Publications

The Big Chino Subbasin is a groundwater basin that includes the Verde River headwaters in Yavapai County in north-central Arizona. Groundwater in the southern part of the subbasin is found primarily in the Big Chino and Williamson Valleys. The former is a potential municipal water source for growing communities in Yavapai County, particularly groundwater from the Big Chino Water Ranch, about 15 mi

Beginning in the late 1970s, 10- to 15-year cyclical oscillations in salinity were observed at lower Colorado River monitoring sites, moving upstream from the international border with Mexico, above Imperial Dam, below Hoover Dam, and at Lees Ferry. The cause of these cyclical trends in salinity was unknown. These salinity cycles complicate the U.S. Bureau of Reclamation's (Reclamation) responsibi

One of the desired outcomes of dam decommissioning and removal is the recovery of aquatic and riparian ecosystems. To investigate this common objective, we synthesized information from empirical studies and ecological theory into conceptual models that depict key physical and biological links driving ecological responses to removing dams. We define models for three distinct spatial domains: upstre

The Navajo (N) aquifer is an extensive aquifer and the primary source of groundwater in the 5,400-square-mile Black Mesa area in northeastern Arizona. Availability of water is an important issue in the Black Mesa area because of continued water requirements for industrial and municipal use by a growing population and because of the arid climate. Precipitation in the area typically ranges from less

The U.S. Geological Survey monitors groundwater-storage change and land-surface elevation change caused by groundwater withdrawal in Tucson Basin and Avra Valley—the two most populated alluvial basins within the Tucson Active Management Area. The Tucson Active Management Area is one of five active management areas in Arizona established by the 1980 Groundwater Management Act and governed by the Ar

We have developed a screening tool to visualize and conceptualize the filtering properties of a layered vadose zone. Climate projections indicate that rainfall timing and magnitude may change and impact groundwater resources. This increases the importance of understanding how the vadose zone filters infiltration variability and ultimately affects recharge and groundwater resources. An approximate

Core IdeasWe describe an approximation for filtering of periodic infiltration in layered soil.Transitions in soil‐water properties between soil layers affect the filtering.Errors are smaller in soils where changes in soil‐water properties are small.Infiltration and downward percolation of water in the vadose zone are important processes that can define the availability of water resources. We prese

Study RegionThis study region encompasses the Transboundary San Pedro and Santa Cruz aquifers which are shared between the states of Sonora (Mexico) and Arizona (US). Special regional considerations include a semi-arid climate, basin-fill aquifers with predominantly montane recharge areas, economic drivers in the mining, trade, and military sectors, groundwater-dependent cities with expanding cone

This report summarizes analyses of middle Verde River watershed environmental flows detailed in U.S. Geological Survey Scientific Investigations Report 2017-5100, “Preliminary synthesis and assessment of environmental flows in the middle Verde River watershed, Arizona," by N.V. Paretti, A.M.D. Brasher, S.L. Pearlstein, D.M. Skow, B. Gungle, and B.D. Garner.

Changes in the amount of water stored in underground aquifers cause small changes in Earth’s gravitational field. The U.S. Geological Survey’s Southwest Gravity Program has developed methods for measuring terrestrial gravity changes with part-per-billion precision. The measurements allow scientists to map changes in groundwater storage and to improve models that simulate groundwater flow.

Conceptual and numerical models were developed to understand and simulate monthly flow-weighted dissolved-solids concentrations in the Colorado River at Imperial Dam. The ability to simulate dissolved-solids concentrations at this location will help the Bureau of Reclamation satisfy the binational agreement on the volume and salinity of Colorado River water delivered to Mexico. A robust spatial- a

Hydrologic model input datasets such as climate, land use, elevation, soil, and geology information are available in a range of scales for use in water resources investigations. Smaller spatial and temporal scale input data allow groundwater recharge models to simulate more physically realistic processes and presumably result in more accurate estimates of groundwater recharge. Projected climate da