Long-term
Variations in Hydraulic Head
in a Karstic Aquifer:
Roswell Artesian Basin, New Mexico
Seasonal
and
Final Technical Report
August 2007
Open-File Report 503
New Mexico Bureau
of Geology and
Mineral Resources
Lewis Land,
and Brad T. Newton
Mirror Lake
i
New Mexico Bureau of Geology and Mineral Resources
A Division of New Mexico Institute of Mining and Technology
Socorro, NM 87801
(575) 887-5508
Fax (575) 835-6333
E-mail: lland@gis.nmt.edu
ii
Long-term
Variations in Hydraulic Head
in a Karstic Aquifer:
Roswell Artesian Basin, New Mexico
Seasonal
and
Final Technical Report
August 2007
Open-File Report 503
Lewis Land,
and Brad T. Newton
New Mexico Bureau of Geology & Mineral Resources
iii
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
Project Funding
Funding and support for this investigation
were provided by the Pecos Valley Artesian
Conservancy District; the New Mexico Bureau of Geology and Mineral Resources; and
the Department of Research and Economic
Development at the New Mexico Institute of
Mining and Technology.
Project Personnel
Lewis Land, Ph.D., Principal Investigator,
Hydrogeologist, New Mexico Bureau of
Geology & Mineral Resources, and
the National Cave & Karst Research
Institute, Carlsbad, NM,
lland@gis.nmt.edu
Tasks: Project management; data collec tion, compilation, and interpretation;
technical report.
Brad T. Newton,
Hydrosphere Resource Consultants,
Socorro, NM
Tasks: Data collection and interpreta-
tion; technical report.
Brigitte Felix Kludt, GIS Specialist, New
Mexico Bureau of Geology & Mineral
Resources, bfk@gis.nmt.edu
Tasks: GIS; cartography; drafting; report
design, layout and production.
An abridged version of this report has been published in the February, 2008 issue of the Journal
of the American Water Resources Association.
Cover Photo: View south overlooking Mirror
Lake, Bottomless Lakes State Park.
iv
R oswell A rtesian B asin
TA BLE OF C ON T E N T S
I. ABSTRA C T �������������������������������������������������������1
II. INTRO DUC T I ON �����������������������������������������2
III. BACKGR OUN D��������������������������������������������5
Artesian aquifer����������������������������������������������������6
Salinity of the artesian aquifer���������������������������8
Artesia Group confining beds�����������������������������9
Shallow aquifer�����������������������������������������������������9
IV. Manag em ent of wat er
re sources in t h e A rtesian
Basin ���������������������������������������������������������������� 11
V. Me thods ����������������������������������������������������� 11
VI.R e sults ��������������������������������������������������������� 12
Artesian aquifer ������������������������������������������������ 12
Artesian aquifer: Chloride content����������������� 15
Shallow aquifer�������������������������������������������������� 15
Variations in hydraulic head:
Artesian aquifer�������������������������������������������� 17
Variations in hydraulic head:
Shallow aquifer��������������������������������������������� 17
Artesian aquifer: Seasonal cycles�������������������� 19
Artesian aquifer: Long-term variations in
head����������������������������������������������������������������� 26
VII. Discussion���������������������������������������������� 27
VIII. Conclusions�������������������������������������� 29
REF ERENC E S������������������������������������������������������ 30
FIG U R E S
Figure 1–Regional map of southeastern
New Mexico. ���������������������������������������������������3
Figure 2–West-east hydrostratigraphic
section illustrating regional ground water
flow patterns within the artesian and
shallow aquifers. ��������������������������������������������5
Figure 3–Diagrammatic cross-section
showing shelf-to-basin facies relationships
within Guadalupian strata in southeastern
New Mexico. ���������������������������������������������������6
Figure 4a–Physiographic features of the lower .
Pecos Valley. .������������������������������������������������ 13
Figure 4b–Configuration of hydraulic head
in the artesian aquifer,
January-February, 2005. ���������������������������� 14
Figure 5–Chloride concentration in the
artesian aquifer, March, 2005. ����������������� 16
Figure 6–Configuration of the water table
in the shallow aquifer,
January-February, 2005. ���������������������������� 18
Figure 7–Change in hydraulic head in the
artesian aquifer, 1975-2005. ��������������������� 20
Figure 8–Change in hydraulic head in the
artesian aquifer, 2004-2005. ��������������������� 21
Figure 9–Change in water levels in the
shallow aquifer, 1975-2005. ��������������������� 22
Figure 10–Change in water levels in the
shallow aquifer, 2004-2005. ��������������������� 23
Figure 11a–Hydrograph of the Greenfield
monitoring well, showing very pro nounced annual cycles and longer-term
variations in hydraulic head in the
artesian aquifer. ������������������������������������������� 24
Figure 11b–Detail from figure 11a hydro graph, showing seasonal irrigation cycles
over a five year period, 2000 - 2005. ������ 24
Figure 12a–Hydrograph of the Berrendo
observation well. ����������������������������������������� 25
v
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
Figure 12b–Irrigated agriculture and precipita tion in the Artesian Basin. ������������������������������ 25
PLATES
Plate 1–Configuration of hydraulic head in
the artesian aquifer, January-February, 2005 (same as Figure 4b)
Plate 2–Chloride concentration in the artesian aquifer, March, 2005 (same as Figure 5)
Plate 3–Configuration of the water table in the shallow aquifer, January-February, 2005
(same as Figure 6).
Plate 4–Change in hydraulic head in the artesian
aquifer, 1975-2005 (same as Figure 7).
Plate 5–Change in hydraulic head in the artesian
aquifer, 2004-2005 (same as Figure 8).
Plate 6–Change in water levels in the shallow
aquifer, 1975-2005 (same as Figure 9).
Plate 7–Change in water levels in the shallow
aquifer, 2004-2005 (same as Figure 10).
The following Plates are maps from Welder (1983).
Plate W-8–Structural contour map of the top
of the San Andres Limestone, Roswell Basin (Welder, Figure 3).
Plate W-9–Map showing configuration of the
base of the valley fill, Roswell-Artesia area,
New Mexico (Welder, Figure 5).
Plate W-10–Map showing configuration of the
top of the artesian aquifer in January, 1975,
Roswell Basin (Welder, Figure 6).
Plate W-11–Map showing thickness of the
confining bed, Roswell Basin (Welder,
Figure 7).
Plate W-12–Map showing saturated thickness
of the valley fill in January, 1975, Roswell
Basin (Welder, Figure 8).
Plate W-13–Map showing the generalized
vi
potentiometric surface of the artesian
aquifer in January, 1926 (Welder, Figure 9).
Plate W-14–Map showing the potentiome tric surface of the artesian aquifer in
January, 1975 (Welder, Figure 12).
Plate W-15–Map showing the generalized
change in hydrostatic head of the artesian
aquifer, 1926-1975, Roswell Basin (Welder,
Figure 13).
Plate W-16–Map showing configuration of
the water table in the shallow aquifer in
January, 1975, Roswell Basin
(Welder, Figure 20).
Plate W-17–Map showing change in hydr ostatic head of the shallow aquifer,
1938-1975, Roswell Basin
(Welder, Figure 21).
Plate W-18–Map showing the chloride
concentration of water samples from the
artesian aquifer in 1978, Roswell Basin
(Welder, Figure 26).
R oswell A rtesian B asin
I. A BST RAC T
Water levels in the karstic San Andres limestone aquifer of the Roswell Artesian Basin,
New Mexico, display significant variations on
a variety of time scales. Large seasonal fluctuations in hydraulic head are directly related to the
irrigation cycle in the Artesian Basin, lower in
summer months and higher in winter when less
irrigation occurs. Longer-term variations are the
result of both human and climatic factors. Since
the inception of irrigated farming more than a
century ago, overappropriation of water resources has caused water levels in the artesian aquifer
to fall by as much as 230 ft (70 m). The general
decline in hydraulic head began to reverse in
the mid-1980s due to a variety of conservation
measures, combined with a period of elevated
rainfall toward the end of the twentieth century.
Key terms: Ground water; karst; artesian aquifer; Roswell Artesian Basin
1
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
I I. INTR OD U C T ION
The Roswell Artesian Basin is located in
the lower Pecos Valley of southeastern New
Mexico (Figure 1), on the northern fringe of the
Chihuahua Desert. Summers are long and hot
and precipitation is sparse, averaging less than
13 inches/yr (33 cm/yr), most of which occurs
as intense, localized thunderstorms during the
summer monsoon season (Motts and Cushman,
1964). However, for more than 100 years the
Roswell Basin has also been one of the most intensively farmed areas in the state, the principal
crops being alfalfa, cotton, sorghum and chiles.
The Basin derives virtually all of its irrigation
water from ground water stored in an artesian
carbonate aquifer and a shallow alluvial aquifer,
and has been described by many workers as a
world-class example of a rechargeable artesian
aquifer system (e.g., Havenor, 1968).
Since the inception of irrigated agriculture
in the Artesian Basin in the early 20th century,
most of the discharge from both the artesian
and shallow aquifers has been from wells.
However, substantial natural discharge from
the artesian aquifer still occurs along the Pecos
River, through fractures and solution channels
formed in overlying evaporitic confining beds.
