Summary Appraisals 

of the Nation's 

Ground-Water ResourcesRio Grande Region 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 813-D 

Summary Appraisals of the 

Nation's Ground-Water ResourcesRio Grande Region 

By S. W. WEST and W. L. BROADHURST 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 813-D 

A discussion of ground-water alternatives 

in water resource planning 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1975 
UNITED STATES DEPARTMENT OF THE INTERIOR 

Cecil D. Andrus, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

First printing 1975 

Second printing 1977 

Library of Congress Cataloging in Publication Data 

West, Samuel Wilson, 1921-

Summary appraisals of the nation!s ground-water resources-Rio Grande region. 

(Geological Survey Professional Paper 813-D) 

Bibliography: p. 

Supt. of Docs. No.: I 19.16:813-D 

1. Water, Underground-Rio Grande watershed. 2. Water-supply-Rio Grande watershed. 

I. Broadhurst, William Leslie, 1905- joint author. II. Title. III. Series: United States Geological Survey Professional 

Paper 813-D. 

GB1019.W4 553'.79'097644 74-34169 

For sale by the Branch of Distribution, U.S. Geological Survey 

1200 South Eads Street, Arlington, VA 22202 
CONTENTS 

Page 

Abstract _________________________________ D1 

Page 

Withdrawal and consumption of ground water _ _ _ _ _ _ _ _ _ D19 

Possible alternatives in ground-water management _ _ _ _ _ _ _ 24 

San Luis Valley subregion ------------------ 25 

Albuquerque subregion -------------------- 26 

El Paso subregion ----------------------- 27 

Pecos Valley subregion _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 28 

Introduction _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1 

The physical setting _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 

The economic setting ------------------------- 5 

The legal setting---------------------------- 10 

The ground-water supply----------------------- 11 

San Luis Valley subregion ------------------- 13 

Albuquerque subregion______________________ 14 

Closed basins subregion __ __ _____ _ ____ __ ____ 29 

Lower Rio Grande subregion ----------------- 29 

El Paso Special utilization of underground space _ _ _ _ _ _ _ _ _ _ 29 subregion ------------------------ 15 

Pecos Valley subregion _ ----- _______________ 17 Information needed for planning ground-water management _ 30 

Summary and conclusions --------------------- 33 

References _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 35 

Closed basins subregion --------------------- 17 

Lower Rio Grande subregion ------------------ 18 

ILLUSTRATIONS 

Page 

FIGURE 1. Map of the Rio Grande Region, showing six subregions based on physiography and ground-water resources D3 

TABLE 

2. Map showing generalized terrain __ ~ ___________________ - ____ ---___ ----- __ ---- 4 

3. Map showing population distribution __________________________ --____ ----__ ---- 6 

4. Graph showing population trends-------------------------------------------- 7 

5. Map showing areas of irrigated land ------------------------------------------ 8 

6. Map showing mineral and petroleum deposits ------------------------------------ 9 

7. Map showing generalized distribution of geologic units ________________ - _____ --___ ---- 12 

8. Diagrammatic cross section of the San Luis Valley --------------------------------- 13 

9. Block diagram of the Rio Grande Valley at Albuquerque, N.Mex. ------------------------ 15 

10. Cross section showing the ground-water reservoir in valley fill at Elephant Butte Reservoir in New Mexico 16 

11. Cross section showing the ground-water reservoir in valley fill at Las Cruces, N.Mex. ------------ 16 

12. Diagram showing the complex relationship between the ground-water flow system and the surface water in the 

Pecos Valley at Roswell, N.Mex. -------~--------------------------------- 17 

13. Cross section showing the ground-water reservoir in valley fill of the Tularosa basin in New Mexico __ -- 18 

14-16. Maps showing ratios between: 

14. Ground water withdrawn and surface water withdrawn ___________ - ____ --- ___ ---- 20 

15. Water withdrawn for public supplies and water withdrawn for irrigation ____________ --- 21 

16. Water withdrawn and water consumed ___ -------------------------------- 22 

17. Map showing areas of water-level decline --------------------------------------- 23 

18. Graph showing relationship between rate of water loss by evapotranspiration and depth to water table in the San 

Luis Valley _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 26 

19. Map showing areas in which ground-water studies have been made ______________________ -- 31 

20. Map showing land ownership or control ---------------------------------------- 32 

21. Map showing types of studies needed __________________________ - ______ - _____ -- 34 

TABLES 

Page 

1. Population, personal income, and industrial earnings: Historical and projected _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ D7 

2. The water budget ----------------------------------------------------- 14 

III 

SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER 

RESOURCES-RIO GRANDE REGION 

By 8. W. WEST and W. L. BROADHURST 

ABSTRACT 

The Rio Grande is an interstate and international stream which 

begins in high mountains of Colorado, flows across New Mexico, and 

forms the boundary between Texas and Mexico. Precipitation ranges 

from 8 inches (20 em) to more than 30 inches (76 em), but irrigation is 

required for growing crops throughout the region. 

The population of the region has been increasing rapidly, from 

750,000 in 1929 to 1, 700,000 in 1970, and it is expected to increase to 

2,500,000 by 2020. The basic economy of the region was agricultural until recent years. Since 1950, the mining and petroleum industries have 

increased much more rapidly than agriculture. 

Annual precipitation on the region is about 86 million acre-feet 

(110,000 hm3); however, all but 4 million acre-feet (4,900 hm3) is 

returned to the atmosphere by evapotranspiration. The ground-water 

reservoirs contain an aggregate of 5,800 million acre-feet (7,200,000 

hm3) of fresh and slightly saline water in storage, which could be 

withdrawn through wells. In contrast, the surface reservoirs have a 

combined storage capacity of only 18 million acre-feet (22,000 hm3). 

Thick deposits of valley fill in stream and intermontane valleys comprise the principal ground-water reservoirs. In most areas they are 

capable of yielding large supplies of water to wells. In some areas, 

limestone constitutes major aquifers. 

Withdrawal of ground water in the region in 1970 was 2.7 million 

acre-feet (3,300 hm3), of which 88 percent was used for irrigation. 

About 53 percent of the water withdrawn was consumed. Ground water 

has been "mined" in some areas, and severe declines in water levels 

have resulted. 

The loss of water by evapotranspiration in wetlands and 

phreatophyte areas is 2.5 million acre-feet (3,100 hm3) per year. In 

comparison, about 3. 7 million acre-feet (4,600 hm3) per year of surface 

water and ground water is consumed by man's activities. 

Salvage of water lost to noneconomic evapotranspiration in wet and 

phreatophyte-infested areas offers the greatest possibility of improving 

the effective water supply in the region. Salvage of half the water lost 

would increase the effective supply by 1.2 million acre-feet (1,500 hm3) 

per year. The usable water supply could be increased tremendously by 

drawing on the large reserve of ground water in storage, but this 

withdrawal could affect the flow of streams in some areas. 

The region appears to offer several possibilities for utilizing underground space for purposes other than the withdrawal of water, such 

as waste disposal, artificial recharge, water-quality control, and 

development of geothermal energy. 

Planners for ground-water management should have detailed information on the physical parameters that affect ground water, so improved management would be possible. 

INTRODUCTION 

Water resources are neatly catalogued, for convenience, as surface water and ground water. According 

to common usage, surface water is defined as any water 

on the land surface, regardless of whether it was derived 

directly from precipitation or from discharge of ground 

water. Ground water, in contrast, is defined as water 

below the land surface in the zone of saturation, 

regardless of whether it was derived from direct infiltration of precipitation or from infiltration of water flowing 

across or standing on the land surface. Traditionally, 

surface water has received more attention than ground 

water, because surface water is visible, is easily 

measured, and commonly can be diverted for use by 

gravity flow. Although ground water is out of sight, 

modern technology has provided tools for its measurement and utilization. Technology has also shown such a 

close relationship between surface water and ground 

water that they cannot be treated as separate sources of 

water. A change in the regimen of either will generally 

affect the other. In this report, the ground water is 

emphasized, because surface water has been fully appropriated and numerous structures exist for its regulation. In contrast, vast supplies of ground water lie 

beneath the surface. 

In the past, much of the systematic planning for 

economic development or management of water 

resources has been straightforward and simple. The 

flows of principal streams were measured, and plans 

were drawn for diverting water from the streams to 

points of use. If variations in streamflow presented 

problems in meeting water demands, the situation was 

improved by building dams to regulate the streamflow 

by surface storage and controlled release. 

Ground water has not been entirely ignored in waterresources development, but, in general, it has not been 

considered in systematic planning for total water 

D1 
D2 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

management. Although ground water comprised 21 percent of the water used in the United States in 1970, planning for ground-water development has been limited to 

the municipal, water district, or private level, except for 

a few instances, and the impact of ground-water 

development on surface supplies has been largely 

neglected. This report attempts to place ground water in 

its· proper perspective in regard to the total water 

resources. 

This report is one of a series that will constitute a 

national compendium on ground water for the guidance 

of planners. New data for this appraisal were not 

collected. The many excellent reports dealing with the 

occurrence, development, and use of ground water for 

selected areas of the Rio Grande Region, from the 

headwaters to the mouth of the river, have been utilized. 

Also, unpublished data in the files of Federal, State, and 

other agencies and statements from many individuals 

concerned with the water problems of the region added 

to the information. 

This report summarizes the knowledge of the groundwater resources of the region and evaluates deficiencies 

in our knowledge. The primary objectives are to direct 

attention to the locations and storage capacities of the 

principal ground-water reservoirs, to delineate the types 

of information needed for fuller evaluation of the opportunities for ground-water management, and to describe 

the role of ground-water reservoirs in meeting the 

region's water needs. 

Although some of the water that falls as precipitation 

in the United States is used in Mexico and vice versa . ' 

that topic is not within the scope of this report. Of 

primary concern for this study are the water problems of 

the Rio Grande Region within the United States, including the drainage basin of the Pecos River and certain 

closed basins in Colorado, N~w Mexico, and Texas. 

Numerous individuals in the district offices of the U.S. 

Geological Survey in Colorado, New Mexico, and Texas 

furnished many publications, permitted use of material 

being prepared for publication, and gave freely from 

their store of knowledge. Individuals in the New Mexico 

State Engineer Office provided unpublished records and 

reviewed the report. 

Special thanks are extended to State officials and 

their staffs, including H. P. Burleigh, Executive Director 

of Texas Water Development Board; S. E. Reynolds, 

State Engineer of New Mexico; and C. J. Kuiper, State 

Engineer of Colorado. Data, assistance, and encouragement were received from many others. Grateful 

acknowledgement is extended to Dr. Gerald Thomas 

President of New Mexico State University, Dr. Joh~ Clark, Director of New Mexico Water Resources 

Research Institute, and Jesse Gilmer, Texas member of 

the Rio Grande Compact Commission. 

Most numbers in this report are given in English units 

followed by metric units in parentheses. The conversions 

to metric units were made as follows: 

English 

Unit ' Abbrevi- Multiplied ation by 

Acre ________ acre ____ 0.4047 

Acre-foot _____ acre-ft _ _ _ .0012335 

Foot ________ ft ______ .3048 

Gallons per minute _____ gpm ____ 5.45 

Inch ________ in. ----~ 2.54 

Mile ________ mi _____ 1.6093 

Square mile ____ mF _____ 2.59 

Metric 

Unit Abbreviation 

Hectare 

Cubic hectometre 

Metre 

Cubic metres 

per day 

Centemetre 

Kilometre 

Square kilometre 

ha 

hm3 

m 

Chemical concentrations are given only in metric units 

- milligrams per liter (mg/1). For concentrations less 

than 7,000 mg/1, the numerical value is about the same 

as for concentrations in the English unit, parts per 

million. 

THE PHYSICAL SETTING 

The Rio Grande is an interstate and international 

stream. It rises in southern Colorado, flows southward 

more than 400 miles (640 km) across New Mexico, and 

then forms the boundary between Mexico and Texas for 

about 1,250 miles (2,000 km) from El Paso to its mouth 

at the Gulf of Mexico (fig. 1). The total length of the 

river is about 1,800 miles (2,900 km). 

The region ranges in altitude from sea level at the Gulf 

to a little more than 14,000 feet (4,300 m) on the higher 

peaks near the headwaters. The upper half of the region 

is characterized by disconnected mountain ranges and 

intervening intermontane valleys, except for the Pecos 

Valley, which lies mostly east of the principal mountain 

ranges. High hills and mountains or tablelands 

predominate locally in the northern half of the region. 

The southern half of the region is characterized by 

tablelands, canyons, and plains (fig. 2). The mountains 

and tablelands slope steeply, almost precipitously in 

some areas, toward the valley floors. Coalescing alluvial 

fans lie at the foot of many mountains and form intermediate slopes between the mountains and ~alley 

floors. · 

The altitude of irrigated lands averages about 7, 700 

feet (2,300 m) in the San Luis Valley, 5,000 feet (1,500 

m) in the Albuquerque area, 3,800 feet (1,200 m) in the 

Las Cruces-El Paso area, 3,400 feet (1,000 m) in the 

Roswell-Carlsbad area, 2,600 feet (790 m) in the Pecos 

area, and only a few tens of feet in the coastal area. 

