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Research about Pima County, Arizona

Source-linked reports with geographic coverage including Pima County, Arizona.

17 recordsLinked to original sources
USGS2007

Estimated infiltration, percolation, and recharge rates at the Rillito Creek focused recharge investigation site, Pima County, Arizona

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 unsaturated zone is fundamental to quantifying and forming an accurate description of streambed recharge. In addition, improved estimates of recharge from ephemeral-stream channels will reduce uncertainties in water-budget components used in current ground-water models. This chapter presents a summary of findings related to a focused recharge investigation along Rillito Creek in Tucson, Arizona. A variety of approaches used to estimate infiltration, percolation, and recharge fluxes are presented that provide a wide range of temporal- and spatial-scale measurements of recharge beneath Rillito Creek. The approaches discussed include analyses of (1) cores and cuttings for hydraulic and textural properties, (2) environmental tracers from the water extracted from the cores and cuttings, (3) seepage measurements made during sustained streamflow, (4) heat as a tracer and numerical simulations of the movement of heat through the streambed sediments, (5) water-content variations, (6) water-level responses to streamflow in piezometers within the stream channel, and (7) gravity changes in response to recharge events. Hydraulic properties of the materials underlying Rillito Creek were used to estimate long-term potential recharge rates. Seepage measurements and analyses of temperature and water content were used to estimate infiltration rates, and environmental tracers were used to estimate percolation rates through the thick unsaturated zone. The presence or lack of tritium in the water was used to determine whether or not water in the unsaturated zone infiltrated within the past 40 years. Analysis of water-level and temporal-gravity data were used to estimate recharge volumes. Data presented in this chapter were collected from 1999 though 2002. Precipitation and streamflow during this period were less than the long-term average; however, two periods of significant streamflow resulted in recharge—one in the summer of 1999 and the other in the fall/winter of 2000. Flux estimates of infiltration and recharge vary from less than 0.1 to 1.0 cubic meter per second per kilometer of streamflow. Recharge-flux estimates are larger than infiltration estimates. Larger recharge fluxes than infiltration fluxes are explained by the scale of measurements. Methods used to estimate recharge rates incorporate the largest volumetric and temporal scales and are likely to have fluxes from other nearby sources, such as unmeasured tributaries, whereas the methods used to estimate infiltration incorporate the smallest scales, reflecting infiltration rates at individual measurement sites.

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USGS2006

The Ajo Mining District, Pima County, Arizona: Evidence for middle Cenozoic detachment faulting, plutonism, volcanism, and hydrothermal alteration

Introduction: The Ajo porphyry copper deposit and surrounding Upper Cretaceous rocks have been separated from their plutonic source and rotated by detachment faulting. Overlying middle Cenozoic sedimentary and volcanic rocks have been tilted and show evidence for two periods of rotation. Following these rotations, a granitic stock (23.7?0.2 Ma) intruded basement rocks west of the Ajo deposit. This stock was uplifted 2.5 km to expose deep-seated Na-Ca alteration.

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USGS2005

Effects of drought on shrub survival and longevity in the northern Sonoran Desert

Effects of drought on shrub survival and longevity in the northern Sonoran Desert. J. Torrey Bot. Soc. 132: 421–431. 2005.—Permanent vegetation plots in the northern Sonoran Desert, USA, provided an opportunity to assess the effects of recent drought on desert shrubs and to examine survival in relation to rainfall variability during the past 76 years. Survival and maximum longevity of six species were determined for eight intercensus periods between 1928 and 2004. Average annual survival was Ambrosia deltoidea , 0.9167 ± 0.0415; Encelia farinosa , 0.7952 ± 0.0926; Janusia gracilis , 0.9334 ± 0.0247; Krameria grayi , 0.9702 ± 0.0270; Larrea tridentata , 0.9861 ± 0.0174; and Lycium berlandieri , 0.9910 ± 0.0077. The longest-lived species were Larrea , Lycium , and Krameria , with average maximum life spans of 330, 211, and 184 years. Janusia , Ambrosia , and Encelia were much shorter lived, with average maximum longevity of 53, 40, and 16 years. Winter rain equalled or exceeded 90% of the long-term average accumulation except during 1948 to 1959 (65% of average) and from 2001 to 2003 (49% of average). Summer rain did not drop below 90% of the average accumulation in any period. The 1950s drought caused modest declines in survival of Ambrosia , Encelia , Janusia , Krameria , and Lycium . The effects of the recent drought were much more pronounced, resulting in sharp declines in survival and maximum longevity of Ambrosia , Encelia , Krameria , and Larrea , and modest declines for Lycium . Despite heightened mortality during the recent severe drought, 72% of the deaths observed between 1928 and 2004 occurred during periods of average or better-than-average rain, providing support for the idea that demography of shrubs in arid regions is influenced by continuous as well as episodic processes.