This natural discharge, which presently amounts
to roughly 30,000 acre-ft/yr (~37 million m3/yr)
but was much greater in pre-development times
(Barroll and Shomaker, 2003), is made manifest
by a complex of karst springs, sinkhole lakes
and extensive wetlands that occur along the
west bank of the Pecos at Bitter Lakes National
Wildlife Refuge (Figure 1) (Land, 2005). Along
the eastern margin of the Pecos River valley,
discharge from the artesian aquifer has formed
a chain of large gypsum cenotes in the Seven Rivers Escarpment at Bottomless Lakes State Park
(Land, 2003).
2
In the early history of development of the
artesian aquifer, many wells flowed to the surface
with yields as high as 5,700 gpm (21,500 l/min)
(Welder, 1983), and high-volume springs west
of Roswell fed tributary streams flowing into
the Pecos River. However, decades of intensive
pumping caused substantial declines in hydraulic
head in the aquifer. By the mid-20th century total
ground water diversions in the Artesian Basin
approached 400,000 acre-ft/yr (493 million m3)
(Barroll and Shomaker, 2003), and Hantush
(1957) estimated that withdrawals from the
artesian aquifer exceeded recharge amounts by
~250,000 acre-ft/yr (308 million m3/yr). By then
most springs in the Artesian Basin were dry, and
tributary stream flow had almost completely
ceased except for rare flood events.
Increased appropriations from both the shallow and artesian aquifers had also reduced base
flow into the Pecos River (Thomas, 1963; Havenor, 1968). In 1978 there were approximately
1,500 high-yielding irrigation, industrial, and
public-supply wells in the Roswell Artesian Basin, and water levels in the artesian aquifer had
declined in some areas by as much as 230 ft (70
m) (Welder, 1983). In 1975, a basin-wide investigation of water levels was conducted by the U.S.
Geological Survey (USGS) and the New Mexico
Office of the State Engineer (NM OSE). The
results of that investigation, documented in a
report by G.E. Welder (1983), showed significant
water level declines in all areas of the Roswell
Basin.
The Welder report is still widely cited and
used for managing water resources in the Artesian Basin, although the data set is now over 30
years old and water levels have risen significantly
since Welder’s measurements were made. For this
reason, the Pecos Valley Artesian Conservancy
R oswell A rtesian B asin
104°W
105°W
103°W
Texas
New Mexico
NEW MEXICO
25
Santa Rosa
Pe
co
s
Ri
Vaughn
ve
r
Fort Sumner
Clovis
285
34°N
Lincoln Co.
60
35°N
106°W
70
C A P I TA N M
TS
.
S LOPE
380
Roswell
Artesian
Basin
Chav es Co.
E ddy Co.
Artesia
82
S
R
AC
Alamogordo
BLSP
S
82
(Ogallala
Aquifer)
BLNWR
Roswell
PECO
NTO
A M EM
OUN
T
70
O t ero Co.
Llano
Estacado
fig. 4, 6-10
fig. 2
AI
N
S
380
GU
33°N
Carrizozo
Hobbs
Capitan Reef
AD
A
(buried)
Carlsbad
L
E
UP S .
T
M
Delaware
Basin
32°N
285
10
0
0
10
20 Miles
fig. 3
20 Kilometers
Figure 1−Regional map of southeastern New Mexico, showing location of Roswell Artesian Basin, Bitter Lakes National Wildlife
Refuge (BLNWR) and Bottomless Lakes State Park (BLSP). Dashed lines show lines of section for figures 2 and 3. The Pecos Buckles
are indicated by light solid lines extending northeast across the Pecos Slope. Outcrop in the eastern Sacramentos and Guadalupe
Mountains consists primarily of carbonate rocks of the San Andres Formation (Sacramentos) and the Capitan Reef and backreef units
of the Artesia Group (Guadalupes).
3
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
District (PVACD), the agency responsible for
metering wells in the Artesian Basin, requested
that the New Mexico Bureau of Geology and
Mineral Resources (NMBGMR) conduct a new
basin-wide study of hydraulic head in the shallow and artesian aquifers. This paper documents
the results of that investigation.
4
R oswell A rtesian B asin
III. Bac k ground
The Roswell Artesian Basin is typically characterized as a two-aquifer system, a paradigm
established by early investigators in the Basin
(e.g., Fiedler and Nye, 1933). The system consists of an eastward-dipping carbonate aquifer
overlain by a leaky evaporitic confining unit,
which is in turn overlain by an unconfined alluvial aquifer (Figure 2). The carbonate aquifer
is artesian to the east but under water table conditions in the western outcrop area on the Pecos
Slope. Historically, the carbonate aquifer in the
Roswell Basin is referred to as the “artesian
aquifer”, regardless of its confined or unconfined
state. The alluvial aquifer is commonly referred
to as the “shallow aquifer”.
The western boundary of the Artesian Basin
is defined by the intersection of the regional water table with the top of the Glorieta sandstone,
the basal member of the San Andres Formation (Figure 2) (Kinney et al., 1968; Welder,
1983). Variable amounts of water move from
the relatively low-permeability Glorieta into the
overlying San Andres limestone, which makes
up the greater part of the artesian aquifer. The
Yeso Formation, a heterogeneous unit composed
of siltstone, mudstone, carbonates and gypsum,
serves as a lower confining unit for the artesian
system.
The artesian aquifer becomes confined ~6
miles (10 km) west of the city of Roswell, where
the eastward-dipping San Andres limestone
passes beneath gypsum and mudstones of the
W
E
Pecos Slope
recharge area
Six Mile
Buckle
Border
Buckle
potentiometric
surface
4000
Roswell
alluvial
aquifer
Pecos
River
Bitter Lakes
sinkholes
1400
Bottomless
Lakes
sinkholes
1200
3500
Yeso
Fmn.
3000
0
2500
0
Glo
rie
ta
SS
10 mi.
fresh water15 km saline water interface
Seven Rivers
aquitard
San Andres
Artesian Aquifer
v.e. = 30x
1000
elevation (meters)
elevation (feet)
4500
discharge area
800
Figure 2−West-east hydrostratigraphic section illustrating regional ground water flow patterns within the artesian and shallow
aquifers. Arrows indicate general direction of ground water flow. Line of section shown in figure 1.
5
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
Artesia Group. Most of the agricultural activity
in the Basin is concentrated east of the confinedunconfined boundary in a 12 mile (20 km) wide
strip west of the Pecos River. The eastern boundary of the Basin is a no-flow boundary along
the Pecos River, across which very little ground
water moves. Water along the eastern boundary
flows southward within the artesian aquifer or
upward through leaky confining beds into the
shallow aquifer. East of the river the lower San
Andres is an oil and gas reservoir, and the same
interval that produces potable water for the city
of Roswell a few miles to the southwest contains
oil and brines with chloride concentrations as
high as 39,000 ppm (Havenor, 1968; Gratton
and LeMay, 1969). The west and east boundaries of the basin converge ~18 miles (30 km)
north of Roswell (Welder, 1983).
The southern boundary of the basin is also
regarded as a no-flow boundary, but its position
is not well-defined. It is generally located (somewhat arbitrarily) along the Seven Rivers Hills
north of Carlsbad, an area where the San Andres
Formation begins to undergo a transition in the
subsurface from shelf limestones and dolomites
to shelf margin facies with lower porosity and
permeability (Welder, 1983; Miller, 1969).
Artesian Aquifer
Ground water is stored in the carbonate
aquifer in multiple erratically developed, highly
porous and transmissive zones within the middle
Permian (Guadalupian) San Andres limestone,
and to a lesser extent in the overlying Grayburg
Formation of the Artesia Group (Figure 3).
Water-bearing zones in the artesian aquifer
rise stratigraphically from north to south, occurring near the middle of the San Andres Formation in the northern part of the Basin, and in
carbonate rocks of the Grayburg Formation and
upper San Andres in the southern part of the
Basin near Artesia. Water-producing zones also
rise stratigraphically from west to east, occurring
in the basal Glorieta sandstone along the western
N
S
Roswell
Carlsbad
Shelf
Margin
Northwest Shelf
San
And
res
Yeso
Formation
(Leonardian)
LS A
Artesia Group
Confining Unit
Tansill
Yates
Seven Rivers
er
Ba
se
of
Gu
ad
alu
f
e
Re
n
ita ifer
p
u
Ca Aq
GraybQueen
urg
quif
Delaware
Basin
pia
nr
Delaware
Mountain
Group
oc
ks
Figure 3−Diagrammatic cross-section showing shelf-to-basin facies relationships within middle Permian Guadalupian strata in southeastern New Mexico. Backreef units of the Artesia Group change facies from carbonates in the near-backreef section to interbedded
evaporites and mudstone farther north, where they serve as confining beds for the artesian aquifer. Line of section shown in figure 1.
