HR: 13:55h
AN: H23G-02    [Abstracts]
TI: Hydrodynamic interactions of free-flowing fluids and pore-fluids in bedforms
AU: * Cardenas, M
EM: cardenas@nmt.edu
AF: Earth and Environmental Science, NM Inst. of Mining and Technology, 801 Leroy Place, Socorro, NM 87801 United States
AU: Wilson, J L
EM: jwilson@nmt.edu
AF: Earth and Environmental Science, NM Inst. of Mining and Technology, 801 Leroy Place, Socorro, NM 87801 United States
AB: The physical and chemical complexity of the interface between porous bed interstitial water and surface water, sometimes referred to as the {\it hyporheic zone} in river-aquifer systems, has yet to be understood in detail. But, we do know that ecologically and environmentally significant processes occurring in these zones control the distribution of solutes, colloids, and dissolved gases from ripple to global scales. In fact, previous model computations show that the entire ocean volume could be recycled through such systems in 14,000 years. The biochemical processes occurring in these areas are mediated by fluid flow, as mass diffusive flux is usually orders of magnitude smaller than that of advective transport. Thus, a holistic view of these systems necessarily begins with a comprehensive knowledge of the hydrodynamics. The coupled fluid flow in open areas and their underlying porous bedforms are examined in this study. We numerically simulate steady viscous flow in these coupled systems by solving the Navier-Stokes and continuity equations that govern the free area and then use the pressure solution from this domain as a boundary for the porous subsurface domain governed by the groundwater flow equation. Numerical experiments were used to determine fundamental relationships between bedform geometry, free area Reynolds number ({\it Re}), exchange zone depths ({\it d}), and total fluxes through the bed surface ({\it q}). The results are as follows: 1) {\it d} and {\it Re} are functionally related through a Michaelis-Menten saturation-growth -like model; 2) {\it q} and {\it Re} follow a quadratic relationship; 3) {\it d} scales linearly with bedform length ({\it L}) and nonlinearly and non-monotonically with bedform height ({\it H}); 4) {\it q} increases as bedforms get steeper (high {\it H}/{\it L}); 5) the relative location of the bedform crest becomes a more important factor as {\it Re} increases; {\it d} is minimized when the crest is in the middle of the bedform and is maximized when the crest is near the downstream end of the bedform; 6) {\it q} is minimized and stabilizes when the crest is near the downstream end of the bedform; 7) eddy reattachment points correspond to subsurface flow divides; flow cells may cross between bedforms; 8) subsurface velocities drop dramatically with depth; the velocity at a point located directly underneath the crest and at the same elevation as the trough is less than 3% of the velocity at the crest.
DE: 4211 Benthic boundary layers
DE: 4546 Nearshore processes
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1860 Runoff and streamflow
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting