Residents along Quebec's Richelieu River honked their car horns and waved in delight as Canadian soldiers arrived Thursday to help flood victims in St-Jean-sur-Richelieu, south of Montreal.

Soldiers were deployed to the flooded region a day after Quebec Premier Jean Charest asked the Canadian Forces for help. 

About 500 soldiers have been sent to the area from CFB Valcartier. Another 100 reservists from the Montreal area were dispatched to the flood zone to support local emergency officials already on the ground.

"Basically, we'll be filling out sandbags, distributing whether food or water, protecting any infrastructure, or if requested, evacuating people," said 2nd Lt. Julien Beauchamp-Laliberté.

At least 3,000 homes and businesses have been flooded in the Richelieu Valley, and 1,000 people had left their homes by Thursday morning in the worst flooding in the region in 150 years.

The area's Royal Military College is among the buildings cleared.

Premier says flooding 'exceptional'

Charest flew to the waterlogged region Thursday afternoon to survey the damage, and said he'd never seen such flooding.

mi-mary-adams-220

Mary Adams wades through a flooded street. ((Peter Akman/CBC))

"These floods are the most important that we've seen in Quebec since the disaster of the Saguenay-Lac-St-Jean in the 1990s," the premier told reporters, referring to the flash flood in 1996 that washed out the Saguenay after torrential rains.

"It's not the same thing of course, and we're fortunate there has not been a loss of life, but it's the most important floods we've seen in Quebec in the last 50 years."

Quebec will compensate people and municipalities for some of the damage. But he warned that the government couldn't pay for everything.

"Programs will never manage to compensate people for everything they have lost," Charest said.

"It hurts me to say this today. But it's not true that we can compensate everything. It's impossible."

He said the waters were continuing to rise and that it would take time just to stop the flooding, let alone rebuild. "Yes, we get floods in Quebec in the spring, but this is exceptional, and it doesn't seem to be stopping," Charest said before his visit.

"We hope the waters will subside as quickly as possible and we'll be able to start the reconstruction process."

Flood threat spreads

The Richelieu's water level rose to 1.2 metres above normal Wednesday, and Environment Canada is predicting rain for the area until Saturday.

mi-flooding-ugc-300-riaz7766

Quebec's Montérégie region is experiencing the worst flooding in 150 years. ((Courtesy of Riaz Lakhanisky))

The number of municipalities affected by the breached banks of the Richelieu jumped from 10 to 17 Thursday, due to high water levels in two tributaries to the north.

Six emergency shelters have been set up for people seeking refuge.

Septic tanks have also overflowed in several municipalities, prompting town officials to install portable toilets for residents.

Flood watches are in effect for other areas of the province.

Water levels are rising rapidly north of Quebec City, in the Beauce, and in the Lower St. Lawrence region.

Heavy rainfall warnings are in effect for all of those regions, with between 10 and 25 milimetres expected to fall by the end of Thursday.

Winter snowmelt, heavy rain

Environment Canada explained that this year's heavier-than-usual winter snowfall — and not just this week's continual downpour — is responsible for the floods.

It said the snow in the U.S. Adirondacks melted into Lake Champlain and, with this week's rain, a startling volume of water poured across the border into the Richelieu River.

"This is a really unique phenomenon," said René Héroux, an Environment Canada meteorologist.

"To understand how we wound up with a phenomenon of this magnitude, you need to go back to last winter."

Prime Minister Stephen Harper issued a statement to say the federal government is ready to help those affected by the flooding.

"Our thoughts and prayers are with the families of the Richelieu Valley during the devastating floods that have hit the region this month," Harper said.

With files from the Canadian Press