Because of its geographic position and wide range in 

altitude, the region has a variety of climatic zones, including semitropic, arid, and arctic. As shown by 

available records, annual precipitation averages more 

than 30 inches (76 em) in the mountainous headwaters 
36 

RIO GRANDE REGION 

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Source: President's Water Resources 

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0 100 200 MILES 

0 100 200 KILOMETRES 

FIGURE 1.-The Rio Grande Region, showing six subregions based on physiography and ground-water resources. 

D3 
D4 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

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EXPLANATION 

Flat to irregular plains 

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Tablelands with moderate to high· relief, 

including local mountain ranges 

High hills and mountains 

Rio Grande Region 

boundary 

0 

0 

Source: U.S. Geological Survey, The National Atlas 

of the United Stat_es of America (1970, p. 62) 

100 200MILES 

100 200 KILOMETRES 

FIGURE 2. - Generalized terrain. Most of the region consists of tablelands with moderate to high relief. Mountains are limited 

mostly to the northern half of the region. 
RIO GRANDE REGION D5 

in Colorado and New Mexico, less than 8 inches (20 em) 

in the intermontane valleys in Colorado, southern New 

Mexico, and western Texas, and about 25 inches (64 em) 

along the Gulf Coast. Rainstorms of high intensity during summer are common throughout most of the region. 

Average precipitation for the entire basin is about 12 inches (30 em) a year. That part of the basin within the 

United States has an area of approximately 135,000 

square miles (350,000 km2)- about 86 million acres (35 

million ha). Therefore, total annual precipitation on the 

region averages about 86 million acre-feet (110,000 hm3). 

But the considerable variability of precipitation from 

year to yea.r and the recurrence of prolonged dry periods 

. between wet periods create the major problems of water 

supply. Irrigation is required for. growing crops 

throughout the region. 

Temperatures vary widely, depending on latitude and 

altitude, but the entire region experiences a high percentage of bright sunny days. Both Alburquerque and El 

Paso have at times boasted of more than 365 consecutive 

days during which the sun made an appearance, and 

each city has about 75 percent of maximum possible 

sunshine. 

Evaporation of water from lakes and reservoirs in the 

region ranges from 42 inches (110 em) in the San Luis 

Valley to 80 inches (200 em) near Big Bend, Tex., depending on temperature, humidity, wind velocity, and 

depth of water. Water loss by evaporation from the 

Elephant Butte and Caballo Reservoirs in southern New 

Mexico is estimated to be 255,000 acre-feet (310 hm3) per 

year (Sorensen and Linford, 1967), and the loss from all 

the storage reservoirs, including small ponds, and from 

streams is about 950,000 acre-feet (1,200 hm3) per year 

(Meyers, 1962). 

The average growing season ranges from 90-120 days in 

the San Luis Valley, Colo., to 365 days in the lowermost 

part of the region near the Gulf of Mexico. The length of 

growing season, the types of crops grown, and the 

amount and timeliness of precipitation significantly 

affect the amount of water required for growing irrigated 

crops. 

Much of the region is sparsely vegetated, as would be 

expected in areas of low rainfall. The prevalent types of 

vegetation are grasses, desert shrubs, juniper, pinon, 

forest trees, and alpine shrubs, depending on the 

altitude of the land and the amount of precipitation. 

The steep slopes, the high-intensity rainstorms in 

summer, and the sparse vegetation combine to cause 

rapid runoff and erosion. The resultant sediment loads of 

tributary streams tend to overload the Rio Grande, causing aggradation along a large part of its course in New 

Mexico and rapid filling of surface storage reservoirs. 

THE ECONOMIC SETTING 

Human occupation of the Rio Grande Region has a 

long and varied history. Parts of the region were inhabited by nomadic Indians for thousands of years 

before the first white men arrived. These nomads were 

replaced by pastoral Pueblo Indians, who built villages 

in the valleys and tilled nearby irrigated farms. The first 

Spanish colonists arrived in 1598, establishing the first 

white settlement in the region near the present San Juan 

Indian Pueblo, at the confluence of the Rio Chama and 

the Rio Grande. Many Spanish colonists followed, and 

numerous villages were established along the Rio Grande 

and its tributaries. Descendants of the Pueblo Indians 

and Spanish colonists still constitute a significant part of 

the population in the northern part of the region. Since 

the region became a part of the United States, it has experienced a large influx of people from all parts of the 

United States, as well as from several foreign countries. 

For centuries the water supply in the Rio Grande and 

its tributaries was adequate to meet the small demands 

of the pastoral Indians and Spanish colonists. In the present century, the demands for water have been increasing dramatically, owing to extensive irrigation, new 

industries, rapid increase in population, and construction of numerous military facilities. The population of 

the region increased from 750,000 in 1929 to 1, 700,000 in 

1970 and is expected tq increase to 2,500,000 by 2020. In 

addition to the resident population, thousands of 

tourists visit the region each year. Of particular interest 

to tourists are national parks (Carlsbad Caverns, N. 

Mex.; Big Bend, Tex.; and Guadalupe Mountains, 

Tex.), national monuments, state monuments, 

prehistoric Indian sites, other areas of historic interest, 

and areas of great scenic beauty. The principal population centers are Albuquerque, N. Mex., and El Paso, 

Tex. The distribution of population is shown in figure 3, 

and population trends are shown in figure 4. 

From early Pueblo Indian times to recent years, the 

basic economy of the region was related to agriculture. 

Successful production of crops depended on irrigation, 

and most of the irrigated lands are on or adjacent to the 

flood plains of perennial streams (fig. 5). In some areas, 

irrigation with ground water has been pursued for many 

years. Water is a limiting factor in agricultural expansion, so the earnings from agriculture have not increased 

significantly during the last 20-30 years, because the surface water has been fully appropriated and ground-water 

development has been limited by small supplies or has 

been restricted to protect surface-water rights. 

The earnings from economic activities that require less 

water per dollar of earnings than irrigation agriculture 

increased rapidly during 1950-70. These activities are expected to continue their growth, as shown in table 1. The 
D6 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

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EXPLANATION 

POPULATION 0 250,000 

0 50,000 

• 25,000-50,000 

0 10,000-25,000 

• 2,500-10,000 

Rio Grande Region 

boundary 

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100 200 MILES 

100 200 KILOMETRES 

\ \ .. : 

\.,.!.... Harl~i!ri 

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Bro~ ' . FIGURE 3. - Population distribution. Most of the population is concentrated along the major rivers - the Rio Grande and the 

Pecos River. The largest cities are Albuquerque, N. Mex., and El Paso, Tex. 
RIO GRANDE REGION D7 

2600 

2400 

2200 

2000 

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1930 1940 1950 1960 1970 1980 1990 2000 2010 2020 

Source: U.S. Water Resources Council ( 1972a) 

FIGURE 4.- Population trends. The population of the Rio Grande Region has been increasing rapidly, and the trend of the last 

decade is expected to continue for the next 50 years. Dashed lines indicate projected trends. 

TABLE 1. -Population, personal income, and industrial earnings: Historical and projected 

[Adapted from U.S. Water Resources Council (1972a). Values are based on the value of the dollar in 1967) 

~M------------------------------

Population (midyear) ___________ _ Per capita income _____________ _ Earnings per worker ____________ _ 

Industrial earnings (in 

thousands of dollars): 

Agriculture, forestry, fisheries _____ _ 

Mining, oil, and gas ------------ Contract construction __________ _ Manufacturing ______________ _ 

Tra~sp<;>rtation and public 

ubhbes ----------------- Wholesale and retail trade _______ _ 

Finance, insurance, and real 

estate __________________ _ Services _________________ _ Government _______________ _ 

Total _________________ _ 

1950 

1,238,201 

$1,503 

$3,882 

$286,783 

58,603 

129,595 

107,846 

142,256 

290,476 

47,158 

162,963 

334,698 

$1,560,382 

1969 

1,684,853 

$2,456 

$5,665 

$282,653 

112,375 

196,828 

276,003 

229,654 

545,115 

131,629 

539,388 

1,089,227 

$3,402,870 

1980 

1,845,500 

$3,597 

$8,253 

$287,200 

131,200 

291,700 

413,800 

330,900 

866,300 

208,700 

941,400 

1,790,000 

$5,261,600 

2000 

2,154,100 

$6,717 

$14,639 

$358,500 

189,000 

628,500 

843,900 

638,800 

1,856,700 

455,900 

2,230,100 

4,039,700 

$11,241,400 

2020 

2,536,000 

$12,274 

$25,599 

$628,300 

287,200 

1,329,800 

1,761,600 

1,256,900 

3,927,100 

980,500 

4,986,100 

8,649,600 

$23,807,600 

distribution of minerals and petroleum is shown in figure I significant part of the mineral industry of the region, but. 

6. Innumerable sand and gravel quarries constitute a they could not be shown in figure 6. 
DB SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

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Rio Grande Region 

boundary 

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a 

Source: President's Water Resources 

Policy Commission ( 19 SO) 

I 

1aa 

1a0 2aa MILES 

1

1 I 

2aa KILOMETRES 

FIGURE 5.- Areas of irrigated land. Most of the irrigated land is alongside the Rio Grande and the Pecos River. 
110° 

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EXPLANATION 

IBI!coal 

RIO GRANDE REGION 

~ Extensive natural gas 

~ and some oil 

~ Extensive oil and L.:..:::J some natural gas 

c Copper 

G Gold 

Iron 

L Lead 

Ma Manganese 

Mo Molybdenum 

p Potash 

s Silver 

T Tin 

z Zinc 

• Mine or mineral deposit 

Rio Grande Region 

boundary 

Source: U.S. Geological Survey, The National Atlas 

of the United States of America ( 1970. p. 1 78-181) 

0 100 200 MILES 

0 100 200 KILOMETRES 

FIGURE 6. - Mineral and petroleum deposits. Extensive mineral deposits are found in the northern half of the region. 

Innumerable sand and gravel quarries are not shown. 

D9 
D10 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

THE LEGAL SETTING 

Management of the surface waters of the Rio Grande 

Region is subject to international treaty, interstate compacts, and laws of three States. Management of ground 

water within each State is subject to regulation by that 

State. 

In the late 1880's, water shortages experienced by 

Mexican users near Ciudad Juarez resulted in protests to 

the United States by Mexico, alleging that shortages 

resulted from increasing diversions for irrigation in New 

Mexico and Colorado. The International Boundary 

Commission, United States and Mexico, was directed to 

investigate the water situation in the upper Rio Grande, 

and as a result of that investigation, an embargo was 

placed on further surface-water dev~lopment in the two 

States until the problem could be resolved. In 1906, the 

United States and Mexico negotiated a treaty whereby 

Mexico was guaranteed an annual delivery of 60,000 

acre-feet (74 hm3) of water in perpetuity, with the provision that the two Nations would share shortages in times 

of drought (Sorensen and Linford, 1967, p. 148). 

Both the Rio Grande main stem and the Pecos River 

are subject to apportionment of surface water under interstate compacts. The Rio Grande Compact specifies 

that Colorado must deliver to New Mexico a specified 

quantity of water in proportion to water available at index stations in Colorado, and that New Mexico must 

deliver to Texas a specified quantity of water in proportion to water available at index stations in New Mexico. 

At times, both Colorado and New Mexico have been 

delinquent in water deliveries. The Pecos River Compact 

specifies the proportion of Pecos River water that New 

Mexico must deliver to Texas. Uncontrolled development of ground water in either the Rio Grande or the 

Pecos River valleys could make it impossible to deliver 

the specified quantities of surface water down the 

natural river channels; however, orderly development 

and management of the ground-water reservoirs in conjunction with management of the rivers could assure 

delivery of the specified quantities annually for the 

foreseeable future. 

When the Colorado Constitution was adopted in 1876, 

it provided for appropriation of the water of natural 

streams not previously appropriated. All natural streams 

were declared to be the property of the public. The 

courts in Colorado have, in effect, defined "waters of a 

natural stream" by ruling that if the waters in question 

would reach a natural watercourse or were in a natural 

watercourse, they were waters of a natural stream. In 

cases involving water pumped from wells, some courts 

have adjudicated on the theory that underground waters 

are waters of a natural stream. Other courts have held 

that for adjudication purposes waters produced from 

wells are not waters of a natural stream (Sparks, 1970). 

In 1965 the Colorado Legislature passed a new groundwater law. Section 148-18-1 of the law states: 

It is hereby declared that the traditional policy of the state of 

Colorado requiring the water resources of this state be devoted to 

beneficial use in reasonable amounts through appropriation, is affirmed with respect to the designated ground waters of this state, as 

said waters are hereinafter defined. While the doctrine of prior appropriation is recognized, such doctrine should be modified to permit 

the full economic development of designated ground-water resources. 

Prior appropriations of ground water should be protected and 

reasonable ground water pumping levels maintained, but not to include the maintenance of historical water levels. All ground waters in 

this state are therefore declared to be subject to appropriation in the· 

manner herein defined. 

The law also specifically prohibits the diversion of 

ground water outside the State for use within another 

State. 

The State Engineer of Colorado administers the laws 

relative to the distribution of surface waters, including 

ground waters tributary thereto. 

In 1969 the Colorado Legislature enacted a bill that 

revised the entire water code and allowed for the use of 

ground water in conjunction with surface water. It is now 

possible to change the point of diversion from a surface 

diversion to a well diversion. 

By 1970, about 30,000 wells had been drilled in 

Colorado, none of which had adjudicated water rights. 

