river flooding MAINSTEM RIVER FLOODING
Flooding is typically a
seasonal problem during late winter and spring when the snowpack begins to melt.
This snowmelt, in addition to frequent rain showers, can lead to high water
on many of the major rivers across the Inland Northwest. Many different types
of bulletins are issued by the National Weather Service during flooding episodes.
Some of the bulletins pertained to flooding on small rivers and streams while
other products deal with flooding to only mainstem rivers.
A mainstem river is a primary
river that is monitored by one or several gages; it also receives stage forecasts
from the River Forecast Center. The mainstem rivers which the NWS Spokane has
the warning responsibility span from the east slopes of the Cascades to the
Idaho panhandle. In eastern Washington, the rivers include: Columbia, Entiat,
Methow, Okanogan, Similkameen, Wenatchee, Pend Oreille, Snake, Palouse, Grand
Ronde and Spokane, in addition to the Little Spokane and Hangman Creek. In north
Idaho, the rivers include: St. Joe, Kootenai, Coeur d'Alene and Clearwater.
A River Statement is issued
for forecast or actual minor flooding. This means mainly where only low lying
farmland is inundated, and no homes or businesses are being threatened in the
area.
A Flood Warning is issued
when any of the mainstem rivers are forecast to rise above flood stage, leading
to considerable inundation of land and roads along with a threat to life and
property. The forecast of river levels are provided by the River Forecast Center
who has the responsibility of keeping a watchful eye on all mainstem rivers.
Flood warnings are also issued for many rivers and lakes where no forecast points
exist, but is appears flooding will cause a threat to life and property. These
rivers include: Colville, Kettle, Priest, Sanpoil and Stehekin. The lakes include:
Lake Chelan, Hauser Lake, Hayden Lake, Liberty Lake, Newman Lake, Priest Lake
and Lake Wenatchee. Since these waterways are not forecast and have little real
time observations, coordination with the local officials and spotters is important
to give an accurate warning on general trends.
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