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

24

HYDROLOGIC AND HUMAN ASPECTS OF THE 1976-77 DROUGHT

..".,....

water demands were met generally by water
withdra wn from storage in surface-and ground-
water reservoirs.
The amount of snow in the western moun-
tains is a very important factor with respect
to uses of water for agriculture and hydro-
electric power. The snowpack acts as a natu-
ral reservoir storing moisture in the winter and
releasing it in the spring and summer. The
snowmelt runoff provides water for both near-
by areas and areas such as those along the
Missouri and Platte Rivers, that are long dis-
tances from the mountains. Also, the seasonal
distribution of precipitation in the Pacific
Coast States, where about 85% of the precipi-
tation falls between November and March and
very little from June through September,
makes the snowmelt contribution to the water
supply of the moisture deficient areas a
valuable resource both in quantity and in
timing.
Therefore, the deficient precipitation over
large parts of the nation and the poor snow-
packs in the Cascades, the Rocky Mountains,
the Sierra Nevada, and other mountains in the
Western States were the most important
causes and the earliest indications of the
drought in 1976 and 1977.
An extended freeze is not generally a fac-
tor in a drought, but the drought conditions
were intensified over a large area of the Mid-
west and East during the extremely cold
winter of 1976-77. Water supplies that were
dwindling were reduced even more when water
was taken out of circulation as it was being
stored temporarily as ice. In addition, the
distribution of water was hampered by the
freezing and bursting of water lines. The
severe winter conditions increased the concen-
tration of dissolved solids in streams and
decreased the dissolved-oxygen concentra-
tions. .. ..
The following subsections contain drought
information for 10 of the WRC regions by
region and brief statements about conditions in
the other 11 regions. For the reader's benefit,
a summary,of the main features of the drought
in each of the 10 regions is presented ahead of
the rest of the information.

Great Lakes-WRC Region 04

The Great Lakes Region (fig. 9) includes all
of Michigan, and the fringe areas of Minne-

sota, Wisconsin, Illinois, Indiana, Ohio, Penn-
sylvania, and New York that drain into the
Great Lakes.
The most recent dry spell prior to 1976-77
in Wiscosin was in 1963 when spring runoff did
not fill the reservoirs before the dry summer
began. Runoff was low in parts of the region
during the 1924, 1925, 1931, 1934, 1940, 1941,
1955, 1958, 1963, and 1964 water years. The
most widespread drought was that in 1931.
Hindsight has verified the fact that the
recent drought started in the northwest part of
the region in May 1976 and progressed to the
south and east. By August 1976, almost the
entire region had deficient precipitation, but
the most serious effects were in Michigan,
Minnesota, and Wisconsin. The Palmer index
dropped to -4 at many locations and to -9 in
northern Wisconsin and northeastern Minnesota
for extended periods. High summer tempera-
tures and an extremely cold winter augmented
the drought. Rain in the late summer and fall
of 1977 eliminated the severe drought condi-
tions.
Monthly runoff reached new record lows
for the month generally in the fall of 1976 or
the winter of 1976-77. Low-flows had prob-
abilities less than 0.02 at several sites. New
minimum water levels occurred in many wells,
and a large number of wells went dry. No
major water-quality problems were reported.

Precipitation and Runoff

Precipitation during 1975 was generally
above average throughout the Great Lakes
Region, and this trend continued through
March 1976. Significant negative departures
from normal began to show up in Minnesota in
April 1976 such as at Duluth where the April
precipitation was only 29 percent of normal.
Deficient precipitation occurred in May 1976
over large parts of Minnesota, Wisconsin, and
Michigan and southeastward to Ohio, and by
August only small parts of Indiana and Ohio
had above normal rainfall. The pattern of
deficient rainfall shifted continuously during
the fall of 1976, and parts of Wisconsin,
Illinois, and Ohio dropped below 25 percent of
normal in November. Rainfall over most of
the region increased to normal or above during
February, March, and April 1977. Dry weather
returned to Michigan and Wisconsin in May,