Why does my stormwater flood in heavy rain?

Stormwater problems are usually visible if you go outside during the rain, which almost nobody does. Ten minutes in a raincoat identifies the cause more reliably than an hour of speculation afterwards, because you can see where water arrives, where it pools and where it is not going.

The common causes

• Downpipes discharging onto the ground rather than into a pipe, which puts a roof worth of water beside the footings.
• Silted or root-blocked stormwater lines, which is very common in older properties and often never inspected.
• Regrading from landscaping, paving or a new shed, which reverses the fall the site was built with.
• Pipework that was adequate for the original roof and is now carrying an extension, a carport and a patio roof as well.
• Blocked or undersized surface pits with grates full of leaf litter.

Why it matters beyond the puddle

Water repeatedly soaking the ground beside a house is a leading cause of foundation movement in Australian reactive clay soils, and that produces cracking that costs far more than the drainage would have. Persistent damp against the base of walls also drives rising damp and termite conditions.