Geohydrology and water resources of the Tucson basin, Arizona

Abstract

The major source of water in the Tucson basin is the vast volume of ground water in storage in the aquifer underlying the basin. Ground water is pumped for irrigation, public supply, and industrial uses and is partially replenished by the infiltration of streamflow along the major streams and the basin perimeter. The basin is in southeastern Arizona and is a broad northwest-trending valley arcuately bounded by mountain ranges on the eastern and western sides. The 1,000-square-mile basin is about 50 miles long and is 15 to 20 miles wide in the southern and central parts and 4 miles wide at the northwest outlet. The surface of the basin slopes northwestward from an altitude of about 3,500 feet at the southern edge to an altitude of about 2,000 feet at the northwestern edge. The mountains on the west side of the basin range from 3,000 to 6,000 feet in altitude, and those on the east side range from 6,000 to 8,000 feet in altitude. The mean annual precipitation is only about 12 inches on the basin surface and 25 inches or slightly more in the mountains. Because most of the precipitation is evaporated or transpired, the mean annual streamflow past gaging stations on the major streams is only about 10,000 to 20,000 acre-feet. The major streams generally are dry during more than 300 days each year, and the flows generally last 3 days or less. Because of the erratic occurrence and quantity of flow, streamflow is not used directly as a water supply. The mean annual streamflow out of the basin is slightly more than 17,000 acrefeet. The aquifer that underlies the basin surface consists of the Pantano Formation and Tinaja beds of Tertiary age and the Fort Lowell Formation and surficial deposits of Quaternary age. These units are more than 2,000 feet thick and are composed mainly of loosely consolidated to moderately cemented silty sand to silty gravel. In the south-central part of the basin and in a small area in the northern part, a thick section of clayey silt to mudstone fills a structural depression caused by downfaulting of the Pantano Formation and the older units. The chemical quality of the ground water in most of the basin is suitable for public supply. Most of the water in the upper part of the aquifer contains less than 500 mg/1 (milligrams per liter) dissolved solids, and in most of the area the range in dissolved-solids content is from 250 to 1,500 mg/1; in El E2 WATER RESOURCES OF THE TUCSON BASIN a few isolated places concentrations as great as 3,000 mg/1 occur. The dissolved solids are mainly calcium, sodium, and bicarbonate. Ground water in the northern and northeastern parts of the basin generally contains less than 300 mg/1 dissolved solids and is moderately hard; elsewhere the dissolved-solids content generally ranges from 300 to 500 mg/1, and the water is hard. In the deep part of the aquifer the water generally contains less than 500 mg/1 dissolved solids, mainly sodium and bicarbonate, and is soft; but where the aquifer grades into clayey silt or mudstone, the water may contain more than 2,000 mg/1 dis...

Relative contributions of transient and steady state infiltration during ephemeral streamflow

“…The alluvial deposits, which are derived from the surrounding mountain ranges, are about 10 m thick and consist predominantly of loose to moderately compacted sands and gravels, and contain less than 10% clay and silt. The underlying basin-fill deposits, which extend to depths of several hundred meters, consist of unconsolidated to poorly consolidated interbedded gravel, sand, and silt [Davidson, 1973;Hoffmann et al, 2002]. Depth to the water table is about 42 m at the study site.…”

“…Sediments at the Dodge Boulevard study site consist of an upper layer of recent alluvial stream channel deposits and a second deeper layer of Pleistocene or older basin-fill deposits [Davidson, 1973]. The alluvial deposits, which are derived from the surrounding mountain ranges, are about 10 m thick and consist predominantly of loose to moderately compacted sands and gravels, and contain less than 10% clay and silt.…”

“…[2] Infiltration in alluvial ephemeral stream channels has been identified as an important source of aquifer recharge in arid and semiarid environments [Smith, 1910;Davidson, 1973;Hanson and Benedict, 1994]. Numerous infiltration and recharge investigations have been conducted to quantify the contributions of streambed recharge to the water budget for resource planning [Wilson et al, 1980;Ronan et al, 1998].…”

Summary of the Southwest Alluvial Basins, Regional Aquifer-System Analysis, south-central Arizona and parts of adjacent states

“…The extent of the areas exhibiting confined conditions depends on the lateral extent and continuity of the fine-grained confining bed. Significant variations in hydraulic head with depth indicate upward vertical gradients in some locations and downward vertical gradients in other locations (Halpenny and others, 1952;Davidson, 1973).…”

Trichloroethylene and 1,1-dichloroethylene concentrations in ground water after temporary shutdown of the reclamation well field at Air Force Plant 44, Tucson, Arizona, 1999

“…For practical considerations, such as the cost of drilling wells and the expense of pumping water from great depths, only about the upper 1,000 ft of the aquifer is utilized as a water source. The mountains surrounding the basin are composed of various types of bedrock, which yield little or no water and therefore are not considered to be part of the regional aquifer (Davidson, 1973).…”