Prescott AMA Groundwater Flow Model Update Report
October 31, 2006
Daniel Timmons
Abe Springer
Northern Arizona University

Prepared for Arizona Department of Water Resources
Contract #: 2005-2592
Final Report

Executive Summary
In 1995, the Arizona Department of Water Resources developed a regional
groundwater flow model to quantify the impacts of various management programs on the
groundwater resources of the area. The Prescott AMA groundwater flow model has been
updated with new geologic and hydrogeologic data and the active model area has been
expanded from approximately 220 square miles to 250 square miles. The model has also
been calibrated to an expanded database of measured groundwater levels and discharge
targets from 1939 to 2004.
The results of the transient simulation indicate that the groundwater resources of
the Prescott AMA continue to be depleted on a regional basis. This has resulted in
decreased groundwater storage in the aquifers of the area. In addition, natural
groundwater discharge from the area has decreased with potential impacts on riparian
areas and downstream users.

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Acknowledgments
The authors would like to acknowledge the many individuals and organizations
that contributed to the successful completion of the model update. We would like to
thank the Arizona Department of Water Resources for allowing us the opportunity to
work on this project. In particular, we thank Frank Corkhill, Keith Nelson, Dale Mason
and Wesley Hipke of ADWR for contributing their time, effort and experience to the
project. Gerry Wildeman, Leslie Graser, Gordon Wahl, Bill Remick and Frank Putman
provided important input during the modeling and review processes. In addition, we
would like to express our appreciation to the Prescott AMA Groundwater User Advisory
Committee for providing the funding for the model update.
We acknowledge the Arizona Water Institute, the United States Geological
Survey, and the Yavapai County Water Advisory Council for their various contributions.
Finally, we would like to thank Carol Johnson at the City of Prescott, John Munderloh at
the Town of Prescott Valley, and Mark Holmes and Chris Bartels at the Town of Chino
Valley for their time and first-hand knowledge of the communities within the Prescott
AMA.

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Table of Contents
Executive Summary……………………………………………………………………….2
Acknowledgments………………………………… ……………………………………..3
Chapter 1: Introduction and Background…………………………………………………8
Introduction ………………………………..…………………………………….8
Goals and Objectives …..………………………..………………………………..8
Model Area ………………………………..……………………………………...8
Previous Investigations ………………………..……………….………………..10
Chapter 2: The Hydrogeologic System ……………………………….. ..………………10
Regional Setting ………………………………..………………………………..10
Geologic Structure ...……………………………..……………………………...10
Modifications to Geologic Structure …………………………………………….10
Hydrostratigraphic Units ………………………………………………………...11
Chapter 3: The Conceptual Model ……………………………………………………...13
The Aquifer System ……………………………………………………………..13
Hydrostratigraphic Units ………………………………………….……………..13
The Upper Alluvial Unit Aquifer ………………………….…………….13
The Lower Volcanic Unit Aquifer ………………………………………14
The Predevelopment Hydrologic System ……………………………………….14
Natural Groundwater Discharge ………………………………………...14
Groundwater Pumpage ………………………………………………….15
Groundwater Recharge ………………………………………………….15
The Developed Hydrologic System …………………………………………….15
Natural Groundwater Discharge …………………………...……………15
Groundwater Pumpage …………………………………….……………16
Groundwater Recharge ………………………………………………….17
Chapter 4: The Numerical Groundwater Model ………………………….…………….18
Stress Period Setup ...……………………………………………………………18
Code Selection …….…………………………………………………………….18
Model Assumptions and Limitations ……………………………………………18
Model Inputs/Boundary Conditions …………………………………..…………19
Model Grid ………………………………..…………………………..…………19
Model Layers and Aquifer Conditions ……………………………….…………20
Boundary Conditions …………………………………………………..………..21
MODFLOW-2000 Input Packages …………………………………….………..21
Water Level Data ………………………………………………………….…….22
Groundwater Pumpage Data ……………………………………………….……22
Groundwater Discharge Data ………………………………………………..…..22
Aquifer Parameter Data ………………………………………………………....23
Chapter 5: Model Calibration …………………………………………………………...24
Results of the Steady-State Simulation ………………………………………….25
Steady-State Water Budget ……………………………………………………...25
Steady -State Calibration Error Analysis ………………………………………..25
Discussion of Steady-State Simulation Results ...……………………………….25
Results of the Transient Simulation ……………………………………………..26

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Transient Water Budget ………………………………………………………..26
Transient Calibration Error Analysis …………………………………………..27
Discussion of Transient Simulation Results …………………………………..27
Chapter 6: Conclusions ………………………………………..………………………28
Additional Data Needs ………………………………………………………….28
Water Level Data ………………………………………………………..28
Flow Data ……………………………………………….………………28
Aquifer Test Data ………………………………………………………..28
Recharge Data ……………………………………………...……………29
References ………………………………..……………………………………………...30
Appendix I: Tables ……….…………………………………………………………33-43
Appendix II: Figures …………………………………………………………………44-59
Appendix III: Hydrographs …………………………………………………………60 -71
Appendix IV: Additional Figures ………………………………………………...…72-74
Appendix V: Steady-State Calibration Targets …………………………………….75 -77
List of Tables
1. Simulated and Conceptual Steady State Water Budgets for the
Updated Prescott AMA Groundwater Flow Model ……………………………..34
2. Simulated Pumpage Applied to the Updated Prescott AMA
Groundwater Flow Model (1999-2004) …………………………………………35
3. Non-AMA Pumpage Applied in the Mint Wash Area to the
Updated Prescott AMA Groundwater Flow Model ...…………………………...36
4. Simulated Flood Recharge Applied to the Updated Prescott
AMA Groundwater Flow Model ………………………………………………..37
5. Simulated Artificial Recharge Applied to the Updated Prescott
AMA Groundwater Flow Model ………………………………………………..38
6. Combined Statistical Summary of Steady State Error Analysis
for the UAU (Layer 1) and LVU (Layer 2) ……………………………………..39
6a. Statistical Summary of Steady State Error Analysis for the
UAU (Layer 1) …………………………………………………………………..39
6b. Statistical Summary of Steady State Error Analysis for the
LVU (Layer 2) …………………………………………………………………..39
7. Simulated and Conceptual Transient Water Budgets
(1940 and 2004) …………………………………………………………………40
8. Combined Statistical Summary of Transient Error Analysis
for the UAU (Layer 1) and the LVU (Layer 2) …………………………………41
8a. Statistical Summary of Transient Error Analysis for the UAU……………………...41
8b. Statistical Summary of Transient Error Analysis for the LVU ……………………..41
9. Simulated Transient Water Budget for the Updated Prescott
AMA Groundwater Flow Model (1939-1998) ………………………………….42
10. Simulated Transient Water Budgets for the Updated
Prescott AMA Groundwater Flow Model (1999-2004) …………………………43

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List of Figures
1. Location of the Prescott Active Management Area,
Yavapai County, Arizona………………………………………………………...45
2. Active model area of the updated Prescott AMA groundwater
flow model ………………………………………………………………………46
3. Thickness of the Upper Alluvial Unit in the updated Prescott
AMA groundwater flow model …………………………………………………47
4. Thickness of the Lower Volcanic Unit in the updated Prescott
AMA groundwater flow model …………………………………………………48
5. Measured and simulated heads in the Upper Alluvial Unit from
the steady-state simulation of the updated Prescott AMA
groundwater flow model (1939) ………………………………………………...49
6. Difference between measured and simulated heads from the
Upper Alluvial Unit from the steady-state simulation of the
updated Prescott AMA groundwater flow model (1939) ……………………….50
7. Measured and simulated heads in the Lower Volcanic Unit from
the steady-state simulation of the updated Prescott AMA
groundwater flow model (1939) ………………………………………………...51
8. Difference between measured and simulated heads in the
Lower Volcanic Unit from the steady-state simulation of the
updated Prescott AMA groundwater flow model (1939) ……………………….52
9. Location of head targets used for calibration of the transient
simulation of the updated Prescott AMA groundwater flow model …………….53
10. Measured and simulated heads in the Upper Alluvial Unit from
the transient simulation of the updated Prescott AMA
groundwater flow model (2005) ………………………………………………...54
11. Measured and simulated heads in the Lower Volcanic Unit from
the transient simulation of the updated Prescott AMA
groundwater flow model (2005) ………………………………………………...55
12. Hydraulic conductivity values in the Upper Alluvial Unit of the
updated Prescott AMA groundwater flow model ……………………………….56
13. Hydraulic conductivity values in the Lower Volcanic Unit of the
updated Prescott AMA groundwater flow model ……………………………….57
14. Specific yield values in the Upper Alluvial Unit of the updated
Prescott AMA groundwater flow model ………………………………………...58
15. Specific storage values in the Lower Volcanic Unit of the updated
Prescott AMA groundwater flow model ………………………………………...59
List of Hydrographs
1.
2.
3.
4.
5.

Prescott AMA:
Prescott AMA:
Prescott AMA:
Prescott AMA:
Prescott AMA:

Northern Little Chino Valley Area ………………………………..61
Northern Little Chino Valley Area ………………………………..61
Northern Little Chino Valley Area ………………………………..62
Central Little Chino Valley Area ………………………………….62
Central Little Chino Valley Area ………………………………….63

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6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.

Prescott AMA: Central Little Chino Valley Area ………………………………….63
Prescott AMA: Central Little Chino Valley Area ………………………………….64
Prescott AMA: Southern Little Chino Valley Area ……………………………......64
Prescott AMA: Southern Little Chino Valley Area ……………………………......65
Prescott AMA: Northeast Little Chino Valley Area……………………………......65
Prescott AMA: Lonesome Valley Area ……………………………………………66
Prescott AMA: Southern Lonesome Valley Area …………………………….……66
Mint Wash Area ..……………………………..…………………………….….......67
Prescott AMA: Table Mountain Area ……………………………………….……..67
Prescott AMA: Prescott Valley Santa Fe Wellfield ……………………….……….68
Prescott AMA: Upper Lynx Creek Area …………………………………………..68
Prescott AMA: Upper Lynx Creek Area …………………………………………..69
Prescott AMA: Upper Agua Fria Sub-basin Adjacent to Lynx Creek……………..69
Prescott AMA: Groundwater Discharge at Del Rio Springs……………………….70
Prescott AMA: Groundwater Discharge at Agua Fria River…………………….…71

List of Additional Figures
1. USGS 09502900: Del Rio Springs Near Chino Valley ……………………………..73
2. USGS 09503000: Granite Creek Near Prescott, AZ ………………………………...73
3. USGS 09502960: Granite Creek at Prescott, AZ ……………………………………74
4. USGS 09503700: Verde River Near Paulden, AZ …………………………………..74

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Chapter 1: Introduction and Background
Introduction
The Prescott Active Management Area (AMA) in Central Arizona is one of five
AMAs in the State of Arizona. Established by the Groundwater Management Act of
1980, the Active Management Areas are areas where groundwater management is needed
to address the impacts of large-scale groundwater withdrawals on groundwater resources.
The stated management goal of the Prescott AMA is to achieve “safe-yield” by the year
2025 (Corkhill and Mason, 1995). Safe-yield is defined as the condition where long-term
groundwater withdrawals do not exceed recharge to the aquifer system of the AMA.
Several management programs have been established by the Arizona Department of
Water Resources to achieve the safe-yield goal including “1) groundwater quality
assessment and management, 2) agricultural conservation, 3) municipal conservation, 4)
industrial conservation, 5) augmentation and reuse” (Corkhill and Mason, 1995).
In 1993, the Arizona Department of Water Resources began developing a
groundwater flow model for the Prescott Active Management Area in order to assess
potential impacts of these various management programs. This model was seen as the
first step in a modeling effort that was to be continually revisited and improved as time
and new data warranted. The model was subsequently updated and used to simulate
groundwater conditions from 1940 to 1999, as well as to predict future groundwater
conditions for the years 1999-2025 (Nelson, 2002).
In 2005, the Arizona Department of Water Resources contracted with Northern
Arizona University to further update the model based on newly available data. This
report documents the model update.
Goals and Objectives
The primary goal of the original Prescott AMA groundwater model was defined
by ADWR as the development of an “analytical tool capable of quantifying the effects of
various management and conservation programs on the groundwater supplies within the
study area” (Corkhill and Mason,1995). The goal of the model update was thus to refine
this analytical tool in order to more accurately quantify the effects of management and
conservation programs. Specific objectives of the study included 1) Extend the active
model area to include the western part of the AMA (referred to as ‘the Mint Wash area’),
2) Redefine the geologic structure based on newly available data; 3) Reevaluate model
parameter values based on newly available data and 4) Extend the transient simulation to
include the years 1999-2004.
Model Area
The Prescott AMA covers 485 square miles in central Yavapai County, Arizona
(Fig. 1). The AMA consists of two ground-water sub-basins, the Little Chino sub-basin
(LIC) and the Upper Agua Fria sub-basin (UAF). The modeled area consists of
approximately 250 square miles of the groundwater basin, but does not cover the
mountainous areas of the AMA. Figure 2 indicates the active model area.

