Stormwater and Surface Flooding on Christchurch Sections

Sumps and soakpits

A lot of Canterbury properties, particularly newer subdivisions in Selwyn and Waimakariri, rely on soakpits rather than a piped connection to the street, because the district councils manage stormwater discharge differently to Christchurch City.

A soakpit works by letting water percolate away into the surrounding gravel and soil. When they silt up, sit in heavy clay, or simply weren't sized for the roof area feeding them, they fill up faster than they can drain and water backs up onto the lawn.

Blocked or undersized downpipes

• Leaves and debris blocking spouting and downpipe heads before water even reaches the stormwater pipe
• Downpipes disconnected or crushed underground, discharging straight into the ground beside the foundation
• Undersized downpipes for the roof area they're draining, common on older extensions and lean-tos
• Flat or reverse-fall sections of buried stormwater pipe holding water instead of carrying it away

Ground movement and flat sections

Post-earthquake settlement has left some sections with a slight dip where there used to be an even fall to the street or the soakpit. Even a small change in grade is enough to leave water sitting rather than draining, especially on the flat land east of the city and around the Avon and Heathcote catchments.

What we check on a stormwater callout

• Spouting, downpipes and any first-flush filters for blockages
• Underground stormwater pipe runs with a CCTV camera where flooding is recurring
• Sump and soakpit condition, capacity and whether they're silted up
• Ground levels and fall around the foundation and paths
• Connection points to the council stormwater network where one exists

Fixes that actually work

Sometimes it's as simple as clearing a blocked sump grate or downpipe. Other times the fix is a new or enlarged soakpit, regrading a low section of lawn, or replacing a length of pipe that's lost its fall.

For properties that flood repeatedly in heavy rain, we'll often recommend a combination: better surface drainage to get water moving quickly, plus more soakage or storage capacity underground to handle the volume once it arrives.

Council responsibility for stormwater

Where a public stormwater main runs past your property, the council is responsible for that pipe, similar to the arrangement with water supply and the toby. Your private stormwater pipework, from your downpipes and sumps to the connection point, is your responsibility to maintain.

Frequently asked questions