Marlborough is racing against the clock to fix broken stopbanks before another round of downpours hits next week.
Another 13mm of rain is expected to be dumped in Blenheim next Monday, following on from the weekend's deluge which wreaked havoc in parts of the South Island.
Marlborough District Council rivers engineer Geoff Dick said the council was attempting to patch three stop banks that broke during the weekend before more heavy rain hits.
One of those "breaches" was in Tuamarina, near Bush Rd, damaging five houses. Their owners had permission to access their belongings, but were not allowed back in.
"We're not sure how much water got into the houses ... The stopbanks will be bombproof by the time we're finished."
Marlborough Mayor John Leggett said the region's civil defence team was conscious that more heavy rain could add more water to Marlborough's "already sodden soil".
More bad weather could affect Queen Charlotte Drive, which reopened on Tuesday for the first time in three days, with traffic measures so workers could continue clearing slips.
"Public safety is the only priority ... Caution is key."
Leggett said the civil defence team was not yet sure how many houses had been damaged by the wild weather.
Marlborough Roads manager Steve Murrin said rain had triggered up to 100 slips in the Marlborough Sounds, varying from two truckloads in size to 5000 cubic metres.
One slip in Kaiuma Bay, north of Havelock, contained about 40 pine trees that needed to be removed before the slip could be repaired.
Another slip in Queen Charlotte Drive had taken out houses in Pukenui Bay and trapped residents in Moenui Bay until noon on Tuesday, when they were freed by repair crews.
Murrin said the crews were unable to reach the residents from the Havelock side of Queen Charlotte Drive because a "big bit of the road had dropped out". The drop would be assessed on Tuesday afternoon to see if it was fixable.
"I'm hoping we have enough width left there to put in a single lane, in the short term. But, ultimately, we're going to have to put a big retainer wall back in there," Murrin said.
Several other sections of Queen Charlotte Drive had collapsed. Other parts looked drivable but had "holed out completely" beneath the road, which was dangerous.
"Both Queen Charlotte Drive and Kenepuru Rd have seen substantial damage. It's probably the worst damage I've seen in the 30-odd years I've been involved with roads."
The only bridge in and out of the Waihopai Valley had been washed away by a river, as had "big sections" of the road.
Murrin said Marlborough Roads was looking at replacing the bridge with a temporary equivalent or creating another track into the valley, so residents could reclaim access.
State Highway 63 was closed as a river had taken seal and pavement from the road, which Marlborough Roads was working to repair. It was set to reopen at 5pm on Tuesday.
"Our priorities have been to open the highways first, then Queen Charlotte Drive, which is a major route, then Kenepuru Rd, and then working on the Awatere and Waihopai valleys."
Deputy Mayor Nadine Taylor said a welfare team was responding to individual requests for food, medicine or help.
"At this point we believe the Wairau River was of a similar size to the 1983 flood, not bigger."
Agriculture Minister Damian O'Connor arrived in Marlborough to survey the damage at noon on Tuesday.