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The towns of Chino Valley, Prescott Valley and Dewey-Humboldt are included
within the model area. While the City of Prescott is located outside the model area in the
bedrock foothills of the Bradshaw Mountains, the City is dependent upon groundwater
pumped from the aquifers of the Little Chino sub-basin. In addition, numerous domestic
wells provide the primary water supply for several thousand households within the AMA.
Previous Investigations
Several geologic mapping studies of Little Chino Valley have been undertaken
since the 1960’s, the most informative being the United States Geological Survey report
provided by Krieger (1965). Krieger (1965) described the stratigraphy and structure of
the Prescott and Paulden USGS Togographic Quadrangles. Schwalen (1967) described a
groundwater study by the Agricultural Experiment Station at the University of Arizona of
the artesian areas of the Little Chino Valley. This report provides descriptions of the
geology, hydrology, streamflow and groundwater development of the Little Chino subbasin from 1940-1965. Matlock, Davis and Roth (1973) updated this report including
groundwater development from 1966-1972.
Wilson’s report (1988) described the hydrogeology and water resources of the
Upper Agua Fria area, while Navarro’s (2002) modeling study characterized the
hydrogeology of the Mint Wash and Williamson Valley areas. A recently published
USGS report by Wirt, Dewitt and Langenheim (2004) provides a geologic framework,
hydrogeologic characterization and geophysical interpretation of the Little Chino subbasin. Another recent USGS report characterizes the hydrogeology of the entire Upper
and Middle Verde watersheds, including the Little Chino sub-basin (Blasch et. al. 2005).
The Arizona Department of Water Resources has also published a collection of
reports describing the hydrologic conditions of the area. In addition to the groundwater
modeling studies by Corkhill and Mason (1995) and Nelson (2002), annual Hydrologic
Monitoring Reports have been published since 2001 (ADWR, 2002, 2003, 2004).

9

Chapter 2: The Hydrogeologic System
Regional Setting
The Prescott AMA is located in the Transition Zone physiographic province of
central Arizona (Fig. 1). Land surface elevations range from about 4,450 to 4,900 feet in
the basin areas to over 7,000 feet in the Black Hills and Bradshaw Mountains. A
topographic boundary creates a surface-water divide that closely corresponds to the
groundwater divide between the Little Chino sub-basin and the Upper Agua Fria subbasin. Runoff and groundwater flow in the Little Chino sub-basin move northward to the
Verde River, while runoff and groundwater in the Upper Agua Fria sub-basin flow south
to the Agua Fria River.
Geologic Structure
The geologic structure of the model area is defined by a structural trough that
trends northwest for a distance of about 25 miles from the southern part of the Upper
Agua Fria sub-basin to the northern part of the Little Chino sub-basin near Del Rio
Springs. The trough appears to have developed in late Tertiary time (10 Ma to the
present) due to crustal extension in central Arizona and in the Basin and Range province
to the south (Wirt et. al., 2004). The basin is bounded to the east by the Coyote fault at
the edge of the Black Hills. Vertical offset on the Coyote Fault is estimated by Krieger
(1965) to range from 0 feet at Humboldt to about 1,200 feet near the Indian Hills.
The northern end of Little Chino Valley is likely bound by a largely concealed
northwest trending normal fault. Displacement across the fault is uncertain, as there are
no wells deep enough to penetrate both sediment fill and lati-andesite, but may exceed
180 m near Del Rio Springs (Wirt et. al, 2004).
It has previously been suggested that the western side of northern Chino Valley
may also be bound by a continuous fault (Ostenaa et. al., 1993). Recent work, however,
suggests that this may not be the case. While Big Wash follows a pre-Hickey fault north
of Table Mountain, it is unclear whether this fault extends to the northern end of Little
Chino Valley (Wirt et. al 2004). Instead, alluvial fans extend away from lati-andesite
flows which thicken into Little Chino Valley. While a buried normal fault may be
concealed beneath the fans, there is no drillhole data to prove the continuity of such a
fault.
Modifications to Geologic Structure
In 2001, ADWR drilled several monitoring wells in locations throughout the
AMA where the geologic conditions were uncertain. Monitoring Well #1 (55-587403)
was drilled in central Little Chino Valley east of Granite Creek near Black Hill (B(15-0108DAA). Based on previous geologic interpretations of basin depth provided by Krieger
(1965) and Oppenheimer and Sumner (1980), it was expected that the drilling would
encounter alluvial materials to a depth of around 935 feet, under which several hundred
feet of volcanic deposits were believed to exist. However, actual geologic conditions
were far different from those expected. Less than 100 feet of alluvial materials were

10

found, while interbedded volcanics flows and cinders were encountered between 55 feet
and 695 feet below land surface. Below these volcanic deposits, sands, gravel and
conglomerate were found to a depth of around 810 feet before the basement unit was
encountered. (Corkhill, 2001)
In addition to this new monitoring well, the USGS report Hydrogeology of the
Upper and Middle Verde River Watersheds, Central Arizona includes a cross-section that
runs through the Black Hill area. On this cross-section, Black Hill is depicted as an
intrusive flow of Tertiary age Hickey basalt cutting through the overlying sediments.
Based on these two new pieces of information, Black Hill was conceptualized as an
intrusive volcanic center overlying a granitic pluton.
ADWR Monitor Well #2 (55-587404) was drilled in northeast Lonesome Valley
(B(16-01)23ACA). The drilling of this well revealed thinner alluvial deposits than
expected based on previous geologic interpretations of the area. In addition, the Upper
Alluvial Unit was unsaturated at this location. Thus, the conceptualization of the extent
of the saturated Upper Alluvial Unit was modified in northeast Lonesome Valley.
Based on the drilling log from ADWR Monitor Well #3 (55-588619), an alluvial
depression was conceptualized to exist in the newly active area of Layer 1 to the
northwest of the City of Prescott (B(15-02)22AAB). While previous geophysical studies
(Cunion, 1985) have suggested this area was the center of an intrusive pluton, others have
also interpreted the gravity anomaly in the area as a deep pocket of alluvium
(Oppenheimer and Sumner, 1980). The driller’s log of Monitor Well #3 indicates
approximately 1,200 feet of sand, gravel, clay and mudstone overlying granitic bedrock.
Thus, the gravity anomaly observed in the area is likely the result of the substantially
deeper bedrock existing in the area.
Several well logs from the Prescott Valley North Wellfield were reviewed in
order to determine whether structural changes were warranted in this area. Based on this
review, it was found that the actual thickness of the Upper Alluvial Unit was well
approximated by the original model. While well logs indicate that the Lower Volcanic
Unit is thicker than 200 feet in localized areas in and around the Prescott Valley North
Wellfield, there is currently insufficient data regarding the areal extent of these thicker
deposits to warrant structural changes to the model in this area.
Hydrostratigraphic Units
While a wide variety of rock types are found in the model area, these rock types
have been grouped into three hydro-stratigraphic units with similar hydrologic properties
(Corkhill and Mason, 1995). From oldest to youngest, these units are the Basement Unit,
the Lower Volcanic Unit (LVU), and the Upper Alluvial Unit (UAU). The Basement
Unit consists of a variety of igneous and metamorphic rocks that are generally dense,
nonporous and nearly impermeable (Wilson, 1988). The Basement Unit forms the floor
and sides of the groundwater basins and is not considered an aquifer for the purposes of
this modeling study. Magnetic and gravity data suggest that the basement unit underlying
much of Little Chino Valley may be Prescott Granodiorite (Wirt et. al. 2004). In several
areas, this Prescott Granodiorite appears to exist as a plutonic unit, cutting through
overlying rock units.

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The Lower Volcanic Unit is generally composed of a sequence of Tertiary age
basaltic and andesitic lava flows interbedded with layers of pyroclastic and alluvial
material (Corkhill and Mason, 1995). In the area northeast of Granite Mountain near
Mint Wash, fractured and decomposed granite is included within the Lower Volcanic
Unit. This Lower Volcanic Unit is modeled in the Little Chino sub-basin and the
northwest portion of the Upper Agua Fria sub-basin in the area of the Prescott Valley
Santa Fe well field. The Lower Volcanic Unit aquifer exists in confined artesian
conditions in northern Little Chino Valley and in the Santa Fe well field area.
The Upper Alluvial Unit consists of a wide variety of sedimentary, volcanic and
younger alluvial rocks. The saturated Upper Alluvial Unit forms an unconfined aquifer
which is distributed throughout the basins of the Prescott AMA.

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Chapter 3: The Conceptual Model
The Aquifer System
The groundwater flow system in the Prescott AMA consists of two distinct subbasins: the Little Chino sub-basin and the Upper Agua Fria sub-basin. The Little Chino
sub-basin consists of an Upper Alluvial Unit aquifer and a Lower Volcanic Unit aquifer;
however, only the Upper Alluvial Unit aquifer is present in the Upper Agua Fria subbasin. The groundwater divide between the two sub-basins generally corresponds with
the surface-water divide and loosely follows US 89A from the Indian Hills to Glassford
Hill. Surface runoff and groundwater flow in the Little Chino sub-basin move
northward towards the Verde River, while runoff and groundwater in the Upper Agua
Fria sub-basin flow south to the Agua Fria River.
Hydrostratigraphic Units
For the purposes of the numerical model, the complex geology of the Prescott
AMA has been simplified into two hydrostratigraphic units: an Upper Alluvial Unit
aquifer and a Lower Volcanic Unit aquifer.
The Upper Alluvial Unit Aquifer
The Upper Alluvial Unit aquifer consists primarily of the saturated alluvial and
volcanic deposits that fill the structural trough that trends northwest across the Little
Chino and Upper Agua Fria sub-basins. In addition, the Upper Alluvial Unit aquifer
extends to the west between Granite Mountain and Table Mountain terminating at Mint
Wash. The deep structural pocket identified by Oppenheimer and Sumner (1980) in
Township 15N 2W is filled with alluvial deposits of the Upper Alluvial Unit aquifer.
The saturated Upper Alluvial Unit forms the main unconfined aquifer throughout
the model area. Natural recharge to the Upper Alluvial Aquifer occurs primarily through
infiltration along the mountain fronts of the model area and in ephemeral stream
channels. Infiltration from canals and excess irrigation water contributes recharge to the
Upper Alluvial Unit aquifer in agricultural areas. The City of Prescott and the Town of
Prescott Valley have also developed artificial recharge facilities that allow for the
infiltration of treated effluent and surface water supplies into the Upper Alluvial Unit
Aquifer.
Natural discharge occurs at three locations in the model area. Groundwater is
discharged from the Little Chino sub-basin as spring flow at Del Rio Springs and
subsurface flow out of the model area to the northwest of Del Rio Springs. It is believed
this subsurface flow heads northeast through faulted Paleozoic rocks and lati-andesite
towards spring-fed Stillman Lake and Lower Granite Spring (Wirt et. al., 2004).
In the Upper Agua Fria sub-basin, discharge occurs as baseflow in the perennial
reach of the Upper Agua Fria River near Humboldt.
Evapotranspiration from small riparian areas at Del Rio Springs and along the
Agua Fria River near Humboldt also accounts for comparatively minor groundwater
discharge from the Upper Alluvial Unit in the model area. For modeling purposes,

13

however, groundwater consumption by evapotranspiration was undifferentiated from the
groundwater discharge that also occurs in these locations.
Discharge from the Upper Alluvial Unit also comes from groundwater pumpage.
Numerous small-capacity domestic wells tap into the Upper Alluvial Unit aquifer
throughout the model area, while large capacity agricultural and municipal wells in the
Upper Agua Fria sub-basin also pump from the Upper Alluvial Unit aquifer.
The Lower Volcanic Unit Aquifer
In much of the Little Chino sub-basin, a thick unit of vesicular volcanic flows
interbedded with cinders, tuff and alluvial materials underlies the Upper Alluvial Unit
aquifer. These materials are the same as the “artestian” aquifer described by Schwalen
(1967) and are designated the Lower Volcanic Unit aquifer. Northeast of Granite
Mountain near Mint Wash, fractured and decomposed granite underlie the conglomerate
of the Upper Alluvial Unit aquifer and are included within the Lower Volcanic Unit
aquifer.
Natural discharge from the Lower Volcanic Unit occurs as spring flow at Del Rio
Springs and as subsurface flow out of the model domain to the northwest of the springs.
This subsurface flow heads northeast towards Stillman Lake and Lower Granite Springs,
eventually emerging as baseflow in the Verde River (Wirt et. al, 2004).
Groundwater pumpage has been the major source of discharge from the Lower
Volcanic Unit aquifer since the 1940’s. The Lower Volcanic Unit aquifer of the Little
Chino sub-basin has provided most of the irrigation and municipal water that has been
pumped within the model area.
The Predevelopment Hydrologic System
Prior to the initiation of large-scale agricultural and municipal groundwater
pumping from the Little Chino sub-basin, steady-state conditions are assumed to have
characterized the groundwater flow system of the model area (Corkhill and Mason, 1995,
Schwalen, 1967). In the steady-state, a long-term equilibrium between groundwater
inflow and groundwater outflow was established and groundwater levels remained
largely constant with time. It should be noted that this steady-state condition was not a
natural equilibrium, but included discharge from groundwater pumpage and recharge
from excess irrigation water and canal seepage. However, it is believed that the
simulated groundwater pumpage rate represents a limited stress on the system, which had
not experienced a significant loss of storage prior to 1940 (Nelson, 2002). Substantial
groundwater development did not begin In the Upper Agua Fria sub-basin until the
1960’s; therefore, near-equilibrium conditions in the Upper Agua Fria sub-basin are
believed to have persisted for several decades longer than in the Little Chino sub-basin.
Natural Groundwater Discharge
In the Little Chino sub-basin, natural groundwater discharge occurred at two
places during the steady-state period, as surface flow at Del Rio Springs and as
subsurface flow out of the model area to the northwest of Del Rio Springs. Conceptual

