The Rio Grande Seminar

Fall & Spring Semesters, 2007-2008

Various times & locations

A multi-disciplinary seminar covering physical, social, and legal issues associated with the Rio Grande.

Friday, March 14, 3:00 pm

Tapy Lecture Hall (201)

Rio Grande Basin Flow in Response to Climate Change

Julie Coonrod, Ph.D., P.E.

Associate Professor, Civil Engineering, University of New Mexico

A portion of a larger study, co-authored with Brian Hurd of NMSU, “Impacts of Global Warming on New Mexico’s Water Resources – An Assessment of the Rio Grande Basin” will be presented.

Eight watersheds that feed the Rio Grande were analyzed historically and then with a range of climate scenarios. Thirty years of monthly precipitation and temperature data were spatially averaged over each watershed. A hydrologic model was calibrated for the watersheds using the monthly values of average precipitation, average temperature, and stream flow. Six climate change scenarios altering precipitation and temperature values were applied to the hydrologic model. In each case, the aggregated average stream flow of the eight watersheds was less than the aggregated average stream flow for the historical period analyzed. The stream flow data was subsequently used in an economic model as part of the larger study. The economic model estimated a range of economic losses to New Mexico with the upper end being $300 million.

3:00pm, Friday, November 30, 2007

Tapy Hall 201

“Red Acid Everywhere”: Hydrology and Impacts of a Mine Tailings Dam-Break Flood

on Soda Butte Creek, Montana and Yellowstone National Park

Grant A. Meyer, Department of Earth and Planetary Sciences, University of New Mexico

Soda Butte Creek is a tributary of the Lamar and Yellowstone Rivers in Yellowstone National Park, with headwaters in the New World mining district, Montana. From 1933-1953, pyrite-rich tailings with elevated Cu, Pb, As, and Zn were placed in the McLaren impoundment on upper Soda Butte Creek just above Cooke City. On or about June 24, 1950, the dam failed, producing peak discharges in upper reaches as much as one order of magnitude greater than the 100-yr flood (Q₁₀₀). Near the Lamar confluence 30 km downstream, the reconstructed peak discharge of ~90 m³/s still exceeded the Q₁₀₀ of 70 m³/s. Although peak stream power locally exceeded 300 W/m², little channel or floodplain modification is discernible between 1949 and 1954 airphotos. Using the estimated volume of water released, flood hydrographs were reconstructed at 4 sites 9.5 to 24 km downstream of the dam. Despite flood wave attenuation, flood duration at all sites was < 1 hr. Accordingly, total energy expended per unit channel area was small, from 100-220 kJ/m². In contrast, 63,000 kJ/m² were expended at the 24 km site during a 16-day interval in June 1996, when Q₁₀₀ and peak stream power of 70 W/m² were reached and bank erosion was notable. Although erosion was geomorphically insignificant, abundant overbank flow and rapid decline from peak discharge allowed accumulation of up to 0.7 m of tailings-contaminated sediment on the floodplain, at high levels that are only rarely reached by large natural floods. Metal concentrations in these deposits show a weak but significant exponential decline downstream because of dilution by uncontaminated sediment entrained in the flood, with high local variability (e.g., 2 km below the dam Cu ranges from 210-1220 mg/kg). No significant downstream trends exist in mean particle size, sorting, or thickness in the tailings deposits, consistent with deposition in a brief surge of high sediment concentration. The estimated total mass of floodplain tailings is only 2-3% of that currently in the impoundment, but contaminated deposits continue to impair riparian vegetation. Metals from these deposits also enter Soda Butte Creek through bank erosion and leaching and contribute to reduced diversity of aquatic macroinvertebrates. Natural 50- to 100-yr floods in 1996 and 1997 removed only a small part of the contaminated floodplain sediment through bank erosion; they also failed to lower in-channel Cu concentrations, apparently because increased erosion of mine waste during high flows balances increased inputs of uncontaminated sediments, resulting in no net change. These geomorphic processes controlling movement of contaminated sediments indicate that mine waste will persist for centuries in Soda Butte Creek and imply that long-lasting impacts will occur in similarly affected streams worldwide.

3:00pm, Friday, November 9, 2007

Tapy Hall 201

Mapping Vegetation and Monitoring Water Tables:
Toward Estimating Evapotranspiration in the Rio Grande Bosque

Kristin Vanderbilt, Research Assistant Professor, UNM Biology

Jim Thibault, Research Scientist, UNM Biology

The UNM Ecohydrology group has been researching methods for estimating evapotranspiration in the Rio Grande bosque since 1999. In this seminar, Kristin Vanderbilt will discuss the use of SPOT imagery to map vegetation change in the Albuquerque reach in support of a method that scales ET from eddy covariance tower measurements to the riparian corridor. Jim Thibault will then present data about water table hydrographs relative to ET estimates at four eddy covariance tower sites, which vary hydrologically and by vegetation type. His research illustrates the disparity in riparian ecosystems’ ET responses to changes in the water table.

The offering of this seminar was spurred by our participation in the Urban Flood Demonstration Program with the Corps of Engineers.

During the Fall, 2006 semester the seminar was offered weekly. The talks are posted.

This seminar is organized by Julie Coonrod. Please send questions or comment to jcoonrod@unm.edu.