Under existing laws, if rights on the wells are adjudicated, they will be subordinate to all the surface 

decrees and generally will have a priority date later than 

1950 (Sparks, 1970). 

The Pueblo Indians in the Rio Grande Valley of New 

Mexico were operating acequias (community ditches) 

along perennial streams to support subsistence farming 

when Coronado led the first Spanish exploration through 

the area in 1540. From 1609 until 1680, Spanish colonists 

established several villages along the Rio Grande and its 

perennial tributaries and began the same type of subsistence farming that prevailed among the Pueblo Indians. When Mexico gained its independence from Spain 

in 1821, the territory including the Rio Grande Valley 

passed from Spanish to Mexican rule, but the water 

rights of both the Indians and the colonists were 

recognized by Mexico. The territory was ceded to the 

United States in 1848 by the Treaty of Guadalupe 

Hidalgo, and again the water rights of residents were 

recognized by the new government. 

The Rio Grande Valley was still sparsely settled when 

ceded to the United States, so there was little competition for water, and the local acequias served the people 

well. With the influx of American settlers in the latter 

part of the 19th century, the competition for water 

became serious, so the Territorial Legislature of New 

Mexico passed the first legislation to regulate the appropriation of surface water in 1905, and the legislation 

was rewritten in 1907. Also in 1905, the legislature 
RIO GRANDE REGION Dll 

adopted an act to regulate the use of artesian wells and 

to prevent the waste of subterranean flows of water 

(Mechem, 1961). 

When New Mexico became a State in 1912, the constitution contained the following sections pertaining to 

water rights: 

1. All existing rights to the use of any waters in this state for any 

useful or beneficial purpose are hereby recognized and confirmed. 

2. The unappropriated water of every natural stream, perennial or 

torrential, within the state of New Mexico, is hereby declared to belong 

to the public and to be subject to appropriation for beneficial use, in 

accordance with the laws of the state. Priority of appropriation shall 

give the better right. 

3. Beneficial use shall be the basis, the measure and the limit of the 

right to the use of water. 

The first ground-water statute was passed by the State 

in 1927. It provided that 

All waters in the State found in underground streams, channels, arte· 

sian basins, reservoirs, or lakes, the boundaries of which may be 

reasonably ascertained by scientific investigations of surface indications, are hereby declared to be public waters and to belong to the 

public, and subject to appropriation for beneficial uses under the existing laws of this state relating to appropriation and beneficial use of 

waters from surface streams. 

This law was declared invalid by the New Mexico 

Supreme Court, because it attempted to extend existing 

legislation by reference (Mechem, 1961). In 1931 the 

statute was reenacted in a form the court outlined in its 

opinion on the 1927 act. The 1931 statute was not 

challenged in the courts until 1949, and in 1950 the New 

Mexico Supreme Court upheld the statute (Mechem, 

1961). It is still the law governing ground-water appropriation and use in New Mexico. 

Under the New Mexico law, the State Engineer, after 

adequate evaluation, may declare an "underground 

water basin" and control further development of ground 

water in order to protect prior water rights. The State 

Engineer has declared 14 such basins in the Rio Grande 

Region, the largest of which extends on each side of the 

Rio Grande from Elephant Butte Reservoir to the 

Colorado-New Mexico line. The State Engineer defines 

and declares such basins whenever it becomes apparent 

that regulation is necessary to (1) prevent impairment of 

existing rights, (2) insure beneficial use of water, and (3) 

provide for an orderly development of ground-water 

reservoirs. The New Mexico Supreme Court has found 

that it is unreasonable to attempt a legal distinction 

between ground water and surface water, because of 

their interrelationship. 

Texas does not have provisions for statewide administration and control of ground water in its legal 

code. The courts, in implementing statutes on the books, 

have in general applied the principle of the law of capture (riparian rights)· in ground-water disputes (Dixon, 

1961). In 1949 the Texas Legislature enacted the 

"Underground Water District Act" (Art. 7880-3c), which 

authorized water districts to take action to promulgate 

rules regarding the conservation and use of percolating 

ground water. However, the districts were not authorized 

to regulate the use of underground water in defined 

channels or the underflow of rivers, both of which are 

subject to appropriation the same as surface water. 

Districts can be created by the legislature, the Texas 

Water Rights Commission, and county commissioners' 

courts. Prior to creation of an underground-water conservation district, the Water Rights Commission must 

determine through studies conducted by the Texas 

Water Development Board that an underground-water 

reservoir, or subdivision thereof, having. definable boundaries and meeting other predetermined requirements 

actually exists. The district is a corporate unit which can 

own property and act in all ways as an entity having 

financial and legal responsibilities. The initial legislation was amended in 1955 to strengthen the power of the 

districts with regard to well spacing, regulation of 

production, and prevention of waste (Dixon, 1961). This 

legislation was amended again in 1972. 

THE GROUND-WATER SUPPLY 

The total water supply of the Rio Grande Region is the 

sum of the surface-water runoff, the ground-water outflow (which is small), and the natural evapotranspiration. Annual precipitation averages about 12 inches (30 

em) on the 86 million acres (35 million ha) within the 

region; however, all but 4 million acre-feet (4,900 hm3) of 

the precipitation returns to the atmosphere through 

natural evapotranspiration. The runoff, or water yield, of 

the region and part of the natural evapotranspiration 

represent the water that can be controlled or modified to 

a degree by man. For example, man may be able to intercept for economic use (agricultural, municipal, and 

industrial supplies) water that normally is lost to noneconomic consumption by native vegetation. Also, he 

may import more water or intercept for beneficial use the 

water that runs off to the Gulf of Mexico. A small 

amount of surface water is imported into the region by 

transmountain diversion. 

The ground-water reservoirs of the region contain an 

aggregate of more than 5,800 million acre-feet (7,200,000 

hm3) of fresh (less than 1,000 mg/1 dissolved solids) to 

slightly saline (1,000-3,000 mg/1 dissolved solids) water 

in storage, which under the laws of nature is available to 

wells. In contrast, the surface reservoirs of the region 

have a combined storage capacity of only 18 million acrefeet (22,000 hm3 ). 

The ground-water reservoirs of the region can be 

classified on the basis of rock characteristics, 

physiography, and geographic distribution. For convenience of description, the rocks have been divided into 

four basic types: (1) valley fill - unconsolidated to 

poorly consolidated sand and gravel interbedded or in-
D12 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