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USGS2002

Characteristics of shallow deposits beneath Rillito Creek, Pima County, Arizona

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, generally are sandy gravels or gravelly sands. On average, the stream-channel deposits are 44 percent gravel, 51 percent sand, 2 percent silt, and 3 percent clay. The underlying basin-fill deposits also are sandy gravels or gravelly sands but have, on average, a larger component of silt and clay than the stream-channel deposits?about 9 percent silt and 6 percent clay. Porosity values for the stream-channel and basin-fill deposits are similar: about 31 and 34 percent on average, respectively. Volumetric moisture content and percent saturation, however, generally were lower in the stream-channel deposits than in the basin-fill deposits. Moisture content in the stream-channel deposits ranged from 2 to 40 percent and averaged about 18 percent, whereas moisture content in the basin-fill deposits ranged from 7 to 47 percent and averaged about 24 percent. Saturation in the stream-channel deposits ranged from 9 to 100 percent and averaged about 58 percent; saturation in the basin-fill deposits ranged from 30 to 100 percent and averaged about 69 percent. Porosity and moisture content correlate with silt and clay content. Cumulative thickness of water in the 100- to 125-foot thick unsaturated zone obtained by integrating the moisture content over depth, ranged from 17.2 to 40.4 feet. Matric potential for saturation levels at the time of sample collection generally was less than -1 bar for deposits that were less than 35 percent saturated. Matric potential generally was greater than -0.1 bar for deposits that were more than 65 percent saturated. Moisture-retention curves are a function of the physical properties, such as porosity and grain size, of the sediments. The shapes and van Genuchten fitting parameters of moisture-retention curves for the stream-channel deposits are different from those of the basin-fill deposits. For instance, the fitting parameter, a, for stream-channel deposits ranged from 4.56 to 1,220 bar-1 and averaged 220 bar-1, whereas a for basin-fill deposits ranged from 4.22 to 67.9 bar-1 and averaged 22.8 bar-1. The residual water content for the basin-fill deposits is greater than that for the stream-channel deposits. Relative hydraulic conductivity of the stream-channel deposits is less than relative hydraulic conductivity of the basin-fill deposits at the same matric potential. Unsaturated hydraulic conductivity for moisture conditions that existed at the time of sample collection typically was more than two orders of magnitude less than saturated hydraulic conductivity. Saturated vertical hydraulic conductivity of the stream-channel deposits is about an order of magnitude greater than that of the basin-fill deposits. The equivalent hydraulic conductivity of stream-channel deposits ranges from 2 to 7.3 feet per day, and averages about 4 feet per day, whereas the equivalent hydraulic conductivity of the basin-fill deposits ranges from 0.06 to 1.5 feet per day and averages 0.61 foot per day. The equivalent vertical hydraulic conductivity of the entire unsaturated zone cored is 0.75 foot per day. Assuming no vertical to horizontal anisotropy, the equivalent horizontal hydraulic conductivity generally is about two to three times that of the equivalent vertical hydraulic conductivity. The difference between average equivalent vertical and horizontal hydraulic conductivity values results from the differences in methods used to calculate the respective values. Electrical methods were useful in discriminating between stream-channel deposits and basin-fill deposits. In general, electrical conductivity of the stream-channel deposits was less than 30 millimhos per meter and averaged 27 millimhos per meter. The conductivity of the basin-fill deposits was greater than that of the stream-channel deposits and averaged 44 millimhos per meter. The greater conductivity probably is related to factors such as greater moisture content and fraction of fine sediments in the basin-fill deposits. Apparent resistivity measured with two-dimensional resistivity soundings generally decreased with depth. The resistivity values from the near-surface measurements represent dry stream-channel deposits and averaged 303 ohm meters. The resistivity values for basin-fill deposits generally were less than 140 ohm meters and less than 100 ohm meters when saturated. Seismic-velocity values for the recent alluvium (stream-channel and terrace deposits) ranged from 1,150 to 2,200 feet per second, whereas values for basin-fill deposits ranged from 2,000 to 11,650 feet per second. The average seismic velocity for the stream-channel deposits (1,300 feet per second) was less than that for the terrace deposits (1,600 feet per second). Saturated basin-fill deposits had an average velocity of 7,800 feet per second, whereas unsaturated basin-fill deposits had an average velocity of 2,750 feet per second.