14

estimates for the groundwater discharge flow rate at Del Rio Springs range from 2,700
acre-feet/year to 3,800 acre-feet/year (Foster, 2001) (Table 1). These estimates are based
on the maximum and minimum annual surface-water measurements reported from Del
Rio Springs for the period 1940-1945 (Schwalen, 1967) plus an estimated 400 acrefeet/year of evapotranspiration and unreported diversions upstream of the gauge (Foster
2001). Conceptual estimates for subsurface flow are even more uncertain, ranging from
2,000 acre-feet/year (Corkhill and Mason 1995) to 5,600 acre-feet/year (SRP, 2000).
In the Upper Agua Fria sub-basin, natural groundwater discharge occurred as
perennial baseflow in the Agua Fria River near Humboldt. Conceptual estimates for
Agua Fria River baseflow range from 1,500 acre-feet/year to 2,500 acre-feet/year (Table
1).
Groundwater Pumpage
Groundwater pumpage in the steady-state simulation totaled approximately 1,500
acre-feet, exclusively in the Little Chino sub-basin. This rate is consistent with the
pumpage used by Nelson (2002) and is based on approximately 50% of estimated
agricultural demand for 1937-1939. Pumpage was distributed vertically between the
Lower Volcanic Unit and the Upper Alluvial Unit at a ratio of 3:1.
Groundwater Recharge
Recharge in the steady-state simulation also followed the conceptual model of
Nelson (2002). While recharge was spatially redistributed to allow for recharge along
Mint Wash, the total mountain front recharge rate of 4,000 acre-feet/simulation (7,000
acre-feet/year) was kept the same. Incidental agricultural recharge was applied at a rate
of 50% of both groundwater pumpage and surface water deliveries in agricultural areas
for a total of 2,200 acre-feet (Nelson 2002). Canal recharge from the Chino Valley
Irrigation Ditch (CVID) was estimated at about 950 acre-feet (Nelson 2002).
The Developed Hydrologic System
Minimal changes from Nelson (2002) were made to stresses applied to the model
for the period 1939-1999. Changes to groundwater pumpage, mountain-front recharge
and flood recharge were made due to the expanded model area. From 1999-2005, new
stress values were included based on previously used methodology.
Natural Groundwater Discharge
Limited measurements exist of naturally occurring groundwater discharge as
spring flow at Del Rio Springs and baseflow in the Agua Fria River. Annual maximum
and minimum discharge at Del Rio Springs from 1940 to 1945 were reported by
Schwalen (1967). Matlock et. al (1973) published average discharge rates for the period
1965 to 1972, while average rates for the period 1984 to 1989 were published by Corkhill
and Mason (1995). Since 1997, a USGS gauge has been operational at Del Rio Springs
(USGS 09502900) and provides a continuous data stream for groundwater discharge at

15

the springs (Appendix IV). Conceptual estimates for groundwater discharge in 1940
range from 2,700 to 3,800 acre-feet per year, including approximately 400 acre-feet/year
for evapotranspiration and unreported upstream diversions (Foster 2001). The USGS
gauge at Del Rio Springs measured approximately 950 acre-feet of flow for 2004
(Appendix IV). Conceptual estimates of groundwater discharge at Del Rio Springs for
2004 range from 950 acre-feet/year to 1,350 acre-feet/year. Thus, conceptual estimates
of the decrease in groundwater discharge at Del Rio Springs range between 1,750 acrefeet per year and 2,850 acre-feet/year over the time period from 1940 to 2004.
For 1940, estimates of subsurface flow from the model area to the north range
from 2,000 acre-feet/year (Corkhill and Mason, 1995) to 5,600 acre-feet/year (SRP,
2000). In 2004, the USGS estimated that the Little Chino sub-basin contributes
approximately 14% of the baseflow of the Verde River at Stewart Ranch (Wirt et. al.,
2004). For 2004, this equates to approximately 1,900 to 2,000 acre-feet/year. This
contribution to the Verde River is conceptualized as coming from the subsurface flow
leaving the model area to the northwest of Del Rio Springs.
Groundwater discharge as baseflow in the Upper Agua Fria River was estimated
as 1,500 to 2,500 acre-feet/year for 1940 (Corkhill and Mason, 1995). While a USGS
gauge has been operational at Humboldt since 2001 (USGS 09512450), the gauge
captures a great deal of surface runoff that makes baseflow separation techniques difficult
(Appendix IV). For 2003, however, ADWR estimated groundwater discharge as
baseflow in the Agua Fria River as approximately 1,300 acre-feet/year (ADWR, 2004).
Thus, conceptual estimates of the decrease in natural groundwater discharge from the
Upper Agua Fria sub-basin range between 200 acre-feet per year and 1,200 acre-feet per
year over the period of 1940 to 2003 (Tables 1 and 7).
Groundwater Pumpage
Groundwater pumpage for agricultural purposes from 1939-1983 was applied to
the Little Chino sub-basin based on estimated irrigated acreage, areal distribution of
historic irrigation rights, estimated consumptive crop use, an estimated irrigation
efficiency of 50% and a vertical pumpage distribution of 3:1 LVU to UAU (Nelson,
2002). After 1983, groundwater withdrawal rates for agricultural, municipal and
industrial uses were based on annual reports provided by groundwater users in the
Prescott AMA (Table 2). Domestic pumpage rates were applied based on estimates
provided in ADWR Hydrologic Monitoring Reports. Agricultural and turf-related
pumpage were applied only during irrigation stress periods from April through October,
while other pumpage was applied uniformly throughout the year (Nelson, 2002).
Approximately four square miles of the added Mint Wash area are outside of the
Prescott AMA boundaries. In this area, groundwater pumpage rates are not reported to
ADWR. Groundwater pumpage for the American Ranch development was based on the
estimated water demand prepared by Clear Creek Associates (2001). Pumpage for the
American Ranch development was applied at a rate of 150 acre-feet/year for 2002, and
126.4 acre-feet/year for 2003 and 2004. In addition, approximately 350 domestic wells
are located in the active model area, but outside the AMA. Pumpage from these wells
was estimated based on an average pumpage rate of 0.33 acre-feet per year per well
(ADWR, 2002). Based on this formula, non-AMA domestic pumpage within the active

16

model area was estimated at 115 acre-feet/year for 2004. As development in this area has
largely occurred since 1980, no non-AMA domestic pumpage was applied for the years
1939-1979. Domestic well pumpage rates were linearly interpolated between 1980 and
2004 (Table 3).
Groundwater Recharge
Incidental agricultural recharge was estimated at 50% of agricultural groundwater
pumpage and 50% of surface water deliveries (Nelson 2002). Seepage along the CVID
canal was estimated at approximately 40% of surface water deliveries, for a total canal
seepage recharge over the transient simulation from 1939 – 2005 of about 62,000 acrefeet (Nelson 2002). Mountain-front recharge was applied at a uniform rate of 5,750 acrefeet per year.
Flood recharge was applied based on the wetted area approach used by Nelson
(2002) (Table 4). In addition to flood recharge along Granite Creek and the Lynx
Creek/Agua Fria River drainage, flood recharge along Mint Wash was assigned to 12
cells based on an estimated channel width of 30 feet/cell, channel length of 2640 feet/cell,
and an estimated recharge rate of 0.25 feet/day.
Artificial recharge of effluent and surface water was applied at the City of
Prescott’s Airport Recharge Facility and along the channel of the Agua Fria River near
Prescott Valley’s Wastewater Treatment Facility based on annual reports provided to
ADWR and information provided by the Town of Prescott Valley (Table 5).

17

Chapter 4: The Numerical Groundwater Model
The Prescott AMA groundwater model simulates the steady-state groundwater
conditions that characterized the groundwater flow system circa 1939, as well as the
transient-state conditions of the period of large-scale groundwater development from
1940 to 2005.
Stress Period Setup
The steady-state model simulates the 210 day agricultural pumping season from
April through October 1939. The 210 day simulation consists of one stress period and
one time step.
The transient model simulates the period from November 1939 through March
2005. Each year is divided into two stress periods, a 210 day irrigation season from April
through October and a 155 day non-irrigation season from November through March.
Each stress period is further divided into 20 time steps with a time step multiplier of 1.2.
The increase in time steps within the stress periods of the updated model enabled the
seasonal variation in groundwater conditions to be more accurately simulated by the
model than by previous versions of the Prescott AMA model.
Code Selection
The original model developed by Corkhill and Mason (1995) utilized the Modular
Three-Dimensional Finite-Difference Groundwater Flow Model (MODFLOW)
developed by the USGS (McDonald and Harbaugh 1988). For the purposes of this study,
MODFLOW-2000 was selected as the model code (Harbaugh et al. 2000). The selection
of MODFLOW-2000 as the model code was based on the following criteria:
1) use of the model code is well-documented in the academic literature,
2) the model code has been widely used by hydrologic professionals and is generally
accepted as a valid model for simulating groundwater flow,
3) graphical user interfaces developed for the code allow for relatively simple and
efficient adjustment of model parameter values, and
4) the model code allows for automated parameter estimation based on inverse modeling
techniques.
The graphical user interface program Groundwater Vistas 4.21 was utilized to run
MODFLOW-2000 (Environmental Simulations, Reinholds, PA). Groundwater Vistas
was chosen as the graphical user interface because the software package incorporates
MODFLOW, MODFLOW-2000 and several different parameter estimation packages
into a single interface.
Model Assumptions and Limitations
As with all groundwater models, several assumptions have been necessary to
allow for numerical modeling of the complex aquifer system of the Prescott Active
Management Area. Though necessary, the assumptions do place limitations on the

18

interpretation of model results. Some of the major assumptions of the original model
which also apply to this model update include the following:
1) The Prescott AMA groundwater flow model is a regional model which
is not intended to provide site-specific determinations of hydrologic
conditions.
2) Hydraulic heads computed within each model cell represent the
average head within the saturated area of that cell.
3) Simulated recharge is applied directly to the uppermost active model
cell.
4) The Lower Volcanic Unit aquifer can be treated as an isotropic, porous
medium. Additionally, groundwater flow in the Lower Volcanic Unit
aquifer is laminar (that is, non-turbulent) and can be approximated using
Darcy’s equation (Darcy 1856). On a regional scale these assumptions are
reasonable; however, they may not apply on the local level due to nonlaminar and turbulent flow conditions which may occur in fractures and
cavities.
5) The available water-level data adequately represent the groundwater
flow system within the model area. In most areas this assumption is
reasonable, however, there are certain data deficient areas where the
assumption is questionable.
6) Recharge from precipitation falling directly on the groundwater basin
areas of the model domain is negligible. Because annual precipitation in
basin areas averages about 12 to 14 inches per year, and surface-water
evaporation rates exceed 60 inches per year. In addition, depth-to-water
considerations preclude effective recharge by direct precipitation on the
basins.
7) Evaporation of water from the water table is considered negligible.
This is due to the fact that the depth-to-water in most parts of the study
area is greater than 50 feet.
8) Evapotranspiration losses from riparian vegetation are negligible. This
assumption is due to the very limited area of riparian vegetation in the
model area. Evapotranspiration losses in those areas are included with the
groundwater outflows of the basin. (Corkhill and Mason 1995)
Model Grid
The updated model did not alter the model grid from the original model’s 2
layers, 48 rows and 44 columns. Grid cells remain a half mile in length and width.
However, the active area of the model was expanded from approximately 220 square
miles to nearly 250 square miles, as the active area was extended to include areas in
western Little Chino Valley and the Mint Wash area (Figure 2).

19

Model Layers and Aquifer Conditions
The Prescott AMA model is a two layer model (Figure 2). Layer 1 consists of the
unconfined Upper Alluvial Unit aquifer which extends throughout both the Little Chino
sub-basin and the Upper Agua Fria sub-basin. Layer 2 consists of the Lower Volcanic
Unit aquifer, which is modeled as a convertible confined/unconfined aquifer throughout
the northern half of the model area.
The thicknesses of the model layers were assigned based on well log data and
gravity data. The thickness of the Upper Alluvial Unit aquifer varied from 0 feet along
the margins of the basins to over 1000 feet in the central trough of the basins and in the
alluvial depression northwest of the City of Prescott. In most areas, Layer 2 was assigned
a uniform thickness of 200 feet due to sparse geologic data. However, changes to model
layer elevations and thicknesses from the original model were made in several areas
based on newly available data (Figures 3 and 4).
Based on the results of the drilling of ADWR Monitor Well # 1, B(15-01)08DAA
(55-587403) and a recently published USGS report (Wirt et. al 2004), Black Hill was
interpreted as a local intrusive volcanic center. To simulate this new conceptualization,
the Upper Alluvial Unit (Layer 1) was rendered inactive at Black Hill (Row 19, Column
22), while the thickness of the Lower Volcanic Unit (Layer 2) was increased to 800 feet
(Figure 6). The contact between the LVU and the basement unit was elevated from a
depth of 1135 feet below land surface to a depth of 800 feet. The Lower Volcanic Unit in
the cells immediately adjacent to Black Hill was thickened to 400 feet, leaving
approximately 100 feet of saturated Upper Alluvial Unit above the LVU. As there is no
indication of hydrologic disconnection between Black Hill and the surrounding areas, the
hydraulic conductivity of modified cells in the Black Hill area were adjusted to provide
similar transmissivity values to unmodified cells in the immediate vicinity of Black Hill.
The drilling of ADWR Monitor Well #2, B(16-01)23ACA (55-587404) also
required adjustment of the model layer elevations in the northeast corner of Lonesome
Valley. As the Upper Alluvial Unit aquifer was unsaturated at Monitor Well #2, several
cells in this area in Layer 1 were rendered inactive. In addition, the top elevation of
several cells in the Lower Volcanic Unit was increased to more accurately reflect the
drilling data. Finally, the thickness of the Lower Volcanic Unit at several cells was
increased from 200 feet to 300 feet in order to maintain saturated conditions and to
correspond with the drilling data (Figure 4).
The drilling of ADWR Monitor Well #3, B(15-02)22AAB (55-588619) revealed a
thick pocket of alluvium approximately 1200 feet thick northwest of the City of Prescott.
The areal extent of the pocket was estimated based on the depth to basement map
prepared by Oppenheimer and Sumner (1980). The model layer elevations in this area
were adjusted to reflect these two data sources (Figures 3 and 4).
In 2001, several wells were drilled in the area immediately south of Del Rio
Springs (Allen, Stephenson & Associates 2001). Based on the logs of these wells, the
thickness of the Upper Alluvial Unit was adjusted in several cells in this area.
While previous numerical models developed by ADWR did not include the
westernmost portion of the AMA, rapid development in the Mint Wash area over the past
10 years has caused rapid declines in water levels measured in several wells in the area.
Due to these increasing impacts on the groundwater resources of this area, it was

