USGS FY10 workplan to publish the regional groundwater flow model Yavapai
County scenario results and to continue hydrologic data collection in support of the
understanding the hydrologic system of the Upper and Middle Verde River
Watersheds, and adjoining areas
Introduction
A numerical groundwater flow model simulating the groundwater system of the
upper and middle Verde River Watersheds, Coconino Plateau, and Mogollon Highlands
has been developed by the U.S. Geological Survey (USGS) in cooperation with the
Arizona Department of Water Resources (ADWR) under the Rural Watershed Initiative
(RWI) and Yavapai County. The numerical model enables examination of groundwater
development scenarios, and identification of potential attendant effects on surface-water
resources. Groundwater development scenarios developed by Yavapai County were
intended to be examined during FY09; however, the model was not sufficiently
completed to allow scenario analysis and not all of the planned scenarios were delivered.
The 3 scenarios will therefore be simulated and published during FY10.
In addition to scenario publication, selected ongoing basic data collection
activities will continue that will add to hydrologic data and assist in evaluating the
accuracy of the groundwater flow model. The data collection tasks include operation of
the Williamson Valley streamflow gaging station and precipitation gage, continued
operation of 8 continuous groundwater level stations, collection of stable isotopes of local
precipitation and Verde River water, analysis of stable isotopes in ephemeral channel
flow samples, and seasonal monitoring of aquifer storage change at 12 well sites. Figure
1 depicts planned monitoring.
Publication of the numerical modeling scenario results
The USGS will publish a USGS series report with results of scenario modeling
from Yavapai County Technical Advisory Committee (TAC) defined scenarios. The
document will be published in an electronic PDF format only and will be publicly
available through a Persistent URL.
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The document will include the input datasets, operation of the model, and results
of the groundwater model, but will not discuss assumptions involved in developing the
input scenarios and the implications of the modeling results.
The report will contain geospatial figures of the inputs and outputs for effective
communication of results. Yavapai County TAC recommendations will be considered in
development of this report on the primary water resource questions pertaining to the
provided scenarios.
Williamson Valley Stream-Flow Gaging Station and Precipitation Gage
Long-term monitoring of streamflow is critical to the understanding of
groundwater recharge and discharge and as such is essential for proper construction and
calibration of groundwater models. The value of data increases with length of record;
longer records facilitate evaluation of trends caused by climate variability, vegetation
changes, land-use changes, or changes in groundwater withdrawals. The USGS stream
gage at Williamson Valley Wash (Fig. 1) was re-activated in FY2001 to record surface
water that flows toward the Big Chino Valley and infiltrates into the subsurface, often
before it reaches the Valley. While Big Chino Wash, the major drainage in Big Chino
Valley, is dry most of the year, flows from some of the perennial tributaries end at the
valley margin, indicating that tributaries contribute a portion of the total recharge to the
valley aquifer system. The Williamson Valley gaging station, therefore, allows an
estimation of streamflow available for recharge below the station. Operation and
maintenance of the gaging station and periodic discharge measurements will be
conducted through this task. The integrity of the data will be verified and the data
populated into the USGS NWIS database.
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Figure 1. Proposed hydrologic monitoring locations in the Upper and Middle Verde
River Basins.
Continuous Groundwater Level Monitoring
Wells currently instrumented for continuous water-level altitude monitoring will
be maintained and continue serving real-time water level data to the web. Long-term
records of seasonal and annual water-level fluctuations began at 7 of the wells in March
2000. Records at 1 well began last year after switching 1 of the original 8 sites for a more
benficial well. These data will complement information collected by staff of the ADWR
Field Services Program. These wells provide a critical continuous record of groundwater
conditions that is essential for understanding both climate and human impacts on the
system and for maintaining the regional groundwater flow model.
After examining the well network for the FY09 workplan, the AzWSC
recommended replacing well A-16-01 07 DDD in the Little Chino Valley with a deep
well in the area of the silt and clay in the Big Chino. Available continuous records at well
A-16-01 07 DDD indicate linear rates of water-level decline follow periodic sharp waterJan 6, 2010
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level rises after recharge events. These trends could more efficiently be documented by
seasonal or even annual water-level measurements, which would free-up continuous
monitoring equipment for use at another well. Well B-17-02S04DBC1 was chosen as the
replacement well. These wells, as well as other monitoring wells that have long-term
water-level records, can be used as calibration checks for any groundwater flow model.
