John P Hoffmann (Former Employee)

A large fraction of ground water stored in the alluvial aquifers in the Southwest is recharged by water that percolates through ephemeral stream-channel deposits. The amount of water currently recharging many of these aquifers is insufficient to meet current and future demands. Improving the understanding of streambed infiltration and the subsequent redistribution of water within the...

Ground-water recharge in the arid and semiarid southwestern United States results from the complex interplay of climate, geology, and vegetation across widely ranging spatial and temporal scales. Present-day recharge tends to be narrowly focused in time and space. Widespread water-table declines accompanied agricultural development during the twentieth century, demonstrating that...

The upper and middle Verde River watersheds in central Arizona are primarily in Yavapai County, which in 1999 was determined to be the fastest growing rural county in the United States; by 2050 the population is projected to more than double its current size (132,000 in 2000). This study combines climatic, surface-water, ground-water, water-chemistry, and geologic data to describe the...

A local ground-water flow model is used to simulate four recharge scenarios along Rillito Creek in northern Tucson to evaluate mitigating effects on ground-water deficits and water-level declines in Tucson's Central Well Field. The local model, which derives boundary conditions from a basin-scale model, spans the 12-mile reach of Rillito Creek and extends 9 miles south into the Central...

No abstract available.

No abstract available.

Stream temperature has long been recognized as an important water quality parameter. Temperature plays a key role in the health of a stream’s aquatic life, both in the water column and in the benthic habitat of streambed sediments. Many fish are sensitive to temperature. For example, anadromous salmon require specific temperature ranges to successfully develop, migrate, and spawn [see...

Characteristics of the stream-channel and basin-fill deposits beneath a 12-mile reach of Rillito Creek, Pima County, Arizona, were obtained to describe the geohydrologic system. The findings presented here are part of a larger project to improve the understanding of recharge processes beneath ephemeral streams. The stream-channel deposits, which range in thickness from 15 to 40 feet...

Increased agricultural and recreational activities and recent growth of population centers within the Verde River basin have led to concerns about the quality and quantity of water flowing onto the Fort McDowell Indian Reservation. The purpose of this study was to determine the quality and quantity of water in the Verde River and in the shallow stream-channel deposits in the vicinity of...

Grande Wash is a tributary of the Verde River and drains an area of 13 square miles within the McDowell Mountains and the Town of Fountain Hills in Central Arizona. The wash enters the Fort McDowell Indian Reservation at the eastern boundary of Fountain Hills and is incised in coarse-grained alluvium that is contiguous with the alluvial aquifer along the Verde River. The aquifer is used...

A study of the geology, ground-water occurrence, and estimated well yields from the Mariana Limestone was done to investigate ground-water availability in the Kagman area, Saipan. The Mariana and Tagpochau Limestone formations form the major aquifer in the Kagman drainage basin. The Mariana Limestone, which is the major water-bearing unit in the Kagman area, ranges in thickness from 300...

The Navajo Nation and Hopi Tribe of the Black Mesa area, Arizona, depend on ground water from the N aquifer to meet most tribal and industrial needs. Increasing use of this aquifer is creating concerns about possible adverse effects of increased ground-water withdrawals on the water resources of the region. A thorough understanding of the N aquifer is necessary to assess the aquifer's...