Simulation of ground-water flow in alluvial basins in south-central Arizona and parts of adjacent states

Abstract

The Regional Aquifer-System Analysis (RASA) program was started in 1978 after 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 important components 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 of any changes brought about by human activities, as well as 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.

Geochemical Quantification of Semiarid Mountain Recharge

“…The value of near S estimated from the map was 250 ± 100 m, which includes a conservatively large uncertainty term to account for variability over the region of interest and possible errors in reinterpreting the map. Although the difference between the approximate depths of the water table (100 m bgs) and the bedrock surface (700 m bgs) near S is larger, the estimate of is appropriate, given the conceptual model in which insignificant flow occurs below the uppermost portion of the Pantano formation, whose surface is about 200 m bgs near S (Gettings and Houser 2000; Anderson and Freethey 1995).…”

“…The silts and clays, as well as units below the Basin Fill, also transmit lesser amounts of water. Modeling studies have predicted only small ground water fluxes at depths greater than 305 m relative to those at shallower depths (Anderson and Freethey 1995; Goode 2000).…”

Water management in a mountain front recharge aquifer

“…For all of the above effects, under the appropriate circumstances the flows can represent either additions to or depletions of the alluvial aquifer. Anderson and Freethey [1995] argue that the hydrology of the regional and alluvial aquifers is such that for certain purposes it may be difficult to separate them. We thank a reviewer for pointing this out, as it greatly simplified the heuristic modeling of the aquifer.…”

The Effect of Modeled Recharge Distribution on Simulated Groundwater Availability and Capture

“…Basin-fill aquifers can be recharged by this excess precipitation through groundwater flow from direct recharge in permeable mountainous areas, by runoff from mountain areas into basin alluvium, along intermittent and ephemeral streams and playas in valley floors, or through some combination of these processes (Stonestrom et al 2007). Historically, groundwater models in the region typically simulated aquifer recharge along mountain fronts (Hollett 1985;Hanson et al 1990; Thomsen and Eychaner 1991;Hanson and Benedict 1994;Anderson and Freethey 1995). Although some more recent groundwater models include mountain-front recharge (Mason and Bota 2006;Erwin 2007;Friehoefer et al 2009), others have begun to add direct recharge in permeable highelevation areas and/or recharge in ephemeral channels that drain bedrock areas (Nelson 2002;Faunt et al 2004;Nelson 2007;Pool and Dickinson 2007;Halford and Plume 2011;Pool et al 2011).…”