Flood-Prone Country — How to Build Fences That Survive

If you've got country along the Macquarie, Lachlan, Belubula, or any of the creeks and rivers across the Central West, you know what floods do to fences. The 2022 floods reminded everyone — fences that took weeks to build can be destroyed in hours. But smart design and the right materials mean your fences survive better and go back up faster.

UNDERSTANDING FLOOD DAMAGE

Floods destroy fences in three main ways:

Water force: Moving water pushes against the mesh like a sail, putting enormous lateral force on pickets and strainers. The taller the mesh and the faster the water, the greater the force.

Debris: Logs, branches, hay bales, and other debris floating in floodwater pile up against fences, creating a dam effect. The debris load multiplies the force on the fence by orders of magnitude. A single log jammed against a fence can pull out a strainer assembly.

Scour: Floodwater erodes soil from around the base of pickets and strainers, undermining their holding power. Posts that were solidly set before the flood are loose and leaning afterward.

DESIGN PRINCIPLES FOR FLOOD-PRONE FENCING

Principle 1: Let the water through. The biggest mistake is building a solid barrier across a flood path. You want fencing that allows water (and debris) to pass through rather than building up against it.

On known flood paths, consider:

• Floodgates: Hinged panels of mesh that lay flat when water pushes them down, then spring back up when the water recedes
• Drop-down sections: Short sections of fence that are designed to break free at specific points (using light-gauge tie wire instead of permanent clips) so the mesh drops to the ground and water passes over
• Removable panels: Where you know floods are coming (river flats that flood every few years), build permanent strainer assemblies with removable mesh panels that you take out before the flood arrives

Principle 2: Build stronger strainers. Strainer assemblies on flood-prone country need to be overbuilt. Use larger diameter posts (200mm+), set deeper (800mm minimum), with concrete and extra bracing. If the strainers survive, rebuilding the fence between them is straightforward. If the strainers go, you're starting from scratch.

Principle 3: Sacrifice the cheap stuff, protect the expensive stuff. Star pickets are $8-$13 each. Strainer assemblies are $200+ each. Design your fence so that pickets and mesh take the damage while strainers survive. Using lighter tie wire to clip mesh to pickets in flood zones means the mesh separates from the pickets before the force transfers to the strainers.

MATERIAL CHOICES FOR FLOOD ZONES

Pickets: Use standard 180cm pickets at normal spacing in the flood zone, but accept that you may need to replace bent or loosened pickets after a flood. Our 2.1kg/m heavy pickets handle flood forces better than lighter pickets — more steel resists bending.

Mesh: Standard hinged joint mesh works. Some producers use lighter-gauge mesh in flood zones because it's cheaper to replace. That's a false economy if the mesh needs to contain stock — go with standard quality and accept the replacement cost.

Wire: HT wire survives floods well because it's elastic — it stretches under load and returns to shape when the force is removed. MT wire is more likely to stretch permanently.

Strainers: Treated hardwood minimum 200mm diameter or steel. Concrete every strainer post in flood-prone areas — the concrete mass adds weight that resists scour undermining. Use longer stays and double-brace strainers at creek crossings.

CREEK AND RIVER CROSSINGS

Where a fence crosses a creek or waterway, specific techniques help:

Suspend the mesh: Instead of running mesh to ground level through the creek, stop the mesh at the bank top on each side and run plain wire across the low section. Wire passes less debris than mesh and is easier to repair.

Use flood gates: A swing gate across the waterway that opens under water pressure and closes when the water drops. These are available commercially or can be fabricated from mesh and hinges.

Build separate sections: Treat the creek crossing as its own fence section with strainer assemblies on each bank. When the crossing section gets damaged, you repair only that 20-50m section, not the entire fence line.

AFTER THE FLOOD

Once the water recedes:

1. Walk the entire fence line and assess damage before you start repairs

2. Remove debris first — don't try to strain mesh that's got logs jammed in it

3. Check strainer assemblies for scour and lean before retensioning

4. Replace bent pickets — don't try to straighten them, they're weakened

5. Retension or replace mesh sections as needed

6. Reset any floodgates or drop-down sections

Keep a stockpile of spare pickets, clips, and mesh offcuts specifically for post-flood repairs. Having materials on hand means you can get fences back up quickly before stock escape.

For flood-zone fencing materials and advice, contact us at 76 Astill Drive, Orange, or phone 0434 093 077. We've supplied replacement fencing for dozens of properties after the recent Central West floods and we understand what works in this country.