UZIG-News - October 1997 - Issue 7

Newsletter of the Unsaturated Zone Interest Group (UZIG) of the US Geological Survey (USGS). The purpose of this newsletter is to enhance communication within the UZIG. It should not be quoted or cited as a publication. Send desired changes in the mailing list to jrnimmo@usgs.gov. Please contact authors or other people mentioned in UZIG-News with any questions, comments, or suggestions.

++ Next Nationwide UZIG Meeting ++

The consensus at the last UZIG meeting (Las Vegas) was that we should meet every two years, meaning September 1998 for the next time. The location is undecided--possibilities include Albuquerque, NM, Menlo Park, CA, and Ithaca, NY--but other suggestions are welcome. Ideally the site would be easy to get to, and near one or more UZIG members who know the scene and can advise on logistics. It is nice but not essential to have possible tours of nearby labs or field sites. Please send suggestions to Rick Healy (rwhealy@usgs.gov).

++ International Workshop on Unsaturated Hydraulic Properties ++

A workshop "Characterization and measurement of the hydraulic properties of unsaturated porous media" will be held in Riverside, CA October 22-24, 1997, just before the Soil Science Society of America (SSSA) meeting in nearby Anaheim. This workshop is cosponsored by the USGS through the Office of Ground Water, in addition to USDA-ARS, DOE, NASA, EPA, the USNRC, the US Army Research Office, and the University of California. The purpose of the workshop is to critically review current measurement techniques and to discuss alternative theoretical or empirical methods for estimating the hydraulic properties from more easily measured data. Eight UZIG members will give presentations. For more information, check the workshop home page (http://www.ussl.ars.usda.gov/HYPROP/hyprop.htm) or contact John Nimmo (jrnimmo@usgs.gov).

by Geoff Delin (delin@usgs.gov) and Kris Nelson (kjnelson@usgs.gov)

The UZIG has a preliminary web page -- the URL is http://wwwmn.cr.usgs.gov/mnlocal/uzig/

The web page gives a description of "Who" we are, "What" our mission is, plus "When and Where" we meet. Other subheadings provide access to the UZIG "Newsletters", UZIG equipment "Resources", notes from previous UZIG "Meetings", a description of "Future Plans" relating to unsaturated zone hydrology such as workshops and meetings, and a "Directory" of UZIG members. A "Photos" section illustrates examples of unsaturated zone technology in action, with pictures contributed by UZIG members. A "Links" subheading includes hot links to other USGS interest groups and projects/programs associated with unsaturated zone hydrology. The current web page is a first draft that will be expanded and improved. At present it is internal (USGS only).

This web page belongs to all of the UZIG. We need your feedback and input. Any comments, suggestions, etc. can be directed to Geoff Delin (delin@usgs.gov) or John Nimmo (jrnimmo@usgs.gov). Items especially needing input include the following:

1. Does the "About UZIG" page contain the appropriate information to describe our group?
2. Are there any other "Resources" that should be added either to the "Inventory" or another subcategory?
3. Is the "Directory" accurate regarding your information? Is there any additional information that you'd like to see added to the directory page?
4. Are there additional "Future Plans" that need to be added?
5. Are there any other links that you would like to see added to the "Links" page?
6. If you have any pictures that illustrate unsaturated zone instrumentation, or use of UZ technology in the field, please contact Geoff Delin and he will add your examples to the "Photos" web page. A digital version of your image is preferred but a print or slide is acceptable.

by Jim Constantz (jconstan@usgs.gov)

The MRGB Program is a five-year study, scheduled for completion in 2000, involving researchers from GD, NMD, and WRD, along with researchers from other public agencies and universities. to improve the understanding of the hydrology, geology, and land-surface characteristics of the MRGB. Jim Bartolino (NM, WRD) manages District research and coordinates NRP involvement.

The MRGB is approximately 120 km from north to south and 40 km in width; Albuquerque is situated on the east side of the Rio Grande in the center of the basin. Mountains surrounding the basin include the Sandia, Manzano, Los Pinos, Sangre de Cristo, Nacimiento, Lucero, and Jemez Ranges. Fact Sheet FS-034-97 gives a general description of the basin, the water issues, and cooperating agencies. The Unsaturated Zone Interest Group has a number of researchers who are currently investigating recharge mechanisms within the MRGB. The five recharge mechanisms of interest are: (1) recharge directly from the Rio Grande, (2) recharge from tributaries of the Rio Grande, (3) diffuse recharge from inter-arroyo areas, (4) mountain-front recharge occurring through the unsaturated zone at the edges of the basin, and (5) mountain recharge occurring through fracture flow and deep groundwater-flow paths to the aquifer directly beneath the mountains. Current estimates suggest that as much as half of all recharge in the MRGB occurs directly from the Rio Grande and its appreciable riparian zone. There is great uncertainty concerning the relative contribution to total recharge from the other four recharge mechanisms. Tributary, inter-arroyo, and mountain-front recharge occur primarily through the unsaturated zone, and are the focus of this note. This will include an overview of research on method development, measurement and modeling of recharge from tributaries, inter-arroyo areas, and mountain-fronts on the east side of the basin from the Santa Fe River in the north to Abo Arroyo in the south.

