Ground-Water ResourcesDevelopment and Management 

Ground-Water ResourcesDevelopment and Management 

By C. S. Conover 

GEOLOGICAL SURVEY CIRCULAR 442 

Washington, D. C. 1961 
United.States Department of the Interior 

STEWART L. UDALL, SECRETARY 

Geological Survey 

THOMAS B. NOLAN, DIRECTOR 

Free on application to the U. S. Geological Survey, W aJhington 25, D. C. 
Ground-Water Resources-Development and Management 

By C. S. Conover 

Presented August 24, 1960, to Ground Water Section of the 

Western Resources Conference, Boulder, Colo. 

Th:'e need for broader appreciation# evaluation# and management of our ·ground-water 

resources is becoming more evident every 

day. Also# as development of our water resources approaches a finite limit# it becomes 

evident that ground waters and surface waters 

must be developed and managed as one water 

supply. This integration~ like the solution of 

many other problems# is easier said than done. 

Effective development and management of 

ground water# whether singly or in conjunction with surface water# requires knowledge 

and appreciation of its physical environment. 

Though ground water and surface water are 

phases of the hydrologic cycle and therefore 

are interdependent# their prime common denominator is the fact that both are wet. There 

are other common factors# of course# such as 

chemical character# but many of the physical 

situations in which ground water and surface 

water exist are quite different. It is only because they are different that we have water 

during dry periods. Mother nature planned it 

this way# and if man is to make maximum use 

of ground and surface waters he must fully 

understand and tailor his actions to take advantage of these different environmental 

factors. 

Take storage# for example. In most areas# 

the volume of ground water in storage is several times that of surface water. In the United 

States as a whole# the quantity of water in 

underground storage# within half a mile of the 

land surface# is several times that in all the 

large lakes of the North American Continent 

and more than 100 times the annual runoff of 

streams in the United States (Nace# 1960 # p. 3). 

Though the volume of ground water in storage 

is large# its natural rate of replenishment is 

1 

small in comparison. For the United Stat~s 

as a whole# several hundred years would be 

required to replenish the stored ground water # whereas streams are replenished seasonally. An outstanding example of large 

storage and small replenishment is offered 

by the southernHigh Plains in Texas and New 

·Mexico. Overall# the ground water in storage 

in the Texas portion is about 200 million acrefeet# but if exhausted it would take considerably more than 1,000 years to replace (U.S. 

Senate Select Committee on National Water 

Resources# 1960a# p. 15). 

The rate of movement of ground water also 

contrasts sharply with that of surface water. 

Generally# ground water flows inches or feet 

per day. whereas the flow in streams is me asured in feet per second or minute. The contrast in rates of flow is illustrated by the 

movement of ground watP.r in the aquifer supplying Houston. Tex. Houston# the largest city 

of the United States dependent mainly on wells 

for municipal supply~ is served by an aquifer 

having a better-than-average capability for 

transmitting water. Even so, a cross section 

of the aquifer 45 miles wide and 600 feet thick 

is required to transmit 80 mgd (million gallons per day) to the Houston area at a hydraulie gradient of 10 feet per mile. New York 

City obtains three times as much water from 

Croton Reservoir through a pipeline less than 

14 feet in diameter (Thomas, 1951, p. 98). 

The flow in streams is such that water from 

a large area can be gaged at a single location. 

Surface reservoirs also can be gaged at a 

single location. However, permeable earth 

materials offer significant impedance to flow 

of ground water, with the result that a ground• 

water reservoir (aquifer) must be gaged at 

many points if the status of the resource is to 

be evaluated. Water-level measurements in 
a single observation well may indicate conditions in only a small part of an aquifer. 

Though stream channels are not simple 

conduits~ they can be easily mapped and me asured. The same is not true of aquifers. Aquifers are composed of a wide range of earth 

materials deposited by many geologic processes. The very nature of geologic processes 

insures that the materials composing aquifers 

will vary in character both laterally and vertically. Formations that are water bearing 

(aquifers) in one locality may change laterally 

to become nonwater bearing -(aquicludes) in 

another area. Several aquifers may be present in a particular area, separated vertically 

by aquicludes~ and both water-table and artesian conditions may exist. The source ofwat e r to and the area of discharge from an a quifer may be distant or nearby. Therefore 1 

aquifers are not easily mapped. However~ 

they must be mapped, their water-bearing 

characteristics determined~ and their hydrologic regimen evaluated before decisions can 

be made as to optimum development and management of the ground-water resource over 

a long period of time. 

