Work continues to clear the Broadway underpass
The project director of the company which built Belfast's Broadway underpass has said a design fault was not to blame for its flooding.
The underpass, part of the Westlink motorway, was at one point on Saturday under 20 feet of water.
Its citybound carriageway is to reopen at 0630 BST on Tuesday the countrybound later, the Roads Service has said.
Leo Martin, of Highway Management Construction, said the heavy rain had been an "extraordinary event".
"To get a month or three-quarters of a month's rain in 12 hours is fairly exceptional rainfall," he said.
"No doubt the culvert did its job, it was designed and built exactly in accordance with specifications and put into practice.
"But unfortunately you can't countenance for severe weather conditions like this."
Mr Martin said there was still some water in the underpass and work was continuing to clear it and the mud and sludge with it.
"We hope to be in a position, perhaps some time tomorrow (Tuesday) to open the road," he said.
Meanwhile, Northern Ireland's executive ministers are to be updated about the response to the weekend flooding as clearing up after the deluge continues.
Traffic managed to flow without major delay along the Westlink.
However, flooding on the railway line at Portadown has caused disruption to the Enterprise service.
An investigation has been ordered by Roads Minister Conor Murphy into how the underpass flooded.
The minister visited it over the weekend.
It is thought a pumping station beside the road was overwhelmed when a nearby river overflowed.
Hundreds of homeowners are beginning the process of applying for special compensation to help repair some of the damage.
The executive is making £1,000 available to every flooded home.
People whose homes have been damaged can contact an emergency helpline on 0800 707 6965.
In County Tyrone, nine local farmers saved some homes from flooding by using their slurry pumping equipment to control water levels in the village of Beragh.
Some homes were damaged, but local SDLP councillor Seamus Shields said the men prevented an even greater disaster.
"They succeeded in pumping the rising flood waters to the western outskirts of the village main street where there is a sufficient downward slope to allow the water to escape," he said.
Nearly a month's rain fell in just a few hours on Saturday afternoon causing rivers to burst their banks in counties Antrim, Down and Londonderry.
Brian Kennedy's home was flooded when the Sixmilewater overflowed.
"The fridge will have to be replaced, the washing machine, tumble dryer - all gone," he said.
Environment Minister Sammy Wilson announced a compensation package for anyone whose home was affected, which will be accessible through local councils.