Geohydrology and water resources of alluvial basins in south-central Arizona and parts of adjacent states

Abstract

The Regional Aquifer-System Analysis (RASA) Program was started in 1978 following a congressional mandate to develop quantitative appraisals of the major groundwater systems of the United States. The RASA Program represents a systematic effort to study a number of the Nation's most important aquifer systems, which in aggregate underlie much of the country and which represent an important component of the Nation's total water supply. In general, the boundaries of these studies are identified by the hydrologic extent of each system and accordingly transcend the political subdivisions to which investigations have often arbitrarily been limited in the past. The broad objective for each study is to assemble geologic, hydrologic, and geochemical information, to analyze and develop an understanding of the system, and to develop predictive capabilities that will contribute to the effective management of the system. The use of computer simulation is an important element of the RASA studies, both to develop an understanding of the natural, undisturbed hydrologic system and the changes brought about in it by human activities, and to provide a means of predicting the regional effects of future pumping or other stresses. The final interpretive results of the RASA Program are presented in a series of U.S. Geological Survey Professional Papers that describe the geology, hydrology, and geochemistry of each regional aquifer system. Each study within the RASA Program is assigned a single Professional Paper number, and where the volume of interpretive material warrants, separate topical chapters that consider the principal elements of the investigation may be published. The series of RASA interpretive reports begins with Professional Paper 1400 and thereafter will continue in numerical sequence as the interpretive products of subsequent studies become available.

Inferring time‐varying recharge from inverse analysis of long‐term water levels

“…The angle q represents the slope of the impermeable bottom boundary from the midpoint of the basement to the recharge boundary, which allows for common bedrock geometries in basins of the southwestern United States [Anderson and Freethey, 1996]. The elevation of the bottom boundary was 0 m for all x when q = 0°, and increased to 1539 m at the inflow boundary when q = 13°.…”

“…Basin discharge may occur as underflow to adjacent, downgradient basins, losses to low-altitude streams, or by evapotranspiration where the groundwater levels approach the land surface. The geometry of the idealized basin aquifer system (Figure 1) is rectangular with groundwater flowing from the upgradient areas and the mountain fronts, toward the basin center and downgradient areas [Anderson and Freethey, 1996].…”

“…The basin is bounded by impermeable mountains on the east and west, and drained by the San Pedro River, a northward flowing intermittent stream. Recharge to the basin occurs mainly by mountain front recharge, by infiltration in stream reaches, and by underflow from adjacent basins [Anderson and Freethey, 1996]. The aquifers consist of a lower section of a mid-Tertiary cemented conglomerate, a lower basin fill of sand, gravel, silt, and clay layers and lenses with some cementation, and an upper basin fill of unconsolidated sandy, silty clay [Brown et al, 1966;Corell et al, 1996].…”

“…[22] Groundwater flow models were developed using MODFLOW [McDonald and Harbaugh, 1988] for several idealized basin geometries [Anderson and Freethey, 1996] (Figure 3), and used to simulate the response of an unconfined aquifer to single and multiple-frequency periodic recharge rates. For each geometry, a one-dimensional flow line was chosen along a flow tube between the recharge and discharge boundaries.…”

Longitudinal hydraulic analysis of river‐aquifer exchanges

“…[2] The exchange of water between groundwater and surface waters regulates the quality and availability of water resources throughout the United States [Anderson et al, 1992;Torak et al, 1996;Winter et al, 1998;Sophocleous and Perkins, 2000;Harvey et al, 2004]. Exchanges between rivers and aquifers are particularly important in regions such as the Pacific Northwest where precipitation and runoff are unevenly distributed through the year [Kjelstrom, 1995;Konrad et al, 2003].…”