GROUND WATER IN NORTH-CENTRAL TENNESSEE

HUMPHREYS COUNTY 155
and elsewhere the dug wells prove inadequate in periods of drought,
In these localities cisterns for the storage of rain water are the usual
source of domestic supply. A few wells have been drilled through
the residual chert and find water at the top of the solid rock or in
channeled limestone just below. The maximum draft upon any of
these wells, however, has been only about 20 gallons a minute. Sev­
eral wells in the vicinity of McEwen Nos. 163, 164, 165 and 166
(pp. 159-160) are reported to pass through 200 to 230 feet of uncon-
solidated gravel or residual chert before reaching solid rock. This
unconsolidated material is water-bearing in well 164 and may yield
some water to wells 163, 165, and 166. It is not known whether the
water-bearing beds are gravel that belongs to the Tuscaloosa forma­
tion (see pp. 31-33) or whether they are composed of residual chert.
In the more rugged parts of the county most domestic water
supplies are derived from springs, although some are derived from
dug wells and a few from drilled wells. In these areas, however, the
water-bearing zones in the limestone are likely to be extremely dis­
continuous so that drilling for water is uncertain. To judge from the
experience in other counties, drilling may be unsuccessful if water is not
found within 50 or 75 feet below near-by perennial streams. Tubular
springs of relatively large discharge are numerous and constitute an
adequate water supply to meet the probable future needs of most of
these rugged areas. Tubular springs (pp. 92-95) are especially numer­
ous in the southwestern part of the county, in the vicinity of the
confluence of Tennessee, Duck, and Buffalo Rivers, where the lime­
stone has been channeled by subsurface drains adjusted to the surface
streams. Some of the subsurface channels cut across stream meanders
or join converging surface streams above the point of confluence.
Such channels have been formed during several stages of the dissection
of the Highland Rim plateau. The largest of the tubular springs in
this part of the county, and the largest spring known to exist in the
region covered by this report, is Hurricane Rock Spring (No. 181, pi. 4
and p. 161). This spring is on the east bank of the Duck River about
half a mile upstream from the mouth of Beech Creek and 4 miles from
the Tennessee River. It issues from a single solution conduit about
15 feet wide and 5 feet high in the Camden chert. The conduit is
adjusted to the present stage of the Duck River, and its orifice is
submerged during periods of high water. When observed by the
writer, on September 9, 1927, the discharge of the spring was about
60 cubic feet a second (27,000 gallons a minute), and the water was
essentially free from suspended matter and had a temperature of 62 °F.
This discharge presumably is approximately the seasonal minimum,
although the maximum discharge and the variability of the spring
over a long period are not known. The source of the spring is gener­
ally ascribed locally to the "whirl," a persistent and strong eddy in the