Twenty Three Years Ago I Was Given The Opportunity To Select From All The Geographic Provinces Of The Mid – And Western United

One Hundred Years of Hydrogeology – Where Do We Go From Here?

M. S. Bedinger P.O. Box 790 Carlsborg, WA 98324 [email protected]

J.R. Harrill 608 Highland Street Carson City, NV, 89703 [email protected]

Hydrogeologic Consultants to the National Park Service

Transcript of paper presented at the GSA 2003 Annual Meeting and Exposition, Seattle, Washington, November 2-5, 2003

Slides refer to the accompanying PowerPoint presentation of the same title

Introduction

This talk on hydrogeological contributions of the past 100 years will dwell mostly with the development of knowledge of the regional ground-water flow systems. This is an aspect that I am familiar with through current and previous work in the Great Basin. My earlier work was on Task I the USGS project in the Basin and Range Province that evaluated potential geohydrologic environments isolation of radioactive waste. My current work in the Death Valley region is in partnership

1 with Jim Harrill, my co-author on this paper. We are consultants to the National Park Service on the Death Valley ground-water flow system.

My introduction to the Great Basin on the ground was by Gene Rush, a hydrogeologist, many of you know, who made some of the early reconnaissance studies of ground-water basins in Nevada. Gene Rush had observed, as others had, that Native American names for many closed basins had hydrologic significance. Basins with Indian names starting with the letters P - A - H are basins where ground water is at or near the playa surface and commonly where large springs occur.

Crystal Springs, Pahranagat Valley

This is true for Pahranagat and Pahrump basins which have, or in the case of Pahrump Valley, had large springs before heavy irrigation pumping. Both valley floors have shallow water tables.

Basins having no water at the surface were suffixed by P - A - H. This holds true for Ivanpah and Nopah neither of which held large springs. Nor do these basins have shallow ground-water for evapotranspiration from their playas.

Another very basic but significant hydrologic insight to the Great Basin was recorded prior to the 20th century by John C. Fremont who explored the northern part of the region from the Rockies to California and named the Great Basin in early 1840’s. Fremont’s basis for defining the limits of the Great Basin was that collection of basins with closed drainage having no outlet to the ocean. He designated the region as bounded by the Columbia River drainage on the north, the Sierra Nevada on the west and the Colorado River drainage to the south.

Fremont’s definition is not followed today. The Mojave section is placed in the Sonoran Desert (Hunt, 1967). Nevertheless, Fremont’s designation of the Mojave Desert to the Great Basin is appropriate not only for the closed drainage of its basins, but also because ground water in the Mojave section is tributary to the Great Basin discharge area at Death Valley.

Great Basin geology

2 Dry and wet valleys are important clues to the interpretation of the regional hydraulic gradient that is driven by the regional topographic relief. The bedrock that underlies the mountain ranges is shown in blue and white. The basin fill is brown. The More than 30 ranges are above 10,000 feet. The basin floor of Death Valley is below sea level. The highest basin floors in the Death Valley flow system are 6,500 feet at Long Valley at the foot of the Sierras and 6,800 feet at Monitor Valley in central Nevada. This slide was prepared for the Great Basin RASA study and does not show all of the Great Basin in California.

Throughout its geologic history the Great Basin has been tectonically and sedimentologically active. The most recent tectonic period of block faulting accompanying crustal extension and volcanism, probably started in middle or early Tertiary and has continued to Holocene time. The extension block faulting has produced the characteristic linear northward trending ranges and the intervening closed basins for which the Basin and Range Province is named.

Dixie Valley

This view looking eastward from a window seat in the commuter between Las Vegas and Reno overlooks the playa of Dixie Valley and about five other characteristically linear basins and ranges.

Diagrammatic Cross Section of Faulting in Bedrock

The tectonic history has imprinted the rock mass with joints, faults and fractures that produce permeable zones for ground-water movement. The Tertiary and Holocene episode of extensional block faulting is of significance in producing permeable zones for vertical movement of ground water.

