walking out through it.

The NRCS Texas fence specification puts it plainly. Where a fence crosses a waterway, it calls for floodgates that "allow water and debris to pass and still control livestock," and it calls for end braces on gaps more than 20 feet wide (NRCS spec). Those two lines are the whole idea of a water gap.

Fixed vs swinging water gaps

The Noble Research Institute describes two main approaches (Noble):

Fixed gaps

A fixed gap is a section built across the low spot to stay put. It's built strong enough, or open enough, that normal high water passes through or under it. Fixed gaps can work on small draws with modest flows and not much debris.

Swinging gaps

A swinging gap hangs from above, usually from a cable or pipe stretched across the creek bank to bank. The gate material hangs down to the creek bed, swings downstream when water pushes on it, and drops back when the flow drops. Brush rides over or pushes through instead of piling up against a fixed fence.

Swinging gaps are the usual answer on creeks that flood hard and carry debris, because they give way instead of breaking.

The cable method

Bekaert describes a common way to build a swinging gap: a cable stretched across the banks, tied off to solid anchors on each side, with gate material hanging from it (Bekaert). The hanging material can be panels, chain, or fence sections, depending on what you're holding and how much water you expect.

Bekaert also notes that if the gap is part of an electric fence, it needs a current limiter, so a wet gap doesn't short out the whole fence.

Where to set the posts

Noble recommends setting the posts on each side 2 to 3 feet back from the water's edge (Noble). Banks cut back when water runs high. A post set right at the edge ends up hanging over the creek after a couple of floods, and then it's in the water.

The bank posts anchor the whole gap, so they get braced like a corner. That lines up with the NRCS end-brace requirement for wider gaps. On a pipe or high fence line, the bank posts tie into the fence on either side so the gap doesn't become the weak spot.

When a draw needs one

You need a water gap anywhere the fence crosses:

• A live creek or river.
• A dry draw or wash that runs after hard rain.
• A low spot or swale where water sheets across the fence line.
• A culvert or road ditch where the fence meets it.

If you're not sure, walk the line after a good rain, or look for drift lines of grass and sticks hung in the brush. They show you where water has been and how high it got.

High fence and water gaps

Water gaps on high fence are their own problem. The gap has to hold deer and exotics, which will find any opening under a gate, and still let floodwater through. That usually means heavier hanging material and close attention to the bottom edge. See high fence vs barbed wire for more on what high fence takes.

Check it after every rain

No water gap is set-and-forget. Noble's advice is to check gaps after every significant rain (Noble). Look for:

• Brush and drift caught on the gap or the cable.
• A hanging panel stuck up instead of hanging down.
• Bank posts that have washed out or leaned.
• New openings under the bottom edge where the creek bed scoured out.

Clearing drift after a flood is about as cheap as fence repair gets. Leave it, and the next flood hits a dam instead of a gap. If a flood has already torn out a section, see fence repair and rebuilds.

How a water gap fits the job

A water gap is part of laying out the whole fence line, along with where the corners fall and where the gates go. It also changes the cost of a line, which is one reason we price fence on site. See what drives pipe fence cost.

We haven't listed water gaps by town yet, so ask us about your place and see where we work. When we walk the line, we look at each crossing, how high the water has been, and what you're holding, then lay out a gap that fits. See our water gaps page for how we build them.

Get a quote

Call or text 254-716-5760, or send photos of the crossing and the fence line with the form below. A photo of the creek bank and any drift lines helps a lot. We'll text or call back to set a site visit.