I 

I 

I 

__ _j_ ·. 

I ---------...... I 

I 

I 

I 

I 

I 

I 

~/§ Zl>< ow 

~~~ 

~w ~l:s :z: 

I 

I 

I 

EXPLANATION 

Volcanic rocks 

Consolidated 

sedimentary rocks 

Intrusive igneous and 

metamorphic rocks 

-··-··-··- Rio Grande Region 

boundary 

0 

0 

Source: Modified from Burbank and others 

(1935), Dane and Bachman (1965), 

and Darton and others ( 1937) 

100 200 MILES 

100 200 KILOMETRES 

FIGURE 7.- Generalized distribution of geologic units. Valley fill comprises the principal ground-water reservoirs. 
RIO GRANDE REGION D13 

WEST 

Modified from Emery and others ( 1971) 

FIGURE 8.- The San Luis Valley. The valley is bounded by high mountains and is underlain by valley fill and volcanic rocks; 

the water table is within 12 feet (3.6 m) of land surface in most areas. 

termixed with clay and silt; (2) volcanic rocks -

primarily basalt but including other flow rocks, tuff, and 

small intrusive bodies; (3) consolidated sedimentary 

rocks - primarily shale and sandstone but including 

limestone, gypsum, and salt; and (4) crystalline rocksintrusive igneous rocks and metamorphic rocks. 

The intermontane valleys of the region have been 

partly filled with unconsolidated sand, gravel, and clay 

- termed "valley fill" - derived by weathering and erosion from the rocks in the adjacent mountains and from 

similar rocks in the mountains upstream (fig. 7). 

Alluvial deposits in the Pecos Valley are included in the 

valley-fill category, but the valley fill shown east of the 

Pecos River (fig. 7) is thin and is not a significant 

ground-water reservoir. 

Locally, the valley fill is interbedded with basalt and 

other flow rocks derived from volcanic centers in and 

bordering the valleys. Large masses of basalt and 

andesite are common, especially in the northern part of 

the basin. The valley fill, including the interbedded 

volcanic rocks, is as much as 9,000 feet (2, 700 m) thick in 

New Mexico and is reported to be more ·than 30,000 feet 

(9,100 m) thick in the north-central part of the San Luis 

Valley, Colo. (Gaca and Karig, 1966). The valley fill 

comprises the principal ground-water reservoir in the 

region. In most areas it is capable of yielding a few hundred to a few thousand gallons of water per minute to individual wells. 

The mountains consist of volcanic rocks, consolidated 

sedimentary rocks, and crystalline rocks (fig. 7). The 

volcanic rocks commonly cap plateaus and low mountain ranges and lie above the regional water table. These 

rocks generally are not significant aquifers except where 

they are interbedded with or overlie valley fill. The consolidated sedimentary rocks form most of the hills and 

low mountains. Generally, these rocks are poor aquifers, 

but locally, beds of limestone containing extensive fractures and solution channels lie below the water table and 

yield large supplies of water to wells. In many areas the 

consolidated sedimentary rocks contain soluble 

minerals, such as halite and gypsum - the principal 

sources of dissolved solids in ground water. The 

crystalline rocks generally are dense and yield insignificant quantities of water to wells. 

SAN LUIS VALLEY SUBREGION 

The valley-fill ground-water reservoir in the San Luis 

Valley contains both unconfined and confined aquifers, 

which are separated in places by a clay series or by layers 

of volcanic rocks (fig. 8). These confining beds are discontinuous and lenticular, so it is difficult to differentiate between unconfined and confined aquifers except 

locally. This discontinuity in the clay series permits 

varying degrees of hydraulic connection between the 

aquifers; therefore, all the aquifers in the valley north of 

the San Luis Hills should be considered a single groundwater reservoir (Emery and others, 1971). 

Recharge to the unconfined aquifer is mainly by infiltration of irrigation water from canals, ditches, and 

fields and by upward leakage from the confined aquifer. 

Some water percolates from the many stream& flanking 

the valley, but very little precipitation on the valley floor 

recharges the unconfined aquifer. Natural discharge 

from this aquifer is by evapotranspiration and seepage to 

streams. 
D14 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

The principal source of recharge to the confined 

aquifer is seepage from mountain streams that flow 

across the alluvial fans flanking the valley floor. At the 

edge· of the valley the clay series is absent, permitting 

recharge to beds that constitute the confined aquifer in 

the main part of the valley. The mountain streams show 

significant losses as they cross the porous surface of the 

fans. The confined aquifer underlies most of the valley, 

and the water has sufficient head to flow at the land surface. The natural discharge from the confined aquifer is 

by springs and by upward leakage through the confining 

beds into the unconfined aquifer. A small amount discharges as underflow into· New Mexico. 

The ground-water reservoir in the San Luis Valley underlies about 2 million acres (809,000 ha). It ranges in 

thickness from a featheredge around the rim of the valley 

to as much as 7,000-9,000 feet (2,100-2,700 m) beneath 

much of the area and to a reported thickness of more 

than 30,000 feet (9,100 m) locally (Gaca and Karig, 

1966). If we assume the average thickness of the 

permeable deposits to be 5,000 feet (1,500 m), the 

volume of reservoir material is 2 million X 5,000, or 

about 10 billion acre-feet (12 million hm3), and if the 

average specific yield is 0.2 (20 percent), the amount of 

water in storage in the reservoir available to wells is 

about 2 billion acre-feet (2.5 million hm3). 

In 1967 about 2,800 wells in the. San Luis Valley 

yielded more than 300 gpm (1,635 m3

/d) each. Of this 

total, 2,160 were completed in the unconfined aquifer. In 

addition to the large-capacity wells, there are more than 

7,000 small-capacity flowing wells. The annual water income to the San Luis Valley averages about 2.5 million 

acre-feet (3, 100 hm3); about 1.5 million acre-feet (1,800 

hm3) is streamflow derived chiefly from snowmelt in the 

surrounding mountains, and about 1 million acre-feet 

(1,200 hm3) is from precipitation on the valley floor. Annual discharge of water from the valley also averages 2.5 

million acre-feet (3,100 hm3)-about 2 million acre-feet 

(2,500 hm3) by evapotranspiration and about 500,000 

acre-feet (620 hm3) as flow across the State line (table 2). 

The streamflow at the State line averages 445,000 acrefeet (550 hm3), and ground-water underflow is 55,000 

acre-feet (68 hm3). About half the evapotranspiration is 

noneconomic; that is, it does not contribute to the 

growth of plants having economic or commercial value. 

Much of the noneconomic consumption is by 

phreatophytes in areas where the depth to water is less 

than 12 feet (3.6 m). 

According to Powell (1958), the quality of water in the 

confined aquifer is generally better than that in the unconfined aquifer. The concentration of dissolved solids in 

41 samples from the confined aquifer ranged from 70 to 

437 mg/1, and the concentration in 271 samples from the 

unconfined aquifer ranged from 52 to 13,800 mg/1. The_ 

least mineralized water in the unconfined aquifer occurs 

on the west side of the valley. The mineral concentration 

increases toward the sump area of the closed basin, 

probably because of solution from the rocks and concentration by evapotranspiration in areas having a shallow 

water table. 

ALBUQUERQUE SUBREGION 

The valley fill in the Rio Grande depression, which underlies about 5,000 square miles (13,000 km2), or 

3,200,000 acres (1,300,000 ha), comprises the principal 

ground-water reservoir in the Albuquerque subregion 

(fig. 9). The thickness of the fill is not well known, but it 

may average about 4,000 feet (1,200 m). The maximum 

thickness is probably about 9,000 feet (2, 700 m) 

(Dinwiddie, 1967). The estimated volume of recoverable 

fresh ground water in storage in this and other groundwater reservoirs is 2,300 million acre-feet (2,800,000 

hm3); an additional 540 million acre-feet (670,000 hm3) 

of recoverable slightly saline water is in storage, making 

a total of 2,800 million acre-feet (3,400,000 hm3) of fresh 

TABLE 2. - The water budget 

Subregion 

San Luis Valley ______ _ 

Albuquerque --------- El Paso ------------ Lower Rio Grande _____ _ 

Pecos Valley --------- Closed Basins ________ _ 

Income 

Surface-water inflow 

(ac-ft 

per yr) 

0 

500,000 

4

730,000 

5620,000 

0 

0 

Surface-water yield 

(ac-ft 

per yr) 

1,500,000 

1,500,000 

200,000 

700,000 

1,700,000 so 

Surface-water outflow' 

(ac-ft 

peryr) 

500,000 

399(),000 

260,000 

0 

360,000 

0 

Outgo 

Evapotranspiration 

Man's 

activities 

(ac-ft per yr) 

1,000,000 

300,000 

500,000 

1,000,000 

800,000 

130,000 

Wetlands and phreatophytes 

(ac-ft per yr) 

1,000,000 

400,000 

500,000 

200,000 

280,000 

100,000 

Storage capacity 

Surface 

water 

(ac-ft) 

400,000 

230,000 

2,500,000 

14,000,000 

650,000 

0 

Ground 

water2 

(ac-ft) 

2,000,000,000 

2,800,000,000 

230,000,000 

20,000,000 

410,000,000 

290,000,000 

Total (rounded) ___ ------- 5,600,000------- 3, 700,000 2,500,000 18,000,000 5,800,000,000 

'Includes some ground-water underflow. 2

Recoverable fresh and slightly saline ground water in storage. 3

Surface flow at San Marcial above Elephant Butte Reservoir. •Surface flow below Elephant Butte Reservoir. 5

The sum of surface-water outflow from both the El Paso and the Pecos Valley subregions. 6

Some runoff from mountainous areas, which infiltrates the ground or evaporates in playas. 
RIO GRANDE REGION D15 

Santa Ana 

Sandia Crest 

Elev 10,682 

n..,. 

u. 

o E 

g g ~'-o 

N 

Valley fill 

EXPLANATION 

Fault 

Arrows show direction 

of relative movement 

Direction of groundwater flow 

FIGURE 9.- The Rio Grande Valley at Albuquerque, N.Mex. High mountains bound the valley on the east; agricultural lands 

and the older part of the city are in the inner valley, where the water table and the river level coincide. 

and slightly saline water in storage (based on a specific 

yield ranging from 5 to 15 percent) (table 2). 

The yield of 83 large-discharge wells that tap the 

valley fill in the Albuquerque area ranges from 240 to 

2,000 gpm (1,300 to 11,000 m3/d) and averaged 860 gpm 

(4,700 m3/d) (Bjorklund and Maxwell, 1961). Volcanic 

rocks in the northern part of the subregion locally yield 

water to wells. Consolidated sedimentary rocks are not 

significant aquifers, except in the Rio San Jose valley 

near Grants, N. Mex., where yields of more than 2,000 

gpm (1,300 m3/d) per well have been obtained from 

limestone (Gordon, 1962). 

Recharge in the subregion is from precipitation on the 

valley fill and associated volcanic rocks, from infiltration 

of surface water diverted for irrigation, and from intermittent runoff during intense rainstorms. In the 

northern part of the subregion, some recharge is from 

runoff of snowmelt. 

The chemical quality of ground water varies widely in 

this subregion. A study of municipal water supplies in 

New Mexico (Dinwiddie and others, 1966a, b) revealed 

that the concentration of dissolved solids in municipal or 

community water supplies in this subregion ranges from 

125 to 2,620 mg/1 and that the water supply for 23 communities exceeds the concentration of 500 mg/1 

recommended for public water supplies by the U.S. 

Public Health Service (1962). The quality of municipal 

water supplies is probably an indication of ground-water 

quality in general, although even higher concentrations 

can be expected locally, because public supplies are 

generally drawn from the best water available. The 

water in the valley fill of the Rio Grande Valley is better 

in quality than in most of the tributary valleys along the 

west side of the subregion. 

EL PASO SUBREGION 

A bedrock high in the vicinity of Elephant Butte 

Reservoir tends to separate the ground-water reservoirs 

in the Albuquerque subregion from those in the El Paso 

subregion. Some ground water is forced to the land surface where the valley fill becomes narrower and thinner 

in this area. A section across the Rio Grande Valley and 

adjacent areas near Elephant Butte Reservoir is shown 

in figure 10. 

As in the San Luis Valley and the Albuquerque subregions, the major ground-water reservoir in the El Paso 

subregion is valley fill. The thickness of the fill and interbedded volcanic rocks in the Las Cruces area is locally 

more than 5,000 feet (1,500 m) and probably averages at 

least 3,000feet(910m)(fig.11). The valleyfillnarrowsin 

the vicinity of El Paso but widens again into the Hueco 

bolson east o£ the Franklin Mountains and in broad band 

alongside the Rio Grande down to Fort Quitman. The 

fresh and slightly saline ground water stored in these 

reservoirs is about 230 million acre-feet (280,000 hm3). 

(table 2). 

Individual wells in the Las Cruces-El Paso area yield 

as much as 3,000 gpm (16,400 m3

/d) and average about 

1,000 gpm (5,400 m3/d). Farther down the valley the 
D16 

.... 

u. 

E g 0 0 0 ...... oN 

0 

0 

0 

~ 

0 g o_ o Ltl Ltl 

0 

0-0 

0 0 

0 

M 

0 

0 

0 0 o-N 

Ltl 

0 

0 

0 

WEST 

SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

Engle Valley 

Valley 

fill 

--

Fra 

Cristobal 

Jornado 

Del Muerto 

San Andres 

Mountains 

EAST 

SEA 

LEVELL---------------------------------------~~--------------------------~~~~~~~~~~~~~ Modified from Kelley( 1955, fig. 3) 

0 5 10 MILES 

0 5 10 KILOMETRES 

FIGURE 10.-The ground-water reservoir in valley fill at Elephant Butte Reservoir in New Mexico. The ground-water reservoir is 

thinner and narrower here than at most places in New Mexico. 

WEST EAST .... 

u. 

E g 0 0 o_ ~ 

CXl 

0 

0 

~ 

0 

0 -Ltl 

Ltl 

0 

g 

Ltl 

0 0 

~- ~ 

La Mesa 

"'"t-----

0 

0 0 0 0 N_<;t 

0 

0 -o 

Ltl 

M 

8-

Valley fill 

0 

I 

0 

1 2 3 4 5 MILES I I •• ' ·, I I 

2 3 4 5 KILOMETRES 

Modified from King and 

others (1971, fig. 5) 

FIGURE 11. -The ground-water reservoir in valley fill at Las Cruces, N. Mex. A buried ridge of volcanic rock divides the broad 

ground-water reservoir. 

yields are much smaller, ranging from about 100 to 500 

gpm (54 to 2,700 m3/d) (Davis and Leggat, 1965). 

in the minimum rainfall belt. Infiltration from surface 

water diverted for irrigation locally provides significant 

Recharge is relatively small, because the subregion is recharge. 
RIO GRANDE REGION D17 

The chemical quality of water in the valley-fill 

aquifers in the El Paso subregion varies widely, both 

laterally and vertically. The water in the shallow alluvial 

deposits along the river generally contains higher concentrations of dissolved solids than the water in the underlying older fill, but the salinity may increase at 

depths of a few thousand feet in the older fill. The dissolved solids in water in the river alluvium have been 

concentrated by evapotranspiration in areas where the 

water table is shallow and by return of irrigation water, 

which contains dissolved soil salts and fertilizers. The 

concentration of dissolved solids in ground water of the 

Las Cruces-El Paso area ranges from about 200 to more 

than 6,000 mg/l (Davis and Leggat, 1965). 

PECOS VALLEY SUBREGION 

Consolidated sedimentary rocks, which consist of 

shale, sandstone, limestone, gypsum, and salt, 

predominate in the Pecos Valley subregion. Beds of 

limestone and, locally, gypsum are excellent aquifers in 

some areas. However, extensive deposits of gypsum and 

salt contribute large quantities of dissolved solids to the 

water in the subregion. The valley fill constitutes 

productive aquifers where it is thickest, such as in the 

Roswell basin (fig. 12) and in several areas between the 

Texas-New Mexico line and Girvin, Tex. 

The quantity of fresh and slightly saline ground water 

in storage in the subregion is about 410 million acre-feet 

(510,000 hm3) (table 2). Most of the water is stored in 

valley-fill and sandstone reservoirs; but in the Roswell 

and Carlsbad areas, some 10 million acre-feet (12,000 

hm3) is stored in limestone and gypsum reservoirs, and 

an equal amount is stored in limestone and sandstone in 

the Texas part of the subregion. 

Valley 

~ fill 

Consolidated 

~ 

~ 

sedimentary rocks 

Water --table 

Direction of ground-water flow 

Wells completed in either the limestone or the valley 

fill in the Roswell basin generally yield more than 300 

gpm (1,600 m3/d) each, and yields of 1,000-3,500 gpm 

(5,400-19,000 m3/d) are common. The limetone aquifer 

has outcrops west of the Pecos River near Roswell, N. 

Mex., that accept recharge readily from direct precipitation and from surface flow. The overlying valley-fill 

aquifer is recharged by upward leakage of artesian water 

from the limestone aquifer and by infiltration of a part of 

the water used for irrigation. 

The chemical quality of ground water varies widely in 

the subregion, ranging from fresh to briny (less than 

1,000 to more than 35,000 mg/1). All or part of the water 

supply for 16 communities in the New Mexico part of the 

subregion contains more than 500 mg/l dissolved solids. 

The concentration of dissolved solids in municipal 

supplies ranges from 150 mg/l in the northern part to 

2,410 mg/l for one community in Chaves County. The 

chemical quality of public water supplies in the Texas 

part of the subregion is comparable. 

In some areas, as fresh ground water is withdrawn it is 

replaced by more saline water, which mixes with the 

fresh water in storage and causes a general deterioration 

in water quality. 

CLOSED BASINS SUBREGION 

The closed basins subregion comprises the Estancia, 

the Jornada del Muerto, and the Tularosa basins in New 

Mexico and the Salt basin in New Mexico and Texas. All 

these basins have internal surface drainage, but some 

water may move underground to adjacent basins or subregions. 

Modified from Mower and others ( 1964, fig. S) 

FIGURE 12. -The complex relationship between the ground-water flow system and the surface water in the Pecos Valley at 

Roswell, N. Mex. 
D18 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

.... 

u.. 

0 

0 

~ ~- 0 

0 

M 

0 0 0 0 0 10- co N 

0 0 0 0 o- o N U) 

WEST EAST 

San Andres Mountains 

Tularosa Basin 

0 0 o_ o LO 0 .... '<:!' 

0 

8-0 

.... 0 

0 

N 

0 

0-

LO 

L~~~L~----------~~~~~~----------------------------------------------------~~~~~~=-~~ 

0 5 10 MILES 

0 5 10 KILOMETRES 

FIGURE 13. -The ground-water reservoir in valley fill of the Tularosa basin in New Mexico. The reservoir is large, but fresh 

water is found only in narrow bands adjacent to the mountains. 

Valley fill predominates in the closed basins and constitutes the principal ground-water reservoirs. The fill 

consists of both alluvial deposits at the foot of the mountains and lake deposits in the central part of each basin, 

except in the Jornada del Muerto basin. The lake 

deposits consist of silt, clay, and evaporites, especially 

