WSP08775

• File Number: 8056
• Description: Drought Preparedness
• State: CO
• Basin: Statewide
• Date: 1/1/1979
• Author: USGS
• Title: Hydrologic and Human aspects of the 1976-77 Drought
• Water Supply Pro - Doc Type: Report/Study

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CHRONOLOGY OF THE 1976-77 DROUGHT

55

southern ranges, In Washington during the
January storm, the water content of the snow-
pack remained about constant, which meant
that the subnormal snowpack was farther
below normal after the storm than it was be-
fore, The ensuing precipitaiton was not suf-
ficient to replenish the snowpack up to normal;
therefore, the spring and summer runoff from
snowmelt was deficient.
The abnormally low winter precipitation
caused poor soil moisture conditions though
normal or greater precipitation in March in
western Washington, in May in Idaho, Oregon
and Washington, and in August and September
in most of the region improved conditions. See
figure 7 for an index of the drought severity.
The water content of the snowpack in the
Columbia River basin was less than the pre-
vious record low amounts from January to May
1977 (fig, 21) and ranged from 30 percent of
normal on January 1 to 50 percent of normal
on April 1. Bare snow courses were prevalent
by May 1. Snowmelt started earlier than
usual-in the latter part of April in the
Flathead River basin. This abnormal timing
brought storage in many Montana reservoirs
above 100 percent of average for May I-a
deceptive statistic because the remaining
snowpack had very little water left to contri-
bute to the seasonal runoff that usually occurs
in May and June, The maximum discharge for
the year occurred in May on many streams;
and later, some smaller streams went dry for
the first time since observations have been
recorded,
The difference in the areal extent of the
snowpack in part of the Columbia River basin
between 1976 and 1977 is depicted in figure
22, The snowcover in April 1976 is shown in
figure 22a, and that in April 1977 is shown in
figure 22b, The photographs were obtained
from Landsat satellite imagery and cover an
area approximately 115 mi on a side, Lake
Washington at Seattle and part of Puget Sound
near Tacoma are near the left edge, Mt,
Rainier is near the bottom edge, Lake Chelan
is the dark eel-like image in the upper right,
and the Columbia River is the dark line from
the upper right corner down to the lower right
edge past Wenatchee in the right center.
Some cloud cover obscures the ground in parts
of figure 22a.
Streamflow in western Montana dropped
into the below normal range (less than 75 per-

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Jan. 1

Feb. 1

Mar. 1

Apr. 1

May 1

Figure 21. Water content of Columbia River
basin snowpack as a percentage of the
April 1 average.

cent of normal) by March 20, 1977. Normal,
though declining, runoff occurred in May in
those basins that included some high elevations
where remnants of the snowpack still existed;
otherwise, flow was below normal. Many
streams were nearing record low flows for the
month of June. The Middle Fork Flathead
River near West Glacier had not been so low
since 1941, and the Clark Fork at St. Regis
was lower only in 1926 and 1931. The low run-
off continued for the remainder of the water
year, and the annual runoff near West Glacier
was the third lowest in 38 years of record and
that at St. Regis was the second lowest since
records began in 1911.
During the spring of 1977 streamflow in
Idaho fluctuated between normal and defi-
cient, depending upon the range of elevation in
a basin, the water content of the small snow-
pack, and the precipitation during the spring.
Many irrigators received only 60 to 80 percent
of their usual supply, but with prudent use of
the supply and fortuitous timing of some rain
during the growing season, irrigated crops
fared very well, The usual irrigation season
was shortened about 30 days so that water
could be stored for future use.
By May 1, 1977, flow in the Snake River at
Weiser was the lowest it had been since 1924,
and the mean flow for June was the lowest
monthly mean in 67 years of record. Drought
conditions continued through September 30,
the end of the water year; therefore, the mean
annual runoff was the minimum of record at