20

determined that the model update would extend the active area of the model to include
Mint Wash and surrounding areas. This was accomplished by extending the active area
of both the Upper Alluvial Unit (Layer 1) and the Lower Volcanic Unit (Layer 2),
increasing the number of active model cells from 1144 to 1258.
Boundary Conditions
The active model area encompasses the main groundwater basin area of the
Prescott AMA. In most locations, the active model area is bounded by impermeable
Basement Unit formations that form the “inactive” part of the model. Figure 2 indicates
the active model area. The inactive areas were assigned the constant flux boundary
conditions of No-Flow to simulate the impermeable Basement Unit.
Constant flux boundary conditions were also used to simulate recharge and
groundwater pumpage throughout the model area.
Head-dependent boundaries were used to simulate natural groundwater discharge
from the model area. Spring flow at Del Rio Springs, underflow to the Big Chino Valley,
and baseflow at the Agua Fria River were all modeled using head-dependent boundary
conditions.
MODFLOW-2000 Input Packages
The model was constructed using several modular input packages: 1) the BASIC
package, 2) the Layer-Property Flow Package (LPF), 3) the WELL package, 4) the
RECHARGE package, 5) the DRAIN package, 6) the General Head Boundary package,
and 7) the Pre-conditioned Congugate-Gradient 2 solver.
The BASIC package in MODFLOW-2000 has been modified from the BASIC
package of MODFLOW in several ways to remove parts that have been incorporated into
the Global Process discretization file (Harbaugh et. al 2000). These include the number
of layers, rows, and columns in the grid, as well as the number and length of stress
periods. The BASIC package in the updated model was used to define active and
inactive model cells and to assign starting heads.
The Layer-Property Flow (LPF) package replaced the Block-Centered Flow
(BCF) package used in the original model. Similar to the BCF package, the LPF package
contained the hydraulic conductivity values used to compute the conductance terms used
in the finite-difference equations. However, while the BCF package utilized a leakance
coefficient (VCONT) to calculate vertical flow, the LPF package utilizes vertical
hydraulic conductivity values to calculate vertical conductance and flow. The LPF
package also contains the values for Specific Yield and Specific Storage used to calculate
the rate of movement of water into and out of storage. In addition to utilizing specific
storage as opposed to storativity, the LPF package differs from the BCF package because
it allows for the use of automated parameter estimation techniques.
The WELL package simulated groundwater pumpage from the aquifer system for
agricultural, municipal, industrial and domestic uses.
The RECHARGE package simulated groundwater recharge to the aquifer system
from various sources including mountain-front recharge, incidental agricultural recharge,
flood recharge, artificial recharge, and canal seepage recharge.

21

The DRAIN package simulated natural groundwater discharge as spring flow at
Del Rio Springs and as baseflow along the Agua Fria River.
The General Head Boundary (GHB) package was used to simulate underflow
from the model area to the northwest of Del Rio Springs.
The PCG2 solver was used to implement the preconditioned conjugate-gradient
method to solve the matrix of finite-difference equations by iteration (Hill 1990). This
solver provided a more numerically stable solution that the SIP solver used in the original
model.
Water Level Data
For the steady-state simulation, static water-level data were needed for initial
model inputs, model calibration and statistical analysis of model accuracy. Initially,
water-level data were obtained from the ADWR-Groundwater Site Inventory (GWSI)
database; however, water-level measurements for the pre-development conditions
existing circa 1939 are limited in number and only available for the artesian area of Little
Chino Valley. The number of measured values were deemed insufficient for accurate
model calibration; thus, estimation techniques were utilized to develop additional head
target values. In areas such as the Upper Agua Fria Basin where steady-state conditions
are believed to have continued until the 1960’s, water-level measurements from later
dates were used as the static water level for the predevelopment conditions. In other data
deficient areas, target values were assigned based on the potentiometric surface
developed by ADWR during the original modeling study (Corkhill and Mason 1995).
Appendix V summarizes the water-level data used for calibration targets for the updated
model.
Water-level data were also needed for the transient simulation of 1940-2005.
Target head values for model calibration and statistical analysis of the transient
simulation were taken from the GWSI database.
Groundwater Pumpage Data
The steady-state simulation utilized the pumpage data compiled from various
sources during the original modeling study. These sources include Schwalen (1967),
Matlock, Davis and Roth (1973), Wigal (1988), Foster (1993), Prescott (1993), and the
ADWR-ROGR database. For the period 1999-2004, pumpage data for municipal,
agricultural and industrial purposes uses were obtained from annual values reported to
ADWR by individual well owners. Exempt domestic pumpage was simulated based on
estimated values reported in various ADWR reports including ADWR (2003), ADWR
(2004) and Nelson (2002).
Groundwater Discharge Data
Groundwater discharge data from Del Rio Springs and the perennial reach of the
Agua Fria River were used for calibration and statistical analysis. Data from Schwalen
(1967), Wilson (1988), and ADWR (1994d) were used for the period 1940-1993. Data
from the USGS gage at Del Rio Springs were used for the period 1997-2004, while data

22

from ADWR Hydrological Monitoring Reports (2002, 2003, and 2004) and the USGS
gage on the Agua Fria River at Humboldt were used for the period 2001-2004.
Aquifer Parameter Data
Initial aquifer parameter data (hydraulic conductivity, specific yield, specific
storage) were based on the current ADWR model inputs for these parameters that were
originally developed from several sources including well logs, pumping tests, specific
capacity measurements and others. Changes to the distribution of hydraulic conductivity
values were made in a few locations in the model area.
The distribution of hydraulic conductivity in the area south of Del Rio Springs
was adjusted to reflect results of pumping tests and geophysical studies conducted in the
area in 2001 (Allen, Stephenson & Associates, 2001). These data indicated a northeast
trending structural barrier in the Lower Volcanic Unit to the southeast of Del Rio
Springs. It is believed this structural barrier serves to funnel groundwater flow in the
direction of the springs.
The reach of Granite Creek was also assigned a distinct zone of hydraulic
conductivity. The surficial deposits of Granite Creek have been mapped as Quaternary
alluvium, while the surrounding basin areas are considered Quaternary sediments (Wirt
et. al). In general, alluvial deposits in intermittent stream channels such as Granite Creek
have larger grain sizes and higher hydraulic conductivity values than basin-fill deposts
such as those that extend throughout the Little Chino sub-basin (Schwartz and Zhang,
2003). In addition, it was necessary to increase the hydraulic conductivity of the reach of
Granite Creek in order to allow for flood recharge imposed during the transient
simulation to effectively disperse throughout the model area.
In addition, several small localized zones of hydraulic conductivity present in the
original model were combined into larger areas due to the lack of hydrologic data
justifying further discretization.

23

Chapter 5: Model Calibration
According to Hill (1998), better models will have “three attributes: better fit,
weighted residuals that are more randomly distributed, and more realistic optimal
parameter values.” Questions to be asked when evaluating the adequacy of model
calibration include the following:
1. Is the conceptual model of the system under investigation reasonable?
2. Are the mathematical representations of the boundary conditions
reasonable for the objectives of the study?
3. Does the simulated head and flow distribution mimic the important
aspects of the flow system, such as the direction and magnitude of the
head contours?
4. Does some quantitative measure of head and flow differences between
the simulated and observed values seem reasonable for the objectives
of the investigation?
5. Does the distribution of areas where simulated heads are too high and
areas where simulated heads are too low seem randomly distributed?
If they are not randomly distributed, then is there a hydrogeologic
justification to change the model and make the residuals more random
areally? (Hill 1998)
The steady-state Prescott AMA model was calibrated to 72 head targets as well as
flux targets for discharge at Del Rio Springs and baseflow at the Agua Fria River. There
were 26 head targets in the Upper Alluvial Unit (Layer 1) and 46 head targets in the
Lower Volcanic Unit (Layer 2) (Figures 6 and 8). Twenty-two of the targets in the LVU
were used as calibration targets in earlier versions of the Prescott AMA model. Twentythree of the targets in the LVU were developed for this model, while all 26 targets in the
UAU were new to this model. Eleven of the UAU targets and one of the LVU targets
were taken from the observed potentiometric surface produced by the original modeling
study. The remaining fifteen UAU targets and twenty-one LVU targets were taken from
the GWSI database maintained by ADWR. See Appendix V for a list of steady-state
targets.
The transient Prescott AMA model was calibrated to 2324 target values at 113
different wells. 716 target values at 45 wells were located in Layer 1, while 1608 target
values at 68 wells were located in Layer 2 (Figure 9). All of the target values were taken
from the GWSI database.
While previous modeling studies of the Prescott AMA relied on trial and error
techniques to achieve calibration, automated parameter estimation techniques have since
become widely available. This study relied on automated parameter estimation as one of
the techniques used for calibration. The computer code PEST was used to perform
inverse modeling, posed as a parameter estimation problem (Watermark Numerical
Computing, Brisbane). PEST calculates parameter values that minimize a weighted
least-squares objective function through non-linear regression using a modified GaussNewton method (Hill, 1998). This is an iterative form of non-linear regression that relies
on a damping parameter and a Marquadt parameter to function properly. For a more
thorough description of inverse modeling and automated calibration, see PEST: ModelIndependent Parameter Estimation (2002) and Hill (1998).

24

The use of PEST provided estimated optimal parameter values for horizontal and
vertical hydraulic conductivity as well as conductance for the head-dependent boundaries
in the model. While utilizing these estimated parameter values in the model minimizes
the objective function and provides a close fit between observed and simulated heads and
fluxes, inverse modeling does not always provide the most optimal calibration according
to Hill’s three primary criteria: better fit, random residuals, and realistic parameter
values. The optimized parameter values calculated by PEST provide the best fit to
observed heads and fluxes; however, the program does not take randomness of residuals
and realism of parameter values into consideration. Thus, the results of PEST were used
as initial parameter values and subsequently modified by manual techniques in order to
bring model parameter values into closer agreement with pumping test results and to
achieve a more random array of head residuals. See Figures 12 and 13 for the final
calibrated values of hydraulic conductivity.
Results of the Steady-State Simulation
The results of the steady-state simulation were evaluated by comparing simulated
water budgets with conceptual estimates and model heads with measured water levels.
Steady-State Water Budget
The results of the steady-state indicate that the simulated water budget compares
well with the conceptual water budget (Table 1). Model input values for recharge and
groundwater pumpage match conceptual estimates. Model output values for groundwater
discharge from Del Rio Springs were at the upper limit of conceptual estimates, while
simulated discharge at the Agua Fria River was well within conceptual estimates.
Simulated subsurface flow from the Little Chino sub-basin was also within conceptual
estimates.
Steady-State Calibration Error Analysis
Simulated heads from the steady-state solution were compared with 50 measured
and 22 estimated groundwater levels from the steady state period. These include 26
targets in the Upper Alluvial Unit and 46 targets in the Lower Volcanic Unit. See
Chapter 4 for a discussion of the target data utilized for the model calibration. Tables 6
6a and 6b provide statistical summaries of the calibration error analysis.
Discussion of Steady-State Simulation Results
The simulated ‘natural’ discharge rate out of the Little Chino sub-basin from
groundwater discharge at Del Rio Springs and subsurface flow out of the model area to
the north totaled about 7,600 acre-feet per year. The simulated discharge rate for Del Rio
Springs was about 3,500 acre-feet per year, which is within conceptual estimates. This
discharge rate represents an improved correspondence between simulated and conceptual
steady-state discharge from Del Rio Springs when compared to previous versions of the