6
R oswell A rtesian B asin
margin of the Basin, and in the upper San Andres limestone near the Basin’s eastern boundary
(Figure 2). Water-producing intervals range in
thickness from a few inches up to 100 ft (33 m),
but are usually less than 50 ft (15 m) thick. Some
wells may penetrate as many as five separate producing zones. Wells producing from the artesian
aquifer are completed open-hole, with casing
installed only to the top of the aquifer. Small
differences in head are known to occur between
water-bearing zones, but hydrostatic pressures
tend to equalize throughout the well bore with
time (Welder, 1983). Average discharge from
wells completed in the San Andres Formation
is ~1,300 gpm (4,900 l/min), although highyielding wells have been pumped for as much as
3,300 gpm (12,500 l/min). Wells producing from
the Grayburg in the southern part of the Basin
may yield up to 1,000 gpm (3,800 l/min) (Motts
and Cushman, 1964). Hantush (1957) conducted
aquifer tests in the artesian aquifer and measured transmissivities that ranged from 7,500 to
196,000 ft2/day (700 – 18,200 m2/day).
Kelley (1971) noted that the uppermost unit
of the San Andres Formation, the Fourmile Draw
Member, changes facies from south to north,
grading laterally into evaporitic rocks. The San
Andres is ~1,150 ft (350 m) thick in the subsurface east of the Pecos, with about 100 ft (33 m)
of Glorieta sandstone at its base. However, as
much as 600 ft (180 m) of evaporites have been
removed from the upper part of the section by
subsurface dissolution in the northwestern Artesian Basin, leaving an extensive solution breccia
(Bachman, 1984, 1987). The San Andres aquifer
is just 260 – 460 ft (80-140 m) thick in the vicinity of the Pecos River.
Secondary porosity in the artesian aquifer is
developed in vuggy and cavernous limestones;
intraformational solution-collapse breccias, or
“rubble zones” (Motts and Cushman, 1964);
and solution-enlarged fractures and bedding
planes. Much of the porosity and permeability
has formed by subsurface dissolution of evaporites within the upper 200 – 300 ft (60-90 m)
of the San Andres Formation during late Permian time when the formation was exposed to
erosion, and then subsequently enhanced by
continued circulation of ground water (Welder,
1983). The upper San Andres is often described
as having a “worm-eaten” or “honeycombed”
appearance in outcrop and core due to leaching of evaporites (Fiedler and Nye, 1933; Motts
and Cushman, 1964). The karstic nature of the
artesian aquifer is well-illustrated by the breccia zones, particularly common in the upper San
Andres, where they consist of tilted and rotated
blocks of carbonate rock up to 2 ft (60 cm) in
diameter, imbedded in a silt matrix. Many of
the cavernous openings in the San Andres are
developed within these breccia zones (Motts and
Cushman, 1964), which are also intervals where
lost circulation frequently occurs during drilling
operations. Evidence of cavernous porosity in the
subsurface includes bit drops of as much as 16 ft
(5 m) during water well drilling (Havenor, 1968).
Recharge to the artesian aquifer, estimated to
be ~300,000 acre-ft/yr (370 million m3) (Barroll
and Shomaker, 2003), occurs by direct infiltration from precipitation, and by runoff from
intermittent losing streams that flow eastward
across the Pecos Slope, a broad area east of the
Sacramento Mountains where the San Andres
limestone is exposed in outcrop (Figures 1 and
2). Enhanced recharge occurs through sinkholes
and solution-enlarged fractures associated with
the Pecos Buckles. These structures, which include the Border, Six-Mile, and Y-O Buckles (Figures 2 and 4), are wrench fault zones of probable
Laramide age that extend SW-NE for several
tens of miles across the Pecos Slope (Motts and
Cushman, 1964; Havenor, 1968; Kelley, 1971),
the area referred to by Fiedler and Nye (1933)
as the Principal Recharge Area for the artesian
aquifer. Areas of highest permeability in the
recharge area occur along the major drainages,
along structural zones, and in the vicinity of
carbonate-evaporite facies boundaries (Motts
and Cushman, 1964). In pre-development times,
ground water flowed east and south, down
gradient from the recharge area, then upward
through leaky confining beds into the alluvial
aquifer, and ultimately to the Pecos River (Figure
2). Nowadays most of the down-gradient flow is
7
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
intercepted by irrigation wells in the Artesian
Basin. Discharge from artesian wells for irrigation and municipal water supply amounts to
approximately 350,000 acre-ft/yr (432 million
m3/yr), of which about one-third returns to the
aquifer as irrigation return flow (Barroll and
Shomaker, 2003).
Upward leakage from the artesian aquifer
through overlying confining beds is an important
source of recharge to the shallow aquifer. However, during extended periods of low rainfall the
vertical hydraulic gradient may be reversed. In
1950, the potentiometric surface in the artesian
aquifer was higher than the water table in the
shallow aquifer throughout the Artesian Basin. By 1975, when water levels in the artesian
aquifer were at historic lows, hydraulic head was
reported to be lower than shallow water levels in
some areas of the Basin (Welder, 1983).
Salinity of the Artesian Aquifer
Mineral content of ground water in the artesian aquifer rapidly increases eastward toward
the Pecos River. The principal area where saline
water occurs is in townships 10 and 11-S, Ranges 24 and 25-E, between Roswell and the Pecos.
Saline water, as defined by Hood (1963), is water
containing chloride concentrations greater than
500 parts per million (ppm). The Environmental Protection Agency recommends that water
intended for human consumption not exceed 250
ppm Cl-, but slightly brackish water may still be
used effectively for irrigation and watering livestock. In the freshwater-saltwater transition zone
east of Roswell, water with chloride concentrations greater than 1,000 ppm is commonly used
for those purposes.
Chloride concentrations range from 15 ppm
in the unconfined, western part of the aquifer to
as high as 7,000 ppm in a flowing artesian well
east of Roswell. Discharge from that well was
used as feedstock for a pilot desalination facility
in the mid-20th century. Chloride also increases
with depth in the aquifer. Hood (1963) reported
that in the vicinity of Artesia a difference of just
8
100 – 200 ft in well depth can mean a difference
of several hundred ppm in chloride concentration. Chloride content in the artesian aquifer is
lowest in the spring, and highest in the fall after
the irrigation season is over. The largest seasonal
fluctuations in mineral content occur within the
transition zone (Figure 2) between Roswell and
the Pecos River, where chloride concentrations
may display fluctuations of more than 1,500
ppm during a single irrigation cycle (Hood,
1963; Welder, 1983).
Salinity is highly variable in the sinkholes
and karst springs that line the Pecos River at the
discharge end of the artesian system. Chloride
concentrations measured in sinkhole lakes and
springs at Bitter Lakes National Wildlife Refuge
(Figure 1) range from ~1,100 to 3,500 ppm, with
total dissolved solids (TDS) content varying from
3,600 to 10,000 ppm. Samples collected from a
submerged spring discharging from the lakebed
in Lea Lake, the largest sinkhole lake at Bottomless Lakes State Park, had measured chloride
concentrations of 2,950 ppm and TDS content of
7,987 ppm (Land, 2005). Land (2003) reported
that water in the northernmost sink at Bottomless Lakes had a chloride content of 15,600 ppm
and TDS of 38,200 ppm, greater than the salinity of seawater.
For a number of years during the mid-20th
century, saltwater encroachment from the east
threatened the freshwater supply for the city
of Roswell. The freshwater-saltwater interface
migrates westward during periods of low rainfall
because of the decline in artesian pressure due to
increased irrigation pumping. Extended periods
of high rainfall cause an eastward retreat of the
interface, since irrigation demand on the aquifer
is not as great (Hood et al., 1960). Saltwater
encroachment within the artesian aquifer was
of particular concern during the long drought
of the 1950s, but since then the position of the
freshwater-saltwater interface appears to have
stabilized (Dennis Karnes, PVACD, personal
communication).
R oswell A rtesian B asin
Artesia Group Confining Beds
Bedrock along most of the Pecos River
between Roswell and Carlsbad consists of dolomites, evaporites and redbeds of the Artesia
Group (Figure 3), the backreef equivalent of the
Capitan Reef limestone that is exposed along
the southeast flank of the Guadalupe Mountains
to the south (King, 1948; Hayes, 1964; Kelley,
1971). In the Guadalupe Mountains near Carlsbad, the backreef facies consists predominantly
of carbonates with some sandstone, but to the
north the section becomes increasingly evaporitic. In the Roswell Artesian Basin the Artesia
Group is made up of interbedded mudstone and
gypsum at the surface, with thick, bedded salt
and anhydrite present in the subsurface. This
low-permeability facies of the Artesia Group
serves as a leaky upper confining unit for the
artesian aquifer. Hantush (1957) estimated that
net upward leakage through confining beds
amounted to 12,400 acre-ft/month (~15 million
m3/month). In the southern part of the Basin,
south of Lake Arthur (Figure 4b; Plate 1), the
carbonate facies of the Grayburg Formation,
the lowermost member of the Artesia Group, is
included as part of the artesian system.
Welder (1983) estimated that ~10% of the
ground water pumped in the Artesian Basin is
from moderately permeable zones in confining
beds of the Grayburg, Queen and Seven Rivers
Formations. Producing zones are developed in
solution-enlarged fractures and bedding planes
and in collapse breccias. These zones generally
occur in the upper one-quarter of the section designated as the confining unit, and do not appear
to be laterally extensive.
