WSP10396

• File Number: 8056
• Description: Drought Preparedness
• State: CO
• Basin: Statewide
• Date: 1/1/1964
• Author: USGS
• Title: General Effects of Drought on Water Resources on the Southwest
• Water Supply Pro - Doc Type: Report/Study

OD.ryS90

GENERAL EFFECTS OF DROUGHT ON VVATER RESOURCES

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effects when the river discharge is less than 4,000 cfs.
In 1950 the stage-discharge relation was affected by
t.ides about 20 percent of the time, and the dissolved
solids exceeded 300 ppm about. 30 percent of the time.
By contrast, in the drought year 1952 the river at t.he
station was affected by tides about 80 percent of the
time, and the dissolved solids exceeded 300 ppm about
75 percent of the time,

QUALITY OF GROUND WATER

Drought alone has little effect upon the quality of
water in most ground~,vater reservoirs. The chief ef-
fect. of drought. is t.o reduce the quantity of natural dis-
charge, without any marked change in quality, par-
ticularly if t.he ground-water reservoir is recharged by
precipitation and if the water is st.i11 usable at. the point
of nat.ural discharge,
In ground-water reservoirs that are recharged by
st.reamflow, t.he quality of water is necessarily depend-
ent. upon that in the stream at the time of recharge, and
if recharge occurs during drought the water may be
more mineralized than usual. Also, if fresh ground
water has a hydraulic connection with saline ,vateI'-
as for example in some coastal aquifers and in fresh-
water aquifers that are in contact wit.h brine aquifers-
a decrease in amount of fresh water may result in
increased concentration of t.he water discharged.
The effects of drought upon the quality of ground
wat.er may be enchanced markedly where man has been
involved, By pumping from wells he may induce flow
of saline water into a fresh-water aquifer that is near
t.he ocean or saline lakes or that overlies or underlies
saline- water aquifers, This pumping may not be re-
lat.ed t.o drought in any way or it may be indirectly re-
lated in that. it is necessitat.ed by deficiencies in pre-
cipit.ation and (or) in surface Wltter, On the other
hand, a deficiency of surface water may result in inter-
ruption of irrigation, which retards leaching or saline
soils and therefore t.he transport. of the soluble salts
int.o underlying ground-wat.er reservoirs. The effects
of drought and development upon the quality of ground-
wat.er vary from one locality to another; many types
of effect.s are described in subsequent det.ailed discus-
sions of specific areas,

ECONOMIC AND RELATED EFFECTS

By J. S. GATEWOOD and ALFONSO 'VILSON
This section concerns the significance of drought to
society. For comparison with the effects of \~ars, pesti-
lence, and other factors that affect the welfare of man-
kind, it might. be desirable to express the effect of
drought; in dollars and cents. But t.he drought in the
Southwest occurred during a period of increasing popu-
lation, increasing industrialization, and inflat.ion of the

dollar, and isolation of the effects of drought upon an
expanding economy is a difficult and controversial op-
eration. The following discussion, therefore, includes
costs of the drought to some extent., but in many in-
st.ances it is limited to comparisons of the. production
of commodities during the drought with the production
in earlier years of greater water supply,
In the Southwest as a whole, where water is at all
times a scarce and valuable commodity, shortage of
water presumably must cause some loss of income: The
effect of drought upon water supplies varies greatly
from place to place; and the effect upon production may
range as \videly, although not necessarily according to
the same patt.ern. For example, of twostr~ams equally
affected by drought, the flow in one may be ample to
serve those who depend on it, whereas the ot.her pro-
vides far less than the demand. The economic effect
of drought thus depends not only upon the magnitude
of the deviation below average water supplies but also
upon the effect of that deficiency upon people.
As an example of t.he reaction of people t.o drought,
consider the water-supply situations of cities in Texas,
as shown in the following table:

Municipal water-supply. sit1tations in Texas during drought years
[Data from Texas State Board of Health]

1%0 1951 1952 1953 1954 1955
~- - - -- --
Numberofcitles:l
Having less than OO-day supply___._n__ __un 12 30 40 u____ nun
Rationing water __________.~,_ "_______~_ __,_u 40 65 77 ----,- _.u._
Using emergency supplies. .n_n_un~_ _nn_ nnn 10 28 nuu n~_n
Hauling water on _ __~___~_______u______ 12 5 9 11 n~_n '__~h
ermanent improvements:
Drilling wells___________________.___~___ _~__u 11' 79 11' 95 69
Building reservoirs_ ..~~~u__~~_~n.n_~ ~n~~~ 6 n.n~ 13 8 9

p

I Number of cities diminished after 1953 because of permanent improvements.

All the given activities could have been caused by
drought, but. not necessarily so. Wells, reservoirs, dis"
tribution systems, and other facilities can wear out or
become clogged so that they need replacement, and t.hey
can also become inadequate with increased demand for
water. Thus the fignres do not provide a measure of
the effects of drought but merely an indication of the
increased attention given to water-supply facilities dur-
ing the years of drought. The public reactions indi-
cated by t.his table include: awareness of impending
crisis ("less than 90-day supply"), reduction in USe to
balance available supply ("rationing water"), emer-
gency operations to counteract the current shortage
("hauling water". and "using emergency supplies"),
and operations that may also provide some insurance
against recurrence of shortages under similar condit.ions
in the future ("drilling wells" and "building reser-
voirs"), These reactions are characteristic of cities and