Date of Award:

12-2009

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Advisor/Chair:

Bethany T Neilson

Abstract

A study reach in a mountain stream highly influenced by groundwater was selected to test common data collection strategies used to characterize and quantify groundwater exchange processes necessary to predict solute transport. The data types collected include: high frequency discharge estimates with the use of rating curves, dilution gauging techniques with instantaneous tracer experiments, groundwater table and stream water surface elevations, vertical head gradients, and hydraulic conductivity estimates. The first two data types were categorized as stream gauging and the remaining three data types as site characterization. The stream gauging data were used to quantify net changes in stream discharge at a reach scale with rating curve predictions and dilution gauging. Each method resulted in opposite net changes at this scale. An error analysis regarding rating curve predictions and dilution gauging suggested that neither method detected groundwater exchange at this scale due to discharge estimates being statistically the same. The error in rating curve predictions was estimated using a 95% joint confidence region of model parameters and the error in dilution gauging was estimated using a first order error analysis. Dilution gauging was also performed at a sub-reach scale to quantify net changes and indicated the groundwater exchange was highly spatially variable, which was not concluded at the reach scale. To quantify a water balance more representative of the exchanges occurring, gross gains and gross losses were quantified by measuring tracer mass recoveries and were found to occur in every sub-reach. However, the error analysis concluded that nearly half of the changes were not significant, which emphasized the importance of quantifying error in stream gauging techniques used to understand surface water-groundwater interactions.

The site characterization data were used to test and verify the water balance results by providing information regarding general trends and spatial variability of surface water-groundwater interactions. This study proved that one data type is not adequate to clearly characterize and quantify surface water-groundwater interactions and researchers must exercise caution when interpreting results from different data types at varying spatial scales.