Although population projections are always inaccurate, estimates are possible. First, note that the Yavapai County General Plan classifies Paulden and the Big Chino as a designated growth area. As of 2016, the Paulden area was one of the fastest growing areas in Yavapai County, showing a 1.3% annual growth rate. The Central Yavapai Highlands Water Resource Management Study projects Big Chino growth at 2.25% per year to over 32,000 by 2030, which would then use about 5,000 afy of groundwater. At build-out in the Big Chino, at the current 2-acre minimum zoning, over 75,000 homes could be built, requiring 26,000 afy of groundwater. Projecting future water use are always difficult, but the best available data yields the following estimates:
Current Groundwater Use
For residential use, the 2010 Census found 10,669 residents in the Big Chino/Williamson Valleys. At average per capita water use rates, we estimate about 1,800 afy of groundwater is used.
Thus the total current groundwater use is in the range of 4,800 afy to 7,500 afy, reflecting the uncertainty in agricultural usage.
Updated December 19, 2018
Planned Uses for Big Chino Water
The 8,067 afy of exemption water will be divided 54/46 between Prescott and Prescott Valley. Prescott has committed 900 afy to the phased expansion of the Deep Well Ranch. Prescott Valley has committed 2,000 afy of their 3,711 afy share of Big Chino exemption water to development on a section of State Trust Lands near the city. Prescott Valley has not committed any exemption water, or the effluent collected from using that water, either to safe yield or to mitigation; presumably PV’s share will be entirely used to support growth and development.
Prescott Council Resolution 3688 states that their share of the HIA water will be dedicated to either safe yield in the AMA or to mitigate the effects of pumping on the Verde River and would not be used for development or growth. Prescott Valley has made no official commitments to use their share of HIA water for safe yield.
Updated December 19, 2018
Future Population Growth
Updated December 19, 2018
Big Chino Valley Pumped Storage Project
ITC Holding, Inc has applied for a preliminary permit to the Federal Energy Regulatory Commission (FERC) to operate a pumped storage energy facility in the Big Chino Valley, about 6 miles south of Seligman. The project will construct a water storage reservoir high on the slopes of Picacho Butte connected by subsurface pipes to another reservoir on the valley floor.
In operation, the project will use inexpensive off-peak electricity to pump water into the high reservoir, often at night. During peak electricity rates periods, typically summer days, water is released from the upper reservoir into the lower reservoir to generate power for sale at peak rates.
Pumped storage is similar to a battery in that it stores and releases electric energy; the process is roughly 80% efficient. The project intends to profit by using the price spread between off-peak and peak power rates and by other contracted services. Possible sources of off-peak power would be regional coal-fired power plants, photovoltaic power, and wind-generated electricity.
For a more complete description of the project, see the CWAG Info Bulletin.
Updated December 19, 2018
Summary of Big Chino Demand
Expanded agricultural irrigation is a huge potential groundwater consumer. There are no state laws restricting new irrigated fields in the Big Chino Valley. One new 1,000 acre alfalfa field could consume 5,000 afy of groundwater. For comparison, in the last decade, agricultural pumping in both Kingman and Wilcox has increased 25,000 afy from out-of-state agribusiness seeking more reliable water supplies than in California. We estimate that expanded irrigation could consume up to 1.6 rivers of water each year!
Legally authorized water exports (includes the Big Chino Water Ranch and Historically Irrigated Acreage water) could consume another 1.6 rivers every year. At this time the total legally exportable water from the Big Chino is 18,813 afy, including the Big Chino Water Ranch and HIA water.
Future groundwater demand from population growth and development in the valley at 1.5% annual population growth could consume up to 20,000 afy, or another 1.6 rivers per year.
The Big Chino Valley Pumped Storage facility will use14,000 afy of groundwater for only two years. The developer intends to mitigate the effects on base flow. If they are successful, there would be very little impact on the river.
Totaling these estimates, legally permitted groundwater demand in the Big Chino could equal FIVE TIMES the current river base flow (now about 13,000 afy).
Updated December 19, 2018
Current & Planned Water Use
Because Arizona water law does not require well users to report their pumping, there is little exact information about current groundwater use in the Big Chino. However, some estimates are possible. For irrigation water use, 2016 aerial surveys indicate 1400-1900 acres of irrigated lands in the Big Chino (including Williamson Valley), the USGS estimates that 3,000 – 3,200 acre-feet/year (afy) of groundwater is used for irrigation. However, the state law on HIA water indicates that up to 5,700 afy is used - an obvious discrepancy. Historical estimates of Big Chino agricultural groundwater pumping report approximately 20,000 afy.
The reservoirs will be initially filled by pumping 28,000 acre-ft of groundwater from the Big Chino sub-basin. The reservoirs are a closed loop system. The only consumptive water use is from evaporation at the reservoir surface and is estimated to be less than1,000 acre-feet/year.