HR: 1340h
AN: H13D-1542    [Abstracts]
TI: Modeling Streambed Hyporheic Exchange Using a Spectral Scaling Based Pumping Model
AU: * Stonedahl, S
EM: s-stone2@northwestern.edu
AF: Northwestern University, 2145 Sheridan Road, Evanston, IL 60010, United States
AU: Harvey, J W
EM: jwharvey@usgs.gov
AF: U.S. Geological Survey, 430 National Center, Reston, VA 20192, United States
AU: Worman, A
EM: worman@kth.se
AF: Royal Institute of Technology, Teknikringen 76, stockholm, 100 44, Sweden
AU: Packman, A I
EM: a-packman@northwestern.edu
AF: Northwestern University, 2145 Sheridan Road, Evanston, IL 60010, United States
AB: Modeling solute transport in rivers is critical to evaluating the transport of contaminants, nutrients, and other water-borne constituents, and thus is inherent to the study of ecosystems and water quality. Our objective is to enable prediction of hyporheic exchange at the bedform-to-reach-scale based on readily measurable system characteristics. We employ a spectral scaling approach as the basis for a generalized analysis of topography- induced exchange in river systems. The model includes the lateral hyporheic zone in addition to the flow directly beneath the streambed. This approach encompasses a larger range of scales than is normally considered in predictive exchange modeling, including subsurface flow induced by very small scale bedforms to much larger features such as meanders. The primary input parameters for modeling are in-stream velocity, sediment permeability and porosity, and detailed measurements of the stream channel topography. The primary outputs are a flow path analysis, water exchange flux across the sediment boundary, and subsurface residence time distribution, which can be compared against field data. Having spatially explicit information allows us to evaluate the contributions of various classes of streambed features in overall hyporheic exchange, a key advantage over the more empirical approach of conducting a stream tracer experiment. The solution method involves Fourier fitting of the topography followed by calculation of the boundary head distribution and then the subsurface head and velocity fields. A sophisticated geometric transformation is required to accurately represent areas of high pressure on the upstream edge of submerged topographic features in meandering channels. We have implemented a Schwarz-Christoffel conformal mapping procedure for this purpose. This method provides consistent results regardless of the orientation of the stream, as well as a reasonable estimation of the three- dimensional boundary head distribution. Lateral (floodplain) exchange is captured by superimposing the Fourier solution for the in-channel hyporheic exchange on a finite-difference solution for broader stream-groundwater interactions. The model is applied to several highly detailed two- and three-dimensional datasets from laboratory flumes, and also to one field site in a headwater agricultural stream.
DE: 1830 Groundwater/surface water interaction
DE: 1860 Streamflow
SC: Hydrology [H]
MN: 2007 Fall Meeting