Thickness of the confining unit varies from
a feather edge in the northern and western parts
of the Basin to ~800 ft (250 m) in the center of
the Basin, and also thickens regionally downdip
to the east (Plate W-11). To the west, the confining beds are truncated by erosion. The different formations of the Artesia Group cannot be
distinguished in their evaporitic facies (Motts
and Cushman, 1964), but the Tansill Formation,
the uppermost unit of the Artesia Group, ap-
pears to be absent in the Artesian Basin due to
erosion (Figure 2). Local variations in thickness
of the confining beds are caused by dissolution
of gypsum in the upper part of the section
(Welder, 1983).
Shallow Aquifer
The unconfined shallow aquifer is contained
within valley fill alluvium deposited on the Pecos
River floodplain during late Tertiary and Holocene time, as the river migrated eastward due
to uplift of the Sacramento Mountains to the
west (Land, 2003). The western boundary of
the shallow aquifer is defined by the zero saturation line in the valley fill, which occurs roughly
12 miles (20 km) west of the Pecos River (Plate
W-12). However, the western boundary is somewhat ambiguous because isolated water-bearing
zones in the upper part of the Artesia Group
(Grayburg and Queen Formations) also produce
in that area. The shallow aquifer is hydraulically
connected to the Pecos River along most of its
eastern boundary. Valley fill alluvium may extend as much as 2 miles (3 km) east of the river,
but it is thin and of low permeability. The shallow aquifer grades into less permeable alluvium
north of Roswell and south of the Seven Rivers
Hills (Figure 4a) (Welder, 1983).
The lowermost unit of the valley fill in the
Artesian Basin is a quartzose conglomerate
cemented to varying degrees with calcium carbonate. This unit is usually no more than 250 ft
(76 m) thick and is the principal water-bearing
zone within the shallow aquifer. The quartzose
conglomerate is overlain by varying thicknesses
of silts and clays that were probably deposited
in ponds and lakes formed by solution-collapse
processes in the underlying Permian evaporites.
This layer is overlain by a carbonate gravel unit
that blankets all the other valley fill deposits,
forming a uniform slope from Permian outcrop
on the Pecos Slope to the Pecos River floodplain
(Lyford, 1973).
The valley fill attains a maximum thickness
of ~300 ft (90 m) in three closed depressions
9
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
formed in the top of the Artesia Group near
Roswell, Hagerman, and Artesia along the west
side of the Pecos River (Plate W-9). These depressions were probably formed by dissolution
and collapse in the evaporitic units of the Artesia
Group. Lyford (1973) observed that gypsum is
absent in the uppermost 50 ft (15 m) of Permian bedrock in those areas where large depressions are present. In 1973 a maximum saturated
thickness of ~250 ft (75 m) was reported for the
shallow aquifer in the closed depressions near
Hagerman and Artesia, and a saturated thickness
of ~300 ft (90 m) in the depression near Roswell
(Lyford, 1973).
Discontinuous water-producing zones found
in the upper 50 ft (15 m) of the Artesia Group
are probably hydraulically connected to the shallow aquifer. Most of the water recharging the
shallow aquifer is from the underlying artesian
system, either from irrigation return flow or
from upward leakage through confining beds of
the Artesia Group (Motts and Cushman, 1964).
Precipitation and surface runoff also contribute
to recharge. The direction of flow is sometimes
reversed during the irrigation season when high
levels of pumping reduce hydraulic head in the
artesian aquifer, at which times water may flow
downward from the shallow aquifer into the
artesian system (Welder, 1983).
Chloride content of the shallow aquifer fluctuates in less systematic ways than in the artesian
aquifer. In most areas of the Basin, increased precipitation will produce a measureable decrease
in salinity in the shallow aquifer. By contrast,
irrigation with brackish water derived from the
artesian aquifer causes an obvious, well-defined
upward trend in salinity of the shallow aquifer
(Hood, 1963).
10
R oswell A rtesian B asin
IV. M anagement of
water resources in
th e Artesian Basin
From the mid-1940s through early 1960s,
there were ~144,000 acres (58,300 ha) of farmland under irrigation in the Roswell Artesian
Basin, using water from both the artesian and
shallow aquifers (the above figure includes an insignificant amount of surface water rights). Prior
to 1966 ground water pumping was not metered,
and irrigation pumping limits had not yet been
set. Many wells were allowed to flow continuously, and it is estimated that pumping rates during this period were as high as 5 – 6 acre-ft/acre/
yr (15,234 – 18,280 m3/ha/yr) (Dennis Karnes,
PVACD, personal communication). Water rights
in the Roswell Basin were adjuticated in 1966,
at which time metering of water wells began.
Irrigated acreage was reduced to ~130,000 acres
(52,600 ha) and water use was limited to 3.5
acre-ft/acre/yr (10,664 m3/ha/yr). During the
period from 1958 - 1985, in an effort to mitigate
the basin-wide decline in water levels, PVACD
plugged 1,518 wells. The Conservancy District
also purchased almost 7,000 acres (2,800 ha) of
irrigated farmland and permanently retired that
land from agricultural activity (Shomaker, 2003).
In 1994 - 95 the New Mexico Interstate Stream
Commission (ISC) purchased and retired an additional 5,800 acres (2,350 ha) of farmland in
the Artesian Basin. In 2004 a consensus plan was
developed for water use on the lower Pecos River
that includes a program of purchase by the ISC
of 11,000 acres (4,450 ha) of water rights (both
shallow and artesian) in the Artesian Basin,
thereby reducing total irrigated farmland in the
Basin to ~106,000 acres (43,000 ha).
V. M et h ods
Potentiometric surface maps were constructed based on water level data collected in January and February, 2005 by the USGS, NM-OSE,
PVACD, and NMBGMR. During winter months
very little irrigation occurs, so water levels are
at their highest in the Artesian Basin and are less
likely to be influenced by local pumping events.
Water levels were measured using standard steel
tape or electric sounding tape. A few deep wells
were measured using a sonar sounding device.
Additional maps were prepared showing changes
in hydraulic head from 1975 to 2005 and from
2004 to 2005. 1975 and 2004 water level data
were derived from USGS and OSE historical records, and were also measured during the winter
months when irrigation was minimal, consistent
with the 2005 data set.
11
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
VI. results
Artesian Aquifer
Configuration of hydraulic head in the artesian aquifer (Figure 4b; Plate 1) indicates that
the general direction of ground water flow is to
the east and southeast. One of the most distinctive features of this map is a broad area east of
the 3,560 ft contour encompassing ~2/3 of the
Basin where the hydraulic gradient is very low
(< 10 ft/mile, or 1.8 m/km). West of this contour
the mapped area enters the eastern foothills of
the Sacramento Mountains, where the principal aquifers are the relatively low permeability
Glorieta sandstone and fractured carbonates in
the Yeso Formation (Welder, 1983). The steepness of the hydraulic gradient along the western
margin of the Artesian Basin requires a change
in contour interval from 10 ft (3 m) to 100 ft (30
m) west of the 3,600 ft contour.The hydraulic
gradient flattens abruptly a short distance east
of the Border Buckle, where the San Andres
limestone becomes the principal water-bearing
zone (Figure 2). The low hydraulic gradient in
this part of the Artesian Basin reflects the much
higher permeability and transmissivity of the San
Andres limestone in contrast to the Glorieta and
Yeso farther west. The same phenomenon has
been observed by previous workers in the Basin
(e.g., Motts and Cushman, 1964; Welder, 1983).
Another conspicuous feature of the potentiometric surface is an area trending NE-SW in the
southern part of the Basin, west of the village of
Lake Arthur, where the hydraulic gradient is very
steep (~50 ft/mile, or 5.6 m/km), a phenomenon
also noted by Welder (1983), who attributed
the closely-spaced contours to a lateral decrease
in permeability within the aquifer. This area
of steep hydraulic gradient occurs immediately
northwest of the KM Fault. The KM Fault lies
12
parallel to the Pecos Buckles and may be related
to those structures. The fault apparently occurs entirely in the subsurface, although Kelley
(1971) observed that the subsurface trace of the
fault coincides with a pronounced southwest
bend of the Pecos River, and with the northeasttrending Long Arroyo east of Lake Arthur. Like
the Pecos Buckles, the KM Fault is thought to
combine right-lateral motion with normal vertical displacement, and latest movement on the
fault may be of Laramide age (Havenor, 1968;
Kelley, 1971). The KM Fault is not well-defined
on structural contour maps of the top of the San
Andres Formation (Plate W-8), although Kelley
(1971) mapped a displacement of as much as
200 ft (60 m) down to the southeast on the top
of the lowermost Rio Bonito member of the San
Andres. Kinney et al. (1968) report that the best
resolution of the structure is on Mississippianage rocks. The KM Fault clearly influences
ground water flow in the southern Artesian
Basin, probably by juxtaposing less permeable
rocks of the Grayburg Formation to the southeast against more highly transmissive rocks to
the northwest. The fault thus acts as a partial
barrier to down-gradient flow, and effectively
separates the southeastern part of the artesian
aquifer system from the main part of the aquifer
to the northwest. Hydraulic head is significantly
elevated on the northwest side of the fault because of this impediment to down-gradient flow.
Many strongly-flowing artesian wells occur within this area of steep hydraulic gradient northwest
of the KM Fault, flowing to the surface during
winter months. In contrast, wells in most other
parts of the Basin have not shown such strong
artesian flow for many years.
