HR: 1340h
AN: H43C-0513    [Abstracts]
TI: Predicting Hyporheic Exchange of Water and Solutes in Streams on the Basis of a Priori Estimates of Stream Physical Characteristics
AU: * Stone, S H
EM: s-stone2@northwestern.edu
AF: Northwestern University, Department of Civil and Environmental Engineering A-236 Tech Institute 2145 Sheridan Road, Evanston, IL 60208-3109
AU: Harvey, J
EM: jwharvey@usgs.gov
AF: U.S. Geological Survey, 430 National Center, Reston, VA 20192
AU: Packman, A
EM: a-packman@northwestern.edu
AF: Northwestern University, Department of Civil and Environmental Engineering A-236 Tech Institute 2145 Sheridan Road, Evanston, IL 60208-3109
AU: Worman, A
EM: Anders.Worman@bt.slu.se
AF: Department of Biometry and Engineering Swedish University of Agricultural Sciences, P.O. Box 7032, Uppsala, 750 07 Sweden
AB: It is very important to accurately model solute transport in rivers in order to analyze contaminant transport, water quality, and a variety of ecological processes. The purpose of this research is to determine the physical characteristics of a stream or river that are sufficient to predict hyporheic exchange and downstream solute transport. In the fall of 2004, we conducted a bromide tracer injection and made physical measurements in Sugar Creek, a small agricultural stream in northwestern Indiana. As is typical for small mid-western agricultural streams, Sugar Creek has been ditched and straightened, and subsequent downcutting through glacial sediments and slumpage of bank sediments composed of finer grain sizes has created a stream of intermediate complexity. In order to relate the observed solute transport to more basic physical characteristics of the stream, we determined the bathymetry of Sugar Creek over a wide range of scales (centimeters to decameters), and measured velocity profiles, the water elevation surface profile, hydraulic conductivity via in situ measurements, and bed sediment grain size distributions throughout the study reach. Our most detailed topographic measurements revealed fine scale bed variations with wavelengths on the order of ten centimeters, while surveying of the entire study reach characterized large scale meanders with wavelengths on the order of five meters. The distribution of wavelengths influences the driving forces that cause solute to enter the bed and banks. Hydraulic conductivity determines the resistance to flow of stream water through the (meander) stream banks and streambed. We used a scaling approach to relate the geometric and hydrogeologic characteristics of the stream to solute transport and also applied a new analytical solution for the subsurface flows resulting from topographic variations over a wide range of spatial scales. These models captured the main features of the observed solute transport. The greatest source of uncertainty in predicting hyporheic exchange resulted from the lack of detailed information on streambed hydraulic conductivity. We are currently conducting additional fieldwork to improve characterization of hydraulic conductivity and evaluate temporal changes in local stream morphology, and will relate these new measurements to the results of multiple prior solute injection experiments. These methods can potentially be used to provide both a priori, order-of-magnitude prediction of hyporheic exchange and much higher-quality estimates of long-term average behavior when used in conjunction with direct observations of solute transport. In the future we intend to test the generality of our method by applying the technique in other streams with varying geomorphology and flow conditions.
DE: 1835 Hydrogeophysics
DE: 1847 Modeling
DE: 1871 Surface water quality
DE: 4534 Hydrodynamic modeling
DE: 7859 Transport processes
SC: Hydrology [H]
MN: Fall Meeting 2005