HR: 14:15h
AN: H53I-03    [Abstracts]
TI: Flow Data for Solute Transport Modeling from Tracer Experiments in a Stream Not Continuously Gaining Water
AU: * Bencala, K E
EM: kbencala@usgs.gov
AF: US Geological Survey, MS 439 345 Middlefield Road, Menlo Park, CA 94025, United States
AU: Kimball, B A
EM: bkimball@usgs.gov
AF: US Geological Survey, 2329 W Orton Circle, West Valley City, UT 84119, United States
AU: Gooseff, M N
EM: mgooseff@engr.psu.edu
AF: Pennsylvania State University, Civil and Environmental Engineering, University Park, PA 16802, United States
AB: In-stream tracer experiments are a well-established method for determining flow data to be incorporated in solute transport modeling. For a gaining stream, this method is implemented to provide spatial flow data at scales of minutes and tens of meters without physical disturbance to the flow of water, the streambed, or biota. Of importance for solute transport modeling, solute inflow loading along the stream can be estimated with this spatial data. The tracer information can also be interpreted to characterize hyporheic exchange time-scales for a stream with hyporheic exchange flowpaths (HEFs) that are short relative to the distance over which the stream gains water. The interpretation of tracer data becomes uncertain for a stream that is not gaining water continuously over intended study reach. We demonstrate, with straight-forward mass-balances, uncertainties for solute loading which arise in the analysis of streams locally losing water while predominantly gaining water (and solutes) over a larger scale. With field data from Mineral Creek (Silverton, Colorado) we illustrate the further uncertainty distinguishing HEFs from (locally) losing segments of the stream. Comparison of bromide tracer with ambient sulfate concentrations suggests that subsurface inflows and outflows, concurrent with likely HEFs, occur in a hydrogeochemical setting of multiple, dispersed and mixed, sources of water along a 64 m sub-reach of the predominately gaining, but locally losing, stream. To compute stream-reach mass-balances (the simplest of water quality models) there is a need to quantitatively define the character and source of contaminants entering streams from ground-water pathways, as well as the potential for changes in water chemistry and contaminant concentrations along flow paths crossing the sediment-water interface. Identification of inflow solute mass requires quantifying water gain, loss, and hyporheic exchange in addition to concentration.
UR: http://smig.usgs.gov/SMIG/transtor_reader2.html
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 1830 Groundwater/surface water interaction
DE: 1871 Surface water quality
DE: 1894 Instruments and techniques: modeling
SC: Hydrology [H]
MN: 2007 Fall Meeting