Land Drainage team leader Tim Joyce says the Heathcote is designed to flood on to grassed areas and roads, but not properties.
Contracting crews have been out checking wet weather grates around the city and removing any debris that could cause water to bank up.
Many Canterbury rivers are flowing higher than they have been for the past year.
While no out of river flooding is expected, Environment Canterbury says "many rivers will be flowing higher than they have been for the last 12 months".
Residents are asked to take extra care near swollen rivers.
The November 14 earthquake and subsequent aftershocks have led to numerous landslide dams being formed in North Canterbury and Kaikoura rivers and streams.
"As a precaution it is strongly advised to keep away from all riverbeds north of the Waiau River in case there are any sudden releases of water," ECan says.
"We expect that the lakes above the landslides in these catchments have filled and over topped. Extra vigilance is advised in the Linton, Ote-Makura [Goose Bay] and Hapuku River catchments."
Extra vigilance is also advised in the Conway River due to an earthquake induced landslide dam in the headwaters.
Some localised surface flooding can be expected in the Waimakariri area.
Environment Canterbury staff are monitoring the condition of flood protection infrastructure. At this stage, no out of river flooding is anticipated.
A close watch is being kept on the Port Hills where the damage caused by February's fire has heightened the risk of slips.
Heavy rain has saturated the soils, making the land susceptible to movement. Geo-technical engineers are on standby but so far no incidents have been reported.
On Banks Peninsula water is being tanked into Birdlings Flat after a problem with the bore supplying water to the settlement's 185 residents. The council says it will continue to tank water into the settlement until the problem with the bore has been fixed.
There is a possibility heavy rain could cause some flooding in the Cooptown/Little River area but so far there have been no reports of flooding.
The embattled tourist town of Kaikoura has been cut off by road for most of the day.
State Highway 1 south of Kaikoura is likely to remain closed all day, the NZTA says.
High volumes of rain caused mudslides to block the highway in the past two days, pushing rock-filled containers over the edge of the road
Five mud and rock slides are now blocking the road in different sections and teams of excavators and loaders are working today to clear the landslips.
"At Site 14, more of the soil and rock has come down in the heavy rain last night," says Steve Mutton, NZTA earthquake recovery manager.
"The shipping containers have again been pushed closer to the sea and an estimated 2000 cubic metres has fallen from that slip face. This slip needs to be cleared and the containers reinstated before the road can reopen."
Waiau/Mt Lyford Inland Rd Route 70 to Kaikoura was reopened at 3pm until 6pm.
Drivers were urged to take extra care, with stop/go sites and traffic lights along the route.
Access to Clarence was restored this morning, with debris cleared from SH1 south of Kekerengu. Parts of the road will be reduced to one lane in several places and 30km/h speed limit.
Flooding at Tirohanga has receded, but drivers need to take extreme care in many places.
North Canterbury farmers are both loving and hating the rain.
The remnants of Cyclone Debbie has brought some much needed rain to the drought-affected region.
But chairman of the North Canterbury Rural Support Trust Doug Archibald says the longer it goes on the worse it gets for farmers.
He says for those people with land damage the rain will cause more mass movement on their farm.
