Storm Season Drainage: Getting a Brisbane Block Ready Before Summer
Brisbane's summer storms drop 50 millimetres in an hour. Swales, ag-drains, soakage and regrading with a compact machine, done in spring before the first storm.
Brisbane does not get gentle rain. A November storm can put 50 millimetres on a block in an hour, and where that water goes decides whether you spend December landscaping or repairing. The work that prevents the damage is done in September and October, when the ground is firm and a compact machine can get around.
Read the block after a storm
The cheapest survey you will ever do is walking the block in the rain. Note where water pools, where it runs across paths, where it comes off the neighbour's block and where it undercuts the retaining wall. Those are the jobs, in that order.
Surface falls first
Most Brisbane drainage problems are surface problems: a lawn that falls toward the house, a path that dams water against a wall. Regrading with a skid steer and a 4-in-1 bucket, or an excavator with a tilt bucket, so that the surface falls away from buildings at two percent or more fixes more than any pipe.
Swales
A swale is a shallow, wide grassed channel that carries surface water across a slope to a safe outlet. On a Brisbane clay block a swale 300 millimetres deep and two metres wide, cut with a tilt bucket, moves storm water that would otherwise sheet across the yard.
Agricultural drains
Where water sits in the ground rather than on it, an ag-drain (slotted pipe in a gravel-filled trench wrapped in geofabric) collects it and pipes it to the stormwater system. Trench 400 to 600 millimetres deep with a narrow bucket, fall the trench at one percent toward the outlet, and keep the pipe wrapped so the clay does not clog it.
Retaining wall drainage
Every retaining wall in Brisbane needs a drain behind it. Water in the backfill of a clay block is what pushes walls over. If an existing wall has no drain, digging one in behind it with a small excavator is a job worth doing before the season.
Soakage
Soakage pits are less useful in clay than in sand, because clay does not drain. They work in the sandier soils near the bay and along the river, and elsewhere only as an overflow. Council rules on stormwater discharge apply; check with Brisbane City Council before connecting anything to the street.
Machines
A 1.5 tonne excavator such as the R15 with a tilt bucket and a narrow trenching bucket does the digging, and an RS06 skid steer moves gravel, spoil and turf. Both fit down a normal side path and tow behind a ute. See what fits your block with the machine finder.