Relationship between Arid Geomorphic Settings and Unsaturated Zone Flow...Chihuahuan Desert, Texas. Digital Download

RI0261D. Relationship between Arid Geomorphic Settings and Unsaturated Zone Flow: Case Study, Chihuahuan Desert, Texas, by B. R. Scanlon, R. S. Goldsmith, and R. P. Langford. 133 p., 48 figs., 8 tables, 10 appendices, 2000. doi.org/10.23867/RI0261D. Downloadable PDF.


To purchase this publication in book format, please order RI0261.

EXCERPTED ABSTRACT
Because geomorphic features can readily be mapped, our ability to characterize unsaturated flow over large areas would be greatly enhanced if relationships between geomorphic settings and unsaturated flow could be identified. The purpose of this study was to evaluate relationships between geomorphic settings and spatial and temporal variability in unsaturated flow at a field site in the Chihuahuan Desert of Texas.

This study differs from most previous studies in the variety of geomorphic settings examined, including drainage areas (Blanca Draw and Grayton Lake playa) and interdrainage areas (basin-fill deposits, eolian sheets, alluvial fans, and a fissure), density of data (approximately 50 sampled boreholes, 3 to 31 m deep), and variety of techniques (physical, chemical, and electromagnetic) used to quantify unsaturated flow.

Keywords: arid lands, chloride mass balance, chlorine-36, electromagnetic induction, geomorphic setting, radioactive waste disposal, recharge, semiarid region, thermocouple psychrometers, unsaturated flow

CONTENTS

 ABSTRACT

 INTRODUCTION

 SITE DESCRIPTION
            Geomorphic History

             Present Geomorphology

METHODS

             Theory

                         Physical Approach

                         Environmental Tracers

                                     Meteoric Chloride

                                     Chlorine-36

                                     Tritium

                                     Stable Isotopes of Oxygen and Hydrogen

                         Electromagnetic Induction

             Field Methods

                         Water Content  

                         Water Potential

                         Electromagnetic Induction         

             Laboratory Methods

                         Sediment Texture and Water Content     

                         Water Potential

                         Meteoric Chloride and Bromide

                         Chlorine-36                   

                         Tritium

                         Stable Isotopes of Oxygen and Hydrogen         

RESULTS AND DISCUSSION   

             Spatial Variability in Sediment Texture and Water Content  

             Spatial Variability in Water Potential and Chloride

                         Preferential Flow

             Temporal Variability in Unsaturated Flow

                         Residence Time Based on Chlorine-36 Data       

             Stable Isotopes of Oxygen and Hydrogen

             Uncertainties in Water Flux and Residence Time Based on the Chloride Mass     Balance Technique

                         Uncertainties in Chloride Transport Mechanisms

              Water Fluxes and Ages Based on Chloride Including Uncertainty Analysis

                  Example Application of Uncertainty Analysis

              Description of Surface Electromagnetic Transects
                   Controls on Apparent Electrical Conductivity

Relationship between Geomorphic Setting and Unsaturated Flow

Comparison with Data from Geomorphic Settings in Other Basins

Comparison of Different Methods of Evaluating Unsaturated Flow Controls on Unsaturated Flow

Conceptual Flow Model

CONCLUSIONS

REFERENCES

APPENDICES
A. Percent gravel, sand, silt, and clay, soil texture classification, and water content from sampled boreholes
B. Tritium concentrations in pore water from sediment samples in the eolian sheet, in the fissure, adjacent to the fissure, and in Grayton Lake
C. Ratios of 3GC1/Ci1n samples from boreholes EF 36, EF 60, EF 92, EF 111, GL 2, and GL 4
D. Uncertainties in residence times calculated from radioactive decay of 36Cl/Cl
E. Stable isotopes of oxygen and hydrogen in precipitation sampled at Eagle Flat
F. Stable isotopes of oxygen and hydrogen in pore water from sediment samples in boreholes EF 64, EF 91, EF 92, EF 96, EF 113, GL 2, and GL 4
G. Calculated diffusivities and evaporation rates based on stable isotope values in EF 64 and
EF 91 profiles
H. Uncertainties in chloride input in interdrainage areas
I. Uncertainties in water flux and age estimated using the chloride mass balance method from uncertainties in chloride input and output
J. Effect of diffusion and anion exclusion on water flux and age estimates based on the chloride mass balance method

