Emergency Management for the Municipality of Wood Buffalo has ordered mandatory evacuations for Grayling Terrace and the most southerly portion of Draper Road in Fort McMurray.

Approximately 340 residents will be affected by the Grayling Terrace evacuation and an additional 78 individuals who live south of Draper Bridge on Draper Road will be removed.

According to a release Thursday afternoon, sloughing — or erosion — along the Hangingstone River is becoming an increasing worry, especially for those living on Beacon Hill’s southwest side.

The sloughing is expected to worsen over the next 48 hours as heavy rainfall is forecast for the area, with a high likelihood that the eroding materials may cause further backups downstream in Grayling Terrace.

So far, emergency responders’ efforts to slow the erosion along the riverside have proved unsuccessful.

Thousands of sandbags already in place

Thousands of sandbags line the eroding banks of the Hangingstone River as Fort McMurray, Alta., residents work desperately to save their homes.

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Efforts are underway to stabilize retaining walls and banks along the Hangingstone River. (CBC)

As many as 2,000 sandbags are piled three and four high, a temporary berm created by residents and volunteers. The river is slowly finding its way toward back yards of homes along the river, leaving homeowners in fear their houses may eventually slide into the raging water.

"It's not a matter of 'if,' it's 'when' it's coming," said resident Dave Courture watching in awe from the banks. "We all know it is."

He said the normally placid river can be walked across in mid-summer without getting one's knees wet.

"It's just amazing, he said. "I haven't seen anything like it around here."

Homeowners have put aside documents and belongings and, in some cases, loved ones in case an evacuation is ordered. Kelly Tuohey sent her two-year-old twins to stay with a friend.

"My friend, she took my babies and my paperwork," she said through tears.

"Our concern in this home is that if we flood it's not covered by insurance," she added.

But her bigger headache now is the eroding banks.

"What if the property goes? Landslide — that's my worry," said Tuohey.

While she's thankful for the efforts of volunteers in placing the sandbags, she wonders about their effectiveness.

"My fear is erosion will get us first so these sandbags will be in the river," she said. "The river will come and get us."

The latest forecasts call for anywhere from 50 to 100 millimetres of rain over the next 48 to 72 hours.

With files from CBC's John Archer