U.S.
GEOLOGICAL SURVEY
Professional Paper 1702
Classification
of Hydrogeologic Areas and Hydrogeologic Flow Systems in the Basin and Range
Physiographic Province, Southwestern United States
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GROUND-WATER RESOURCES PROGRAM
By David W. Anning and A.D. Konieczki
ABSTRACT
The hydrogeology of the Basin and Range Physiographic Province in parts of Arizona, California, New Mexico, Utah, and most of Nevada was classified at basin and larger scales to facilitate information transfer and to provide a synthesis of results from many previous hydrologic investigations. A conceptual model for the spatial hierarchy of the hydrogeology was developed for the Basin and Range Physiographic Province and consists, in order of increasing spatial scale, of hydrogeologic components, hydrogeologic areas, hydrogeologic flow systems, and hydrogeologic regions. This hierarchy formed a framework for hydrogeologic classification.
Hydrogeologic areas consist of coincident ground-water and surface-water basins and were delineated on the basis of existing sets of basin boundaries that were used in past investigations by State and Federal government agencies. Within the study area, 344 hydrogeologic areas were identified and delineated. This set of basins not only provides a framework for the classification developed in this report, but also has value for regional and subregional purposes of inventory, study, analysis, and planning throughout the Basin and Range Physiographic Province. The fact that nearly all of the province is delineated by the hydrogeologic areas makes this set well suited to support regional-scale investigations.
Hydrogeologic areas are conceptualized as a control volume consisting of three hydrogeologic components: the soils and streams, basin fill, and consolidated rocks. The soils and streams hydrogeologic component consists of all surface-water bodies and soils extending to the bottom of the plant root zone. The basin-fill hydrogeologic component consists of unconsolidated and semiconsolidated sediment deposited in the structural basin. The consolidated-rocks hydrogeologic component consists of the crystalline and sedimentary rocks that form the mountain blocks and basement rock of the structural basin.
Hydrogeologic areas were classified into 19 groups through a cluster analysis of 8 characteristics of each area’s hydrologic system. Six characteristics represented the inflows and outflows of water through the soils and streams, basin fill, and consolidated rocks, and can be used to determine the hydrogeologic area’s position in a hydrogeologic flow system. Source-, link-, and sink-type hydrogeologic areas have outflow but not inflow, inflow and outflow, and inflow but not outflow, respectively, through one or more of the three hydrogeologic components. Isolated hydrogeologic areas have no inflow or outflow through any of the three hydrogeologic components. The remaining two characteristics are indexes that represent natural recharge and discharge processes and anthropogenic recharge and discharge processes occurring in the hydrogeologic area.
Of the 19 groups of hydrogeologic areas, 1 consisted of predominantly isolated-type hydrogeologic areas, 7 consisted of source-type hydrogeologic areas, 9 consisted of link-type hydrogeologic areas, and 2 consisted of sink-type hydrogeologic areas. Groups comprising the source-, link-, and sink-type hydrogeologic areas can be distinguished between each other on the basis of the hydrogeologic component(s) through which interbasin flow occurs, as well as typical values for the two indexes. Conceptual models of the hydrologic systems of a representative hydrogeologic area for each group were developed to help distinguish groups and to synthesize the variation in hydrogeologic systems in the Basin and Range Physiographic Province.
Hydrogeologic flow systems consist of either a single isolated hydrogeologic area or a series of multiple hydrogeologic areas that are hydraulically connected through interbasin flows. A total of 54 hydrogeologic flow systems were identified and classified into 9 groups. One group consisted of single isolated hydrogeologic areas. The remaining eight groups consisted of multiple hydrogeologic areas and were distinguished on the basis of (1) whether all water is removed from the system through evapotranspiration (terminally closed) or whether some water is removed as outflow into another downgradient system (terminally open), and (2) the predominant hydrogeologic component(s) that hydraulically connected the hydrogeologic areas into hydrogeologic flow systems.
The northern, middle, and southern Basin and Range Physiographic Province hydrogeologic regions were identified through a spatial analysis of the distribution of hydrogeologic flow systems. The northern Basin and Range hydrogeologic region contains mostly terminally closed, multiple-area hydrogeologic flow systems that have hydrogeologic areas that are hydraulically connected predominantly through the soils and streams and the basin fill. The middle Basin and Range hydrogeologic region contains hydrogeologic areas that, in most cases, are topographically closed. As a result, most of the hydrogeologic flow systems either are single-area hydrogeologic flow systems, which have no interbasin flows, or are terminally closed, multiple-area hydrogeologic flow systems that have hydrogeologic areas hydraulically connected by interbasin flows, mostly through the basin fill and (or) consolidated rocks. The southern Basin and Range hydrogeologic region mostly contains terminally open, multiple-area hydrogeologic flow systems that delineate the Colorado River and Rio Grande drainages. Most hydrogeologic areas in this region are hydraulically connected predominantly through soils and streams and through basin fill.
Abstract
Introduction
Conceptual model for the spatial hierarchy of the hydrogeology of the Basin and Range Physiographic Province
Delineation of hydrogeologic areas and hydrogeologic flow systems
Classification of hydrogeologic areas
Hydrogeologic regions
Summary and conclusions
References cited
Appendix
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