Water is commonly referred to as a renewable resource. Strictly speaking~ this is true. 

However for many ground-water reservoirs~ 

especially those in the arid and semiarid 

parts of the country~ the question of renewability is academic so far as the life span of 

present water users is concerned. Even in 

humid areas~ ground water withdrawn from 

wells is renewable by natural recharge only 

where the wells are so placed that natural 

discharge is reduced or natural recharge increased by an amount equal to the net consumptive use. If the wells cannot be ideally 

located--or, even if they are but the net consumptive use of water exceeds the natural 

discharge (recharge) of the aquifer--then the 

reserve can be renewed only if the withdrawals are reduced or stopped. 

Year-to-year declines in water level are 

the usual condition in many of the developed 

aquifers of the West. Persistent declines are 

evidence of depletion of ground-water resources. Whether the depletion is ~ocalized 

or aquifer -wide 1 and whether it is temporary 

or willpersist for periods equal to or greater 

than long-term climatic cycles~ depends upon 

the local geohydrologic situation. Lowering 

of water levels is a natural consequence of 

pumping of wells~ so that even in humid areas 

2 

of abundant recharge there are declines of 

water level. 

In areas of shallow-lying ground water~ 

particularly in many stream valleys of the. 

West~ rank growths of phreatophytic vegetations consume large quantities of water. The 

area of phreatophytes in California~ Arizona, 

New Mexico, Nevada, Utah, and Colorado currently is estimated as 7 million acres. These 

plants consume 10 to 12 million acre -feet a 

year. The area of phreatophytes in New 

Mexico and Arizona is almost 1 million acres 1 

and the water consumption is 2! to 3 million 

acre-feet per year (U.S. Senate Select Committee on National Water Resources~ 1960b1 

p. 2). Not only do these plants waste large 

amounts of water 1 but the water transpired is 

virtually pure. The chemical character of the 

water remaining therefore has deteriorated. 

Salvage of this wasted water by ~uch me asures as eradication of the vegetation and construction of drains is only partially effective. 

However 1 in many areas capture of this 

wasted water could be easily accomplished 

and would be a natural consequence of the 

lowering of water levels caused by pumping. 

If wells are located with the objective of salvaging water, then the net usable supply can 

be increased and the quality improved. However 1 if wells are installed with water supply 

as the only objective~ then their location may 

be such that the pumped water comes from 

ground -water storage or from streamflow. If 

S01 the individual well owner benefits temporarily at the long-term expense of all water 

users. 

Use of ground water may provide an increase in water supply through the medium of 

recirculation. Thi·s is particularly true in 

irrigated areas, where a significant portion 

of the water applied to the crops may infiltrate to the ground -water body. It is then 

pumped to the land surface for reuse by the 

same individual or his neighbors. Reuse of 

surface water is on a downstream basis 1 each 

succeeding user receiving a supply diminished in quantity and less acceptable in quality. Recirculation of gro~d water 1 though it 

may take place on the same property~ likewise diminishes the quantity and deteriorates 

the quality. In an aquifer, the continued recirculation of water results in an accumulation of dissolved salts~ whereas in a stream 

the water of diminished quality is flushed 

downstream. Thus~ in many areas of groundwater development~ the accumulation of salts 
in the water poses a more serious threat to 

the life of the resource than does the decrease 

of supply. The Wellton-Mohawk area of the 

Gila River basin in Arizona illustrates such 

deterioration through recirculation. In 20 

years the concentration of salts in the ground 

water there increased from 7,000 to as much 

as 16,000 ppm (Thomas, 1951, p. 59). 

Development and management of groundwater resources, to provide the optimum use 

of the water for the benefit of a large segment 

of the population and for the greatest period 

of timel therefore should be based upon scientific hydrology and tailored to the geohydrologic characteristics of the particular aquifer 

in question. 