Figures

1. Location of sampled boreholes, unsaturated zone monitoring equipment, and electromagnetic transects relative to geomorphic settings
2. Daily precipitation recorded in the northern part of the study area during sample collection and monitoring (1993-1998)
3. Interdrainage basin-fill deposits in the foreground vegetated with grasses and Blanca Draw in the background shown by dense mesquite vegetation
4. Typical view of the young eolian sheet vegetated with grasses and soaptree yuccas
5. View of Eagle Flat fissure on aerial photograph taken in 1999
6. Concentration of mesquite trees along fissure
7. Cross section of trench at the Eagle Flat fissure
8. Ponded water in Blanca Draw gully in July 1996
9. Aerial photograph of Blanca Draw and surrounding interdrainage area
10. Grayton Lake playa during a long dry period and adjacent eolian sheet with soaptree yucca
11. Cracks resulting from shrinkage of clay soil in Grayton Lake playa
12. Apparent electrical conductivity, water content, water potential, and chloride measured in a transect from EF 94 in the gully in Blanca Draw to EF 28 and EF 111 in the interdrainage basin-fill deposits
13. Apparent electrical conductivity, water content, water potential, and chloride measured in a transect from the eolian sheet adjacent to Grayton Lake toward the center of Grayton Lake
14. Apparent electrical conductivity, water content, water potential, and chloride measured in a transect at right angles to Eagle Flat fissure
15. Profiles of gravimetric water content, water potential, and chloride concentrations for boreholes EF 91 in the eolian sheet
16. Profiles of gravimetric water content, water potential, and chloride concentrations for boreholes in EF 15 and adjacent to the borrow pit in EF 16
17. Correlation between mean water content and mean percent sand and clay in 37 profiles
18. Comparison of water potential measured with a thermocouple psychrometer and a water activity meter in sediment samples from borehole EF 119
19. Relationship between mean water potentials and mean chloride concentrations calculated from each profile drilled in various geomorphic settings
20. Tritium concentrations and ratios of ³⁶Cl/Cl interdrainage profiles in the areas beneath the fissure and 10 m from the fissure, and in Grayton Lake playa
21. Damping of ³⁶Cl/Cl ratios in preferentially moving water as a result of mixing with matrix water
22. Variation in water content with depth and time in neutron probe access tubes
23. Profiles of gravimetric water content, water potential, chloride, and bromide concentrations for borehole EF 121 0.6 m from neutron probe access tube EF 55NP and borehole EF 122 immediately adjacent to the access tube
24. Temporal variations in water potential monitored by in situ thermocouple psychrometers in the old eolian sheet at depths of 4.9 and 7.6 m, 0.3 to 1.8 m, and 19.3 m
25. Comparison of water potential measured in sediment samples from EF 66 with water potentials monitored by in situ thermocouple psychrometers on May 28, 1996, in the eolian sheet
26. Calculated age based on chloride mass balance and cumulative water versus cumulative chloride for profiles in the interdrainage basin-fill deposits and old eolian sheet and young eolian sheet
27. Vertical ³⁶Cl/Cl profiles in interdrainage areas
28. Decay-corrected ³⁶Cl/Cl ratios using the chloride mass balance age relative to the modern 36Cl/Cl ratio at the site in interdrainage areas
29. Uncertainties in pore water residence time as a result of analytical uncertainties in ³⁶Cl/Cl measurements
30. Plots of δ²H versus δ¹⁸O including data from beneath and adjacent to the fissure and beneath and adjacent to Grayton Lake playa and data from interdrainage profiles
31. Depth profiles in δ²H and δ¹⁸O in pore water samples from boreholes in interdrainage areas, beneath and adjacent to a fissure, and beneath and adjacent to Grayton Lake playa
32. Uncertainties in water flux and age resulting from ±35 percent uncertainty in chloride input in profiles from drainage and fissure areas and interdrainage areas
33. Uncertainties in water flux and age resulting from analytical uncertainties in chloride measurements in profiles from drainage and fissure areas and interdrainage areas
34. Lateral flow beneath the Eagle Flat fissure, shown by dye-tracing experiment
35. Mean water fluxes calculated from chloride data for the various geomorphic settings
36. Electromagnetic induction transect measured with the EM31 meter across the projected line of the fissure where there is no surface expression of the fissure
37. Variations in apparent electrical conductivity along transects at right angles to Blanca Draw measured with EM31 ground conductivity meter
38. Temporal variations in apparent electrical conductivity measured with the EM31 meter at different times in Blanca Draw, the fissure, and Grayton Lake playa
39. Relationship between apparent electrical conductivity measured with the EM31 and EM38 aboveground conductivity meters
40. Relationship between apparent electrical conductivity measured with the downhole EM39 meter and clay content and water content and relationship between water content and clay content in samples from GL 4 adjacent to Grayton Lake
41. Relationship between water content and clay content in the upper 6 m of profiles in and adjacent to Grayton Lake
42. Relationship between apparent electrical conductivity measured with the EM39 downhole meter and clay content and water content and relationship between water content and clay content for profiles in the fissure and 10 m from the fissure
43. Relationship between water content and clay content in profiles in the fissure and 10 m from the fissure
44. Relationship between apparent electrical conductivity measured with the EM39 downhole meter and chloride content in samples from EF 110, EF 93, and EF 111
45. Relationship between mean water potentials and mean chloride concentrations calculated from profiles drilled in drainage and interdrainage areas in the Hueco Bolson, interdrainage alluvial fans at Beatty, Nevada, and Ward Valley, California, and at the Nevada Test Site
G1. Plots of 62H and 6180 relative to f(z)
J1. Effective diffusivities for chloride
J2. Advective and diffusive chloride fluxes for EF 111, EF 60, and EF 91 calculated using effective diffusivities