25

model which over-simulated discharge from Del Rio Springs (Corkhill and Mason 1995)
(Nelson 2002).
The simulated subsurface groundwater discharge was about 3,900 acre-feet per
year. This is also within conceptual estimates; however, it should be noted that
considerable uncertainty exists regarding the conceptual subsurface groundwater
discharge rate (Table 1). The simulated subsurface discharge rate is also higher than the
simulated values of previous models; however, it was expected that reducing discharge
from Del Rio Springs to within conceptual estimates would result in greater subsurface
flow from the Little Chino Sub-basin.
The simulated groundwater discharge rate in the Upper Agua Fria sub-basin was
about 2,025 acre-feet per year. This is within the conceptual estimates of baseflow in the
Agua Fria River near Humboldt (Corkhill and Mason 1995).
The error associated with the head residuals was within the calibration goals of
the model. Results indicate that the error associated with the residuals was 2.0% of the
total head change in the groundwater system. This is significantly better than the 5%
criterion often used to define an acceptable model (Anderson and Woessner 2002).
In addition to the statistical analysis, qualitative assessment was also required to
ensure that the calibration followed the criteria set out by Hill (1998). Figures 6 and 8
indicate the spatially distributed residuals. The distribution of residuals in the Upper
Agua Fria sub-basin are generally random; that is, there is no clear spatial pattern of
simulated heads being too high or too low. Simulated heads in the Little Chino Subbasin, however, are consistently higher than measured heads. While this bias is
undesirable, it represents a reasonable compromise between achieving model-wide
calibration acceptability and randomness in the distribution of model residuals. In
addition, this bias was necessary in order to adequately simulate the groundwater
discharge rates out of the Little Chino sub-basin and to accurately simulate the
groundwater declines observed over the transient period.
Finally, proper calibration requires the use of reasonable parameters. While there
are limited field data regarding the hydrologic properties of the aquifers in the Prescott
AMA, the hydraulic conductivity and storage values used in the model fall within
conceptual estimates.
Results of the Transient Simulation
Results of the transient simulation were evaluated by comparing simulated water
budgets with conceptual estimates and simulated heads with measured water levels. See
Hydrographs 1-20 for groundwater level changes in twenty separate wells over the
transient simulation (1939-2004).
Transient Water Budget
Table 7 shows model simulated water budgets for 1940 and 2004. As expected,
the water budget for 1940 shows differences from earlier versions of the model similar to
those seen in the steady-state water budget. Decreased discharge from Del Rio Springs
and increased subsurface discharge were seen compared to earlier versions of the model;

26

however simulated values were all within conceptual estimates. For 2004, model
simulated results were compared with conceptual estimates.
Transient Calibration Error Analysis
Simulated heads were compared with groundwater levels measured throughout
the period of the transient simulation (1940-2004). A total of 2,324 target values at 113
different wells were used for statistical error analysis, including 716 target values in the
Upper Alluvial Unit aquifer and 1,608 targets in the Lower Volcanic Unit aquifer. See
Tables 8a, 8b, and 8c for the summary of the results of the statistical error analysis.
Discussion of Transient Simulation Results
The results of the transient simulation indicate that, overall, the simulated
groundwater system experienced a net loss of storage and an increase in capture of
groundwater discharge. These results follow conceptual estimates as well as previous
modeling results (Corkhill and Mason 1995, Nelson 2002). Over the period from 1940 –
2004, groundwater discharge from the Little Chino sub-basin (as groundwater discharge
at Del Rio Springs and subsurface flow out of the model area) has declined from around
7,600 acre-feet/year to around 2,700 acre-feet per year, a decline of 4,900 acre-feet/year.
Discharge from the Upper Agua Fria sub-basin as baseflow in the Agua Fria River also
declined approximately 700 acre-feet/year over the period 1940-2004. Over the period
from 1939-2004, simulated groundwater storage in the Upper Alluvial Unit aquifer and
Lower Volcanic Unit aquifer has declined by approximately 500,000 acre-feet.
The results from the transient simulation residual error analysis were within the
calibration goals (Table 8, 8a, and 8b).
Hydrograph 13 indicates stable simulated water levels in the Mint Wash area from
1940 until the 1980’s and 1990’s. This follows the conceptual understanding of the area
as hydrologically disconnected from the main agricultural and municipal pumping center
in the Little Chino sub-basin, which showed steep groundwater declines from the
beginning of the transient simulation.
In addition, while recent USGS estimates of subsurface flow out of the Little
Chino sub-basin were not used as calibration targets, the rate of simulated subsurface
flow for 2004, 1400 acre-feet per year, is within 30% of the estimated values (Wirt et al,
2004).

27

Chapter 6: Conclusions
The Prescott AMA Groundwater Flow Model was updated with new geologic and
hydrogeologic data. The model area was extended to include the rapidly developing area
near Granite Mountain and Mint Wash. Automated parameter estimation techniques
were utilized to provide initial parameter values which were subsequently manipulated
through trial-and-error to achieve a better calibration based on the criteria set out by Hill
(1998). The model was calibrated to the quasi-steady state conditions of 1939 and to the
transient conditions of 1939 through 2004.
The Prescott AMA Groundwater Flow Model indicates that the groundwater
system of the Prescott AMA has experienced a net loss in groundwater storage and
natural groundwater discharge since 1940.
Additional Data Needs
This project has been greatly aided by data collected by ADWR, other agencies,
and private firms over the past five years. Enhanced well monitoring, additional well
drilling, and geochemical studies have provided new data that has improved the
delineation of the extent of aquifer units and allowed for improved simulation of the everchanging responses of the aquifer system to new stresses. However, in the course of the
model update project, several data deficient areas were identified. Future modeling
studies would be improved by further studies or data collection projects in the following
areas:
Water Level Data
The calibration of the transient simulation relied on the annual water level data
measured and collected by the ADWR-Basic Data Section. Increasing the number of
regularly measured “index” wells would allow for a more accurate calibration. In
particular, water level data in Lonesome Valley and the area between Table Mountain
and the Town of Chino Valley would be useful.
Flow Data
The stream flow data from the USGS gages in the AMA has been useful in
determining natural groundwater discharge and flood recharge rates. Additional flow
data along Lynx Creek, the Agua Fria below the confluence with Lynx Creek and along
lower Granite Creek would enable better estimates of recharge along these important
drainages.
Aquifer Test Data
In many areas of the model, hydraulic conductivity and storativity data is
unavailable and was estimated during the calibration procedure. Additional aquifer test
data to provide field-based measurements of these aquifer properties would be useful for

28

future model updates. This data should be collected when new well pump tests are
performed.
Recharge Data
One of the more uncertain parameters in the Prescott AMA groundwater flow
model remains recharge. Future investigations of rates of natural recharge and incidental
agricultural recharge would be useful for improving the model calibration. Geochemical
studies could potentially be used to better quantify the amounts of recharge from these
two sources. In addition, future modeling studies would ideally employ inverse modeling
techniques to investigate the relative rates of these different sources of groundwater
recharge.

29

References Cited

ADWR, 2002, Prescott Active Mangement Area 2001-2002 Hydrologic Monitoring
Report, Hydrology Division, 18 p.
ADWR, 2003, Prescott Active Mangement Area 2002-2003 Hydrologic Monitoring
Report, Hydrology Division, 21 p.
ADWR, 2004, Prescott Active Mangement Area 2003-2004 Hydrologic Monitoring
Report, Hydrology Division, 28 p.
ADWR, 2005, 1984 – 2004 Groundwater pumpage data from the ADWR – Registry of
Groundwater Rights (ROGR) database.
Allen, Stephenson & Associates, 2001, New Well Installation and Completion Report:
The Ranch at Del Rio Springs, Town of Chino Valley, Arizona. Prepared for the
Bond Ranch at Del Rio Springs, LLC. Nov. 8, 2001, 16 p.
Anderson, C.A., and Woessner, W.W., 2002, Applied Groundwater Modeling:
Simulation of Flow and Advective Transport. Academic Press Inc.
Blasch, K.W., Hoffman, J.P., Graser, L.F., Bryson, J.R. and Flint, 2005, A.L.
Hydrogeology of the Upper and Middle Verde River Watersheds , Central
Arizona, U.S. Geological Survey Scientific Investigations Report 2005-5198,
101 p.
Corkhill, E.F. Preliminary summary of the results of drilling two monitor wells in the
Prescott AMA. Arizona Department of Water Resources Memorandum. Aug. 10,
2001.
Corkhill, E.F. and D.A. Mason, 1995, Hydrogeology and Simulation of Groundwater
Flow, Prescott Active Management Area, Yavapai County, Arizona: Arizona
Department of Water Resources, Modeling Report No. 9, 143 p.
Clear Creek Associates, 2001, Hydrologic Analysis of Proposed American Ranch
Development, Yavapai County, Arizona.
Cunion, EJ, 1985, Analysis of Gravity Data from the Southeastern Chino Valley Area,
Yavapai County, Arizona, Northern Arizona University Department of Geology.
Darcy, H., 1856, Les fontaines publiques de la ville de Dijon, V. Dalmont, Paris, 570,
590-594.
Foster, P., 1993, personal communication from Phil Foster to ADWR concerning average
domestic well pumpage in the Prescott AMA.

30

Foster, P., 2001, personal communication from Phil Foster to ADWR concerning surface
water diversions above the Del Rio Springs gauge.
Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, M.G., 2000, MODFLOW-2000,
the U.S. Geological Survey modular finite-difference ground-water flow
model_User guide to modularization concepts and the ground-water flow
process: U.S. Geologcial Survey Open-File Report 00-92, 121 p.
Hill, M.C., 1990, Preconditioned conjugate gradient 2 (PCG2), a computer program for
solving ground-water flow equations: U.S. Geological Survey Water Resources
Investigations Report 90-4048, 43 p.
Hill, M.C., 1998, Methods and Guidelines for Effective Model Calibration, U.S.
Geological Survey Water-Resources Investigations Report 98-4005.
Krieger, M.H., 1965, Geology of the Prescott and Paulden Quadrangles, Arizona: U.S.
Geological Survey Professional Paper 467, 127 p.
Matlock, W.G., Davis, P.R., and Roth, R.L., 1973, Groundwater in Little Chino Valley,
Arizona, Technical Bulletin 201, Agricultural Experiment Station, University of
Arizona, 19p.
McDonald, M.G., and Harbaugh A.W., 1988, A modular three-dimensional finitedifference ground-water flow model: U.S. Geological Survey Techniques of
Water- Resources Investigations, book 6, chap. A1, 586 p.
Navarro, Luis, 2002, Characterization and Ground-Water Flow Modeling of the Mint
Wash/Williamson Valley Area, Yavapai County, Master’s Thesis, Northern
Arizona University Department of Geology, 158 p.
Nelson, Keith, 2002, Application of the Prescott Active Management Area Groundwater
Flow Model Planning Scenario 1999-2025: Arizona Department of Water
Resources, Modeling Report No. 12, 46 p.
Oppenheimer, J.M, and Sumner, J.S., 1980, Depth-to-Bedrock Map (Prescott), Lab of
Geophysics, University of Arizona, Tucson, Arizona. .
Ostenaa, D.A., and others, 1993, Groundwater Study of the Big Chino Valley, Section II
of III, Geologic Framework Investigations, Volume 1 of 2, Seismotectonic Report
93-2, United States Bureau of Reclamation, Denver, Colorado, 30 p.
PEST: Model-Independent Parameter Estimation, 2002, Watermark Numerical
Computing, 279 p.
Schwalen, H.C, 1967, Little Chino Valley Artesian Area and Groundwater Basin:
Technical Bulletin 178, Agricultural Experiment Station, University of Arizona,

31

Tucson, Arizona, 63 p.
Schwartz, F.W., and Zhang H, 2003, Fundamentals of Groundwater: John Wiley and
Sons, Inc.: New York, 583 p.
SRP (Salt River Project), 2000, Letter from SRP to ADWR regarding methodology for
determining rate of pre-development groundwater discharge out of LIC sub-basin.
USGS 09502900, Del Rio Springs Near Chino Valley, Online, 08/30/2006, Available at:
http://waterdata.usgs.gov/az/nwis/uv?09502900
USGS 09512450, Agua Fria River Near Humboldt, AZ, Online 08/30/2006, Available at:
http://waterdata.usgs.gov/az/nwis/uv?09512450
Wilson, Richard, 1988, Water Resources of the Northern Part of the Agua Fria Area,
Yavapai County, Arizona, U.S. Geological Survey, Arizona Department of Water
Resources Bulletin 5, Tucson, Arizona, 109 p.
Wirt, Laurie, DeWitt, Ed and V.E. Langenheim, 2004, Geologic Framework of Aquifer
Units and Ground-Water Flowpaths, Verde River Headwaters, North-Central
Arizona, U.S. Geological Survey Open File Report 2004-1411, 43 p.
Wigal, D.V. Adequacy Report for Shamrock Water Company – 1988.
Prescott, 1993, Groundwater pumpage data, and other related water-use data supplied by
Brad Huza, City of Prescott to ADWR.