Block Diagram of Wet and Dry basins.

The study of the development of today’s concept of regional flow reveals the changing concepts of interbasin and regional flow. Early field hydrologists

3 recognized some cases of interbasin flow of ground water; but, they considered interbasin flow to be the exception rather than the rule.

The first recognition of interbasin flow was perhaps in 1909 by Mendenhall (1909 p. 13) who suggested many of the desert springs in southern Nevada are not dependent on rainfall in the area immediately surrounding the springs but that their source is from distant mountains.

Meinzer in 1917 (1917, p. 150) reported that water from a valley near Tonopah, Nevada leaks through a mountain range into an adjacent valley. But, for the most part, bedrock separating the basin blocks was considered impermeable. This rationale was expresses by Carpenter in 1915 ( p. 18), who noted that rocks exposed in the mountains of southeastern Nevada generally act to close the adjacent valleys by making the sides and bottoms of the valleys practically impervious. But, even Clark stated that several topographically closed valleys higher in altitude than adjacent valleys lose water through fissures in the rocks because water levels in the higher valleys are far below land surface.

The playa of the dry valley, shown in brown, is well above the water table. Carpenter (1915) recognized that such a basin receives recharge but having no surface discharge of ground water, the ground water must flow to adjacent lower basins where discharge takes place.

The wet valleys are shown with blue playas. The topographically highest basin is depicted in low permeability rock and is here designated a single valley system. There is a local circulation cell from local recharge and discharge within the valley. In addition, it is also recognized that, at depth, there is a ground–water gradient, a potential for ground-water flow, from this basin to the lower basins on the right of the section.

The more I work with flow systems of the Great Basin the more I am prone to believe impermeable rocks are the exception rather than the rule.

Eureka Valley

4 This is Eureka Valley whose playa is several hundred feet above the water table. The view is eastward to the Last Chance Range that separates the valley from Death Valley. The regional potential is inferred to be below the valley floor.

Ground water from Eureka Valley flows south along the regional gradient to Saline Valley.

Saline valley

Saline Valley contains a shallow lake and a surrounding area of evapotranspiration from the water table. Thermal springs occur on the valley floor. The regional potential surface is inferred to be above the valley floor.

George Burke Maxey and Thomas Eakin in 1949 proposed a method for evaluating the water budgets of such closed basins -- the method included estimating recharge to the basin as a percentage of precipitation in elevation classes and estimating ground water discharge as a function of phreatophytes and depth to ground water.

Basin Boundaries and Recharge (no slide)

The work of quantifying the budgets for the many basins in Nevada and Utah proceeded basin by basin over several decades. The water budgets by the Maxey- Eakin method are empirical. The procedure was useful in the early delineation of regional flow. Improved quantitative techniques have been introduced in the measurement and analysis of recharge and discharge. But, for most of these basins, the Maxey-Eakin budgets are still the only budgets that have been made.

Eakin’s White River Flow System

Regional flow systems composed of many basins were first recognized and defined in the carbonate rock section of the Great Basin. Eakin (1966) used water budgets of several basins in southeastern Nevada to hypothesize an interbasin flow system he named the White River System. Eakin used the recharge and discharge of each basin to show the balance that was contributed to the down gradient basins. The

5 direction of the regional gradient was recognized from the elevation of shallow water levels in adjacent basins.

Other early studies from 1965 to 1975 contributed to the understanding of interbasin ground-water flow: These include Eakin and Winograd (1965), Eakin and Moore (1964), Mifflin (1968), Mifflin and Hess (1969), and Winograd and Throdarson (1975).

Mifflin’s Equipotential Map

A synoptic view of regional ground-water potential was first offered by Mifflin in a 1968 publication. Whereas the flow system delineation of Eakin (1966) was based primarily on water budget studies, Mifflin’s equipotential map was based on inference of the regional head from the surface elevation of thermal springs. Mifflin plotted and contoured the outlet elevation of all springs having water temperatures of greater than 80 degrees F.