gypsum. These evaporites are a common source of high 

salinity in ground water in the central parts of the 

basins. The valley fill commonly is thin around the 

margins but may be a few thousand feet thick in the 

deeper parts of the basins. A generalized section across 

the Tularosa basin is shown in figure 13. Yields as large 

as 2,400 gpm (13,000 m3/d) have been obtained from individual wells in the fill, and yields of several hundred 

gallons per minute are common. 

Limestone constitutes an important aquifer in the 

northern part of the Salt basin, where it is a source of 

water for irrigation. 

The volume of fresh and slightly saline ground water 

stored in the closed basins is summarized below: 

Basin Volume (ac-ft) 

Estancia ___ _ _ _ __ _ _ _ _ ___ 10,000,000 

Jornada del Muerto _________ 110,000,000 

Tularosa _ _ _ _ _ _ __ _ _ _ _ __ _ 150,000,000 

Salt _ ___ _ _ _ _ _ __ _ _ _ _ _ _ _ 20,000,000 

Tota} _________ - ---- 290,000,000 

In addition to the fresh and slightly saline water in 

storage, large volumes of more saline water are stored in 

each of the basins. McLean (1970) estimated that about 

60 million acre-feet (74,000 hm3) of water with a 

dissolved-solids content of more than 3,000 mg/1 is in 

storage in the Tularosa basin. Similar estimates for the 

other basins have not been made. The fresh water (less 

than 1,000 mg/1) is limited to narrow bands in the valley 

fill next to mountain ranges of most basins. The concentration of dissolved solids in ground water ranges from 

about 200 mg/1 to more than 100,000 mg/1. 

A study of public water supplies in southeastern New 

Mexico by Dinwiddie (1963) showed that the supplies for 

16 communities in the New Mexico part of the subregion 

contain concentrations of dissolved solids higher than 

500 mg/1. Public supplies have not been developed in the 

J ornada del Muerto. 

LOWER RIO GRANDE SUBREGION 

The ground-water reservoirs in the lower Rio Grande 

subregion are insignificant in comparison with those in 

the other subregions. Most of the aquifers are consolidated sedimentary rocks consisting of sandstone and 

limestone (Brown and others, 1965). In the northernmost 

and the southernmost parts of the subregion, stream 

alluvium along the Rio Grande is the principal aquifer 

(Baker, 1965). The estimated quantity of fresh and 

slightly saline water in the subregion is only 20 million 

acre-feet (25,000 hm3 ) (table 2). 

The yields of wells in this subregion are highly variable 

depending on the type of aquifer. Yields range from a few 

tens of gallons per minute to as much as 3,000 gpm 
RIO GRANDE REGION D19 

(16,000 m3/d). Beds of limestone are the most productive. 

The water generally contains from a few hundred to a 

few thousand milligrams per liter dissolved solids. 

WITHDRAWAL AND CONSUMPTION OF 

GROUND WATER 

Withdrawal of ground water in the Rio Grande Region 

in 1970 was 2, 700,000 acre-feet (3,300 hm3), in comparison to a withdrawal of 4,300,000 acre-feet (5,300 

hm3) of surface water (fig. 14). The largest part of the 

ground water (88 percent) was used for irrigation (fig. 

15). About 180,000 acre-feet (220 hm3) (5 percent) of the 

ground water withdrawn was used for public supplies 

(ground water furnished 58 percent of all the public 

supply requirements). The largest metropolitan areas 

(Albuquerque and El Paso) depend entirely on ground 

water as a source of public supplies. The average per 

capita use of public supplies in the region is 228 gallons 

per day, or 0.86 m3

/d (Murray and Reeves, 1972). 

Ground water withdrawn for all uses other than irrigation and public supplies was only 7 percent (fig. 15). Of 

the total water withdrawn from all sources for all uses, 53 

percent was consumed and 47 percent returned to the 

streams or ground-water reservoirs (fig. 16). 

About 680,000 acre-feet (840 hm3) of ground water was 

withdrawn for use in the San Luis Valley in 1970, mostly 

for irrigation (fig. 14). Of this amount, about half 

(340,000 acre-feet, or 420 hm3) was consumed, and half 

was returned to the ground-water reservoir. In comparison, about 1 million acre-feet (1,200 hm3) of ground 

water was lost by noneconomic evapotranspiration from 

wetlands and phreatophyte areas (Emery and others, 

1971) (table 2). 

Withdrawal of ground water in the San Luis Valley 

has not significantly affected the quantity of water in 

storage. In fact, the amount of ground water in storage 

has been greatly increased, owing to extensive use of surface water for irrigation. 

The amount of ground water withdrawn in the Albuquerque subregion in 1970 was 160,000 acre-feet (200 

hm3), but only 67,000 acre-feet (83 hm3) of the water 

withdrawn was consumed (figs. 14 and 16). The 

remainder (93,000 acre-feet, or 110 hm3) returned to the 

river or the underground reservoir. About 400,000 acrefeet (490 hm3) of water per year is lost to noneconomic 

evapotranspiration in this region (table 2). Overall 

changes in ground-water storage have been insignificant. 

In some areas the quantity of ground water in storage has 

increased, owing to infiltration of surface water diverted 

for irrigation, and in other areas the quantity in storage 

has decreased, owing to extensive withdrawal of ground 

water. 

The amount of ground water withdrawn in the El Paso 

subregion in 1970 was 390,000 acre-feet (480 hm3) (fig. 

14), of which about one-fourth was for municipal, industrial, and military uses and the remainder was for 

irrigation. Pumpage exceeds recharge in the Mesa and 

artesian well fields, and water levels have declined more 

than 60 feet (18m) (fig. 17). However, in both the upper 

and the lower valleys, where most of the pumping is for 

irrigation and the amount of ground water pumped annually varies inversely with the amount of surface water 

available, water levels have fluctuated a few feet but 

show no overall decline. 

The amount of ground water withdrawn for use in the 

Pecos Valley subregion in 1970 was about 480,000 acrefeet (590 hm3) in New Mexico and 680,000 acre-feet (840 

hm3 ) in Texas (fig. 14). About 55 percent, or 638,000 

acre-feet (790 hm3), was consumed, and the remainder 

was returned to the ground-water reservoir. 

The estimated loss of water by noneconomic 

evapotranspiration along the main stem of the Pecos 

River in New Mexico is 185,000 acre-feet (230 hm3) per 

year (Sorenson and Borton, 1967a), and the loss along 

the main stem in Texas is about 90,000 acre-feet (110 

hm3) per year (table 2). An additional 5,000 acre feet is 

lost from tributaries and closed depressions. 

Ground water has been extensively "mined" in several 

areas, especially near Roswell and Carlsbad, N. Mex., 

and in Pecos and Reeves Counties, Tex. (fig. 17). The 

rate of "mining" in the Roswell basin, is estimated to be 

120,000 acre-feet (150 hm3) annually (Sorensen and Borton, 1967a). Water levels have declined as much as 225 

feet (68 m) in the artesian aquifer in the Roswell basin 

and more than 300 feet (91 m) in Reeves and Pecos 

Counties, Tex., since ground-water development began. 

The amount of ground water withdrawn for use in the 

closed basins in 1970 was 200,000 acre-feet (250 hm3) 

(fig. 14). More than 50 percent of this was consumed, 

and the remainder was returned to the ground-water 

reservoir. Most of the water was used for irrigation, but 

about 9,000 acre-feet (11 hm3) was for public supplie.s, 

including military supplies. 

Evapotranspiration losses in the New Mexico part of 

the closed basins subregion is only 50,000 acre-feet (62 

hm3) per year - mainly as direct evaporation from 

playas in the Estancia basin (Sorensen and Borton, 

1967b). An equivalent amount probably is evaporated 

from playas in the Texas part of Salt basin. 

The amount of ground water withdrawn in the lower 

Rio Grande subregion in 1970 was 85,000 acre-feet (100 

hm3) (fig. 14), mostly for supplemental irrigation in the 

coastal area. Data are not available to show percentage 

consumed or water-level changes effected. 

Table 2 summarizes, by subregions, the water supply, 

the water consumed by man's activities and by 

evapotranspiration from wetlands and phreatophyte 
D20 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

I 

I 

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I 

I / 

/ 

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SUMMARY OF 

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All water withdrawn 

equals 7,000,000 ac-ft 

0 

I 

0 

Rio Grande Region 

boundary 

100 

I I 

.. 

/' ·. 

\ 

200 MILES 

I 

I 100 200 Kl LOMETRES 

FIGURE 14.- Ratio between ground water withdrawn (upper number) and surface water withdrawn (lower number). The ratio 

varies widely from one subregion to another. Units are thousands of acre-feet. 
I 

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RIO GRANDE REGION D21 

0 

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.. I §I~ ul --~RADO _l KANSAS -- • NEW ME'Xico--r-- ---------OKLAHOMA __ _ 

I .___Q..~Q..~---., I TEXAS I 

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__ _J I MEXICO - ~ 

SUMMARY OF 

WATER USE 

Public supplies 

(5 percent) 

All water withdrawn 

equals 7,000,000 ac-ft 

Rio Grande Region 

boundary 

' 

0 

I 

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100 

I I 

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FIGURE 15. - Ratio between water withdrawn for public supplies (upper number) and water withdrawn for irrigation (lower 

number). The ratio is larger in the Albuquerque and El Paso subregions than in the others. Units are thousands of acre-feet. 
D22 

34 

SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

I ··- 2ooo\ ~1;:1 _J_' ~~970 • ~~~~ -- -- . ) /. 8 ~ I ---- .::::::......._ I I --:a ,- _ COLORADO I KANSAS 

1 

1 · · · NEWMExico-r---L---------O'KLAHOMA _____ _ 

I : I I OKLAHOMA 

I • I TEXAS ..., 

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1 / /. •• I I 

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SUMMARY OF WATER 

CONSUMPTION 

returned 

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to streams 

or ground 

(46 Percent) 

\'· ,, All water withdrawn 

equals 7,000,000 ac-ft 

\ . "'' \ . ']., 

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boundary \ \ .. --

0 

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100 

I I 

200 MILES 

I 

200 KILOMETRES 

\ 

................... 

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FIGURE 16. - Ratio between water withdrawn (upper number) and water consumed (lower number). About half the water 

withdrawn is consumed. Units are thousands of acre-feet. 

....... 
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EXPLANATION 

@ 

Areas where water 

levels have declined 

more than 20 feet 

(6m) 

Rio Grande Region 

boundary 

0 

0 

RIO GRANDE REGION 

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C.::lju:l 

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ul _ COLORADO ..1 KANSAS . NEWM'EXiCC>_T__ ---------OKi-:\HOMA ____ _ 

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100 200 MILES 

100 200 Kl LOMETRES 

FIGURE 17.- Areas of water-level decline. Water levels have declined more than 20 feet (6 m) in many areas, owing to overdraft 

of ground water. 

D23 
D24 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

areas, and the surface and subsurface storage capacity. 

This tabulation shows that more than half as much 

water is consumed by evapotranspiration in wetlands 

and areas infested with phreatophytes (2.5 million acrefeet, or 3,100 hm3, per year) as is consumed by man's activities (3.7 million acre-feet, or 4,600 hm3, per year). 

Man's use of water commonly creates potential 

sources for ground-water pollution. The areas of highest 

potential for pollution due to man's activities are in 

irrigated areas, in areas of mining and petroleum 

production, and in the large metropolitan areas. 

In general, the water underground is less susceptible to 

pollution than the water in streams and lakes. If ground 

water does become polluted, the pollution is likely to 

persist much longer than a similar pollution of surface 

water. 

The most widespread pollution from man's activities 

in the region results from irrigation. When fields are 

irrigated, part of the water is evaporated from the soil or 

transpired by the crops, leaving a greater concentration 

of salts in the remaining water. Also, part of the fertilizer 

added to fields is dissolved and carried down to the 

ground-water reservoirs. Another major source of pollution from man's activities is sewage effluent from cities 

and individual home sewage systems. The sewage 

effluent may cause bacterial pollution as well as 

chemical pollution. Effluents from industrial plants, 

mines, and oil fields commonly contain high concentrations of dissolved solids and require special management to avoid severe pollution of ground water. 

Soluble minerals in the host rocks are the principal 

sources of dissolved solids in ground water in the Rio 

Grande Region. Large areas in the region are underlain 

by consolidated sedimentary rocks that contain gypsum 

and salt or by valley fill derived by erosion of those rocks. 

These minerals have caused large quantities of ground 

water in the region to become unfit for many uses, especially in the Pecos Valley and closed basins subregions. In ground-water discharge areas, the salts in the 

water are further concentrated by evapotranspiration. In 

some areas, saline ground water is discharged to streams 

and transported to other areas, where it reenters the 

ground and causes a deterioration in the chemical 

quality of the water in those areas. 

POSSIBLE ALTERNATIVES IN 

GROUND-WATER MANAGEMENT 

Management and use of water under any alternative 

has both beneficial and adverse effects. In planning 

water management, the effects and the related cost of 

each alternative should be considered. 

The use of ground water for meeting the water 

demands of a region is a possible alternative in watermanagement planning that should be considered, keeping in mind that ground water and surface water are actually a single resource. Ground-water reservoirs can be 

used for input, storage, and withdrawal of water the 

same as surface reservoirs. General alternatives that 

should be considered in planning ground-water management' a,re. described below. 

Under natural conditions, water from precipitation 

and surface flow infiltrates the ground and moves slowly 

underground toward points of discharge at lower 

elevations. In general, underground storage space is 

available in recharge areas, but the underground reservoirs are completely filled and are spilling in the discharge areas, generally along major stream valleys or in 

natural lakes or playas. Ground-water discharge 

provides the base flow of perennial streams, and the 

ground-water contribution throughout the year may exceed the direct overland flow of water. 

The principal beneficial effect of maintaining full 

ground-water reservoirs relates directly to the 

maintenance of surface streams or base flow. Wet areas 

and associated phreatophytes, sustained by groundwater discharge, provide unique habitats for many 

species of wildlife. Free-flowing springs and spring pools 

are common in many ground-water discharge areas. The 

circulating ground water also flushes soluble salts from 

the underground reservoirs and soil zones. 

Adverse effects of maintaining full ground-water reservoirs include benefits foregone from lack of potential 

economic development, inability of many areas to support a human population at desirable places to live, and 

limited space for storage of additional water during 

periods of excess precipitation and streamflow. The 

closed basins subregion is dependent almost entirely 

upon withdrawal of ground water for human habitation. 

On the other hand, much water is lost by evaporation in 

the closed basins, and the concentration of salts in the 

water in and near discharge areas is increased by 

evaporation, causing a general degradation of water 

quality. 

The principal aquifers in the Rio Grande valley and its 

major tributaries are directly connected with the 

streams. The dominant beneficial effect of utilizing 

ground water from a stream-connected aquifer is 

assurance of a water supply whenever the need is 

greatest and, thus, the maximum potential economic 

return from water use. Ground water use can also assure 

a water supply for large human populations at desirable 

places to live, such as at Albuquerque and El Paso. 

Lowering of the water table through extensive groundwater withdrawals in areas of ground-water discharge 

can reduce significantly the quantity of water lost by 

noneconomic evapotranspiration and provide additional 

space for underground storage of water during periods of 

excess precipitation and streamflow. Ground water requires little treatment for human consumption, as it is 

free of sediments and generally free of bacteria. 
RIO GRANDE REGION D25 

The principal adverse effect of ground-water 

withdrawal from stream-connected aquifers is reduction 

in streamflow due to interception of natural groundwater discharge and to induced infiltration from 

streams. Lowering of water levels by extensive groundwater withdrawal can adversely affect wildlife habitats 

that are dependent on wet areas and phreatophytes. 

However, water levels could be lowered several feet in 

many areas without destroying all the phreatophytes, 

because of the ability of some to grow roots to tens of feet 

to obtain their water supply. Lower ground-water levels 

would dry up some springs and spring pools. A deterioration in water quality would result from extensive 

withdrawals of ground water in some parts of the Rio 

Grande Region. 

The induced infiltration from streams could be controlled by constructing lined canals for transport of surface water past areas of ground-water pumping. 

Aquifers in the closed basins subregion generally are 

isolated from perennial streams. Ground-water 

withdrawal from these aquifers can be limited to an 

amount equal to or less than the average discharge that 

can be intercepted, thus assuring a relatively small yield 

of water indefinitely; or ground-water withdrawal can 

exceed the average discharge (commonly termed 

"mining" of ground water), thus providing a larger 

supply of water during a finite period of time. 

The principal beneficial effect of developing groundwater supplies from aquifers that are isolated from 

streams is provision of water for economic development 

and for human populations where no other source of 

water exists. Lowering of ground-water levels in areas of 

natural discharge can salvage water otherwise lost to 

noneconomic evapotranspiration. Lowering of water 

levels will also provide additional storage space, which 

can be refilled by recharge during periods of excess 

precipitation and runoff. Otherwise, the excess runoff 

would enter playa lakes and be lost from the basin by 

evaporation. 

Continuous withdrawal of ground water in excess of 