Two cones of depression occur in the southern part of the Artesian Basin, southeast of the
R oswell A rtesian B asin
Sou
t
O
hB
Cre errend
ek
o
R20E
Be
rr
en
do
N
S
Cr prin
eek g
g
pr i n
R25E
ile Draw
Thirteenm
B
R23E
R25E
ek
Cre
Dexter
Nat. Fish
Hatchery
Zubi Draw
R29E
R28E
R27E
R26E
Dexter
R24E
R26E
Bottomless
Lake
State
Park
r
ve
Ri
os
ile
3725000
Roswell
c
Pe
6M
ek
R24E
8 Kilometers
Bitter
Lake
National
Wildlife
Refuge
R24E
R22E
4
C H A V E S
Cr
e
al
e
0
SS
T13S
1:650,000
4
8 Miles
0
Salt Creek
Wilderness
R23E
R22E
R21E R21.5E
Rocky Arroyo
uc
kl
k
Can
Hager man
R21E
Ri
oH
on
do
Ma
ch o
L
T10S
T11S
id
dl
e
R28E R29E
R27E
R26E
3700000
E
M
R25E
Long Ar royo
de
rB
uc
kl
T09S
del
Salt Cre
e
P
yo
e
T08S
T12S
33°15'N
rro
Bo
r
L I N C O L N
33°30'N
le A
roy
o
570000
R24E
R23E
Ar
Mi
dd
R20E
R22E
R21E
T07S
S
R20E
545000
3675000
520000
Hagerman
e
uc
kl
B
d Cr
eek
O
T16S
Eag
le C
T17S
Artesia
reek
R26E
R27E
R28E
R29E
W.S. Huey
Waterfowl
Area
C
Hope
Rio Peñ
asc
o
E
T18S
Pecos River West
Canal
32°45'N
Cottonwood Creek
R24E
R25E
R23E
Arthur
3650000
33°N
S
R21E
O
R20E
Walnut Lake
Creek
3625000
Croo
ke
Squ
aw
Cre
T15S
ek
R19E
Rio Felix
Y-
T14S
s
P
North S
even Riv
er
E D D Y
KM
H
rs
ve
Ri
OTERO CO.
R19E
105°W
R23E
104°45'W
n
ve
Se R24E
104°30'W
s
ill
Brantley Reservoir
Brantley Lake
State Park
R25E
R26E
104°15'W
3600000
Fa
ul
t
Old Lake McMillan
R27E
R28E
104°W
Figure 4a−Physiographic features of the lower Pecos Valley.
13
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
0
4000
0
0
40
0
40 reek
C
M
6-
le
ck
0
40
35
30
00
35 4
0
lt
Sa
4000
Bu
ile
Pecos R
iver
45
0
400
Bo
Bu rde
ck r
le
4500
50
35
39
00
570000
36
00
38
00
60
35
5000
520000
CO.
3510
35 20
0
Bu
ck
le
3500
Y-
O
fig. 12a
3700000
LINCOLN
33°30'N
0
410
Figure 4b−Configuration of
hydraulic head in the artesian
aquifer, January-February, 2005.
Contour interval = 10 ft below
3,560 ft; and 100 ft above the
3,600 ft contour. Heavy dashed
line shows eastern boundary of
Artesian Basin. Filled circles are
wells completed in the artesian
aquifer. Large green circles are
observation wells. Blue triangles
are flowing artesian wells.
Locations of monitoring wells
from figures 11 and 12-a are
indicated.
Roswell
3500
3500
0
50
0
80
34
4000
0
34 6
Dexter
35
0
42
00
41
00
Hagerman
4000
390
0
0
340
Lake Arthur
33°N
450
0
33 80
ix
Fel
Rio
0
350
33 60
33 40
33 30
Ri
oP
eñ
asc
o
00
35
30
34
32 40
33 2
0
33
50
33
40
32 9
0
33
00
32
70
104°45'W
104°30'W
32 30
3240
32 50
0
40
0
ul
Fa
KM
4000
10 Kilometers
32 60
32 80
33 1
0
33 3
0
33
80
70
33
t
90
33
10 Miles
10
34
40
34
33
60
60
34
34
50
34
80
60
32
70
34
34
20
20
35
10
35
34
00
30
35
0
500
14
40
35
4500
0
105°W
5
50
35
34
90
CO.
60
35
EDDY
37
00
CHAVES
CO.
32°45'N
0
55
5
80
32
3500
1:610,000
330
0
Hope
00
36
0
33 0
4500
0
33 20
Artesia
00
38
0
3650000
20
34
400
0
0
500
0
34 4
0
fig. 11
Brantley
Reservoir
3600000
33°15'N
3510
Rio Hondo
R oswell A rtesian B asin
KM Fault near Artesia. These features, although
legitimate depressions in the potentiometric surface, also reflect in part the heterogeneous nature
of the artesian aquifer. The Grayburg Formation is the principal water-bearing zone in the
southern part of the Basin, where transmissivities
are generally lower than to the north. However,
some wells in this area also produce water from
the upper part of the San Andres limestone. For
example, a well centered in the small cone of
depression south of Artesia is 840 ft (256 m)
deep and is completed in the Grayburg (Figure
4b; Plate 1).Water levels are 40 ft (12 m) higher
in the Artesia-A monitoring well, less than a mile
to the southwest. The Artesia-A well was drilled
to a depth of 1,007 ft (307 m) and completed in
the San Andres limestone portion of the artesian
aquifer.
The influence of the Pecos Buckles on ground
water movement within the artesian aquifer is
less obvious, but this may be due to the small
number of wells measured in the western part
of the Basin. The influence of the YO Buckle is
shown by a trough in the potentiometric surface
southeast of the Buckle near the center of the
Basin (Figure 4b; Plate 1), a phenomenon also
observed by previous workers (e.g., Kinney et al.,
1968). There is no obvious change in hydraulic
gradient associated with the Border and Six-Mile
Buckles, although the potentiometric surface in
the vicinity of those structures is not well-constrained because of the limited number of data
points in the northwest part of the map.
Broad mounds and noses on the potentiometric surface appear to roughly coincide with
east-flowing tributaries of the Pecos River, such
as Cottonwood Creek and Walnut Creek, immediately south and north respectively of the EddyChaves county line. Although these features are
not well-defined due to limited well control in
the western part of the Basin, their association
with surface drainage systems on the Pecos Slope
probably reflects areas of enhanced permeability
along the course of these losing streams, which
serve as linear recharge zones to the artesian
aquifer (Duffy et al., 1978).
Artesian Aquifer: Chloride Content
Chloride data were only available for the
northern part of the Artesian Basin, from the
Roswell area south to the vicinity of Dexter
(Figure 5; Plate 2). The most distinctive feature of
the chlorides map is a broad lobe of saline water
projecting toward the city of Roswell, with chloride concentrations ranging from 500 to >7,000
ppm, located in townships 10 and 11-S, ranges
24 and 25-E. This lobe of brackish water has also
been reported by previous workers (e.g., Hood et
al., 1960; Hood, 1963; Havenor, 1968; Welder,
1983). Hood (1963) used the 500 ppm chloride
contour to define the position of the freshwatersaltwater interface in the artesian aquifer. During
the mid-20th century, the interface was migrating westward at a rate of about a tenth of a mile
per year (Hood et al., 1960), and threatened the
municipal water supply for the city of Roswell.
However, the postion of the interface appears to
have stabilized in recent years. Data collected for
this study show that in most areas the present
position of the 500 ppm chloride contour lies a
few tenths of a mile east of its position in 1978.
Shallow Aquifer
The shallow aquifer is of more limited extent
than the artesian aquifer, extending to ~12 miles
(20 km) west of the Pecos River (Figure 6; Plate
3). The aquifer is thin to non-existent and not
much utilized in the northern part of the Basin
northwest of Roswell. In general, ground water flows east through the shallow aquifer and
discharges into the Pecos River. An exception to
this rule is a distinctive ridge in the water table
trending SW-NE near the Chaves-Eddy County
line, west of Lake Arthur
The most conspicuous feature of the shallow
aquifer is a broad cone of depression west of the
town of Hagerman, over 12 miles (20 km) across
on the N-S axis and over 120 ft (36 m) deep.
Unlike most other communities in the Artesian
Basin, wells in the Hagerman area are completed
primarily in the shallow aquifer. The Hagerman
15
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
ek
Salt Creek
Wilderness
1880
Pecos R
35 00
Bitter
Lake
National
Wildlife
Refuge
ek
1400
311
771
200
S
10 out h
Ber
0
r e n d o C r ee k
84
0
100
232
N
215
Sp
572
644
424
747
700
624
224
rin
g
66
111
Cr
eek
321
Roswell
761
591
496
920
725
457
115
543
438
1120
180
52
1240
1340
755
ond
o
505
250
Cr
ee
k
200
rin
328
111
149
758
1000
400
96 142
186
113
139
142
282
158
S
Sp
439
574
646
29
305
300
nal
19
Bottomless
Lake
State
Park
n Ca
Hagerm a
40
0
200
2680
1860
282
g
Rio
H
360
100
7440
2420
3500
223
1440
537
531
2000
1380
1040
990
1780
3700000
Cr
e
479
3680000
en
do
kle
rr
Bu
c
4000
33°30'N
Be
YO
id
dl
e
300
400
M
4
100 500 00
0
500
1000
iver
Salt Cre
6M
ile
Bu
ck
le
40 00
3720000
550000
Figure 5−Chloride concentration
in the artesian aquifer, March,
2005. Filled circles are wells
measured for chlorides. Contour
interval variable, in parts per
million. Dashed line shows 500
ppm chloride concentration in
the artesian aquifer in 1978,
from Welder (1983). Solid red
contour line indicates the present
position of the 500 ppm chloride
concentration.