Tables

1. Characteristics of electromagnetic induction conductivity meters including aboveground EM38 and EM31 meters and the downhole EM39 meter used in this study

2. Geomorphic locations of boreholes drilled, dates drilled, depths, types of analyses conducted on sediment samples, and monitoring equipment installed

3. Sediment texture, water content, chloride, and water potential for boreholes drilled in different geomorphic settings

4. Summary of texture, water content, water potential, chloride, tritium, and water fluxes for different geomorphic settings

5. Uncertainties in water flux and age based on the chloride mass balance method resulting from uncertainties in chloride input, chloride output, and transport processes for profiles in interdrainage and drainage and fissure areas

6. Weighted means and ranges of water, chloride, and clay contents calculated from analyses of sediment samples in the upper 6 m from sampled boreholes and apparent electrical conductivity measured with the EM31 meter

7. Correlation coefficients between apparent electrical conductivity measured with the EM39 meter and clay, water, and chloride content in soil sampled from these boreholes and between water content and clay content

G1. Water content, liquid and vapor tortuosities, effective liquid and vapor diffusivities based on hydrogen fractionation factor, total diffusivity, and evaporation rate




Citation
Scanlon, B. R., Goldsmith, R. S., and Langford, R. P., 2000, Relationship between Arid Geomorphic Settings and Unsaturated Zone Flow: Case Study, Chihuahuan Desert, Texas: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 261, 133 p.

of Investigations No. 261, 133 p. doi.org/10.23867/RI0261D.