| Description |
Hyporheic flow has been identified as a major component of stream flow in Red Butte Canyon. While most hyporheic flow systems tend to have transit times of hours to days, previously conducted stream tracer tests suggest that, in Red Butte, these transit times are much longer. A stream survey of radon concentrations was used to identify specific areas of hyporheic discharge, including spring discharge from a tufa mound that is recharged from the stream approximately 200 m upslope. The hydraulic connection between the stream and the tufa spring was verified by performing an active bromide injection into the stream and monitoring for bromide concentrations in the spring. Two passive techniques, namely, variations of H and O isotope ratios and of noble gas concentrations, were evaluated as means of measuring hyporheic transit times. Peak concentrations of bromide in the tufa spring were observed approximately 18 days after a 24-h injection into the stream, with center of mass transit times of 34-48. However, substantial dispersion resulted in measurable bromide existing 17 weeks after injection. The stable isotope method used storm events with unique H and O isotopic values to reveal an approximately 16-day lag between the stream and the spring that discharges the hyporheic system. Dispersion resulted in significant flattening and spreading of the O and H peaks. However, with better resolution, the stable isotopes are the most promising passive technique. The noble gas method relies on the temperature dependence of the equilibrium solubility of atmospheric noble gases (e.g., Kr and Xe) combined with diurnal and seasonal temperature fluctuation in the stream. However, a 27-h sampling event revealed that the spring had large variations in noble gas concentrations, even though its measured temperature was constant, which could be a result of some exposure to the air before the water is discharged. The noble gases in the spring showed apparent equilibration temperatures similar to the air temperature but lagged by about 13 h. With air temperature appearing to affect the solubility of the gases, and due to the size of the data population, conclusive results from the noble gases could not be determined. |
