Thick ice in Simpson raises flood worries
But Hay River residents are breathing easy

by Cheryl Leschasin
Northern News Services

NNSL (Apr 28/97) - Abnormally thick ice has Fort Simpson worried about the possibility of a spring flood.

Water survey officials met Friday afternoon in the community to prepare for the worst. They will be watching the weather carefully over the next few days.

Officials said they are concerned about the ice thickness. Ice on the Liard River measured 1.78 metres last Tuesday -- normally it's only about 1.08 metres" said Roger Pilling of Environment Canada in Fort Simpson.

"It's too early to know for sure," said Pilling, "but if Liard has trouble, we'll have trouble."

A bottleneck 10 kilometres south of the community is prone to clogging with large chunks of ice, causing downstream flooding when it finally breaks through.

Thick ice, however, does not in itself indicate an impending flood. "If the temperatures stay steadily warm through the day, we'll get a thermal breakup, where the ice just rots away," said Pilling.

The other type of breakup that usually causes flooding is called a dynamic breakup. It is caused by sudden warm temperatures and can be worsened by rainfall.

Fort Simpson officials aren't calling the situation serious yet, but Pilling said this weeks' weather will be "critical."

Fort Simpson was last flooded in 1992.

Floods are caused by a number of contributing factors. First, heavy snow accumulations coupled with suddenly warm temperatures produce high runoffs.

The second factor is ice thickness. When rapidly rising temperatures soften and break up large chunks of ice, narrow passages can jam, causing water to spill over its banks.

The Hay River area isn't likely to flood this year, however, according to Environment Canada water survey official, Murray Jones.

"There's a bit of worry, but the temperature has been pretty steady recently," said Jones.

Water that runs toward Hay River comes from northern Alberta, around the High Level and Indian Cabins area.

Alberta officials determined in April the snow pack in the area is normal to above normal. But NWT water survey officials said they aren't overly concerned about the Hay River basin because temperatures have risen slowly enough to allow runoff to evaporate.

The last three floods in Hay River happened 11 years apart in 1963, 1974 and 1985.