Drainage in Westbrook.

Flat ground, heavy black soil.

Unlike the sloping escarpment suburbs, Westbrook sits on the flat plain, and the soil is deep, highly reactive black cracking clay, much of it Class E or P. Flat plus clay is the hardest drainage situation there is: water has nowhere to run off to, and the ground itself won’t absorb it. After the wet season the low points of a Westbrook block can stay waterlogged for a week, killing lawn, drowning trees and keeping the ground wet against footings. This is ag-drain country, and the geotextile wrap is non-negotiable in this soil.

Getting the fall right.

On a flat block, every millimetre of fall counts. A drain that would work fine on a Highfields slope has to be set with laser-checked grades out here, because there is so little natural fall to work with. We survey the levels carefully, sometimes running ag and stormwater lines a long way to reach a usable outlet, occasionally to a soak or a dam where no kerb is available. Getting that fall right is the difference between a drain that works and one that just sits full of water.

Reactive clay and your slab.

The same black soil that holds water also moves dramatically, swelling 50mm or more when wet and shrinking back when dry. That movement cracks footings, paths and rigid pipe. We bed every stormwater line in graded gravel so it can ride the movement, and an ag drain along the wet side of the house keeps the soil moisture even and protects the slab. We pair that with stormwater drainage for the roof water and surface drains across paving where water sheets.

Typical Westbrook jobs.

• Large ag-drain systems drying out waterlogged acreage ($4,000-$9,000)
• Perimeter ag drains protecting slabs on reactive clay ($3,000-$6,000)
• Long stormwater runs to a usable outlet on flat blocks
• Surface and spoon drains leading sheet water off paving and around sheds
• Blocked and silted stormwater lines cleared and camera-inspected

A worked example.

A Westbrook acreage block where the whole rear yard turned to a bog every winter: we laid 45 metres of wrapped ag drain in a herringbone pattern across the low area, falling to a single outlet at the back corner, all set on laser-checked grades. $6,900, and the yard now drains within a day of heavy rain. For more on drying a wet block see fixing a flooding backyard in Toowoomba.