Many springs and seeps discharge water from the north wall of the valley of
the Snake River between Milner and Bliss, Idaho. These are fed by a large
ground-water body lying east and north of the river, beneath the Snake River
Plain. Much ground water is pumped on the plain, many irrigation wells having
been drilled since 1946. Heavy withdrawal of ground water from wells may
alter the discharge rates and regimens of the springs and may affect downstream
flow of the river. For that reason, the historic record of discharge from
the springs is an important part of the basis on which hydrologic changes can be
determined. The records also would facilitate appraisal of the total groundwater
resources of the Snake River Plain.
This report brings together in a single volume all obtainable records for the
period 1899-1947. The report also includes descriptive data and a brief history
of work done.
The springs occur in a 40-mile reach of the valley of the Snake River between
Milner Dam and Bliss. Most are on the north side of the river but a few are
on the south.
The earliest measurements of record were made by F. S. Shirley and N. S. Dils,
of the U. S. Geological Survey, in 1899. The next were by J. D. Stannard for
the Idaho State Engineer and by Dils in 1902. Few measurements were made
from 1903 to 1916. Somewhat more systematic measurements were made by
the Geological Survey and by local agencies in 1917-20, 1923-25, and 1931, and
at several intervals thereafter. In 1950 the Geological Survey began continuous,
systematic measurements by installing and operating gaging stations on four
representative springs and by making yearly direct measurements of all large
springs. The recent records are not included in this report; they have been
published yearly in a series of reports on stream discharge.
The report includes lists of all published sources from which data were compiled,
and cites many unpublished sources. The principal workers and agencies
that have obtained records are listed also.
The quality and accuracy of the compiled records, as might be expected, are
not uniform, as the records were collected under varying circumstances, by many
individuals, and according to changing or differing standards. The continuity is
generally poor. Nevertheless, the compilation represents the base from which
further work must start and is an extremely valuable record. It represents about
30 large springs and groups of springs, having discharge rates ranging from a
fraction of a cubic foot per second to well over 1,000 cfs. Many smaller springs
and seeps never have been measured. The fluctuation indexes for individual springs or groups range from 2 to 41
percent. The fluctuation index is the mean deviation of the discharge rate from
the arithmetic mean, expressed as a percentage of the arithmetic mean. Although
to some extent the indexes are a measure of the consistency of the record,
they also seem to reflect actual differences in range of discharge, and they indicate
that springs upstream in the Snake River valley fluctuate through a wider range
than do those downstream. The fluctuations are rather slow, which reflects the
equalizing influence of the large ground-water reservoir that supplies the springs.