HR: 14:55h
AN: H23I-06    [Abstracts]
TI: Unbounded, Exact Solution for 3-D Topography Driven Groundwater Flow
AU: * Marklund, L
EM: larsmark@kth.se
AF: The Royal Institute of Technology, Department of Land and Water Resources Engineering, Teknikringen 76, Stockholm, 100 44, Sweden
AU: Wörman, A
EM: worman@kth.se
AF: The Royal Institute of Technology, Department of Land and Water Resources Engineering, Teknikringen 76, Stockholm, 100 44, Sweden
AB: An exact analytical solution is presented for saturated groundwater flow to provide improved understanding of the renewal rate of deep and shallow groundwater and the long-term management of groundwater resources. The solution is derived under the assumptions that the hydraulic potential of the groundwater surface follows the topography and imposes a steady boundary condition for driving the groundwater flow. This assumption is justified in most areas of humid climate. The solution is applicable on a wide range of spatial scales and accounts for decaying permeability with depth, stratified aquifers as well as anisotropy. The flow problem is solved by representing the topography with a three-dimensional spectral scaling solution based on harmonic functions that are independent in x- and y-directions. In most areas the Fourier-series, representing the topography, give a nearly perfect image of the ground surface elevation. The topography is found to be fractal and this imposes a fractal nature of the groundwater flow that is altered by the additional geometrical scales. The groundwater flow solution, based on the Fourier-spectrum, depends on the decay with depth and anisotropy in hydraulic conductivity and stratifications due to quaternary deposits, layered sediments etc. Prior analytical solutions are limited to either two-dimensional flows or harmonic functions uniform in the x- and y- directions, hence making them unable to predict three-dimensional subsurface flows beneath a realistic landscape. However, the most important advantage of this new method is the ability to analyse the impact of different geometrical scales on the groundwater flow. Analyses indicate that in a homogeneous subsurface, shallow groundwater flows would be approximately equally controlled by all scales of topography. Although shorter topographical wavelengths control the surface water flux, their impact decreases faster with depth in relation to longer wavelengths. This induces an increasing importance of large-scale topography with depth. However, the hydraulic conductivity tends to decay with depth and this counteracts the effect of the large-scale topography on the groundwater flow more effectively than the smaller landscape scales. For the depth-dependent hydraulic conductivity applicable to the Fennoscandian bedrock, we find a depth-limitation of the flow cells that tends to reduce the importance of the larger wavelengths on the fluxes at all depths.
DE: 1829 Groundwater hydrology
DE: 1830 Groundwater/surface water interaction
DE: 1839 Hydrologic scaling
DE: 1847 Modeling
DE: 1884 Water supply
SC: Hydrology [H]
MN: 2007 Fall Meeting