Residents across Christchurch and Banks Peninsula are being urged to prepare for significant rainfall, with up to 250mm forecast between Monday afternoon and 10am Tuesday.

The heaviest rain is expected overnight Monday into Tuesday, with Banks Peninsula likely to be the most impacted.

Flooding is possible in some areas, particularly in low lying parts of the district.

Christchurch City Council General Manager City Infrastructure Brent Smith said crews had been preparing for the weather event, especially in areas considered most vulnerable.

“We’re taking our usual precautions by ensuring beach outfalls and wet weather grilles are clear. Pumps and personnel are on standby for the Flockton area and the most critical location in Southshore. The upper Heathcote flood storage basins will be functioning as they should during this event, so people may notice fluctuating water levels in the river,” Smith said.

“If you know there are leaves blocking sumps or drains near your property, it really helps if you can clear them and place the debris in your green wheelie bin.”

The council warned that low lying areas near the Avon and Heathcote rivers may experience flooding.

Residents were advised not to report surface flooding on roads unless there was a genuine safety issue, as roads are designed to cope with stormwater ponding and water should drain once rainfall eases.

“Take care and drive to the conditions, do not drive in any floodwaters. If you do need to travel through pooled water, please drive slowly and carefully, and treat all floodwater as contaminated,” Smith said.

Lake Forsyth has also been closely monitored as water levels have risen in recent days. Smith said strict environmental and consent conditions determine when the lake can be opened.

“The lake has to reach a minimum level of 2.3m in summer, and we can only open early if forecasts show it may rise above 2.7m. Based on the forecasts we had at the time, it didn’t look like the lake would reach that threshold, so we weren’t able to open it.”

He said sea conditions had also prevented an earlier opening.

“We had waves of up to three to four metres over the weekend.

“While the lake cannot be opened at this stage, the team is watching conditions extremely closely and expect to be able to open the lake later this week once conditions allow. We have arranged for resources to be delivered to the site, so as soon as weather conditions improve and a lake opening can be undertaken, this is likely to be Wednesday.”

Little River residents have been urged to prepare for possible flooding, while other parts of Banks Peninsula have been advised to be alert for slips and road disruptions.

Council staff are also monitoring sensors on Lighthouse Road and surrounding areas for any land movement, following significant wet weather damage last year. Staff and contractors remain on standby to respond to any issues during the weather event.