Hydrogeology of the Upper and Middle Verde River Watersheds, Central Arizona

The Big Chino subbasin, in the upper Verde River watershed is 1,850 square miles in area. Within the subbasin, Big Chino Valley and Williamson Valley encompass about 570 square miles excluding the surrounding mountains and the western part of the Coconino Plateau. The valleys are filled with alluvial deposits eroded from adjacent uplands and interbedded basalt flows. Median thickness of the combined alluvial deposits and basalt flows is about 435  feet. The  estimated volume of saturated basin-fill deposits within the valleys is about 155 million acre-feet. Beneath the basin-fill aquifer is a sequence of water-bearing Paleozoic formations that receive recharge where they crop out along the western boundary of the subbasin. Together, the basin-fill sediments and the Paleozoic formations constitute the regional aquifer in the Big Chino subbasin. Water-balance calculations indicate that about 1–2 percent of annual precipitation recharges the regional aquifer. Recharge occurs primarily along the Juniper and Santa Maria Mountains, Big Black Mesa, Granite Mountain, and Bill Williams Mountain. Average winter base flow at the Williamson Valley streamflow-gaging station (09502800) was 3.9 cubic feet per second during 1965–84 and 1.7 cubic feet per second during 2002–03. The  decline is attributed primarily to climate fluctuations. Base flow at the Verde River near Paulden streamflow-gaging station (09503700) averages about 17,700  acre-feet per year. It currently (2003) is about equal to the long-term average but has declined at an annual rate of about 380 acre-feet per year since about the mid-1990s. Ground-water outflow from the Big Chino Valley occurs only as base flow in the Verde River. Declines in ground-water altitudes during the past 50 years are attributed primarily to ground-water withdrawals.

The Little Chino subbasin, in the upper Verde River watershed, is the smallest of the three subbasins in the study area and has had the greatest ground-water development. The regional aquifer underlying the subbasin is composed of sedimentary, volcanic, and basin-fill deposits of Quaternary and Tertiary age. Interfingering of less permeable units, such as lati-andesite, cemented alluvium, and trachyandesite, create confining conditions and artesian flow in some areas. The regional aquifer encompasses an area of about 310 mi2, including Little Chino Valley and Lonesome Valley. Thickness of the basin-fill deposits generally ranges from about 100 to 800 feet; the estimated volume of the saturated basin-fill deposits in the Little Chino subbasin is 33 million acre-feet.

Winter precipitation is the primary source of recharge for the Little Chino subbasin as well as for other subbasins in the upper and middle Verde River watersheds. Water-balance calculations indicate that about 1–2 percent of annual precipitation recharges the regional aquifer in the Little Chino Subbasin. This amount may have been reduced since the predevelopment period (before 1940) by the construction of channel retention facilities along Granite Creek and its tributaries. During predevelopment times a larger volume of ground water flowed north across the southern boundary of the subbasin than flowed south. Recent numerical ground-water simulations indicate a greater flow of ground-water southward across the boundary than northward. Discharge from Del  Rio Springs has declined from about 2,800 acre-feet per year between 1940 and 1945 to about 1,000 acre-feet per year in 2003.

The 2,500-square-mile Verde Valley subbasin of the Verde River ground-water basin coincides with the middle Verde River watershed. The regional aquifer in the subbasin is composed predominantly of Paleozoic units present in the Coconino Plateau and of the basin-fill sediments, including the  Verde Formation. The volume of saturated sediments, which are distributed primarily along the course of the Verde River, is about 112 million acre-feet. Recharge to the aquifer occurs predominantly along the Mogollon Escarpment and on the Coconino Plateau.

About 4 percent of the average annual precipitation results in recharge to the ground-water system; most of the recharge occurs from winter precipitation. Ground water discharges to the major tributaries and directly to the Verde River. Base flows in tributaries have declined in part because of climate fluctuations. Average winter base flow at the Verde River near Camp Verde streamflow-gaging station (09506000) was 148,600 acre-feet per year for 1936–44  and 1989–2003, but base flow declined at an annual rate of about  2,000 acre-feet per year during 1994–2003. Ground-water storage declines are almost entirely caused by ground-water pumping and reductions in natural channel recharge resulting from streamflow diversions. Storage declines are most evident in areas of municipal development where ground-water withdrawals are largest.

A geochemical mixing model was used to quantify fractions of ground-water sources to the Verde River from  various parts of the study area. Most of the water in the  uppermost 0.2 mile of the Verde River is from the Little  Chino subbasin, and the remainder is from the Big  Chino subbasin. Discharge from a system of springs increases base flow to about 17 cubic feet per second within the next 2  miles of the  river. Ground water that discharges at  these springs is derived from the western part of the Coconino Plateau, from the Big Chino subbasin, and from the  Little Chino subbasin.

The relative component of base flow in the Verde River derived from the western part of the Coconino Plateau decreases in the downstream direction, as base flow increases,   relative to the component from the Chino Valley subbasins. By river mile 22, the primary source area is the Big  Chino subbasin, and the contribution from the western part of the Coconino Plateau is negligible. Ground-water discharge from the Verde Valley begins to contribute to base  flow between river miles 22 and 30. The increases in base flow in this reach are primarily due to contributions from  ground water that has recharge source areas at high altitudes along the Coconino Plateau and Black Hills. Ground water that has recharge source areas at low altitudes in the Verde Valley, and ground water from the Coconino Plateau and the Black Hills, also contribute to base flow between river  miles 30 and 89.

Water quality in the study area generally is good for intended uses and shows little effects from human activities. Constituent concentrations in surface water and ground water  generally were well below Federal and State regulations. Constituents exceeding U.S. Environmental Protection Agency Maximum Contaminant Levels or Action Levels include antimony, arsenic, fluoride, lead, nitrate, and selenium. Of  these constituents, arsenic exceeded the MCL in  the greatest number of samples, primarily owing to mineralogy of  the Supai Group and the Verde Formation. Fluoride and sulfate concentrations exceeded the U.S. Environmental Protection Agency Secondary Maximum Contaminant Levels  in a few  samples.

Average water use in the Big Chino, Little Chino, and Verde Valley subbasins was about 12,000, 13,000, and 47,000  acre-feet per year, respectively, for 1990–2003. Agricultural and residential water use exceed other water uses; however, agricultural use within the Chino subbasins has  decreased since the 1960s and 1970s.  

CONTENTS

Abstract

Introduction

Climate

Surface Water

Hydrogeology

Geochemistry and Water Quality

Selected References

Conceptual Model of Hydrologic System

Study Limitations and Considerations for Future Data Collection and Analyses

Summary

References Cited

Glossary

Appendices

Plates

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Send questions or comments about this report to the author, Kyle W. Blasch, (520) 670-6671.

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U.S. Department of the Interior, U.S. Geological Survey Persistent URL: https://pubs.water.usgs.gov/sir20055198 Page Contact Information: USGS Publishing Network Last modified: February 26, 2008 (mfd)

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