32

Appendix I: Tables

33

Table 1
Simulated and Conceptual Steady-State Water Budgets for the

Inflow

Updated Prescott AMA Groundwater Flow Model1
(Figures Rounded to Nearest 50 acre-feet)
Model Simulation
Conceptual
acre-feet/simulation
(acre-feet/year)

acre-feet/simulation
(acre-feet/year)

Mountain Front and

3,900

3,900

Granite Creek Recharge

(6,800 AF/YR)

(6,800 AF/YR)

Agricultural Recharge

2,200

2,200

Canal Recharge

950

950

Total Inflow
Outflow

7,050
Model Simulation

7,050
Conceptual

Groundwater Pumpage

1,500

1,500

Groundwater Discharge

2,000
2
(3,500AF/YR )
1,200 (2,100AF/YR4)

1,300-2000 (2,300 -3,400 AF/YR3)

2,350 (4,100 AF/YR)

6
1,300-2,600 (2,200 -4,500 AF/YR )
(5,600 AF/YR7)

Del Rio Springs
Groundwater Discharge
Agua Fria River
Groundwater Discharge
Subsurface Flow

(2,700 - 3,800 AF/YR3a)
900-1,400
(1,500 - 2,500 AF/YR5)

(2,000 AF/YR8)
Total Outflow
7,050
5,000 - 7,500
The steady-state model simulated the 210 day agricultural season for 1939. The water budget totals
are the totals for this 210 day simulation while figures in parentheses are annualized totals for 1939.
2
contains an undifferentiated ET component estimated at 100-200 ft/yr (Nelson 2002)
1

3

Max and min annual surface water measurements at Del Rio Springs 1940-1945 (Schwalen 1967)

3a

Surface water measurements plus estimated 400 AF/YR for ET demand and unreported

surface water diversions upstream of gauge (Foster 2001)
Contains an undifferentiated ET component estimated at 200 acre-feet/year
5
Corkhill and Mason, 1995
4

6
7
8

Darcy Strip Analysis (Nelson 2002)
Groundwater discharge as subsurface flow based on confined well steady state equation (SRP, 2000)
Corkhill and Mason, 1995 (Note: UAU aquifer only)
34

Table 2
Simulated Pumpage Applied to the Updated Prescott AMA Groundwater Flow Model
(1999-2004)
(Figures Rounded to the Nearest 5 acre-feet)
AMA Pumpage
1999
2000
2001
2002
1
City of Prescott
6750
7515
7650
8320
1
Prescott Valley
3780
4090
4335
4820
Agricultural Users1

2003

2004

8150
4870

8150
5370

5160

6620

5850

6760

4365

5290

1

620

485

1050

1190

1240

1230

Small Providers

1

510

460

565

705

825

745

Exempt
3
Non-AMA Pumpage

2

1200

1365

1535

1700

1830

2000

90

95

100

255

235

240

23750

21515

23025

Non-irrigation Users

1
2

Total Pumpage
18110
20630
21085
ADWR Registry of Groundwater Rights Database

Estimated domestic and exempt well pumpage in Prescott AMA groundwater basin area

only. See pumpage section of this report for further details.
Estimated non-AMA pumpage from domestic wells and the American Ranch

3

development in the Mint Wash area. See Table 2 and the pumpage section of this report
for further details.

35

Table 3
Non-AMA Pumpage Applied in the Mint Wash Area
Year
2004

to the Updated Prescott AMA Groundwater Flow Model
Domestic (acre-feet/year)
American Ranch (acre-feet/year)
115
126

2003
2002

110.4
105.8

126
150

2001

101.2

0

2000

96.6

0

1999

92

0

1998

87.4

0

1997

82.8

0

1996
1995

78.2
73.6

0
0

1994

69

0

1993

64.4

0

1992
1991

59.8
55.2

0
0

1990

50.6

0

1989
1988

46
41.4

0
0

1987

36.8

0

1986

32.2

0

1985
1984

27.6
23

0
0

1983

18.4

0

1982

13.8

0

1981

9.2

0

1980

4.6

0

1939-1979
Total

0
1495

0
402

36

Table 4
Simulated Flood Recharge Applied to the Updated Prescott AMA Groundwater Flow Model
Event Year
1978

Number of
Days per Event
9

Granite Creek
(acre-feet/event)
4320

Lynx Creek
(acre-feet/event)
780

Mint Wash
(acre-feet/event)
49

1980
1983

13
4

6240
1920

1120
350

71
22

1993

39

18720

3370

213

1995

9

4320

780

49

850*

0

0

2003
2004

34

18690

2850

185

Total

108

55060

9250

589

* The 2003 flood event was simulated based on a release from Watson Lake into
Granite Creek. Other drainages were not affected.

37

Table 5
Simulated Artificial Recharge Applied to the Updated Prescott AMA Groundwater Flow Model
Event Year

(Figures to nearest 10 acre-feet)
Prescott
(acre-feet/year)

Prescott Valley
(acre-feet/year)

1988
1989-1993

1100
2100

0
0

1994

2100

500

1995

2100

800

1996

2100

1250

1997

2100

1400

1998

2750

1600

1999
2000

2080
2830

1360
1630

2001

2890

1570

2002

1680

1300

2003
2004

3330
3140

1640
1840

Total

30300

14890

38

Table 6
Combined Statistical Summary of Steady State Error Analysis for the
UAU (Layer 1) and LVU (Layer 2)
Residual = Measured - Simulated (feet)
Residual Absolute Residual
Residual
Minimum Maximum Residual Standard Deviation
Mean
-3.08

Mean
9.14

Standard Deviation Residual Residual
11.78
-37.38
27.66

/ Range in Head
0.020

Table 6a
Statistical Summary of Steady State Error Analysis for the UAU (Layer 1)
Residual = Measured - Simulated (feet)
Residual Absolute Residual
Mean
-5.42

Mean
13.27

Residual

Minimum Maximum Residual Standard Deviation

Standard Deviation Residual Residual
15.49
-37.38
27.66

/ Range in Head
0.026

Table 6b
Statistical Summary of Steady State Error Analysis for the LVU (Layer 2)
Residual = Measured - Simulated (feet)
Residual Absolute Residual
Mean
-1.59

Mean
6.51

Residual

Minimum Maximum Residual Standard Deviation

Standard Deviation Residual Residual
8.29
-22.19
20.4

39

/ Range in Head
0.024

Table 7
Simulated and Conceptual Transient Water Budgets (1940 and 2004)

Inflow

Prescott AMA Groundwater Flow Model
(Figures rounded to the Nearest 100 acre-feet)
Simulated 1940
Simulated 2004

Conceptual 2004

acre-feet/year
5800

acre-feet/year
5800

acre-feet/year
5800

4100

7600

7600

Flood Recharge

0

21700 7

21700

Total Inflow

9900

35100

35100

Simulated 1940
4600
1
3600

Simulated 2004
23000
1300 1

Conceptual 2004
23800
1000 2

Natural Recharge
Recharge: Incidental and
Artificial Recharge

Outflow
Pumpage
Groundwater Discharge

1400 2a

Del Rio Springs (LIC)
Groundwater Discharge
Agua Fria River (UAF)
Subsurface Flow (LIC)

2100 3

1400 3

1300 4

3500

1400

1900-2000 5
1200-2000 6

Total Outflow
Change in Storage

13800
-3900

27100
8000

26500 - 28200
6900 - 8600

1

Contains and undifferentiated ET component estimated at 100-200 acre-feet/year

2

Surface water measurements (mean) at Del Rio Springs (2004) (USGS 2004). Note: Sub-basin

groundwater discharge rate does not reflect estimated ET demand of 100 acre-feet/year.
upstream of gauge
2a
Surface water measurements at Del Rio Springs (2004) plus 400 AF/YR for ET demand and
surface water diversions upstream of gauge (Foster, 2001)
Contains an undifferentiated ET component estimated at 200 acre-feet/year

3
4

Median surface water measurements at Agua Fria River (2004) plus 200 acre-feet/year for

estimated ET demand upstream of gauge
Watson Lake into Granite Creek (ADWR 2004). Other drainages were not affected.
5
6
7

Results of USGS tracer dilution study (Wirt et. al, 2004)
Darcy Strip Analysis (Nelson, 2002)
Flood recharge includes flooding from January - March 2005.
40

Table 8
Combined Statistical Summary of Transient Error Analysis for the
UAU (Layer 1) and LVU (Layer 2)
Residual = Measured - Simulated (feet)
Residual Absolute Residual
Residual
Minimum Maximum Residual Standard Deviation
Mean
10.8

Mean
17.96

Standard Deviation Residual Residual
21.85
-89.56
146.95

/ Range in Head
0.029

Table 8a
Statistical Summary of Transient Error Analysis for the UAU (Layer 1)
Residual = Measured - Simulated (feet)
Residual Absolute Residual
Mean
16.04

Mean
22.87

Residual

Minimum Maximum Residual Standard Deviation

Standard Deviation Residual Residual
24.2
-48.55
71.19

/ Range in Head
0.041

Table 8b
Statistical Summary of Transient Error Analysis for the LVU (Layer 2)
Residual = Measured - Simulated (feet)
Residual Absolute Residual
Mean
8.16

Mean
15.47

Residual

Minimum Maximum Residual Standard Deviation

Standard Deviation Residual Residual
20.05
-89.56
146.95

41

/ Range in Head
0.033

Table 9
Simulated Transient Water Budget for the Updated
Prescott AMA Groundwater Flow Model (1939-1998)*
(Figures rounded to the nearest 1,000 acre-feet)
Inflow
Simulated Totals (1939-1998)
Mountain Front Recharge
Other Recharge

340000
575000

Released from Storage

850000

Total Inflow

1765000

Outflow
Pumpage

920000

Del Rio Springs

195000

Agua Fria River
Subsurface Flow

100000
140000

Taken Into Storage

405000

Total Outflow

1760000

Change in Storage
*All figures are cumulative totals for the period 1939-1998.

-445000

Table 10
Simulated Transient Water Budgets for the Updated

Inflow

Prescott AMA Groundwater Flow Model (1999-2004)
(Figures rounded to the Nearest 100 acre-feet)
Simulated Simulated Simulated Simulated Simulated Simulated

Natural Recharge1
Recharge: Incidental and
Artificial Recharge2,3,4
Flood Recharge5
Total Inflow
Outflow
6
Pumpage
Del Rio Springs (LIC)7

2000
AF/YR

2001
AF/YR

2002
AF/YR

2003
AF/YR

2004
AF/YR

5,800

5,800

5,800

5,800

5,800

5,800

6,000

7,800

7,400

6,400

7,200

7,600

0

0

0

0

900

21,700

11,800
1999
18,100

13,600
2000
20,600

13,200
2001
21,100

12,200
2002
23,800

13,900
2003
21,500

35,100
2004
23,000

1,700

1,700

1,600

1,500

1,400

1,300

7

1,300

1,300

1,300

1,200

1,200

1,400

7

Total Outflow

1,700
22,800

1,500
25,100

1,500
25,500

1,400
27,900

1,600
25,700

1,400
27,100

Change in Storage

-11,000

-11,500

-12,300

-15,700

-11,800

8,000

Agua Fria River (UAF)
Subsurface Flow (LIC)

1

1999
AF/YR

Estimates for long-term average mountain front recharge (Nelson, 2002). Actual annual

volumes may vary significantly from the long-term average.
2

Incidental agriculture recharge estimated at 50% of agricultural water use.

(Corkhill and Mason 1995) (Nelson 2002).
City of Prescott artificial recharge includes treated effluent and surface water. City of
Prescott Annual Underground Storage Facility Reports - Schedule 71.
4
Town of Prescott Valley artifical recharge data provided by John Munderloh - Town of
3

Prescott Valley (09/27/2006)
Flood recharge for Granite Creek, Lynx Creek and Mint Wash estimated based on wetted-

5

area approach (Nelson 2002). Flood recharge for 2003 was simulated based on a release
from Watson Lake into Granite Creek (ADWR 2004). Other drainages were not affected.
Pumpage includes reported pumpage from ADWR Registry of Groundwater Rights

6

Database as well as estimated domestic and exempt well pumpage for the active model
area. See pumpage section of this report for further details.
Model simulated discharge.

7
8

Flood recharge includes flooding from January - March 2005
43

Appendix II: Figures

44

­
COCONINO
MOHAVE

APACHE

NAVAJO

PRESCOTT AMA

YAVAPAI

GILA

LA PAZ

MARICOPA

GREENLEE

GRAHAM

PINAL

YUMA

PIMA
COCHISE

SANTA CRUZ

Figure 1
Location of the Prescott
Active Management Area,
Yavapai County, Arizona.
45

0 12.5 25

50 Miles

US 89

­
"
)

Chino Valley
Valley
Chino

US 8

9A

Prescott Valley
Valley
Prescott

"
)

SR

69

Prescott

"
)

Dewey
Dewey

"
)
AMA Boundary
Layer 1 Active Model Area

"
)

Layer 2 Active Model Area

Humboldt
Humboldt

Road
Stream
Lake
Township and Range

"
)

Municipalities

Figure 2
Active model area of the updated
Prescott AMA groundwater flow model

46

0

1

2

4 Miles

­

T 17N
R 3W

T 16N
R 3W

T 15N
R 3W

T 14N
R 3W

Layer 1 Thickness
High : 1210 ft.

Low : 120 ft.
AMA Boundary
Layer 1 Active Model Area
Stream
Lake
Township and Range

Figure 3
Thickness of the Upper Alluvial Unit
in the updated Prescott AMA
groundwater flow model.

47

0

1

2

4 Miles

­

T 17N
R 3W

T 16N
R 3W

T 15N
R 3W

Layer 2 Thickness (ft.)
200 ft.
250 ft.
300 ft.
400 ft.
5

800 ft.
AMA Boundary
Stream
Lake
Township and Range

Figure 4
Thickness of the Lower Volcanic
Unit in the updated Prescott AMA
groundwater flow model.

48

0 0.5 1

2 Miles

­

T 17N
R 3W
445 0

450

0
445
0
450

0

45
50

4550
46

46

00

4650
00

46

50

00
47

50
46

T 15N
R 3W

00

47

5000
495 0
4900
485 0
480 0

0
460

465 0

T 16N
R 3W

50
47
4750
4800
4850
4900
4950
47

T 14N
R 3W

47

50
48
00
48
50

475

0

470

4700
47
5

00

0

0

0
465

00
48 50
48

4650
46
00

5000

4700

4600
0
455
4550
45
0

Measured Water Level

4500

Simulated Water Level
AMA Boundary
Layer 1 Active Model Area
Stream
Lake
Township and Range

0

Figure 5
Measured and simulated heads in the
Upper Alluvial Unit in the steady-state
simulation of the updated Prescott AMA
groundwater flow model (1939)
(50 ft. contour interval).