Recharge rates beneath the Santa Fe River are the focus of a group coordinated by Carole Thomas (NM, WRD) and Dave Stonestrom (BRR, WR, WRD). Thomas, Stonestrom, Anne Ronan (San Jose State University), Amy Stewart (BRR, WR, WRD), and Jim Constantz (BRR, WR, WRD) are using streamflow, stream temperature, and groundwater-temperature measurements to determine whether temporal patterns in streambed-temperature profiles can be used to estimate streambed infiltration rates. The heat and water flow model VS2DH (Healy and Ronan, WRIR 96-4230), is being used to compare simulated streambed temperatures with measured streambed temperatures, to derive estimates of streambed percolation rates. These rates are compared with streamflow-loss measurements to determine the accuracy of the streambed-temperature procedure for potential long-term monitoring of tributary recharge rates.

Tributary, inter-arroyo, and mountain-front recharge are the focus of a group coordinated by Stonestrom, various subgroups of which are using depth-profiling of chemical and isotopic constituents and physical properties to estimate recharge rates. Stonestrom and Fred Gebhardt (NM, WRD) obtained over 300 bulk and core samples during extensive drilling operations in FY96-97. These were from eight transects across floodplains and paleo-floodplains of three channels: the Santa Fe River, Abo Arroyo, and Bear Canyon near Albuquerque. The samples came from depths as great as 7 meters. Bulk samples are being analyzed by Kathy Akstin (WRR, WR, WRD) and Stonestrom for chloride and bromide. Tritium, and stable isotopes oxygen-18 and deuterium, are being analyzed by Bob Michel and Doug White of the Isotopic Tracers of Hydrological Processes Group (BRR, WR, WRD). Concentrations of tracers and distribution of isotopic species of water with depth lead to estimates of long-term (e.g., 50 year) average recharge rates. Core samples are being analyzed by John Nimmo (BRR, WR, WRD) and Angus Lewis (BRR, WR, WRD) to determine unsaturated conductivities (K) using the steady-state centrifuge method. These K values can indicate recharge if certain assumptions hold, for example that unsaturated flow is steady at the depth of sampling. Detailed modeling of flow through the layered profile allows the testing of these assumptions and the interpretation of measured K values as recharge rates.

Stewart, Stonestrom, Thomas, and Constantz are examining the influence of variations in streamflow hydrographs on spatial and temporal variations in recharge characteristics in Abo Arroyo. The arroyo has been instrumented along its length with temperature sensors, to indicate the presence or absence of streamflow. The goal of this study is to compare streamflow magnitudes to potential transmission losses in numerous reaches between a USGS gaging station and the Rio Grande 20 km to the west. Stewart is developing a surface-water module as an upper boundary in a 3-D heat and ground-water flow model for comparison of simulated surface-water/ground-water flows with measurements obtained from Abo Arroyo. A smaller-scale study is being undertaken at Bear Canyon to examine the utilization of streambed temperature profiles to determine the timing, duration and rate of streambed percolation. These are designed as method development studies for future estimates of mountain-front and tributary recharge on the west side of the Sandia, Manzano, and Los Pinos Mountains.

Saturated zone research of interest to UZIG members includes: (1) well sampling throughout the MRGB to examine carbon-14 and chlorofluorocarbon concentrations for age-dating, by Niel Plummer (BRR, ER, WRD) and Ed Busenberg (BRR, ER, WRD); (2) application of MODFLOW-P as a parameter estimate method to estimate recharge throughout the entire MRGB, by Claire Tiedeman (BRR, WR, WRD); (3) the use of MODPATH and environmental tracers to improve estimates using MODFLOW, by Ward Sanford (BRR, ER, WRD) and Plummer; and (4) examination of the vertical hydraulic conductivity of the aquifer underlying the Rio Grande by Bartolino.

The MRGB Program holds an annual technical workshop for participants in the program and other interested researchers. Published abstracts for the first workshop in November, 1996, are available as Open-file Report 97-116. The second annual technical workshop will be held in Albuquerque, February 10-12, 1998. Reports and information regarding the workshop are available from the research coordinators, Jim Bartolino (jrbartol@usgs.gov) and Dave Stonestrom (dastones@usgs.gov).