Many aquifers may be classified, with respect to development and management, into 

two broad categories: those which have large 

storage but negligible recharge and which are 

not intimately related to streams, and those 

associated with streams. By proper management, a dependable supply of water of acceptable quality can be developed on a virtually 

perennial basis from aquifers of the second 

class-that is, those associated with streams. 

Aquifers of the first class can yield only a 

small perennial supply once their storage is 

depleted. 

Aquifers under the first category-those 

having large storage and little rechargecorrespond generally to those having "reservoir" problems as discussed by Thomas (1951, 

p. 35). In such aquife.rs to limit the use of 

water to the rate of recharge is not feasible 

because of (a) the large demand, (b) the very 

small recharge, or (c) aquifer characteristics 

such that natural discharge cannot be diverted 

or stopped feasibly by development. These 

are the aquifers where water is being mined, 

and must be mined, if the water resource is 

to serve a useful purpose. The problem i:s to 

rEtcognize the mining situation and to manage 

the resource for the greatest good over the 

longest possible time. A large number of developed aquifers in theW est fall into this c·ategory. Included in the are·as of current or potential ground -water mining are the southern 

High Plains of Texas and New Mexico; the 

northern High Plains in Oklahoma, Colorado, 

and Nebraska; and many of the intermontane 

valleys of New Mexico, Arizona, California, 

Nevada, and Utah. 

Consider the southern High Plains of Texas 

and New Mexico as an example of a problem 

3 

of development and management of an aquifer 

having a large volume of water in storage, but 

only a small unit rate of replenishment. 

The southern High Plains, or Llano Estacado, lies south of the Canadian River in 

Texas and New Mexico. It has a total area of 

some 30,000 square miles. Conspicuous escarpments form the east and west borders. 

The north border is the deep canyon of the 

Canadian River. The Ogallala formation is 

the aquifer, and its boundaries are essentially those of the High Plains. The Ogallala 

is thin or absent in some areas but is more 

than 600 feet thick in other areas. The total 

water potentially available from storage in 

the Texas portion in 1958 was about 200 million acre-feet (Cronin, 1959,p. 11), but the 

annual average rate of recharge is only about 

50,000 acre -feet. Storage and recharge in the 

New Mexico part of the High Plains are perhaps a third as great. Thus, total storage in 

the southern High Plains was perhaps 2 50 to 

2 7 5 million acre -feet in 1958. About 40 million 

acre -feet had already been pumped, and the 

current rate of pumping is more than 100 times 

the recharge. Obviously ,limiting development 

to the rate of recharge would mean that the 

large volume of water in storage would not be 

utilized. Further, even if it were decided so to 

limit the development, it would be physically 

almost impossible to carry out the decision if 

the premise were that doing so would result in 

a perennial water supply. The only means of 

developing water from an aquifer ona perennial basis is to locate wells so that, over a 

long time, the natural discharge can be stopped, and therefore diverted to the pumps, or 

the recharge can be increased, or both, in an 

amount equivalent to the consumptive use. 

Most of the discharge from the High Plains 

occurs along or near the eastern escarpment. 

Originally some discharge occurred from 

ground -water lakes such as at Portales, N. 

Mex., and near Muleshoe, Tex. Over most of 

the Plains the water table is more than 50 

feet below the land surface. and lowering of 

water levels in these areas cannot induce 

more recharge. Therefore, it is not pl].ysically possible, except in small areas, to locate wells on the High Plains so that the water pumped will come other than from storage. 

The lowering of water levels caused by 

pumping from a water -table aquifer such as 

the Ogallala formation is transmitted laterally at a slow rate. The major lowering of 

water level occurs in the vicinity of the well. 
The areal spread of the cone of depression is 

independent of the pumping rate and is a function of time and the hydraulic characteristics 

of the aquifer. An increase in pumping, or 

localized heavy pumping, such as caused by 

many wells in one locality, deepens and 

steepens the cone of depression. The water 

can be pumped at such a rate that it is virtually exhausted in the area of heavy pumping, "yet water levels are affected only slightly 

and slowly a few miles away. For example, 

pumping on the High Plains has been concentrated in the areas where the land is suitable 

for irrigated farming and where adequate 

wells can be obtained. As a consequence, water levels have declined more than 100 feet 

in some of these areas and an average of 

more than 50 feet under whole counties 

(Cronin, 1959, p. 10), yet in areas of little or 

no pumping the water levels have not declined, or have declined only a few feet. 