the natural discharge that can be intercepted will have 

the adverse effects of increasing depths to water and increasing pumping lifts. The lower water levels may dry 

up natural wet areas in some basins. Dewatering of unconsolidated sediments may cause subsidence of the 

land surface due to accelerated compaction of the 

sediments. Deterioration in water quality in closed 

basins, due to migration of saline water from discharge 

areas to areas of extensive ground-water withdrawal, is 

common. Continuous pumping of ground water in excess 

of the replenishment rate will eventually deplete the 

water supply, as happens when any resource is mined. 

Because ground water and surface water are so closely 

related "in most of the Rio Grande Region, any alternative for ground-water development must recognize the 

effects of the development on the surface-water supplies, 

and ideally, should integrate the two sources of supply 

into a plan for conjunctive use of ground water and surface water. The following descriptions of potential 

management of ground water are based primarily on 

physical factors and do not fully consider the legal constraints. 

Once the policy for governing the utilization of 

ground-water reservoirs is established, all possibilities 

for management of the water within that policy should 

be considered. The rate of economic return per unit of 

water used varies widely from one type of use to another, 

but water supplies for some uses are critical, regardless 

of cost. After water supplies to meet critical needs have 

been allocated, should further allocations be based on 

the maximum rate of economic return per unit of water 

consumed until all the demands have been met in order 

of highest return? Broadhurst (1964) prepared the 

following rates of economic returns for the specified uses 

on the plains of west Texas: 

Type of use 

Irrigaton of crops: 

Gross return 

(dollars per ac-ft 

of water used) 

Grain sorghum ----------- $50- 100 

Cotton ---------------- 100- 200 

Vegetables ______________ 1,500-2,000 

Secondary recovery of oil _ _ _ _ _ _ _ 120,000 

1

Based on the use of one barrel (42 gal) of water to recover one 

barrel of oil and on a market value of $3.00 per barrel for oil. 

Obviously, the uses that provide the highest economic 

returns have relatively small demands. Regardless of 

how the water supply is allocated, maximum efficiency 

in water use should be achieved to stretch the supply as 

far as possible. The largest potential for increasing the 

effective water supply by improving efficiency is related 

to irrigation of croplands. Better efficiency in irrigation 

could salvage considerable quantities of water commonly 

lost by evaporation and runoff from irrigated fields. 

The salvage of water lost to noneconomic 

evapotranspiration in wet and phreatophyte-infested 

areas (table 2) offers the greatest possibility of improving 

the water-supply situation in the region. 

SAN LUIS VALLEY SUBREGION 

The Closed Basin Division of the San Luis Valley Project, proposed by the U.S. Bureau of Reclamation 

(1963), contemplates salvaging about 101,000 acre-feet 

(124 hm3) of water annually, of which 86,000 acre-feet 

(106 hm3) would be pumped ground water (mostly from 

a salvage area of 109,00 acres, or 44,000 ha) and 15,000 

acre-feet (18 hm3) would be surface water. According to 

the Bureau of Reclamation plan, "Under the assumptions of schedule of construction (1965) and continuation 

of the average rate of debit accrual and the estimate of 
D26 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

annual water salvage, the accrued debit of Colorado 

would be offset in about 35 years." 

If 86,000 acre-feet (110 hm3) of water can be salvaged 

annually from the salvage area of 109,000 acres ( 44,000 

ha), what are the prospects of salvaging 1 million acrefeet (1,200 hm3 ) a year from the 1.5 million acres 

(610,000 ha) where the water table is less than 8 feet (2 

m) below ground surface? This question seems 

reasonable when 1 million acre-feet (1,200 hm3) of water 

per year is being lost from the valley by noneconomic 

evapotranspiration. Under such a salvage program, the 

accrued debit of Colorado could be offset in a year or 

two, or additional economic development based on use of 

ground water would be possible. An electric-analog 

model of the valley has been constructed, and several 

alternatives of ground-water management should be 

evaluated with the model. The sharp decrease in the rate 

of evapotranspiration in the San Luis Valley as the water 

table is lowered is shown in figure 18. 

In addition to the saving of water through increased efficiency in irrigation and through salvage operations, 

consideration should be given to withdrawal from 

ground-water storage. The ground-water reservoir contains about 2 billion acre-feet (2.5 million hm3) of water 

in storage. Withdrawal of 2 million acre-feet (2,500 hm3

) 

a year would cause only a 10 percent decrease in storage 

in 100 years. Most large surface reservoirs in the Rio 

Grande region are being filled with sediment at rates 

near 50 percent in 100 years. (Some surface reservoirs are 

I\ 

\ 

\ 

\ 

00 

0 

0 

\_ 

"' "" ~ ~ I--

1 2 3 4 

0.3 0.6 0.9 1 .2 

ANNUAL EVAPOTRANSPIRATION 

5 Ft 

1.5 m 

Source: Emery and others (1971) 

FIGURE 18. - Relationship between the rate of water loss by 

evapotranspiration and the depth to the water table in the San 

Luis Valley. The rate decreases dramatically as the water table gets 

deeper. 

currently being filled at the rate of 100 percent in 100 

years.) Although the capacity of a surface reservoir being 

filled with sediment is continually decreasing, groundwater reservoirs retain indefinitely a nearly constant 

storage capacity and can be used again and again to 

store and recover water. 

ALBUQUERQUE SUBREGION 

An approach to improving the water-supply situation 

in the Albuquerque subregion could be an expansion of 

conjunctive use of ground water and surface water, 

which is already beirig practiced to some extent. Because 

of the physical connection between the river and the 

ground-water reservoir, withdrawal of large quantities of 

ground water in some reaches would cause a reduction in 

streamflow. On the other hand, a large part of the 

400,000 acre-feet ( 490 hm3) of water now being lost annually to noneconomic evapotranspiration probably 

could be salvaged by lowering ground-water levels in the 

wetlands and phreatophyte areas of the subregion. 

Lowering the ground-water level below the bed of the 

river would cause losses from the river, but once the 

ground-water level is below the river, additional lowering 

would not cause a further increase in loss of water from 

the river. However, ground water that normally would 

discharge into the river would be intercepted before it 

reaches the river. Water losses from the river could be 

controlled in areas where the water table is lowered by 

diverting into an artificial, lined channel the amount of 

streamflow needed to satisfy downstream rights. Excess 

flow could follow the natural channel to recharge the 

ground-water reservoir. The economics of this approach 

have not been analyzed. 

The increasing demand for water in the Albuquerque 

subregion could be met readily by drawing on the large 

volume of water stored in the underground reservoirs. 

About 65 million acre-feet (80,000 hm3) of ground water 

could be withdrawn in the subregion by uniformly lowering the water level100 feet (30m) in the valley fill. This 

approach could more than double the water supply for 

the next 90 years, even if all the water withdrawn is consumed, which rarely is true. An additional400,000 acrefeet (490 hm3) per year would be salvaged in the process 

because evapotranspiration in wetlands and 

phreatophyte areas would be eliminated. 

Large reserves of coal and natural gas have been 

mapped in and adjacent to the Albuquerque subregion 

(fig. 6). Development of these resources for electrical 

power generation to help meet the rapidly growing demand for electrical energy in the Southwest could be 

enhanced by drawing on salvaged water or on the large 

reserves of ground water in storage. 

Some, and possibly all, of the wetlands and 

phreatophyte areas are considered by many to be 

ecologically desirable. Therefore, a uniform lowering of 
RIO GRANDE REGION D27 

water level in the ground-water reservoir would not be 

reasonable. However, a program of ground-water 

withdrawal could be designed to lower the water levels 

significantly more than 100 feet (30m) in some areas and 

significantly less, or none, in selected wet and 

phreatophyte areas. This approach would not permit as 

much salvage of water normally lost to noneconomic 

evapotranspiration. Some areas would be conducive to 

maintaining wildlife habitat by surface irrigation, which 

would use much less water than is now lost by 

evapotranspiration. 

A program could be designed also to utilize the 

ground-water reservoir to replace part of the surface 

storage. Water levels could be lowered by pumping 

ground water into lined canals or pipes for delivery to 

points of use, and excess surface water could be used for 

recharging the underground reservoirs by infiltration, 

either directly from the streambed or indirectly from 

spreading areas or recharge ponds in areas favorable for 

infiltration. This approach has the advantage of salvaging water normally lost to evaporation from surface 

reservoirs (255,000 acre-feet, or 310 hm3, per year from 

Elephant Butte and Caballo Reservoirs), but it increases 

the available supply only in the amount of this salvage. 

Surface reservoirs have recreational values which may 

justify large evaporation losses. However, many 

recreationists prefer a small reservoir of constant size to 

a larger reservoir of widely varying size, and at some 

places surface reservoirs could be regulated for nearly 

constant size by utilizing underground storage for part of 

the water. 

Sewage effluent from municipalities and individual 

homes in the Rio Grande Valley and its principal 

tributaries contributes to the salt load in streams and 

underground reservoirs. The principal chemical constituents added to the water are phosphates and 

nitrates. Methods of removing these constituents are being studied by several organizations at the Federal, 

State, and local level. One method being investigated is 

the spraying of treated effluent on irrigated fields, where 

much of the phosphates and nitrates are adsorbed in the 

soil and used by the crops. An excess of water is applied 

to the land so that a large part returns to the groundwater reservoir after the phosphates and nitrates have 

been adsorbed. This process might work very well on the 

types of soils in much of the subregion. 

The water supply of the subregion possibly could be 

improved to some extent with better watershed management, that is, with control of the types and density of 

vegetation growing on the watershed. 

EL PASO SUBREGION 

Conjunctive use of ground water and surface water has 

been practiced by individuals in the Elephant Butte 

irrigation district for many years. Irrigation water from 

Elephant Butte Reservoir is used when the supply is 

adequate, but when surface water is in short supply, 

more than 90 percent of the land receives supplemental 

ground water from privately owned wells (Sorensen and 

Linford, 1967). ·Part of the water applied to irrigated 

fields returns to the- ground-water reservoir carrying 

soluble soil salts and fertilizers. Consequently, the 

chemical quality of shallow ground water has 

deteriorated extensively, some now containing as much 

as 6,000 mg/l dissolved solids. A systematic approach to 

total water management, including mixing of the 

shallow ground water with deeper water of better quality 

or with surface water possibly would improve the general 

quality of irrigation and municipal water. 

Evaporation loss from Elephant Butte and Caballo 

Reservoirs averages about 255,000 acre-feet (310 hm3

) 

per year (Sorensen and Linford, 1967). This loss could be 

reduced significantly by storing more of the water underground and reducing the surface area of these reservoirs. Elephant Butte Reservoir is used extensively for 

recreation, which must be considered in any alternative 

plan for water management. The recreational value of 

the reservoir possibly would be improved by maintaining 

a smaller surface area of a constant level. 

Large amounts of water are lost by evapotranspiration 

from wetlands and phreatophyte areas. Much of this 

water could possibly be salvaged by lowering the water 

table in selected areas. 

Population has been increasing rapidly in the Las 

Cruces and El Paso areas, creating problems in both 

municipal water supply and sewage disposal. The watersupply problem at Las Cruces primarily involves poor 

quality of the shallow ground water. This problem can be 

solved by drilling deeper wells to get below the zone influenced by return of poor quality water from irrigated 

fields. The water supply for El Paso is placing a heavy 

demand on local ground-water supplies, but large quantities of fresh ground water are available in surrounding 

areas. The long-term effects of ground-water withdrawal 

have been evaluated through use of an electric-analog 

model as part of a cooperative study of the City of El 

Paso, the Texas Water Development Board, and the 

U.S. Geological Survey (Leggat and Davis, 1966). A new 

model to incorporate recently obtained data is being constructed to further refine the analysis of ground-water 

management possibilities and resultant effects in the 

area. 

Treated sewage effluent in the subregion probably 

could be used for irrigation - the nitrates and 

phosphates being used by plants, and the excess effluent 

returning to the ground-water reservoir. 

Because the chemical quality of ground water in the 

subregion is highly variable, consideration should be 

given to mixing the water of best quality with water of 

inferior quality to stretch the supply of usable water. 
D28 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

An interagency study of the subregion, involving both 

State and Federal agencies, is currently (1973) in 

process. This study, termed the "Rio Grande Regional 

Environmental Project," is considering a full range of 

potential resource-development plans, including the 

water resources. Various alternatives in water management will be a part of this study. 

PECOS VALLEY SUBREGION 

The effective supply of water in the Pecos Valley subregion could be increased, and the chemical quality of 

the water improved, by reduction of evapotranspiration 

from wetlands and phreatophyte areas and by reduction 

of evaporation from surface storage reservoirs. Salvage of 

50 percent of the water now lost in these processes would 

increase the effective supply by 140,000 acre-feet (170 

hm3) per year. 

The loss of water to evapotranspiration possibly could 

be reduced by lowering the water table in the wetlands 

and phreatophyte areas. However, the salinity of the 

water in some of the phreatophyte areas is too high for 

direct use of the water, and desalination might be required before it could be used beneficially. In some areas 

of intensive pumping, withdrawal of saline water and 

subsequent desalination would reduce the encroachment 

of saline water into fresh-water zones. 

If it were decided to salvage evapotranspiration loss, 

some wetlands possibly should be preserved, such as 

those at the Bitter Lakes National Wildlife Refuge and 

the Bottomless Lakes State Park. A sparse stand of salt 

cedars and cottonwoods could be preserved in selected 

areas at small loss of water by evapotranspiration by 

lowering the water table slowly to an optimum level. 

Control of ground-water levels could prevent the spread 

and revegetation of salt cedars. 

Water salvaged by control of wetlands and 

phreatophytes could be used to meet the increasing demand for public water supplies, to supplement short 

supplies of irrigation water, or to irrigate new lands. 

Water salvaged by reduction of evaporation losses from 

surface storage reservoirs also could be used for these 

purposes. 

The volume of water stored in surface reservoirs, and 

thus the quantity of water lost by evaporation, could be 

reduced by controlled recharge to and withdrawal from 

the ground-water reservoirs. The limestone aquifer in the 

Roswell basin has a large capacity for receiving, storing, 

and transmitting water. This approach to water storage 

would necessarily have to guarantee delivery of water to 

satisfy prior rights to diversion of surface water. 

The overdraft, or "mining," of ground water has 

resulted in significant decreases in ground water in 

storage and has caused increased pumping lifts. This 

overdraft could be alleviated by sufficient salvage of 

water now lost through evapotranspiration, by artificial 

recharge to the ground-water reservoir, or by reduction of 

irrigation. Salvaged water, as described above, could 

replace some of the ground water being pumped and 

reduce the ovedraft. Artificial recharge could alleviate 

the overdraft, but the supply of water that might be 

available for this purpose is limited. Eventually, reducing the irrigated acreage may become necessary, but that 

would have a severe adverse impact on the economy of 

the area. 

Local floods have caused serious problems in parts of 

the subregion. Under favorable circumstances, the 

floodwaters could possibly be diverted to recharge areas 

before they reached populated areas and irrigated farms. 

However, the floodwaters of the region have been appropriated, and these rights would have to be protected. 

The floodwaters generally carry heavy loads of sediment, 

and the storage capacity of surface reservoirs is reduced 

by accumulation of sediment trapped during floods. In 

contrast, the capacity of underground reservoirs is not 

reduced significantly by deposition of sediments on the 

land surface. 

The high salinity of much of the water in the Pecos 

Valley subregion is one of the most serious water 

problems. It is difficult to manage the fresh water so it 

does not become mixed with the abundant saline water, 

which in effect reduces the supply of fresh water. One 

approach to improving the water quality without reducing the total water supply significantly is pumping and 

desalting in areas of saline-water discharge or in areas 

where saline water is encroaching into fresh-water zones 

of underground reservoirs. An experimental desalting 

plant to obtain data on the feasibility of desalting water 

of a chemical character prevalent in the subregion has 

been operated successfully at Roswell. Another possible 

approach is pumping the more saline water into evaporation ponds. At one place, near Malaga Bend, brine that 

normally discharges into the Pecos River has been intercepted by pumping the water from a well and discharging it into a natural depression. The effect of this 