49

0

1

2

4 Miles

­

T 17N
R 3W
-19
-28
-16
-23
-15
-11

-10
11

T 16N
R 3W

28

-37

-3

-9

-11

-2
-12
5

T 15N
R 3W

0

-1

-9

22
-8

19
-25

T 14N
R 3W

1
2
22
-4
-19

Residual (ft.) (Measured - Simulated)
AMA Boundary
Layer 1 Active Model Area
Stream
Lake
Township and Range

Figure 6
Difference between measured and
simulated water levels in the Upper
Alluvial Unit in the steady-state
simulation of the updated Prescott AMA
groundwater flow model (1939).

50

0

1

2

4 Miles

­

T 17N
R 3W
4450
4500
4500
0
5
5
4 4550

460

0

4600

T 16N
R 3W

5
48

50

46
5

0

470 0

47

4800

46
0

465 0

485

0

50
46

T 15N
R 3W

0

4750

47

50
47

0
47

0
00
47

0

0

0
48

5
47

00
47

00

0

4650

T 14N
R 3W
Measured Heads
Simulated Heads
AMA Boundary
Stream
Lake
Township and Range
Layer 2 Active Model Area

Figure 7
Measured and simulated heads in the Lower
Volcanic Unit from the steady-state simulation
of the updated Prescott AMA groundwater
0 0.5 1
flow model (1939) - (50 ft. contour interval).

51

2 Miles

­

T 17N
R 3W

-3 -3
-16
-7
-15
-22
4
18
7
7
5
0
3
5
1
-3 -1
-2
3
0 1 -3
-4

-11
-1

-5
12

-1

T 16N
R 3W

-5
-12

-6
-7
-7

-10

-4

9

T 15N
R 3W

2

-8

-6
1
20

T 14N
R 3W

Residual (ft.) ( Measured - Simulated)
AMA Boundary
Stream
Lake
Township and Range

10

Figure 8
Difference between measured
and simulated heads in the Lower
Volcanic Unit from the steady-state
simulation of the updated Prescott
AMA groundwater flow model (1939).

52

0 0.5 1

2 Miles

­
US 89

T 17N
R 3W

T 16N
R 3W

T 15N
R 3W
US 8

9A

SR

T 14N
R 3W

69

Layer 1 Targets
Layer 2 Targets
Layer 1 Active Model Area
Layer 2 Active Model Area
AMA Boundary
Stream
Lake
Township and Range

Figure 9
Location of head targets used for calibration
of the transient simulation of the updated
0
Prescott AMA groundwater flow model.

53

1

2

4 Miles

­

T 17N
R3W
4450

4600

4450

4600

4550

4500
50
45

T 16N
R3W

4500

4500

4700

4550

5000

T 15N
R3W

4950
4900
485 0
480 0
4750

5000

4550

465
0

00
46

4700

4750
4800
4850

4900
4950

46

4550

4600
46

50

47

50
46

00
46

50
46

50

5
47
0

T 14N
R3W

4750
47
00

4750
4800
4850

00

46

00
48 50
48

46

50

4600
00
0
455
4550
4500
45
00
44
50

Measured Water Level
Simulated Water Level
AMA Boundary
Layer 1 Active Model Area
Stream
Lake
Township and Range

Figure 10
Measured and simulated heads in the
Upper Alluvial Unit from the transient
simulation of the updated Prescott AMA
groundwater flow model (2005)
(50 ft. contour interval).

54

0

1

2

4 Miles

­

T 17N
R 3W
445 0

4450

4500

450 0

455

4500

0

T 16N
R 3W

0

4800

0
455

4550
46
0

0

46

5
48

00
47

47
5

0

4550

4700

T 15N
R 3W

4650 4650

460 0

485 0

450

50

0

00
47

50
47

00
48

46
5

4750
0

50
47
00
47 0
5
46

460

4500
0

4400

4450

4550
4500
4450

Measured Head

4350
4400

Simulated Head
5

AMA Boundary
Stream
Lake
Township and Range
Layer 2 Active Model Area
1940simcontours

Figure 11
Measured and simulated heads in the Lower
Volcanic Unit from the transient simulation of
the updated Prescott AMA groundwater flow
model (2005) - (50 ft. contour interval).

55

0 0.5 1

2 Miles

­

T 17N
R 3W
25 25
25 25 10
0.6 25 10 25 25
0.6 0.6 25 25 25 25 25
0.6 5 25 25 25 25 25

T 16N
R 3W

0.6 0.6 0.6 5

5 5

5 25 15 15 15

0.6 0.6 5 5

5 5

5 25 15 15 15 15 100

0.6 0.6 5 5

5 5

5 25 15 15 15 15 100 15 15

0.6 0.6 5 5

5 5

5 5 15 15 15 15 100 15 15 15

0.6 0.6 5 5

5 5

5 5 15 15 15 15 100 15 15 15 15 15

0.6 0.6 5 5

5 15 15 15 15 15 15 15 100 15 15 15 15 15

10 10 10 10 10 15 15 15 15 15 15 15 100 15 15 15 15 15 10
10 10 10 15 15 15 15 15 100 15 15 15 15 15 15 10 10 1 1
15 15 15 15 15 100 15 15 15 15 15 15 10 10 1 1

1

15 15 15 100 15 15 15 15 15 10 10 10 10 1

1

15 15 15 100 15 15 15 15 15 10 10 10 10 10 1
15 15 15 15 100 15 15 15 10 10 10 10 10 10 1
15 15 15 100 15 15 15 10 10 10 10 10 10 10 10
5 0.3 0.3 0.4 0.4 0.4

10 10 10 100 10

10 10 10 10 10 10 10 10 10

5 0.3 0.3 0.3 0.4 0.4 0.4 0.4 0.7 0.7 0.7 10 10 10 10 10 10 100 10 10 10 10 10 10 10 10 10 10 10
5 0.3 0.3 0.3 0.3 0.4 0.4 0.4 0.7 0.7 0.7 0.7 10 10 10 10 10 100 10 10 10 10 10 10 10 10 10 10

T 15N
R 3W

5

5 0.3 0.3 0.3 0.3 0.3 0.4 0.7 0.7 0.7 0.7 0.7 10 10 10 10 100 10 10 10 10 10 10 10 10 3 3
5 5 0.3 0.3 0.3 0.3 0.4 0.7 0.7 0.7 0.7 0.7 0.7 10 10 10 100 10 10 10 10 10 10 10 3 3 3
5

5 0.3 0.3 0.3 0.4 0.4 0.7 0.7 0.7 0.7 0.7 10 10 10 100 10 10 10 10 10 10 3

3 3 3

5 5 0.3 0.3 0.3 0.4 0.7 0.7 0.7 0.7 0.7 10 10 100100 3

3 3

3 3 3 3

3 3 3

5 0.3 0.3 0.3 0.4 0.7 0.7 0.7 0.7 10 10 10 10 100 3

3 3

3 3 3 3

3 3 3

3 1

1

10 10 10 10 10 10 100 10 3

3 3

3 3 3 3

3 3 3

3 3

1 1 0.1

10 10 10 10 10 100 10 10 10 3 3

3 3 3 3

3 3 3

3 1

1 4

100 10 10 10 1 1

3 3 3 3

3 3 3

1 1

1 4

4 4 0.1

1 1

1 3 3 3

3 3 3

1 1

1 4

4 4

1

1 1 3 3

3 3 1

1 1

4 4

4 4

4 4

1 1 1 3

3 1 1

1 1

4 4

4 4

4 4

1 1 1

1 1 1

1 4

4 4

4 4

4 4 4

1 1 1

1 1 1

1 4

4 4

4 4

4 4 4

1 1

1 1 1

1 4

4 4

4 4

4 4 3

5

5 5 5

5 5

4 4

4 4

4 3 3

0.8 0.8 5 5

5 5

3 3 3

3

0.8 0.8 4 4

5 5

5 3 3

3

0.8 0.8 0.8 4

4 4 25 3 3

3 3

0.8 0.8 0.8 0.8 0.8 25 3 3

3 3

T 14N
R 3W

3

4 0.1
4 4

3

25 25 25 3
25 25 25 25
25 25
25 25
25 25
25 25
5

Hydraulic Conductivity (ft/day)
AMA Boundary
Layer 1 Active Model Area
Stream
Lake
Township and Range

Figure 12
Hydraulic conductivity values in the
Upper Alluvial Unit of the updated
Prescott AMA groundwater flow model.

56

0

1

2

4 Miles

T 17N
R 3W

­

25 25
25 25 10
25 10

6

6

6 175 6

6

6

6 175 175 175 6

6

6

0.5 0.5 175 175 175 175 175 90 90 90
0.5 0.5 0.5 175 175 175 175 175 90 90 90 90 90
0.5 0.5 0.5 175 175 175 175 175 90 90 90 90 90 90 90
0.5 0.5 90 175 175 175 175 175 90 90 90 90 90 90 90 90
0.5 0.5 90 175 175 175 175 175 90 90 90 90 90 90 90 90 90 90

T 16N
R 3W

0.5 0.5 90 175 175 175 175 175 90 90 90 90 90 90 90 90 90 90 75 75 75 0.1
0.5 0.5 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 75 75 75 0.1
0.5 0.5 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 75 75 0.1
0.5 0.5 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 75 75 0.1 0.1
0.5 0.5 0.5 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 75 15 0.1 0.1
0.5 0.5 0.5 0.5 90 90 90 90 90 90 90 90 90 90 90 90 90 90 75 75 15 0.1 0.1
90 90 90 90 90 90 90 90 90 90 90 90 90 90 75 75 15 0.1 0.1
90 90 90 90 90 90 90 90 40 40 40 90 90 90 75 15 15 0.1 0.1 0.1
0.5 0.5 0.5 0.5 0.5 1 0.4 0.4 0.4 0.4 75 75 75 90 90 40 25 40 90 90 90 75 15 15 0.1 0.1 0.1

T 15N
R 3W

0.5 0.5 0.5 0.5 1

1 0.4 0.4 0.4 0.4 75 75 75 75 90 40 40 40 90 90 75 75 15 15 0.1 0.1 0.1

0.5 0.5 0.5 1

1 0.4 0.4 0.4 0.4 75 75 75 75 75 90 90 90 90 90 75 75 15 15 0.1 0.1 0.1 0.1

0.5 0.5 0.5 1
1
1

1

1

1

1 0.4 0.4 0.4 0.4 0.4 75 75 75 75 75 75 75 75 75 75 75 15 15 15 15 0.1 0.1 0.1
1 0.4 0.4 0.4 0.4 0.4 0.4 15 15 15 15 75 75 75 75 75 75 15 15 15 15 0.1 0.1 0.1

1

4

4

4 0.4 0.4 0.4 0.4 0.4 0.4 15 15 15 15 15 15 15 15 15 15 15 15 15 0.1 0.1 0.1

4

4

4

4 0.4 0.4 0.4 0.4 0.4 0.4 15 15 15 15 15 15 15 15 15 15 15 15 4

4

4

4

4

4

4 0.4 0.4 0.4 0.4 0.4 4 15 15 15 15 15 15 15 15 15 15 4

4

4

4

4

4

4 0.4 0.4 0.4 0.4 0.4 4 15 15 15 15 15 15 15 15

4

4

4

4

4

4 0.4 0.4 0.4 0.4 4

4

4 0.1 0.1
4 0.1 0.1 0.1 0.1

4

4

4 0.1 0.1 0.1 0.1
4 0.1 0.1 0.1

4

4

4

4

4

4

4

4

4

4

0.4 0.4 0.4 0.4 4

4

4

4

4

4

4

4

4

4 0.1

20 20 20 75 75 75 10
20 20 75 75 75 10
20 75 75 75 10
20 20 20 10
10 10 10 10
5

5

Hydraulic Conductivity (ft/day)
AMA Boundary
Stream
Lake
Township and Range

Figure 13
Hydraulic conductivity values in the
Lower Volcanic Unit in the updated
Prescott AMA groundwater flow model.

57

0 0.5 1

2 Miles

­

T 17N
R 3W

T 16N
R 3W

T 15N
R 3W

Specific Yield
0.05
0.06
0.07
0.08
0.09
0.1
0.12
AMA Boundary
Layer 1 Active Model Area
Stream
Lake
Township and Range

Figure 14
Specific yield values in the Upper
Alluvial Unit of the updated
Prescott AMA groundwater flow model.

58

0

1

2

4 Miles

­

T 17N
R 3W

T 16N
R 3W

T 15N
R 3W

Specific Storage Values
0.000001
0.000005
0.00001
5

0.00002
Stream
AMA Boundary
Lake
Township and Range

Figure 15
Specific storage values in the Lower
Volcanic Unit of the updated
Prescott AMA groundwater flow model.

