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How much will the Big Chino Water Ranch cost? Who pays?
The project costs and water quantities are contractually divided between Prescott at 54% and Prescott Valley at 46%. For the limited expenses incurred to date, Prescott has been charging 20% to current water users and 80% to new development. How future costs and water will be allocated is very uncertain and has been made complicated by recent state laws that restrict the application of impact fees. To learn more, read this Op-Ed.
When will the Big Chino Pipeline be built?
In September 2012, the cities and SRP announced plans for monitoring and modeling studies that may take 8 - 10 years to complete. As of 2014, they are attempting to improve our understanding of the hydrogeology of the Big Chino Valley by installing additional monitoring equipment to collect data for modeling purposes. They state that one purpose of the model is to determine if and when mitigation measures will be necessary.
Scientific hydrology principles and the extensive data currently available, however, clearly conclude that if groundwater is transported out of the Big Chino Sub-basin, the natural discharge at Verde Springs will be diminished and therefore mitigation would be necessary to maintain flows in the Verde river.
The complexity of their monitoring and modeling plan and the difficulty of the mitigation issue means that the pipeline likely will not be built before 2022.
Although the three parties intend to issue periodic reports on their studies, the content of their negotiations are not available to the public.
Will we vote on the Big Chino Pipeline and when?
The Charter as written requires a public vote before further expenditures are made on the project. The Charter, however, does allow the city to conduct feasibility studies up to $5 million without a public vote and the city is currently doing such studies and remains under the feasibility studies limit.
Unfortunately, some Prescott officials claim a public vote is not required because the project began before the Charter was amended. The amendment, however, was written to address the Big Chino situation, which was the only existing project affected. The city has never officially stated a vote is required or not required.
When a vote will be required is uncertain and will depend on when the city expects to undertake any further project expenditures beyond feasibility studies or if they intend to exceed the feasibility limit. For more information, read this Op-Ed.
Will the Big Chino Water Ranch harm the Verde River?
Verde River flow is especially sensitive to pumping in the Big Chino because it is the water source for 80-86% of the base flow. Big Chino groundwater surfaces at Verde Springs, the sole source of water for the first 25 miles of the Verde River - some of the finest surviving riparian habitat in Arizona.
Basic hydrology tells us that whenever groundwater is removed, there must be a consequence somewhere in the system. Specifically for the Big Chino, pumping will eventually reduce the base flow of the river by a nearly equal amount. .Arizona water laws authorize the Prescott region municipalities o import approximately 18,000 acre-feet per year (afy) of groundwater from the Big Chino. The base flow of the Verde at the USGS Paulden gage is currently about 14,500 afy. Because the legally authorized water export is greater than the flow of the river, if the full amount of allowed pumping were to occur, Verde Springs would eventually cease to flow and the upper 25 miles of the Verde would become a dry wash, flowing only after precipitation events. The question is not if, but when Verde Springs will be affected
Although large water exports are still in the planning stages, the Verde has already been diminished by agricultural and domestic wells in the Big Chino Valley. Prior to development, the base flow of the Verde measured at the USGS Paulden gage was 21,000 acre-feet per year. Now it is about 14,500 acre-feet per year. We have already lost nearly a third of the base flow to groundwater pumping.
To learn more, read this Op-Ed.
How long will it take to dry up the Verde?
In 2011, the USGS completed the Northern Arizona Regional Groundwater Flow Model (NARGFM), developed at the request of, and for use by, Yavapai County water planners. Because the tri-cities did not believe that that NARGFM was sufficiently accurate, the USGS has not been asked by the county to analyze the effects of pumping in the Big Chino on the Verde River.
However, the Verde River Basin Partnership (VRBP) retained USGS to run NARGFM for the Verde Valley. See this CWAG Op-Ed for a brief description of the results. CWAG has posted a video presenting the results. The full USGS report can be viewed or downloaded.
In general, the VRBP study found:
• Historical pumping has diminished the base flow of Verde River from the headwaters at Paulden to downstream of Camp Verde.
• Future pumping, whether increased, held constant, or decreased, will further diminish the base flow.
• Pumping in the upper watershed contributed to the diminishment of base flow in Camp Verde.
• Portions of the river are at risk of going dry in the future.
• The USGS model is a useful tool to help manage our water resources and to help protect the Verde River.
CWAG's hydrogeologist is now building on the VRBP results to describe how the Big Chino Water Ranch will change the upper Verde River. Full results will be published in late 2014.
What is a Groundwater Flow Model?
The model consists of data describing the hydrogeologic properties of the groundwater basin, plus all wells, streams, springs, recharge sites, and local precipitation. Models often cover very large areas, possibly several watersheds, so the computer files include enormous amounts of physical data describing the study area.
To verify that the model accurately represents the real world, it is calibrated. A starting time with known historical water levels and flows is selected, then the model is asked to calculate levels and flows up to the present time. If the draft model fails to predict accurately the current levels and flows, some internal properties of the model are adjusted, then the test is repeated until the correct results are generated. When the draft model closely predicts current levels and flows based on a known starting point, then the model is considered calibrated and is worthy of use.
To use the model, planners must create a future scenario that would include various stresses to the groundwater system. These stresses could be changes in precipitation, or groundwater pumping with a specific water capacity in a specific location. Using this future scenario, the model can predict future groundwater levels and flows, permitting a water manager to see the future consequences of an action. The groundwater model allows water resource managers to make informed decisions instead of guessing or hoping about the future.
For a more detailed description, see this OpEd.