experiment is still being evaluated. 

Elimination of evaporation from wetlands and 

transpiration by phreatophytes would improve the 

quality of water. The salts are concentrated by these 

processes, and the salts eventually return to the principal water systems, contaminating more of the freshwater supply. Evapotranspiration could be reduced in 

many areas by lowering the water table. 

Management of the scarce water supplies of the subregion possibly could be improved by regarding all the 

sources of supply and storage facilities as a single 

system, managed for the maximum benefit of all users. 

However, this approach would require considerable 

reorganization of the complex managerial structures for 

water that are now in operation. 
RIO GRANDE REGION D29 

CLOSED BASINS SUBREGION 

The large supply of saline water in the closed basins 

subregion offers an opportunity for economic development that could utilize the saline water. One possibility 

might be utilization of the water for cooling in 

powerplants. The unconsumed water from the cooling 

facilities could be reinjected into the underground reservoirs at adequate distances from the withdrawal points 

to permit heat dissipation before the water returns to the 

production wells, thus minimizing the consumption of 

water. The amount of fresh water required for the operation could be provided by desalting. Large supplies of 

fresh water for other uses also could be obtained by 

desalting the saline water. 

Ground water has been "mined" in a large area of the 

Estancia basin. The water table has been lowered as 

much as 50 feet (15 m) in areas of maximum 

withdrawals. The overdraft could be alleviated to some 

extent by inducing recharge to the ground-water reservoir during the infrequent periods of surface runoff and 

by dispersing some of the pumping to areas of natural 

discharge. The quantity of water being lost by 

evaporation from the playas is more than the quantity of 

water being consumed by beneficial uses, and most of 

the water lost is from natural ground-water discharge. 

Ground water also has been "mined" in parts of Salt 

basin. Water levels have declined as much as 20 feet (6 

m) in the New Mexico part and as much as 75 feet (23m) 

in the Texas part. Additional artificial recharge and dispersal of pumping to discharge areas in this basin could 

possibly reduce the overdraft of ground water. Some 

natural ground-water discharge has already been intercepted by pumping. 

LOWER RIO GRANDE SUBREGION 

Because of the limited quantity of fresh ground water 

and the generally adequate supply of surface water in the 

lower Rio Grande subregion, no further consideration is 

given to possible alternatives in this subregion. 

SPECIAL UTILIZATION OF UNDERGROUND SPACE 

Underground space can be used for more than 

providing a normal water supply. In many parts of the 

region, thick accumulations of valley fill lie above the 

water table, and the average porosity of this unsaturated 

material is equivalent to, or higher than, that of the 

saturated material. By constructing spreading ponds, 

excess surface flow from rainstorms could be diverted in 

favorable areas for artificial recharge into the unsaturated fill. Thus, the volume of water in storage could 

be increased significantly in some localities. Also, air 

could be pumped from thick unsaturated material for air 

conditioning buildings, because the air at a given depth 

below land surface has an almost constant temperature 

throughout the year. 

Diversion of excess surface water to recharge facilities 

can regulate the flow of streams without the use of large 

surface storage facilities. The water recharged into the 

ground during periods of excess surface flow will eventually finds its way to a nearby stream as extra groundwater discharge. 

Introduction of excess surface water of good chemical 

quality into aquifers containing water of inferior quality 

can improve the general quality of the ground water. 

This approach would have the greatest potential for 

quality improvement in the Pecos Valley and closed 

basins subregions. 

As the war against pollution mounts, the interest in 

underground storage of wastes is growing. Underground 

space above the zone of saturation or in impermeable 

materials can be used for storage of solid wastes in 

favorable areas, where vaults can be excavated and kept 

dry. If deemed necessary, wastes stored in this manner 

can be recovered at any time. Liquid wastes can be 

stored in saturated materials, where adequate 

safeguards, such as enclosing impermeable beds, are present. These conditions exist in many localities in the 

region where the consolidated sedimentary rocks or the 

valley fill are thick and highly variable in permeability. 

Underground disposal of wastes requires thorough 

testing and analysis of the receiving environment before 

the safety of disposal can be assured. 

The Anaconda Co. has operated an injection well for 

disposal of uranium-mill effluent near Grants, N.Mex., 

since December 1960 (West, 1972). The injection interval 

is sandstone, separated from all fresh-water aquifers by 

relatively impermeable, thick beds of mudstone and 

anhydrite. Large areas in the Rio Grande region should 

have similar features which would permit safe disposal 

of liquid chemical wastes. 

Release of cooling water from thermal electric plants 

and some types of industrial plants has caused severe 

problems of thermal pollution of nearby streams in many 

areas of the United States. The ground-water reservoirs 

in the valley fill of the Rio Grande Region could be used 

as receptacles for thermal waters from these types of 

plants. If the thermal water were injected into the valley 

fill at considerable distances from discharge points, 

either natural discharge points or wells, the heat would 

be dissipated to the rocks and the atmosphere before the 

water could reach the surface again. 

Development of geothermal energy is another special 

utilization of underground space. In favorable geothermal areas, natural steam can be withdrawn through 

wells and used to drive turbines for generation of electricity. Experiments to evaluate the injection of cool 

water into dry geothermal areas for conversion of the 
D30 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

water to steam and recovery of the steam for driving turbines are underway, but the outcome is open to speculation. In some parts of the world, geothermal waters are 

used directly for space heating of homes, offices, and 

greenhouses. 

Several geothermal areas have been identified along 

the margins of the Rio Grande depression, but they have 

not been adequately explored to evaluate their potential 

for energy development. The largest and best known 

geothermal area in the region is the Jemez Mountains 

area of northern New Mexico. Hydrologic studies of that 

area were begun recently (1972). 

Experiments indicate that in favorable areas both 

heating and cooling of buildings can be accomplished by 

direct use of ground water from different depths. 

Shallow ground water, which commonly is cool, can be 

obtained in summer for cooling buildings and can be 

reinjected at greater depths for conservation of the 

water. Warm water from greater depths can be obtained 

for heating buildings in winter and can be reinjected at 

shallow depths to maintain the balance between 

withdrawal and injection. The thick permeable valley 

fill in the Rio Grande Valley should be favorable for this 

application. 

INFORMATION NEEDED FOR PLANNING 

GROUND-WATER MANAGEMENT 

Much work has been done toward evaluating the 

ground-water resources of the Rio Grande Region, as indicated by the references at the end of the report and by 

figure 19, but much more remains to be done before 

systematic planning for ground-water management can 

be accomplished. The types of information needed for 

systematic planning are summarized on the following 

pages. 

Planners for ground-water management must 

recognize the close relationship of ground water and surface water. The planner must have detailed information 

on: (1) the flow characteristics of streams; (2) the position of the streambed in relation to the water table; (3) 

infiltration rates from streams, canals, ditches, and 

irrigated fields; ( 4) potential infiltration rates from 

recharge ponds or spreading areas; (5) the contribution 

of ground-water discharge to streams; (6) the chemical 

quality of ground water and surface water; and (7) the 

changes in ground-water storage due to past management of the water resources. Typically, use of surface 

water causes an increase in ground-water storage, 

because some water is lost to infiltration, and use of 

ground water causes a decrease in storage, which varies 

as a function of ground water withdrawn and consumed. 

The quantity of recoverable ground water in storage to 

different depths should be determined, as it represents 

the reserves available for development. Rough estimates 

of ground-water storage in the major aquifers of the Rio 

Grande Region have been made to show the water 

resources in general perspective. However, more accurate information is needed in areas to be considered for 

systematic ground-water management. 

The physical properties of aquifers control the quantity of water that can be stored or yielded, the rate at 

which water can be added to or withdrawn from the underground reservoirs, and the change in water levels that 

will result from withdrawal of a given volume of water. 

The mineral content of aquifer materials largely controls 

the chemical quality of the ground water. The physical 

properties of the aquifers should be determined by imposing a hydrologic stress to the system (pumping) and 

measuring the response of the system (water-level 

changes). Useful information has already been obtained 

by pumping from individual wells or from well fields and 

measuring water-level changes. Additional information 

could be obtained from existing wells. In some areas the 

depth and spacing of wells are inadequate for acceptable 

tests, and special test wells are needed. 

The depth to water and the pumping lifts that will be 

required must be known in order to estimate pumping 

costs. 

Valley-fill aquifers, the predominant type in the Rio 

Grande Region, commonly contain extensive beds or 

lenses of clay and silt. When water is withdrawn from 

these aquifers, slow drainage of water from the clay may 

permit its compaction. If the clay beds comprise a 

significant part of the valley fill, the compaction due to 

withdrawal of water may result in subsidence of the land 

surface. Therefore, a determination of total clay 

thickness and laboratory determination of hydraulic and 

mechanical properties of the clays would be needed. 

Chemical analyses of ground water from many areas 

are needed to define the variations in quality, both 

laterally and vertically, within the aquifers. Variations 

in chemical quality of water within an aquifer can lead to 

intermixing of fresh and saline water as fresh water is 

withdrawn, because saline water moves into space 

previously occupied by fresh water. Withdrawal of saline 

water reverses the situation but has the same net effect. 

Wetlands and phreatophyte areas should be mapped 

in detail, and the quantity of water lost by 

evapotranspiration should be determined as accurately 

as possible. The significance of these areas as wildlife 

habitats should be evaluated. Eradication of 

phreatophytes by mechanical means and selective 

elimination by controlling ground-water levels should be 

appraised in relation to wildlife habitats and potential 

for water salvage. 

The responses of water-resource systems to the many 

potential hydrologic stresses can best be analyzed by 

employing an electric-analog or digital model, or a com-
EXPLANATION 

Areas where quantitative ground-water 

studies have been made, including 

an electric-analog or a digital model 

Areas where qualitative ground-water 

studies have been made 

Areas where ground-water 

studies have not been made 

Rio Grande Region 

boundary 0 

I 

0 

RIO GRANDE REGION 

I 

100 

100 

I I 

200 MILES 

I 

200 Kl LOMETRES 

\ ··-" 

FIGURE 19. -Areas in which ground-water studies have been made. Quantitative studies have been made in only two areas, and 

several areas have not had even qualitative studies. 

D31 
D32 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

~· '?'.... •• 

EXPLANATION 

More than SO percent Federal 

lands, including public domain, 

national parks and monuments, 

wildlife refuges, Indian reservations, national forests, and 

military reservations 

More than SO percent nonFederal lands, mostly 

privately owned 

Source: U.S. Geological Survey, The National Atlas 

Rio Grande Region 

boundary 

0 

I 

0 

of the United States of America (1970, p. 272) 

I 

100 

100 

I 

200 MILES 

I 

200 Kl LOMETRES 

FIGURE 20.- Land ownership or control. Most of the land in New Mexico is owned or controlled by the Federal Government, and 

most in Texas is privately owned. 
RIO GRANDE REGION D33 

bination of the two, to simulate the ground-water reservoir. Once the models are completed and verified with 

historic records, the effects of alternative plans for water 

management and optimum locations, spacing, and 

depths of wells can be readily analyzed. 

Information on the benefits and costs, both economic 

and environmental, is needed for evaluation of alternative plans for water management. The planners and 

the public should be aware of the benefits and costs of 

water use and the value of benefits foregone if the water 

is not used. The cost analysis of a proposed project 

should include: (1) the cost of the investigative program; 

(2) the cost of the construction program; and (3) the cost 

of the operational program, including the cost of 

monitoring the response of the water-resource system. 

Any proposed project, regardless of benefits and costs, 

must be acceptable within legal, social, and ecological 

constraints. 

Once a water-resource project becomes operational, 

the response of the system to the new stresses should be 

monitored. The monitoring data very likely will show 

that modifications of the models are necessary to improve the predictive capability of the models. Depending 

on the actual response of the water-resource system, 

minor modifications in operations, as well as 

modifications of the models, may be necessary. 

In some instances it might be possible to increase the 

effective supply of water by improved watershed 

management or by weather modification. These 

possibilities should be thoroughly evaluated as part of 

comprehensive water-resources planning. 

All facets of data acquisition and analysis should be 

thoroughly documented with written reports for future 

use and current transfer of knowledge. 

The Federal Government should have a strong interest 

in more detailed evaluation of the ground-water 

resources and possible alternatives in water use, as more 

than 50 percent of the land in the New Mexico part of the 

region is Federally owned or administered (fig. 20). 

The types of studies needed in various parts of the 

region to provide critical information for planning 

systematic ground-water management are outlined in 

figure 21. 

SUMMARY AND CONCLUSIONS 

The Rio Grande is an interstate and international 

stream which begins in the mountains of Colorado, flows 

across New Mexico from north to south, and forms the 

boundary between Mexico and Texas for 1,250 miles 

(2,000 km). The region ranges in altitude from sea level 

at the Gulf of Mexico to more than 14,000 feet (4,300 m) 

in the headwaters area. Annual precipitation ranges 

from 8 to more than 30 inches (20 to more than 76 em), 

depending on altitude and latitude. Irrigation is required 

for growing crops throughout the region. Evaporation 

rates are generally high, causing an annual water loss of 

950,000 acre-feet (1,200 hm3) from reservoirs, ponds, and 

streams. 

The Rio Grande Valley in New Mexico has been inhabited for thousands of years, first by Indians, then 

Spaniards, and, later, Americans. Crops have been 

irrigated since the early part of this millenium. From 

earliest times, most of the Indian and Spanish 

agriculture in northern New Mex:co has been based on 

subsistence farming, and the farms have become smaller 

as the land was divided amongst each new generation. 

The .American settlers established larger farms or 

ranches, and, subsequently, many have been combined 

to create even larger ones. 

The population of the region has been increasing 

rapidly in this century, from 750,000 in 1929 to 1, 700,000 

in 1970. It is expected to increase to 2,500,000 by 2020. 

The basin economy of the region was traditionally 

agricultural until recent years, but agricultural development is now increasing very slowly. Since 1950 the mining and petroleum industries have increased much more 

rapidly than agricultural development. 

Management of surface waters in the region is subject 

to international treaty, interstate compacts, and the 

laws of three separate States. Management of ground 

water is subject to the laws of the State in which the 

ground water occurs, and the laws of each State are quite 

different. 

The renewable water supply of the region is the sum of 

the surface-water runoff, the ground-water outflow 

(which is small), and the natural evapotranspiration. 

Annual precipitation on the region is 86 million acre-feet 

(110,000 hm3); however, all but 4 million acre-feet (4,900 

hm3) is returned to the atmosphere by evapotranspiration. 

The ground-water reservoirs of the region contain an 

aggregate of about 5,800 million acre-feet (7 ,200,000 

hm3) of fresh and slightly saline water in storage, which 

could be withdrawn through wells. In contrast, the surface reservoirs have a combined storage capacity of only 

18 million acre-feet (22,000 hm3). 

Thick deposits of valley fill in stream and intermontane valleys of the region comprise the principal groundwater reservoirs. In most areas they are capable of 

yielding large supplies of water to wells. In some areas, 

consolidated sedimentary rocks, particularly limestone, 

yield a few hundred to a few thousand gallons per minute 

of water to wells. The largest ground-water reservoirs are 

in the San Luis Valley and Albuquerque subregions, 

each of which contains about 2 billion acre-feet 

(2,500,000 hm3) of fresh and slightly saline water. 

The chemical quality of water in the valley-fill 

aquifers varies widely. The dissolved solids in water in 
D34 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

EXPLANATION 

Areas where quantitative ground-water 

information is needed, including an 

electric-analog or a digital model 

Areas where qualitative ground-water 

information is needed 

Areas where ground-water information 

is generally adequate but may 

need updating locally 

0 

I 

0 

OIC/l 