33°15'N
1040
447
869
Dexter
33
0
1
2
3
4
35
00
1:250,000
5 Miles
0 1 2 3 4 5 Kilometers
104°30'W
16
Dexter
Nat. Fish
Hatchery
R oswell A rtesian B asin
cone of depression is a well-known phenomenon
in the Artesian Basin, mentioned frequently in
NM OSE and USGS reports (e.g., Garn, 1988).
A less well-defined cone of depression is located west of the city of Artesia, extending for
about 10 miles (16 km) from south to north and
roughly 40 ft (12 m) deep. A ridge in the shallow
water table west of Lake Arthur separates the
Hagerman and Artesia cones of depression.
The Artesia cone of depression can be extended farther southeast and south into a broad
depression in the shallow water table between
highway 285 and the Pecos River. This depression is 20 to 40 ft (6 – 12 m) deep and extends
to the southern terminus of the shallow aquifer
near the Seven Rivers Hills.
Variations in Hydraulic Head: Artesian Aquifer
The map showing change in hydraulic head
in the artesian aquifer in the 30 year period
since Welder’s (1983) data were collected is not
well-constrained because of the smaller number
of wells for which measurements are available in
both 1975 and 2005. Nevertheless, the data set
clearly indicates a rise in water levels in almost
all areas of the Roswell Artesian Basin, ranging
from 8 to 34 ft (2.4 – 10.4 m) (Figure 7; Plate 4).
The greatest change in water levels since 1975
has occurred in a broad area defined by the +20
ft contour, extending from north to south across
the Pecos Slope over the entire extent of the
Artesian Basin. This is the area originally designated by Fiedler and Nye (1933) as the Principal
Recharge Area for the artesian aquifer.
One area where water levels have risen over
30 ft (9 m) lies near the village of Hope in the
southwestern part of the Basin. This area coincides with the middle reaches of the Rio Penasco. A PVACD monitoring well located on the
north bank of the Rio Penasco, a few miles west
of Hope, has displayed very rapid responses to
storms and flash flood events in the river (Duffy
et al., 1978). Such a rapid response to flood
events probably reflects rapid recharge through
zones of enhanced permeability associated with
karstic openings in the San Andres limestone
where it is exposed in the bed of the river.
Only two wells on either side of the Border
Buckle on the extreme western edge of the Basin
show long-term declines in water levels. These
wells are located in that part of the Basin where
the Glorieta sandstone is the main aquifer.
This basin-wide rise in water levels in the
artesian aquifer stands in remarkable contrast to
the results shown in Welder’s (1983) report. The
Welder report documents historic water level
changes over the course of development of the
artesian aquifer, including maps showing changes
in head for the periods 1926-1975 (Plate W-15)
and 1950-1975. Although data were limited for
the earlier time periods, all of Welder’s maps and
hydrographs show consistent, steady declines in
hydraulic head ranging from 20 – 100 ft (6 – 30
m) in all areas of the Artesian Basin. The data set
used for this investigation is the first to indicate a
significant reversal in that historic trend.
A comparison of water levels in the artesian
aquifer between January, 2004 and January,
2005 (Figure 8; Plate 5) also shows a significant
rise in head, particularly in the southern part
of the Basin, where water levels rose by greater
than 15 ft (5 m) in some areas. This was a period
of exceptionally high rainfall for the lower Pecos
valley. Total rainfall in the Roswell area in 2004
was 16 inches (42 cm), compared to average
annual precipitation of 13 inches (32 cm) in this
part of the state.
Variations in Hydraulic Head: Shallow Aquifer
During the period from 1975 to 2005 water
levels in the shallow aquifer declined by more
than 15 ft (5 m) in two sectors of the Artesian
Basin, and rose an equal amount in other areas
(Figure 9; Plate 6). A significant decline in water
levels is indicated west of Hagerman in Townships 13 and 14-S, Range 25-E. In that area the
Hagerman cone of depression, already well-defined on Welder’s (1983) map of the 1975 water
table (Plate W-16), has increased in depth from
75 ft (23 m) to 120 ft (36 m). In the southern
17
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
570000
M
6-
40 00
le
ck
kle
ek
Bu
c
YO
35
00
3520
35 00
3700000
80
34
3540
4000
33°30'N
3540
Salt C
re
ile
Bu
00
40
Figure 6−Configuration of the
water table in the shallow aquifer,
January-February, 2005. Contour
interval = 20 ft (6 m). Filled
circles are wells completed in the
shallow aquifer.
Pecos R
iver
520000
60
34
Roswell
3500
3440
Rio Hondo
40 00
33°15'N
3420
33 8
0
35
00
0
35 0
3400
Dexter
Hagerman
33
00
ix
Fel
Rio
33 2
0
KM
35 00
33
60
33°N
40 0
0
40
35 35 20
Lake
Arthur
0
34 2
0
35 0
00
35 3480
40
33
CHAVES
CO.
EDDY
CO.
ult
Fa
3650000
0
33 6
33 40
32
80
34
34 40 60
20
33
Hope
00
33
Artesia
32°45'N
40
00
0
33 2
Rio Peñasc
o
32 60
32
80
35 00
5
104°45'W
18
10 Kilometers
3240
35 00
104°30'W
Brantley
Reservoir
104°15'W
3600000
40 00
0
0 0
340 338
80
10 Miles
330
0
32
5
33
60
0
45 0
0
35 0
0
3500
20
34
1:550,000
R oswell A rtesian B asin
part of the Basin the Artesia cone of depression,
which was not present in 1975, is now ~40 ft (12
m) deep.
In the vicinity of Hagerman the shallow
aquifer is the primary source of ground water,
unlike most other parts of the Artesian Basin,
and the increase in depth of the Hagerman cone
of depression reflects continued exploitation of
the shallow aquifer in the 30 year period since
Welder’s (1983) measurements were made. The
area of declining water levels west and south of
Artesia lies near the southern extent of the shallow aquifer, where saturated thicknesses were
less than 100 ft thick in 1975 (Plate W-12), and
the aquifer appears to be have been more sensitive to 30 years of extensive pumping.
In the Roswell area at the north end of the
Basin, the water table in the shallow aquifer rose
from 4 to 17 ft. This rise may in part reflect the
leaky nature of the confining beds, which are
less than 100 ft (30 m) thick in that part of the
Basin (Plate W-11), permitting more efficient
recharge from the underlying artesian aquifer.
The rise in the water table near Roswell is thus
a response to rising water levels in the artesian
aquifer since 1975.
In the Hagerman-Lake Arthur area there has
been a distinct rise in water levels along a SWNE trend closely coinciding with the 2005 ridge
in the water table (Figure 6; Plate 3). This area
of rising shallow water levels is in a part of the
Basin where PVACD purchased and retired irrigated farmland in the mid-20th century.
During the period from January, 2004 to
January, 2005 water levels in the shallow aquifer
rose significantly in almost all areas of the Basin,
probably in response to above average precipitation in 2004 (Figure 10; Plate 7). The most
significant rise in water levels occurred along the
SW-NE trending ridge in the water table between
Lake Arthur and Hagerman.
Artesian Aquifer: Seasonal Cycles
Variations in hydraulic head in the artesian
aquifer occur on multiple time scales. The spiky
character of the hydrograph for the Greenfield
observation well (Figure 11a) reflects the very
pronounced seasonal irrigation cycles typical of
this intensively farmed area near the center of
the Artesian Basin (Figure 4b; Plate 1). Water
levels are at their highest during winter months,
when irrigation is minimal, and in recent years
have shown declines of greater than 180 ft (55
m) during the summer, when irrigation is at a
maximum. Longer-term variations in the historic
record are demonstrated by the scale of these
fluctuations in hydraulic head. At the beginning
of the period of record, in 1940, the winter-summer cycle varied by just 30 ft (9 m). As agricultural activity has expanded in the Artesian Basin
through the latter half of the 20th century, the
amplitude of the seasonal cycles has increased
approximately fivefold.
The Greenfield well is located in a part of the
Basin where many artesian wells still flow to the
surface during winter months. As the Greenfield
hydrograph (Figure 11a) indicates, water levels
in this well were above ground level as recently
as 2001. Under those circumstances, a pressure
reading is measured and the apparent water level
is calculated from an equation relating water
pressure to hydraulic head [D = 2.31P – k; D is
apparent head in feet above ground level, shown
as a negative value; P is pressure in pounds per
square inch; k is height of pressure valve above
ground level].
The drawdown from pumping in the artesian
aquifer is laterally extensive, reflecting the very
high transmissivity of the artesian system – as
much as 196,000 ft2/day (18,200 m2/day) in
the northern part of the Basin (Hantush,1957).