Operation and maintenance of the stations and periodic calibration measurements will be
conducted through this task. The integrity of the data will be verified and the data
populated into the USGS NWIS database.
Stable Isotope Monitoring of Precipitation and Streamflow
During 2002-2009, stable isotopes of precipitation were collected from a range of
elevations to improve the characterization of the relation between elevation and stable
isotope values from precipitation. An improved characterization of precipitation isotopic
content in combination with available data describing the isotopic content of groundwater
will result in a better understanding of the geographic distribution of recharge to the
groundwater system. Improved understanding of the recharge distribution can be used to
improve the groundwater model representation of recharge processes in future updates.
For 2010, this task will continue the collection of stable isotopes at a subset of previously
monitored precipitation sites.
In addition, for FY 2010, USGS will continue collecting and processing repeat
stable isotope measurements on a quarterly basis from the Verde River main stem and
selected tributaries. The Verde River isotope measurements will continue a data set that
began last year to monitor changes in the sources of water to the river that may result
from groundwater withdrawals or changes in recharge rates. Verde River samples will be
collected at the gaging stations at Paulden, Clarkdale, Camp Verde, and the head of
perennial flow where Beaver Creek joins the Verde. The integrity of the data will be
verified and the data populated into the USGS database.
During FY09, USGS in cooperation with several local researchers and volunteers,
began monitoring of winter runoff to provide an estimate of the isotopic signature of
likely recharge, further improving the understanding of recharge processes. This was an
efficient and productive effort and should be repeated in 2010 to establish consistency in
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trends. USGS will process and analyze up to 20 samples for stable isotopes of water from
winter runoff samples, provided the sample collection is carried out by other researchers
or volunteers.
Aquifer Storage Monitoring
During 2009, USGS established aquifer storage monitoring stations at 12
observation wells and completed the initial observations. The purpose of the monitoring
is to establish records for aquifer storage change and develop estimates of aquifer storage
properties; a poorly defined but important aquifer property that influences the response of
the aquifer to changes in withdrawals and recharge. The 12 well sites include 11 wells
where water levels are continuously monitored by USGS or ADWR and 1 ADWR Index
well. Aquifer storage change is estimated through seasonal observations, 3 each year, of
the acceleration of gravity at the wells, which varies with the mass of water stored in the
aquifer. Complimentary observations of soil moisture in the upper 2 ft of soil are also
made at each well for the purpose of evaluating and correcting for the influence of near
surface and non-aquifer variations in water storage on the gravity observations. At least 3
years of gravity records are needed to evaluate the adequacy of changes in gravity and
water levels for estimating aquifer storage properties at each well.
The aquifer storage monitoring network will be evaluated after 3 years for the
need for continued monitoring. Recommendations for continuation or elimination of the
monitoring at each well will be made on a case by case basis. It is expected that gravity
changes will be minimal at some wells that display large water-level change, which will
establish aquifer storage properties in the range of a confined aquifer and continued
monitoring of aquifer storage at the well will not be necessary. Records of gravity and
water-level change at other wells will likely display a range of variations that will result
in a range of hydrogeologic interpretations that may or may not require continued
monitoring. It is expected that new well sites in different parts of the aquifer system will
be introduced to the monitoring network as other sites are eliminated. Eventually, the
monitoring should define water-level and aquifer storage relations for the full range of
the expected hydrogeologic conditions in the study area.
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For FY10 soil moisture at gravity sites will be monitored to better constrain mass
changes in the shallow subsurface that are unrelated to aquifer storage.
Budget
The costs associated with the core project tasks of model scenario publication,
streamflow, well, isotope, and aquifer storage monitoring are included in Table 1.
Personnel needed include two hydrologists, and additional support staff. USGS match
funding will be used to publish the model scenarios.
Table 1. Project costs for regional groundwater model scenario publication, and
monitoring. This budget is presented on the USGS Fiscal Year (Oct 1 to Sep 30).
[Values in thousands of dollars]
Item
FY10
Williamson Valley Stream and Precipitation Gage
16
Continuous Water Level Monitoring
20
Stable Isotopes - precipitation and Verde flow
11
Stable Isotopes – analysis of runoff samples
3
Model Scenario Open-File Report publication
35
Seasonal aquifer storage monitoring
33
Soil moisture monitoring
5
TOTAL
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123
Yavapai County Share
83
USGS Share
40
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