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USGS2001

Implications of seed size for seedling survival in Carnegiea gigantea and Ferocactus wislizeni (Cactaceae)

Larger seeds have been shown to convey benefits for seedling survival but the mechanisms of this process are not well understood. In this study, seed size and seedling survival were compared for 2 sympatric cactus species, Carnegiea gigantea (Engelm.) Britt. & Rose and Ferocactus wislizeni (Engelm.) Britt. & Rose, in laboratory and field experiments in the northern Sonoran Desert. Both species have small seeds, but Ferocactus seeds are nearly twice as long and 3 times as heavy as those of Carnegiea . The difference in size is perpetuated after germination: new Ferocactus seedlings have 4 times the estimated volume of new Carnegiea seedlings. In an outdoor experiment, annual survivorship of both species was low but was 6 times higher for Ferocactus (6 seedlings, 8.1%) than Carnegiea (1 seedling, 1.4%). The pattern of seedling mortality in relation to temperature and rain suggests that, after the initial flush of seed and seedling predation, drought and heat took a greater toll on Carnegiea than Ferocactus seedlings, probably because the larger seedling volume of Ferocactus conferred greater drought tolerance. In addition, F. wislizeni could become established without benefit of nurse plants whereas C. gigantea could not; this might reflect differential tolerance to high soil temperatures.

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USGS1999

Aquifer-storage change in the lower Canada del Oro Subbasin, Pima County, Arizona, 1996-98

Aquifer storage was monitored using gravity methods in the Lower Canada del Oro subbasin from 1996 through 1998 to determine areas of infiltration and amounts of recharge along the Canada del Oro Wash after major surface flow and to estimate aquifer-storage change and specific-yield values for the regional aquifer. Both purposes were addressed by periodic monitoring of changes in aquifer storage and water levels at a network of gravity stations and monitor wells. Water levels and gravity were also monitored near an active withdrawal well for several months for the purpose of estimating specific yield of the aquifer within the cone of water-leel depression at the well.

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USGS1996

Infiltration of wastewater effluent in the Santa Cruz River Channel, Pima County, Arizona

Infiltration of effluent into the Santa Cruz River channel from water-treatment plants near Tucson, Arizona was studied from March 23, 1990, to September 30, 1993. The study reach extended along a 23-mile stream reach from the water-treatment plants, about 5 miles northwest of central Tucson, downstream to Trico Road, about 5 miles west of Marana, Arizona. Data indicate that 88.4 to 90.2 percent of the effluent discharged from the two water-treatment plants infiltrated the Santa Cruz River channel. During 1991 93, the volume of effluent discharge that flowed out of the study area was 2,880, 4,120, and 3,320 acre-feet per year, respectively, and the volume of infiltration was 41,890, 43,640, and 45,670 acre-feet per year, respectively. Intermittent rainstorms resulted in high flows that altered the composition, structure, and geometry of the channel bed and may have caused the infiltration to increase to nearly 100 percent. In comparison, variations in evapotranspiration and open-channel evaporation had a minimal effect on the water budget. In the study reach, 3.2 to 3.9 percent of the effluent was lost to evapotranspiration and open-channel evaporation; 6.2 to 8.3 percent flowed through the reach.

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USGS1978

Areas subject to inundation by the 100-year flood in Avra Valley, Pima County, Arizona

Avra Valley in Pima County, Arizona, is sparsely populated and is used mainly for agriculture and cattle grazing; however, its proximity to Tucson makes it desirable for urban development. Administrators and planners concerned with future land development may use the map report to determine the approximate areas that are subject to inundation by the 100-year flood. Avra Valley is drained mainly by Brawley Wash; Blanco Wash drains the west side of the valley. Most of the natural drainage system consists of small braided channels bordered by narrow bands of dense vegetation, which cause floodwater to spread over wide areas of shallow depths. During the 100-year flood, the areas inundated by Brawley and Blanco Washes may join in several places. (Woodard-USGS)

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