Abstract
Modeling flow and transport in porous media requires the management of complexities related both to physical processes and to subsurface heterogeneity. A thorough approach needs a great number of spatially-distributed phenomenological parameters, which are seldom measured in the field. For instance, modeling a phreatic aquifer under high water extraction rates is very challenging, because it requires the simulation of variably-saturated flow. 3D steady groundwater flow is modeled with YAGMod (yet another groundwater flow model), a model based on a finite-difference conservative scheme and implemented in a computer code developed in Fortran90. YAGMod simulates also the presence of partially-saturated or dry cells. The proposed algorithm and other alternative methods developed to manage dry cells in the case of depleted aquifers are analyzed and compared to a simple test. Different approaches yield different solutions, among which, it is not possible to select the best one on the basis of physical arguments. A possible advantage of YAGMod is that no additional non-physical parameter is needed to overcome the numerical difficulties arising to handle drained cells. YAGMod also includes a module that allows one to identify the conductivity field for a phreatic aquifer by solving an inverse problem with the comparison model method.
Highlights
The flow of water in porous sediments is described in mathematical terms by joining the mass conservation principle with the phenomenological Darcy’s law [1,2]
The first goal of this paper is to propose a code, YAGMod, developed in Fortran90, for the simulation of constant-density, groundwater flow under stationary conditions, which is the extension of the codes developed by our research team over the years [7,8,9,10,11,12,13,14,15,16,17]
Where h( i,j,k) is the hydraulic head at a node (L); K( i−1/2,j,k) and K( i+1/2,j,k) (LT−1 ) are called internode hydraulic conductivities along the x direction; θ( i+1/2,j,k) = θ( i,j,k) + θ( i+1,j,k) /2 is the arithmetic mean of the saturated thicknesses of the cells(i, j, k) and (i + 1, j, k); ∆z( i,j,k+1/2) = ∆z( i,j,k) + ∆z( i+1,j,k) /2 is the distance between two adjacent nodes along the vertical; F( i,j,k) is the cell source term, i.e., the volume of water injected in the cell per unit time (L3 T−1 )
Summary
The flow of water in porous sediments is described in mathematical terms by joining the mass conservation principle with the phenomenological Darcy’s law [1,2]. Niswonger et al [6] use a quadratic approximation of the function that relates horizontal conductance to hydraulic head, over small intervals close to the fully-dry and fully-saturated limits Within this background, the first goal of this paper is to propose a code, YAGMod (yet another groundwater flow model), developed in Fortran, for the simulation of constant-density, groundwater flow under stationary conditions, which is the extension of the codes developed by our research team over the years [7,8,9,10,11,12,13,14,15,16,17]. Relatively simple models and tests, like those proposed in this paper, can be very useful to cope with complex natural systems with a computationally-frugal approach, which can provide first insights into the relevant natural processes, on the most sensitive parameters, etc., as recently shown, e.g., by Hill et al [24]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call