Date of Award
Master of Science (MS)
Department of Geography-Geology: Hydrogeology
Eric W. Peterson
Little Kickapoo Creek (LKC) is a low-gradient, third-order perennial stream with headwaters in Bloomington, IL. The objective of this study is to characterize vertical one-dimensional (1-D) flux rates in the top 150 cm of the streambed, test the viability of a heat tracing method in a low-gradient area, and determine the relationship between stage and 1-D vertical flux rates. In 2009, six wells were installed along the thalweg of the stream in a 25-meter stretch spaced at 5-meter intervals. Each well recorded temperature at five separate depths logging at 15-minute0 intervals from February 2009 to March 2010: 30, 60, 90, and 150 cm. Stage data was collected at 15- minute intervals on the stream bank adjacent to the streambed well array. Vertical flux rates are calculated using temperature sensor pairs at depth with the 1-D conduction-advection-dispersion equation utilized in the VFLUX MATLAB program.
Flux calculations are at the midpoint between a sensor pair, e.g., a flux is estimated at a depth of 45 cm, the midpoint between the 30 and 60 cm sensors. The dominant flux direction at a depth of 15 cm is downward (negative) while the average flux direction at a depth of 45 cm, 75 cm, and 120 cm is upward (positive). Fluxes at a 15 cm depth for all six wells ranges between -0.59 to 0.95 m/d with an average of -0.04 m/d. At a midpoint of 45 cm, 75 cm, and 120 cm fluxes are highly variable with high-frequency spikes and missing data, but all have a baseline upward trend. Due to the errors in flux, the paper focuses on a depth of 15 cm within the hyporheic zone of LKC for the stage correlation analysis. At a 15 cm depth, the average flux across six wells ranges from -2*10-6 m/s to 5*10-7 m/s. The hyporheic zone at LKC has variable flux directions above 15 cm indicating hyporheic exchange with background upwelling groundwater between 15 to 120 cm. Flux rates approach zero in the summer meaning a period of limited hyporheic exchange.
The relationship between stage and flux at the near-surface streambed (15 cm) is a weak, but statistically significant with Spearman’s rank correlations for all six wells at 15 cm depth ranging from -0.032 to 0.369 with an average of 0.085. A negative relationship implies that as stage rises and the stream loses water (negative, downward flux) from the streambed and vice versa. A positive relationship explains that as stage rises the stream is in a gaining condition (upward, positive flux). With the assumption that flux does not have an instantaneous reaction to a change in stage, a cross-correlation analysis was performed. The cross-correlation analysis keeps stage stagnant in time, while flux is temporally shifted forward. The highest Spearman coefficient is 0.442 for well 4. The other five wells have a Spearman coefficient less than 0.20. This research indicates that stage is not a reliable prediction of 1-D vertical flux in the hyporheic zone of LKC. Vertical flux is a multivariate function that can be controlled by the following variables: stream velocity, streambed morphology and topography, streambed conductivity, channel slope, stream sinuosity, vertical gradient in the microscopic stream-streambed and watershed scale, and stream stage or discharge.
Harris, Frances Claire, "Understanding 1-D Vertical Flux Dynamics in a Low-Gradient Stream: an Assessment of Stage as a Control of Vertical Hyporheic Exchange" (2018). Theses and Dissertations. 861.