~~~ 

...:I olz -< 

0 ::G 

ul 

CQ1Q.&\.QQ__T __ .l _________ ~.§!\_§ ____ _ 

NEW MEXICO OKLAHOMA 

f---.Q~H..QMA ___ , 

I TEXAS I 

I I 

I I 

I I 

I I 

ol I 

Ul I ~,~ ~ >< -, 

;3:ll:: "---\ J:l.lj ..____ z, 

I 

100 

I 

I 

I 

I 

I 

. i' ·. 

Rio Grande Region 

boundary 

. . 

100 

I 

200 MILES 

I I 

200 KILOMETRES 

FIGURE 21.- Types of studies needed. 

\ 

·. 

\ .. ~ 
RIO GRANDE REGION D35 

the shallow aquifers have been concentrated by water 

loss due to evapotranspiration and by return of water 

containing fertilizers from irrigated fields to the groundwater reservoir. The water at great depths in the valley 

fill also may have high concentrations of dissolved solids. 

The water of best quality generally is at intermediate 

depths. In the Tularosa basin, most of the water contains 

3,000 to more than 35,000 mg/1. · 

Withdrawal of ground water in the region in 1970 was 

2.7 million acre-feet (3,300 hm3). The major part (88 percent) of this water was used for irrigation. Of the water 

withdrawn, 53 percent was consumed, and 47 percent 

was returned to the streams or ground-water reservoirs. 

Ground water has been extensively overdrawn, or 

"mined," in several areas, especially near Roswell, N. 

Mex., and in Pecos and Reeves Counties, Tex., and 

severe decline in ground-water levels have resulted. 

The loss of water by evapotranspiration in wetlands 

and phreatophyte areas is about 2.5 million acre feet 

. (3,100 hm3) per year in the region. In comparison, 3.7 

million acre-feet ( 4,600 hm3) of water is consumed by 

man's activities. 

Ground water and surface water are really a single 

resource -water - although they commonly are treated 

separately. Ground-water reservoirs can be used for input, storage, and withdrawal of water the same as surface reservoirs, but ground water in storage constitutes a 

large reserve that can be withdrawn at any time. Alternatives that should be considered in ground-water 

management include: (1) maintenance of full groundwater reservoirs, (2) withdrawal of ground water from 

stream-connected aquifers, and (3) withdrawal of ground 

water from aquifers isolated from streams. Each alternative has definite beneficial and adverse effects that 

must be considered. 

Because ground water and surface water are so closely 

related in most of the region, any alternative plan for 

ground-water development must recognize the effects of 

this development on the surface-water supplies and 

preferably should integrate the two sources of supply 

into a plan for conjunctive use of both the ground water 

and the surface water. 

The salvage of water lost to noneconomic 

evapotranspiration in wet and phreatophyte-infested 

areas offers the greatest possibility of improving the 

effective water supply in the region. Salvage of half the 

water lost would increase the effective supply by 1.2 

million acre-feet (1,500 hm3) per year. However, salvage 

of this water could adversely affect the wildlife habitat. 

The usable water supply for the region could be increased tremendously by drawing on the large reserve of 

ground water in storage. Pumping of ground water in 

many reaches of the streams could cause seepage losses 

from the streams. However, if the economics were 

favorable, these losses could be prevented by diverting 

the streams into lined channels. 

Withdrawal of ground water, thus provision of more 

storage space underground, could help to regulate 

streamflow at times of excess flow and in some places 

could prevent floods. Water that enters the ground-water 

reservoirs during periods of excess surface flow would be 

available for later use. Storage of excess water underground has the added advantage of leaving the sediment behind on the land surface rather than letting it 

accumulate in the surface reservoirs. 

The large supplies of saline water in parts of the region 

should have a market for some uses. Removal of the 

saline water would prevent its mixing with fresh water. 

Development of geothermal energy appears to offer 

possibility for meeting part of the energy requirements of 

the future. Preliminary studies indicate geothermal 

areas at several places in the region. 

Planners for ground-water management must 

recognize the close relationship between ground water 

and surface water and must have detailed information 

on the physical parameters that control or affect--each 

supply. Large-scale development without adequate 

evaluation, planning, and wise management can be disastrous. 

REFERENCES 

Armstrong, C. A., and McMillion, L. G., 1961, Geology and groundwater resources of Pecos County, Texas: Texas Board Water 

Engineers Bull. 6106, v. 1, 241 p., v. 2, 295 p. 

Baker, R. C., 1965, Reconnaissance investigation of the ground-water 

resources of the lower Rio Grande basin, Texas, in Reconnaissance 

investigation of ground-water resources of the Rio Grande basin, 

Texas: Texas Water Comm. Bull. 6502, p. L1-L34. 

Baker, R. C., and Dale, 0. C., 1961, Ground-water resources of the 

lower Rio Grande Valley area, Texas: Texas Board Water 

Engineers Bull. 6014, v. 1, 81 p., v. 2, 336 p. 

__ 1964, Ground-water resources of the Lower Rio Grande Valley 

area, Texas: U.S. Geol. Survey Water-Supply Paper 1653, 56 p. 

Baltz, E. H., Jr., and West, S. W., 1967, Geology and ground-water 

resources of the southern part of the Jicarilla Apache Indian Reservation and adjacent areas, New Mexico: U.S. Geol. Survey WaterSupply Paper 1576-H, 89 p. 

Bean, R. T., 1949, Geology of the Roswell artesian basin, New Mexico, 

and its relation to the Hondo Reservoir: New Mexico State 

Engineer Tech. Rept. 9, p. 1-31. 

Bennett, R. R., and Sayre, A. N., 1962, Geology and ground-water 

resources of Kinney County, Texas: Texas Water Comm. Bull. 

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D36 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES 

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RIO GRANDE REGION D37 

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