Hydraulically forced thermal springs are expressions of movement of water from depth heated by the natural geothermal gradient. The numerous thermal springs attest to the inherent permeable nature of a significant network of vertical faults associated with the extensional block faults of the Great Basin. This map embodies the essence of the geology, permeability fabric and topography that give rise to interbasin and regional flow.

Ground-Water Potential and Ground-Water Flow Systems Inferred from Basin Water Budgets

Harrill and others (1988) made use of the basin water budgets in their work in the Great Basin. They also considered the topographic and shallow water-level differences between basins for interpreting the direction of interbasin flow and regional ground-water potential.

The use of the Maxey-Eakin water budgets to define the flow systems yielded systems bounded by topographic divides. Single basins with balanced recharge and discharge components are shown as single basin flow systems. These

6 characteristics are artifacts that reflect the hydrologist’s concept and purpose for defining regional flow.

Single-basin systems can be visualized as the circulation of local recharge and discharge to the basin playa. Beneath such shallow circulation systems there is a regional gradient.

Basin and Range Potentiometric Map

This map prepared in the early 1980’s as part of the Task I study (Bedinger, 1983, written communication), depicts the regional ground water potential based on thermal springs and other surface hydrologic features. These include the terminal and intermediate discharge areas of the flow systems, shown in blue, and the topographic elevations of the wet and dry valleys. Flow systems of the Basin and Range Province were delineated on the basis of the regional potential.

We found that data from thermal springs, as used by Mifflin in 1968, could be supplemented by data from other surface hydrologic features to provide more detail on the regional potentiometric surface.

Prudic, Harrill and Burbey Model Regional Potential Map

The computer model of the carbonate aquifer of the Great Basin by Prudic, Harrill, and Burbey (1995) integrated both water budget data and head data. Here is shown the regional head in the lower layer of the model and a delineation of the regional flow systems for part of the Great Basin.

The continuum of regional head represents also a continuum of ground water flow, assuming the rock is permeable.

Regional Potential with DVRFS boundary.

The regional contour map (Bedinger and Harrill, 2003) shown here is a second generation of the Task I map shown earlier for the area encompassing the Death Valley flow system. The red lines delineate flow system boundaries. The Death

7 Valley flow system was the principal interest. Adjacent areas were included to confidently define the system boundaries.

The boundary of the Death Valley Regional Flow System (DVRFS) model of the U. S. Geological Survey is outlined by the yellow line.

The regional map shows there are potential gradients across some sections of the model boundary. This map was useful in estimating the flows across the lateral boundaries for simulation in the model.

Evolving Flow Systems Concepts (no slide)

We have seen regional flow depicted as compartmentalized multibasin flow systems beginning with Eakin’s delineation of the White River flow system and regional flow depicted by contours of regional potential based on elevations of thermal springs and other indirect criteria for regional head. By fully integrating not only head and flow data but also the hydrogeologic framework, computer models have the potential to provide the most sophisticated definition of regional flow.

These regional flow analyses are all useful and are similar from a regional viewpoint. Differences certainly can be seen. Many of these differences are in detail some of which reflect differences in scope and hydrogeologic concepts.

Where Do We Go From Here? (no slide)

The past hundred years has seen great strides in knowledge of the hydrology of the Basin and Range and in the understanding of regional flow. Studies of geochemistry, heat flow, ground-water modeling, ground-water discharge by evapotranspiration, and infiltration have contributed to the understanding of the hydrology. But, there were gaps left unfilled during the past 100 years. Infiltration modeling for example has made great strides toward a much needed replacement for the Maxey-Eakin method. To fill the gap will require collaboration between both ground water and unsaturated zone modelers.