Thus, for a given amount of pumping the cones
of depression are relatively shallow but very
broad. A five-year detail of the Greenfield hydrograph (Figure 11b) illustrates the extreme sensitivity of the artesian aquifer to specific pumping
events. A secondary peak in water levels occurs
every year in mid-May to mid-June, superim19
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
45
00
570000
00
40
19.8
10
15
19.4
15.7
B
Bu orde
-5 ckle r
le
ck
Bu
Roswell
21.5
16.1
13.1
13.5
-8.8
0
19.2
Rio Hondo
20
8.5
5
45 00
40 00
50
00
Dexter
15
13.4
12.7
23.6
35
00
10
22.7
15
26
Hagerman
ix
Fel
Rio
10.7
25
33°N
7.9
Fa
u
KM
40 0
0
lt
3500
45 0
0
24.3
Lake
Arthur
21.4
24.8
0
35 0
20
3650000
LINCOLN
35 00
16.8
YO
19.6
3500
CO.
10
4000
33°30'N
15
5
0
ek
45 00
33°15'N
M
6-
21
15.9
23.1
0
50 0
le
ck
00
40
Salt C
re
3.4
-1.1
ile
20.1
40 00
Bu
3700000
45
00
Pecos R
iver
5000
20
40
00
4000
4500
00
40
Figure 7−Change in hydraulic
head in the artesian aquifer,
1975-2005. Contour interval
= 5 ft (1.5 m). Filled circles are
wells completed in the artesian
aquifer. Large green circles are
observation wells.
33°45'N
520000
23.8
9.5
Artesia
20
OTERO
EDDY
35 0
0
15
10
10 Kilometers
0
50 0
105°W
5
10 Miles
104°45'W
40 00
17.3
11.2
3500
104°30'W
10
Brantley
Reservoir
3600000
00
55
0
45 00
5
10
0
Rio Peñasc
o
3500
1:610,000
14.3
CO.
CO.
45 00
Hope
40
00
30
CHAVES
32°45'N
20
34.2
00
45
25
R oswell A rtesian B asin
520000
570000
4000
5000
00
40
2.4
-0.6
-0.5
-1.2
-1
40 00
le
ck
M
6-
-0.1
Salt C
reek-0.6
0
ile
Bu
Pecos R
iver
0
45
00
00
40
Figure 8−Change in hydraulic
head in the artesian aquifer,
2004-2005. Contour interval = 5
ft (1.5 m). Filled circles are wells
completed in the artesian aquifer.
Large green circles are observation wells. Blue triangles are
flowing artesian wells.
40
00
-0.9
Roswell
-2.7
1.4
le
-0.3
-0.2
CO.
0
Bu
YO
0
1.3
2.1
-0.1
50
00
Rio Hondo
5.3
45 00
40 00
0.1
Dexter
-1.2
11.9
9.2
-1.4
-0.2
Hagerman
-1.1
-1
ix
Rio Fel
17.7
KM ult
Fa
16.8
3500
45 0
0
40 0
0
33°N
15.5
2.4
Lake
Arthur
7.8
15
-1.2
3650000
0
50 0
0
35 0
0.1
10
LINCOLN
5.3
35
00
B
Bu orde
ck r
le
0.3
3.6
3500
0
0.3
3700000
0.6
35 00
-6
-5
33°15'N
ck
5
4000
33°30'N
-2.5
-0.4
-6.8
-5
0
45 00
-0.4
-0.5
0
35 0
10
0.5
5
14.3
CO.
CO.
8.4
Hope
-4.5
40
00
10.5
10.1
Rio Peñasc
o
EDDY
45 00
12.3
7.1
7.4
9.3
0
CHAVES
00
45
32°45'N
-3.2
-5
0
Artesia
12
9.7
35 0
0
3500
40 00
5
0
60 0
0
105°W
5
10 Miles
0
0
50 0
32°30'N
00
55
0
10 Kilometers
104°45'W
13
10
5
3500
-5.5
Brantley
Reservoir
-5
40 00
1:610,000
3600000
45 00
104°30'W
104°15'W
21
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
3500
5
10
4
3700000
570000
Figure 9−Change in water
levels in the shallow aquifer,
1975-2005. Contour interval = 5
ft (1.5 m). Filled circles are wells
completed in the shallow aquifer.
9
Roswell
6M
15
ile
Bu
3500
ck
le
6
17
10
Rio Hondo
5
7
4000
-3
0
-5
-13
35
00
le
YO
Bu
ck
0
350
Dexter
-10
-15
-17
-3
x
Rio Feli
Hagerman
3500
10
-15
33°N
400
0
EDDY
10
5
-8
18
-1
7
-1
Lake Arthur
8
0
-5
-5
-16
K M u lt
Fa
0
350
CO.
CO.
CHAVES
15
6
3650000
33°15'N
5
-13
-1
0
-15
Artesia
40
00
Hope
32°45'N
-14
Rio Peñasc
o
-4
-32
-3
-25 0
-6
3500
-20
3500
10 Miles
1
0
5
-10
350
0
1:450,000
0
-5
-15
-13
4000
0
104°45'W
22
5
10 Kilometers
3500
104°30'W
Brantley
Reservoir
104°15'W
R oswell A rtesian B asin
570000
0
0
0
1
Roswell
3700000
0
3500
Figure 10−Change in water
levels in the shallow aquifer,
2004-2005. Contour interval = 5
ft (1.5 m). Filled circles are wells
completed in the shallow aquifer.
6
6
0
ck
le
Bu
3500
5
ile
1
6M
2
1
0
Rio Hondo
0
4
-5
0
1
Dexter
le
0
350
0
0
35 0
00
4000
YO
-5
Bu
ck
2
3
-5
3500
0
400
0
0
33°N
1
5
-1
-5
0
K M u lt
Fa
1
Lake Arthur
0
23
6
-17
-1 -3
2
1
15
10
4
5
0
350
EDDY
3
3
3
CO.
CO.
10
0
Hagerman
-1
-5
CHAVES
4
4
x
Rio Feli
3650000
33°15'N
-9
0
1
0
1
2
4
0
4
Artesia
8
4
9
-1
Rio Peñasc
o
0
104°45'W
350
0
4
-8
3500
104°30'W
21
10
10 Kilometers
-5
0
10 Miles
0
5
15
5
3500
0
4000
3500
8
5
-5
5
3
2
4
0
4
2
0
0
7
0
0
1:450,000
4
5
32°45'N
1
3
0
40
00
2
0
-1
Hope
Brantley
Reservoir
104°15'W
23
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
A
Greenfield Observation Well
-50
3550
land surface
0
50
3450
100
3400
Depth to water (ft)
Ground water Elevation (ft)
3500
150
3350
200
1940
B
1950
1960
1970
1980
1990
2000
-50
3550
land surface
0
50
3450
100
3400
Depth to water (ft)
Ground water Elevation (ft)
3500
150
3350
200
2000
2001
2002
2003
2004
2005
Figure 11a−Hydrograph of the Greenfield monitoring well (location shown in Figure 4b and Plate 1), showing very pronounced annual
cycles and longer-term variations in hydraulic head in the artesian aquifer. At various times in the past 40 years of record the Greenfield
well has flowed to the surface. Water levels shown above land surface were calculated from water pressure measurements. Deviation
from the seasonal cycle in the mid-1980s is caused by an incomplete data set for the years 1985 and 1986.
Figure 11b−Detail from figure 11-A hydrograph, showing seasonal irrigation cycles over a five year period, 2000 - 2005.
24
R oswell A rtesian B asin
A
Berrendo Observation Well
0
3580
Welder
data
collected
10
20
3560
30
40
3540
50
60
3520
Depth to water (ft)
Ground water Elevation (ft)
metering of
irrigation wells
begins
70
80
3500
1940
1960
1970
1980
1990
2000
150
35
30
140
25
130
20
15
120
10
110
Annual Precipitation (inches)
Irrigated acreage (thousands of acres)
B
1950
5
100
1940
0
1950
1960
1970
1980
1990
2000
Figure 12a−Hydrograph of the Berrendo observation well (location shown in Figure 4b and Plate 1). Note difference in vertical scale
compared to figure 11.
Figure 12b−Irrigated agriculture and precipitation in the Artesian Basin. Blue solid line shows annual precipitation in the Artesian Basin
region, measured at the Roswell airport. Heavy dashed line indicates mean annual rainfall. Red solid line is the 10 year running mean of
precipitation. Bar graph shows the amount of farmland under irrigation from both the artesian and shallow aquifers from 1940 to 1996.
25
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
posed upon the general mid-year decline in
hydraulic head. This secondary peak reflects the
first cutting of alfalfa, when pumping temporarily stops as the alfalfa crop is harvested.
Artesian Aquifer: Long-term Variations in Head
Water levels in the Artesian Basin have been
falling since development of the artesian aquifer
began early in the 20th century (Kinney et al.,
1968; Welder, 1983). The rate of decline in hydraulic head increased significantly after World
War II, and reached its lowest point in most
areas of the Basin in the mid-1970s, at which
time this decades-long trend began to reverse.
