HR: 0830h
AN: H41D-1028    [PDF]
TI: Channel Morphology, Bed Forms and Aquifer Heterogeneity: Roles in 2-D and 3-D Analysis of Hyporheic Exchange Flows
AU: * Matos, J R
EM: sg96d729@drexel.edu
AF: Jorge Eurico R. Matos, Department of Civil, Architectural and Environmental Engineering,Drexel University, 3141 Chestnut St., Philadelphia, PA 19104-3104 United States
AU: Packman, A I
EM: a-packman@northwestern.edu
AF: Aaron I. Packman, A314 Technological Institute, Northwestern University,2145 Sheridan Road, Evanston, IL 60208-3109 United States
AU: Welty, C
EM: weltyc@drexel.edu
AF: Claire Welty, Center for Urban Environmental Research and Education and Department of Civil and Environmental Engineering, University of Maryland,Baltimore County,TRC 102, 1000 Hilltop Circle, Baltimore, MD 21250 United States
AB: The effects of channel pattern, bed forms and aquifer heterogeneity on flow interactions between stream and groundwater systems are examined in this study. Two and three-dimensional approaches were used to determine the influence of stream meandering patterns and bed forms on the characteristics of stream-subsurface exchange. A grid with 180x256x30 (x, y, z) cells was designed using the correlation scales of the heterogeneous fields generated by the Turning Bands method and the scale of the stream meanders. MODFLOW and MODPATH were applied to evaluate magnitude, direction and spatial distribution of the exchange flow. Particle tracking was performed to define hyporheic residence time distributions. Even though the main purpose of the simulations is the analysis of three-dimensional surface-groundwater interchange in heterogeneous systems, the two-dimensional approach was also adopted to allow comparisons. The model is an idealized case intended to describe how properties of the streambed and aquifer in low-gradient lowland streams contribute to hyporheic exchange. A sine curve was built to represent the meandering stream with variations on wavelength and amplitude. The bed forms were simulated assuming a sinusoidal distribution of pressure head in the bed surface. Various amplitudes and wave lengths were used to cover a range of flow velocities between 20 and 40 cm/s in the channel. The objective is to show the influence of river morphology and the role of natural bed forms on the flow exchange in the hyporheic zone. Flow variances along the wetted perimeter and along transverse cross-sections of the stream were analyzed. Simulations with four meander cycles, four amplitudes and four levels of hydraulic conductivity variance show that as the heterogeneity variance increases so does the hyporheic exchange. Flow variance decreases as the number of meander cycles and amplitudes of the meanders increase. The results for travel time in the meandering stream show a substantially increased travel time between a homogeneous field and all degrees of heterogeneity. MODPATH simulations also showed that heterogeneity increases tailing in cumulative distribution functions of hyporheic residence times. Further simulations will provide additional insights on the role of geomorphic features in controlling hyporheic exchange processes.
DE: 1806 Chemistry of fresh water
DE: 1815 Erosion and sedimentation
DE: 1869 Stochastic processes
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2003 Fall Meeting