8 Application of heat flow and associated geochemistry of thermal waters has not been fully applied to regional problems of hydrogeology. Studies of geothermal systems have been made in California – Coso, Long Valley and Saline Valley. These are studies that demonstrate the use of geochemical and geothermal data to gain an insight to the ground water flow system. The application of these techniques holds promise for aiding our insight on the vertical dimension of regional ground-water flow in the system.

Quantitative analysis and interpretation of seismic related ground-water phenomena is a much needed and fertile field for exploration. The importance of these analyses will grow as water conflicts grow in the region.

Interpretations of origin and migration of ground water based on geochemistry and flow system hydraulics should be mutually consistent. For example, the suggestion based on geochemical studies for migration of ground water from Pahranagat Valley of the White River system to the Death Valley flow system can not be supported by any of the studies of regional flow that are referred to in this talk.

A ground water model can not internally define the flow conditions on its external boundaries. The most common problem in modeling is probably the lack of integrity of the modeled boundary conditions. Knowledge of regional flow systems can serve an essential role in providing a hydrologic context within which to place arbitrarily bounded models.

References Cited

Bedinger, M. S. and Harrill, J. R., 2003, Regional Potential for interbasin flow of ground water, in preparation.

Carpenter, Everett, 1915, Ground water in southeastern Nevada: U.S. Geological Survey Water Supply Paper 365, 86p.

Eakin, T. E., 1966, A regional interbasin ground-water system in the White River area, southeastern Nevada: Water Resources Research, v. 2, p. 251-271.

9 Eakin, T.E., and Moore, D.O., 1964, Uniformity of discharge of Muddy River Springs, southeastern Nevada, and relation to interbasin movement of ground water, in Geological Survey Research 1964, Chapter D: U.S. Geological Survey Professional Paper 501-D, p. D171- DI76.

Eakin, T.E., and Winograd, I.J., 1965, Interbasin movement of ground water in South-Central Nevada—Some implications, in Abstracts for 1964: Geological Society of America Special Paper 82, p. 52.

Harrill, J.R., Gates, J.S., and Thomas, J.M., 1988, Major ground-water flow systems in the Great Basin Region of Nevada, Utah, and adjacent States: U.S. Geological Survey Hydrologic Investigations Atlas HA- 694-C, 2 sheets, map scale 1:1,000,000, with errata sheet.

Hunt, Charles B., 1967, Natural regions of the United States and Canada: W. H. Freeman and Company, 725 p.

Maxey, G.B., and Eakin, T.E., 1949, Ground water in White River valley, White Pine, Nye, and Lincoln Counties, Nevada: Nevada State Engineer, Water Resources Bulletin Number 8, 59 p.

Meinzer, O.E., 1917, Geology and water resources of Big Smoky, Clayton, and Alkali Spring Valleys, Nevada: U.S. Geological Survey Water Supply Paper 423, 176p.

Mendenhall, W.C., 1909, Some desert watering places in southeastern California and southwestern Nevada: U.S. Geological Survey Water Supply Paper 224, 86p.

Mifflin, M. D., 1968, Delineation of ground-water flow systems in Nevada: Reno, Desert Research Institute, Hydrology and Water Resources Publication 4, 111 p.

Mifflin, M. D. and Hess, J. W., 1979, Regional carbonate flow systems in Nevada: Journal of Hydrology, v. 43, p. 217-238.

10 Prudic, D.E., Harrill, J.R., and Burbey, T.J., 1995, Conceptual evaluation of regional ground-water flow in the carbonate-rock province of the Great Basin, Nevada, Utah, and adjacent states: U.S. Geological Survey Professional Paper 1409-D, 102 p.

Winograd, I. J., and Thordarson, W., 1975, Hydrogeologic and hydrogeochemical framework, south-central Great Basin, Nevada–California, with special reference to the Nevada Test Site: U. S. Geological Survey Professional Paper 712-C, 109 p.