The general solution to the problem of optimum development of ground water in areas 

of mining is therefore twofold: conservative 

pumping from adequately spaced wells. The 

exact rate and spacing are a matter of decision which must take into account the aquifer 

characteristics and which revolve essentially 

around philosophical and long -term economic 

considerations. A long -term, stable development permits amortization of capital expenditures for farm equipment, city and highway 

development, schools, etc. Also of importance, a long-term, stable development permits the economy of the region to evolve to a 

level such that conservation and rectification 

measures can be undertaken. In the final 

analysis, all conservation and rectification 

measures are economic - a balancing of cost 

with benefits, either locally,regionally, or nationally. Some conservation and rectification 

measures require research, and research 

takes time -time bought by managed development to permit a stable, growing economy to 

pay for the research. 

An example of management that recognizes 

the two factors of time and spaeed development in ground -water minihg_ is afforded by 

regulatory measures set up by theN ew Mexico 

State Engineer in the Lea County portion of 

the High Plains. Regulation in Lea County is 

based essentially upon assuring a firm minimum 40 -year life of ~xtractable water, for 

agricultural papers. It is accomplished on a 

township basis by taking into account the recoverable water under each township. 

4 

Such farsighted regulated management of 

ground-water mining assures a stable development and economy and also allows the time 

needed to investigate and institute conservation and rectification measures. Such measures could include (a) increasing recharge, 

(b) improving water-application practices, (c) 

substituting crops of lower water requirements, (d) changing from an agricultural to 

an industrial economy, (e) utilizing (perhaps 

demineralizing) inferior waters for certain 

industrial processing, (f) importing surface 

water, and (g) transporting ground water from 

undeveloped to developed areas. 

Transporting ground water from undeveloped to developed areas to alleviate local 

shortages is a distinct possibility in some 

areas of the High Plains, especially for municipal and industrial supplies. Amarillo and 

Lubbock, Tex .• are doing so, and Portales, 

N. Mex., is favorably situated to transport 

water from the sand-dune area to the north. 

A significant part of the High Plains is underlain at less than plow depth by cemented sediments called "caliche" which are not suitable 

for agriculture. The formation of the caliche 

rocks in these areas may be said to have 

effectively saved water for the future, and the 

rocks therefore may be "worth their weight 

in water" to the economy of the Plains. 

Aquifers of the second category with respect to development and management--that 

is, those associated with streams--correspond 

to those having "watercourse" problems and 

generally to those having "pipeline" problems 

as discussed by Thomas (1951, p. 36). These 

are aquifers in which the amount of water that 

can be developed is sufficiently large to warrant management on a perennial basis. The 

ground water in these aquifers is related to 

surface streams, either directly along a 

stream reach or indirectly through spring 

flow or other natural discharge. 

The prime requisites for development of 

water from an aquifer on a perennial basis 

are as follows: (a) the location and character 

of the discharge areas are such that pumping 

from wells can effectively reduce the natural 

discharge from the aquifer, and (or) (b) recharge to the aquifer can be increased in the 

recharge area or induced in the discharge 

area. Development can be perennial if the net 

consumptive use of developed water does not 

exceed the sum of (a) natural discharge stopped and (b) recharge induced or increased, 
by virtue of the development or by other artificial means. 

Ground-water reservoirs in alluvial valleys of essentially perennial streams, wherein 

the surface and ground waters are intimately 

related, fit this category. Examples of such 

are the Middle, the Rincon, and the Mesilla 

Valleys of the Rio Grande in New Mexico and 

the Duncan- Virden and the Safford Valleys of 

the Gila River in New Mexico and Arizona. 

In Colorado the South Platte and Arkansas 

River Valleys and some of their major tributaries also fit this category. 