The hydrograph for the Berrendo observation
well (Figure 12a) shows these long-term water
level variations. Higher-frequency irrigation
cycles are more subdued than those shown on
the Greenfield hydrograph (Figure 11) because
the Berrendo well is located in a housing development within the city of Roswell, several miles
from intense agricultural activity farther to the
south. However, longer-term variations in head
are more apparent, showing that water levels in
the artesian aquifer reached an historic low in
the mid-1970s, when data for the Welder report
were being collected.
From the mid-1970s until around the turn of
the century water levels in the artesian aquifer
steadily increased. Since the year 2000 hydraulic head has begun to decline, roughly coincident with a period of extended drought in New
Mexico (Figure 12b). However, water levels measured for this investigation in January-February,
2005 show an increase over head measurements
in winter, 2004 (Figure 8; Plate 5), a year during
which the Artesian Basin region enjoyed exceptionally high rainfall.
26
R oswell A rtesian B asin
VII. D iscussion
Precipitation cycles and agricultural activity
appear to be the two main factors driving longerterm variations in head in the artesian aquifer.
Average annual precipitation in the Artesian
Basin is ~13 inches/yr (32 cm/yr). However,
annual rainfall in southeastern New Mexico displays very pronounced deviations from the mean
(Figure 12b). Precipitation in 1941 exceeded
33 inches (83 cm), but for most of the period
from 1945 through the late 1960s rainfall was
well below average. This long period of drought
coincided with a long decline in hydraulic head
in the artesian aquifer. Then, beginning in the
late 1970s and continuing through the mid-90s,
the lower Pecos Valley experienced several years
of above average rainfall, a period during which
water levels in the artesian aquifer began to rise.
The expansion of irrigated agriculture
during and after World War II also appears to
have influenced longer-term water level cycles
in the Artesian Basin. Between 1940 and 1950
the amount of irrigated farmland in the Basin
increased by >30% (Figure 12b). During the
period from 1943 to 1968 the area also experienced an extended period of low rainfall. This
unfortunate combination of long-term drought
with a period of rapidly expanding irrigation accounts for the long decline in water levels in the
artesian aquifer through the mid-20th century.
Systematic water conservation measures
began in the late 1950s, when the Pecos Valley
Artesian Conservancy District initiated a program of purchase and retirement of irrigated
farmland in parts of the Artesian Basin. Similar
programs have subsequently been initiated by the
New Mexico Interstate Stream Commission, and
have been included in the 2004 Consensus Plan
for management of water resources on the lower
Pecos River. Adjudication of water rights in the
mid-1960s reduced the amount of legally irrigable land in the Basin and was key to gaining
control of ground water pumping. Metering of
irrigation wells began in 1966, which promoted
conservation and allowed enforcement of pumping limitations. At this time water use for irrigation was restricted to 3.5 acre-ft/acre/yr (10,600
m3/ha/yr). It appears that these conservation
measures, combined with high levels of precipitation during the latter part of the 20th century,
have contributed toward mitigating the historic
decline in hydraulic head in the Artesian Basin.
The same conservation and climatic factors have
also helped to stabilize the position of the freshwater-saltwater interface in the artesian aquifer
(Figure 5; Plate 2).
The increase in head in the artesian aquifer
during the 12 month period from 2004 to 2005
is concentrated along the eastern margin of the
Artesian Basin (Figure 8; Plate 5), in marked
contrast to the 30 year rise in water levels in the
Principal Recharge Area on the Pecos Slope to
the west (Figure 7; Plate 4). It is unlikely that
this short-term rise in water levels in the eastern
sector of the Basin is a direct result of increased
rainfall and infiltration. Rather, the increase in
head is probably an indirect response to high
rainfall, which caused a reduction in irrigation
demand in 2004 and a resulting decrease in
pumping from the artesian aquifer.
Previous workers (e.g., Havenor, 1996,
1998) have used hydrochemical data to argue
that the hydrologic framework of the Artesian
Basin is more heterogeneous and compartmentalized than commonly thought due to regional
structural discontinuities. Such discontinuities
clearly exist, as indicated by, for example, the
increase in hydraulic gradient in the artesian
aquifer west of the KM Fault (Figure 4b; Plate
27
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
1). However, hydraulically continuous behavior
within a large sedimentary basin can sometimes
be masked on a local scale by the flow-sensitive
properties of ground water, such as temperature
and chemical composition (Toth, 1995). The
broad area affected by the 12 month rise in water levels reflects the very high regional transmissivity and hydraulic continuity of the artesian
system, which very effectively permits diffusion
of pressure head throughout the eastern part of
the Basin.
28
R oswell A rtesian B asin
VIII. C onclusions
The Roswell Artesian Basin provides a
world-class example of a rechargeable artesian
aquifer. The very high transmissivity of the
aquifer results from the presence of vuggy and
cavernous porosity and large solution conduits
within the karstic San Andres limestone, caused
in part by dissolution of primary gypsum within
the formation. By the mid-1970s, almost a century of intensive pumping had resulted in very
substantial declines in hydraulic head throughout
the Artesian Basin. However, the current study
suggests that water conservation measures first
introduced in the 1950s, combined with high
levels of rainfall during the latter part of the 20th
century, have helped to reverse the long-term
decline in hydraulic head in the artesian aquifer.
29
NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES
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Bachman, G. O., 1984, Regional geology of Ochoan evaporites, northern part of Delaware Basin: New Mexico
Bureau of Mines and Mineral Resources, Socorro, NM,
Circular 184, 22 p.
Havenor, K. C., 1996, The hydrogeologic framework of the
Roswell groundwater basin, Chaves, Eddy, Lincoln, and
Otero Counties, New Mexico: Tucson, University of Arizona, Ph.D. dissertation, 274 p.
Bachman, G. O., 1987, Karst in evaporites in southeastern
New Mexico: Sandia National Laboratories, Contractor
Report SAND86-7078, 82 p.
Havenor, K. C., 1998, Hydrogeochemical investigation of
the major aquifers in the northern portion of the Roswell
Groundwater Basin, Chaves and Eddy Counties, New Mexico: GeoScience Technologies, unpublished report, 80 p.
Barroll, P. and Shomaker, J., 2003, Regional hydrology of
the Roswell Artesian Basin and the Capitan aquifer, in
Johnson, P., Land, L., Price, G. and Titus, F. (eds.), Water
Resources of the Lower Pecos Region, New Mexico: New
Mexico Bureau of Geology and Mineral Resources, Socorro, NM, 2003 New Mexico Decision Makers Guidebook, p. 23-27.
Duffy, C. J., Gelhar, L. W., and Gross, G. W., 1978, Recharge and groundwater conditions in the western region
of the Roswell Basin: New Mexico Water Resources
Research Institute, Las Cruces, NM, Report 100, 111 p.
Fiedler, A. G. and Nye, S. S., 1933, Geology and groundwater resources of the Roswell Basin, New Mexico: U.S.
Geological Survey Water-Supply Paper 639, 372 p.
Garn, H. S., 1988, Seasonal changes in ground-water levels
in the shallow aquifer near Hagerman and the Pecos
River, Chaves Co., New Mexico: U.S. Geological Survey
Open File Report 88-197, 19 p.
Gratton, P. J. F. and LeMay, W. J., 1969, San Andres oil east
of the Pecos, in Summers, W. K. and Kottlowski, F. E.
(eds.), The San Andres Limestone, a Reservoir for Oil and
Water in New Mexico: New Mexico Geological Society,
Socorro, NM, Special Publication No. 3, p. 37-43.
Hantush, M. S., 1957, Preliminary quantitative study of
the Roswell ground-water reservoir, New Mexico: New
Mexico Institute of Mining and Technology, State Bureau
of Mines and Mineral Resources Division, Socorro, NM,
118 p.
Havenor, K. C., 1968, Structure, stratigraphy, and hydrogeology of the northern Roswell Artesian Basin, Chaves
County, New Mexico: New Mexico Bureau of Mines and
Mineral Resources, Socorro, NM, Circular 93, 30 p.
30
Hayes, P. T., 1964, Geology of the Guadalupe Mountains,
New Mexico: U.S. Geological Survey Professional Paper
446, 69 p.
Hood, J. W., 1963, Saline ground water in the Roswell Basin,
Chaves and Eddy Counties, New Mexico, 1958-59: U.S
Geological Survey Water Supply Paper 1539-M, 46 p.
Hood, J. W., Mower, R. W., and Grogin, M. J., 1960, The
occurrence of saline ground water near Roswell, Chaves
County, New Mexico: New Mexico State Engineer Office
Technical Report 17, 72 p.
Kelley, V. C., 1971, Geology of the Pecos country, southeastern New Mexico: New Mexico Bureau of Mines and
Mineral Resources, Socorro, NM, Memoir 24, 78 p.
King, P. B., 1948, Geology of the southern Guadalupe Mountains, Texas: U.S. Geological Survey Professional Paper
215, 183 p.
Kinney, E. E., Nations, J. D., Oliver, B. J., Wagner, P. G., Siwula, T. A., and Renner, R. E., 1968, The Roswell Artesian
Basin: Roswell Geological Society, Roswell, NM, 32 p.
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New Mexico Bureau of Geology and Mineral Resources
A Division of New Mexico Institute of Mining and Technology
Socorro, NM 87801
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E-mail: lland@gis.nmt.edu