59

0 0.5 1

2 Miles

Appendix III: Hydrographs

60

Hydrograph 1
Prescott AMA: Northern Little Chino Valley Area
4650
4625

Head (feet)

4600
4575
4550
4525
4500
4475
4450
1940

1950

1960

1970

1980

1990

2000

2010

2000

2010

Year
Simulated Value - Layer 2, Row 7, Col 15
Measured Value - Well 55-623528

Hydrograph 2
Prescott AMA: Northern Little Chino Valley Area
4600
4575

Head (feet)

4550
4525
4500
4475
4450
4425
4400
1940

1950

1960

1970

1980

1990

Year
Simulated Value - Layer 2, Row 5, Col 16
Measured Value - Well 55-803169

61

Hydrograph 3
Prescott AMA: Northern Little Chino Valley Area
4550
4525

Head (feet)

4500
4475
4450
4425
4400
4375
4350
1940

1950

1960

1970

1980

1990

2000

2010

2000

2010

Year
Simulated Value - Layer 2, Row 2, Col 14
Measured Value - Well 55-609768

Hydrograph 4
Prescott AMA: Central Little Chino Valley Area
4650
4625

Head (feet)

4600
4575
4550
4525
4500
4475
4450
1940

1950

1960

1970

1980

1990

Year
Simulated Value - Layer 2, Row 12, Col 14
Measured Value - Well 55-635722

62

Hydrograph 5
Prescott AMA: Central Little Chino Valley Area
4650
4625

Head (feet)

4600
4575
4550
4525
4500
4475
4450
1940

1950

1960

1970

1980

1990

2000

2010

2000

2010

Year
Simulated Value - Layer 2, Row 10, Col 15
Measured Value - Well 55-606021

Hydrograph 6
Prescott AMA: Central Little Chino Valley Area
4650
4625

Head (feet)

4600
4575
4550
4525
4500
4475
4450
1940

1950

1960

1970

1980

1990

Year
Simulated Value - Layer 1, Row 7, Col 15
Measured Value - Well 55-602559

63

Hydrograph 7
Prescott AMA: Central Little Chino Valley Area
4650
4625

Head (feet)

4600
4575
4550
4525
4500
4475
4450
1940

1950

1960

1970

1980

1990

2000

2010

2000

2010

Year
Simulated Value - Layer 2, Row 10, Col 11
Measured Value - Well 55-604724

Hydrograph 8
Prescott AMA: Southern Little Chino Valley Area
4650
4625

Head (feet)

4600
4575
4550
4525
4500
4475
4450
1940

1950

1960

1970

1980

1990

Year
Simulated Value - Layer 2, Row 22, Col 17
Measured Value - Well 55-639831

64

Hydrograph 9
Prescott AMA: Southern Little Chino Valley Area
4650
4625

Head (feet)

4600
4575
4550
4525
4500
4475
4450
1940

1950

1960

1970

1980

1990

2000

2010

2000

2010

Year
Simulated Value - Layer 2, Row 16, Col 17
Measured Value - Well 55-639826

Hydrograph 10
Prescott AMA: Northeast Little Chino Valley Area
4650
4625

Head (feet)

4600
4575
4550
4525
4500
4475
4450
1940

1950

1960

1970

1980

1990

Year
Simulated Value - Layer 2, Row 8, Col 22
Measured Value - Well 55-611908

65

Hydrograph 11
Prescott AMA: Lonesome Valley Area
4650
4625

Head (feet)

4600
4575
4550
4525
4500
4475
4450
1940

1950

1960

1970

1980

1990

2000

2010

2000

2010

Year
Simulated Value - Layer 2, Row 11, Col 27
Measured Value - Well 55-625108

Hydrograph 12
Prescott AMA: Southern Lonesome Valley Area
4650
4625

Head (feet)

4600
4575
4550
4525
4500
4475
4450
1940

1950

1960

1970

1980

1990

Year
Simulated Value - Layer 2, Row 23, Col 27
Measured Value - Well 55-805134

66

Hydrograph 13
Mint Wash Area
5100
5075

Head (feet)

5050
5025
5000
4975
4950
4925
4900
1940

1950

1960

1970

1980

1990

2000

2010

2000

2010

Year
Simulated Value - Layer 1, Row 23, Col 4
Measured Value - Well 55-526935

Hydrograph 14
Prescott AMA: Table Mountain Area
4850
4825

Head (feet)

4800
4775
4750
4725
4700
4675
4650
1940

1950

1960

1970

1980

1990

Year
Simulated Value - Layer 1, Row 13, Col 10
Measured Value - Well 55-639825

67

Head (feet)

Hydrograph 15
Prescott AMA: Prescott Valley Santa Fe Wellfield
4700
4675
4650
4625
4600
4575
4550
4525
4500
4475
4450
4425
4400
4375
4350
4325
4300
1940

1950

1960

1970

1980

1990

2000

2010

Year
Simulated Value - Layer 2, Row 33, Col 25
Measured Value - Well 55-613028

Hydrograph 16
Prescott AMA: Upper Lynx Creek Area
4950
4925

Head (feet)

4900
4875
4850
4825
4800
4775
4750
1940

1950

1960

1970

1980

1990

Year
Simulated Value - Layer 1, Row 35, Col 26
Measured Value - Well 55-613045

68

2000

2010

Hydrograph 17
Prescott AMA: Upper Lynx Creek Area
4850
4825

Head (feet)

4800
4775
4750
4725
4700
4675
4650
1940

1950

1960

1970

1980

1990

2000

2010

Year
Simulated Value - Layer 1, Row 33, Col 27
Measured Value - Well 55-613042

Hydrograph 18
Prescott AMA: Upper Agua Fria Sub-basin Adjacent to Lynx Creek
4700
4675

Head (feet)

4650
4625
4600
4575
4550
4525
4500
1940

1950

1960

1970

1980

1990

Year
Simulated Value - Layer 1, Row 39, Col 37
Measured Value - Well 55-613024

69

2000

2010

Discharge (acre-feet/year)

Hydrograph 19
Prescott AMA: Groundwater Discharge at Del Rio Springs
4400
4200
4000
3800
3600
3400
3200
3000
2800
2600
2400
2200
2000
1800
1600
1400
1200
1000
1940

1950

1960

1970

1980

1990

2000

2010

Year
Simulated Discharge (includes an undifferentiated ET component estimated at 100-200 af/yr)
USGS Gauge, 1997-2004 (USGS 1997-2004), plus estimated 100 af/yr for ET
and 300 ft/yr for upstream diversions (Foster, 2001)
1940-1945 (Schwalen, 1967); plus estimated 100 af/yr for ET
and 300 af/yr for unreported upstream sw diversions; does not include
pumping impacts from Santa Fe wells
1965-1972 average (Matlock et al, 1973); plus estimated 100 af/yr for ET demand;
does not include upstream sw diversions (if any)
1984-89 average (Corkhill and Mason, 1995); plus estimated 100 af/yr for ET demand,
does not include upstream surface water diversions (if any)

70

Hydrograph 20
Prescott AMA: Groundwater Discharge at the Agua Fria River

Discharge (acre-feet/year)

2400
2200
2000
1800
1600
1400
1200
1000
1940

1950

1960

1970

1980

1990

2000

2010

Year
Simulated Discharge (includes an undifferentiated ET component estimated at 200 af/yr)
1981 - 1997 average (ADWR, 1998); plus 200 af/yr for upstream ET demand
USGS Gauge (2000-2003); reduced to account for surface water runoff,
plus 200 af/yr for upstream ET demand

71

Appendix IV: Additional Figures

72

73

74

Appendix V: Steady-State Calibration Targets

75

Original Steady-State Targets
Target
#
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

Wells 55 Row Col. Layer UTM X UTM Y Model X Model Y
Year
Measured
#
Measured
Head
No Match
26
16
2
368589 3834723 40596.62 59556.4
1947
4713
639828
24
15
2
367772 3836306 37916.21 64749.9
1940
4675
No Match
23
11
2
364550 3837153 27345.47 67528.7
1940
4756
No Match
15
14
2
366990 3843866 35350.62 89552.7
1939
4609
No Match
15
15
2
367830 3843915 38106.49 89713.5
1940
4604
635722
13
14
2
367014 3845560 35429.36 95110.4
1938
4602
606023
10
15
2
367675 3847307 37597.97 100842
1938
4603
No Match
9
16
2
368759 3848431 41154.36 104530
1939
4599
No Match
8
14
2
366783 3848953 34671.49 106242
1938
4601
606300
8
17
2
369509 3849283 43614.96 107325
1941
4605
No Match
8
14
2
367476 3849343 36945.09 107522
1940
4597
605844
7
13
2
366412 3849636 33454.32 108483
1937
4595
623528
7
15
2
367687 3849895 37637.34 109333
1940
4599
No Match
6
13
2
366551 3850466 33910.35 111206
1940
4599
608276
6
14
2
367087 3850582 35668.86 111587
1937
4596
No Match
6
13
2
366500 3850436 33743.03 111108
1938
4599
617596
6
14
2
366734 3850772 34510.74 112210
1938
4600
No Match
6
13
2
366406 3850992 33434.63 112932
1938
4601
No Match
5
16
2
368754 3851605 41137.95 114943
1939
4577
No Match
5
13
2
366545 3851791 33890.66 115553
1939
4606
No Match
4
15
2
367721 3852298 37748.88 117216
1938
4566
No Match
3
14
2
366689 3852991 34363.1 119490
1938
4542

Target
Value
4713
4675
4756
4609
4604
4602
4603
4599
4601
4605
4597
4595
4599
4599
4596
4599
4600
4601
4577
4606
4566
4542

New Steady-State Targets
Target Wells 55 Row Col. Layer UTM X UTM Y Model X Model Y
Year
Measured
#
#
Measured
Head
From ADWR GWSI Database
23
802111
8
15
2
367715 3848690 37728.22 105379
1944
4598
24
639828
24
15
1
367772 3836306 37916.21 64749.9
1940
4675
25
623530
7
15
1
367727 3849903 37654.1 109590
1938
4556
26
605843
7
13
2
366516 3849724 33679.1 108773
1935
4597
27
613020
37
34
1
383368 3825994 89083.56 30917.9
1956
4666.5
28
613018
37
36
1
384785 3825576 93732.13 29547.5
1969
4659
29
613042
34
27
1
377828 3828666 70906.62 39683.9
1964
4742.2
30
No Match
12
11
2
364906 3845745 28512.25 95717.1
1942
4595.46
31
No Match
5
12
2
365902 3851307 31782.63 113967
1937
4596.6
32
No Match
11
12
2
365910 3846624 31808.67 98600.5
1941
4599.85
33
No Match
8
13
2
366349 3848774 33246.24 105656
1942
4600.42
34
No Match
3
13
2
366689 3852991 34364.67 119489
1937
4540.3
35
No Match
4
14
2
366754 3852158 34575.14 116756
1944
4576.03
36
No Match
14
14
2
366990 3843866 35349.12 89552.2
1937
4609.3
37
No Match
4
14
2
367415 3852179 36744.2 116826
1943
4562.5
38
No Match
8
14
2
367476 3849343 36943.53 107523
1940
4597.21
39
No Match
14
15
2
367830 3843915 38105.68 89714.6
1940
4603.97
No Match
26
17
2
369127 3834931 42361.24 60237.5
1945
4678
40

76

Target
Value
4598
4675
4556
4597
4666.5
4659
4742.2
4595.46
4596.6
4599.85
4600.42
4540.3
4576.03
4609.3
4562.5
4597.21
4603.97
4678

New Steady-State Targets (continued)
Target Wells 55 Row Col. Layer UTM X
#
#
41
No Match
6
17
2
369506
42
No Match
6
17
2
369527
43
606294
8
19
2
370735
44
No Match
18
20
1
371679
45
No Match
17
21
1
372410
46
No Match
16
25
1
376077
47
No Match
12
25
1
376300
48
606295
7
19
2
370749
49
611908
8
22
2
373755
50
625108
11
27
2
377355
51
613028
33
25
2
376469
52
564575
23
8
2
362439
53
639825
21
10
2
363696
54
536656
21
6
2
360845
55
636587
10
21
2
372502
56
613043
38
36
1
384558
57
638550
42
39
1
386962
58
627588
23
5
1
359586
From American Ranch Report (Manera 1999)
59
573965
21
4
1
358982
60
573968
22
4
1
359169
From Head Map (Corkhill and Mason 1995)
61
23
27
2
377819
62
5
16
1
368554
63
6
16
1
368735
64
7
16
1
368614
65
11
14
1
366864
66
2
15
1
367831
67
11
9
1
363104
68
11
19
1
371145
69
23
24
1
375136
70
35
26
1
376788
71
32
28
1
378130
72
3
14
1
367047

UTM Y Model X Model Y
3850917
3850577
3848860
3840811
3842187
3842414
3845739
3849688
3849239
3847145
3829259
3837002
3839033
3838454
3847431
3824971
3821699
3837216

43606.34
43673.93
47521.73
50733.14
53133.31
65163.48
65894.37
47684.46
57543.59
69356.11
66449
20421.01
24542.68
15190.1
53433.41
92678
101040.9
11058.92

112684
111571
105938
79528.4
84044
84789.5
95696.8
108653
107182
100310
41630.1
67033.3
73696
71795.4
101249
27792
17239.2
67735.1

3839047 9077.974 73742.2
3838224 9690.499 71043.8
3837019 70877.75 67089.1
3851598 40482.1 114920
3850754 41075.5 112151
3849910 40679.9 109381
3846917 34937.34 99563.8
3853829 38108.4 122239
3846985 22600
99786.3
3846744 48981.4 98994.5
3837083 62075.55 67300.4
3827445 67495
35677.3
3829820 71899.6
43470
3852985 35536.9 119470

77

Year
Measured
Measured
Head
1938
4605.55
1938
4605.2
1947
4599
1940
4613.72
1940
4618.95
1939
4611.14
1941
4609.47
1948
4592.4
1939
4608.16
1940
4613.02
1971
4663
1999
4805.6
1939
4753.5
1999
4882.6
1942
4621.43
1956
4630.5
1973
4617.9
1992
5033
1999
1999

5019
5012

Target
Value
4605.55
4605.2
4599
4613.7
4618.95
4611.14
4609.47
4592.4
4608.16
4613
4663
4805.6
4753.5
4885
4621
4630.5
4617.9
5033
5019
5012
4630
4505
4515
4535
4575
4445
4670
4600
4625
4855
4725
4450