In such valleys, surface water is usually 

applied to irrigate the lands. A pa:rt of the 

surface water infiltrates to the ground-water 

body and returns to the stream through drains 

and by ground-water seepage. The amount of 

water available for net consumptive use is 

essentially equal to the difference between 

the inflow, primarily that brought in by the 

stream, and the outflow that must be allowed 

by virtue of prior water needs and rights 

downstream (and by the necessity of maintaining salt balance). In many such valleys, 

the valley consumptive use of water exceeds 

the beneficial consumptive use because of the 

areas of native phreatophytic vegetation. For 

example, in 1936 the consumption by irrigated 

lands in the Middle Valley of the upper Rio 

Grande was 157,000 acre-feet, whereas the 

total consumptive use was 583,000 acre-feet 

(Natural Resources Committee 1938, p. 91). 

Streamflow in such valleys is occasionally 

inadequate for the needs. in spite of regulation by surface reservoirs. Consequently, 

wells have been installed. As these wells 

commonly are located at a spot convenient to 

provide water, evapotranspiration by native 

vegetation is reduced little if any; accordingly, net consumptive use of the pumped water results in either diminution of streamflow 

or reduction in ground-water storage, or bc:>th. 

Before pun1.ping is undertaken in most such 

stream valleys, ground water feeds the 

str~ams. After pumping lowers the water 

table the ground -water accretion to the 

streams is reduced or, more frequently, the 

gradient of the water table is reversed so 

that the stream loses rather than gains water. 

Water shortages downstream are ther~by increased, and individuals downstream who are 

able also install wells to satisfy their :water 

needs. Because of this extra~tion from storage, the stream will continue to lose water 

5 

even after normal inflow to the valley is resumed. Therefore, pumping will be continued 

until such time as increased efficiency in water use, reduction of nonbeneficial losses, 

and inflow of excess surface water result in 

replenishment of ground-water storage. 

A study of the effects of pumping in the 

Rincon and Mesilla Valleys of the Rio Grande 

in New Mexico showed that pumping would 

need to be continued for 4 years after a return to normal surface supply following a 5-

year period of 50 -percent -normal surface 

supply. In the absence of excess surface water, pumping there would need to be continued, 

even in years of normal surface supply, unless the debt to ground-water storage could 

be gradually reduced by more efficient use 

of the pumped water and the reduction in 

pumping that would be made possible. It was 

shown that ground water obtained by pumping 

in the Rincon and Mesilla Valleys (where 

losses f~om areas of native vegetation are 

small) does not represent an additional supply or new source of water, but rather a 

change in method, time, and place of diversion of the supply already available (Conover. 

1954, p. 2, 122, 126). During the period of 

shortage of project water supply in the surface reservoirs, individual farmers utilized 

the ground -water reservoir by pumping of 

wells. As a natural consequence the groundwater reservoir was replenished later from 

project water supply by stream losses and 

infiltration from irrigated lands. Pumping in 

such circumstances therefore is, in effect, 

borrowing on future water supplies. 

This unplanned, though somewhat effective, 

use of the ground-water reservoir in conjunction with the surface stream benefits 

those who have wells but works a hardship on 

those who have only surface -water rights. 

Planned development and management of 

ground water in stream valleys can increase 

the water supply by salvaging nonbeneficial 

losses in areas of shallow water and will 

facilitate using the ground-water reservoir 

in conjunction with the surface supply to the 

maximum benefit of all water users. Such 

planned development and management necessitates locating and pumping of wells in harmony with the surface system. If such is 

properly done a perennial water supply can 

result. 

Proper location of pumps includes placing 

wells in areas of shallow water to capture 
water used by native vegetation, and spacing 

of wells so that the storage of ground water 

can be manipulated1 Operation of pumps in 

conjunction with t~1 surface supply entails 

pumping during periods of deficient surface 

supply at a rate such that the ground-water 

reservoir can be replenished during periods 

of excess surface supply. A fully managed 

ground-water and surface -water supply not 

only will maintain but will increase the firm 

supply because of (a) the savings in evaporation resulting from storing surface water 

underground, (b) the capture of floodwaters 

by surface reservoirs made vacant by storing 

water underground, (c) the reduction of evapotranspiration losses by phreatophytes. and 

(d) the recirculation of water by pumping. 

Because of the large volume of water in 

underground storage in many alluvial valleys, 

as compared with the volume of surface reservoirs. a fully managed integrated system 

would be capable of providing a firm supply 

that would span climatic cycles a decade or 

two long. Theoretically. it is possible to control a supply to the extent that no water would 

be allowed to flow to the oceans. However. 

such a system is not desirable or feasible, as 

the salt content of the water would increase 

and the economy of the region would suffer. 

A managed system should therefore provide 

for flushing out excess salt during periods of 

excess precipitation and runoff. 

The population of the 17 Western States is 

expected to continue to increase at a rate exceeding the national average. The present 4 3 

million population of these States is expected 

to reach 108 million in 40 years (U.S. Senate 

Select Committee on National Water Resources, 1960c, p. 9). The need for industrial, 

municipal, and agricultural water likewise is 

expected . to increase. Competition for the 

limited water supply will dictate systematic 

planning, coordination, and integrated development and management of water supplies. 

Integrated development and management of 

surface and ground water will require a better understanding of our ground water resources and the nature and extent of the aquifers. The nature of ground-water investigations is changing as the demand for water 

increases and the limit of the ground-water 

resources is approached. Only some 30 years 

ago most ground -water investigations went no 

further than to determine the occurrence of 

water--that is, where could wells be drilled, 

6 

and what might be their expected yield? The 

concentrated development of wells in some 

areas of the West brought questions of well 

interference and the need for quantitative 

studies of the effects of pumping. Such questions prompted Theis to develop his wellknown nonequilibrium formula in 193 5. The 

trend toward full development of groundwater resources and integration with surfacewater development is creating a demand for 

means of analyzing masses of geohydrologic 

data and parameters to provide a basis for 

choosing among alternate plans for aquifer 

development. Electrical analog models offer 

promise of providing solutions to complex 

problems. Development of such equipment 

for analyzing aquifer systems is now well 

advanced, and examples of their use are 

forthcoming. The results will be only as good 

as the number an_d quality of data fed into 

them will permit, however:,and in many cases 

the necessary data will cost a lot of money to 

acqui.c~. 

in summary, optimum development and integrated management of ground waters, singly 

and in conjunction with surface waters. promises to solve perplexing water problems of 

the West. But the solution will be neither 

easy nor inexpensive. The public, as well as 

those responsible for water-resource development and management, must be informed 

and convinced of the need and value of such 

measures. Large sums will have to be spent 

to acquire the needed information on the 

ground -water reservoirs and their relation to 

the streams, and in many States substantial 

new legislation will be needed to provide the 

basis for planned water management. 

R!::FERENCES 

Conover, C.S.,1954, Ground-water conditions 

in the Rincon and Mesilla Valleys and adjacent areas in New Mexico: U.S. Geol. Survey Water-Supply Paper 1230, 200 p. 

Cronin, J. E •• 1959, Notes on the availability 

of ground water in the South Plains of Texas: 

U.S. Geol. Survey open-file rept., 14 p. 

Nace, R. L •• 1960, Water management, agriculture, and ground-water supplies: U.S. 

Geol. Survey Circ. 415, 12 p. 

National Resources Committee, 1938, Regional planning, pt. 6, The Rio Grande joint investigation in the Upper Rio Grande basin 

in Colorado, New Mexico, and Texas, 1936-

37, v. 1, 566 p. 
Theis, C. V., 1935, The relation between the 

lowering of the piezometric surface and 

the rate and duration of pumping of a well 

using ground-water storage: Am. Geophys. 

Union Trans., v. 16, pt. 2, p. 519-524. 

Thomas, H. E., 1951, The conservation of 

ground water: New York, McGraw-Hill, 

327 p. 

U.S. Senate Select Committee on National Water Resources, 1960a, National water re7 

sources and problems: Comm. Print 3, 42 

p., January. 

---1960b, Evapotranspiration reduction: 

Comm. Print 21, 42 p., February. 

---1960c, Future needs for reclamation 

in the Western States: Comm. Print 14, 45 

p., April. 

INT .DUP. ,D.C.Sl- 8 77 21