Adaptive Groundwater

Boundary Conditions

A dynamic feature of Adaptive Groundwater is the automatic definition of grid-cell boundary conditions based on exact user-defined (one-time) specification of boundary condition geometries. As grid cell dimensions and AMR levels change the hydraulic head and solute concentration B.C.’s, along with river and lake “leaky” boundary conditions, for each cell in the numerical mesh are automatically updated to most closely match the B.C. geometries. For example, rivers are defined only once by the centerline coordinates (x,y,z) and the river width and bed thickness. Hydraulic properties such as water surface elevation (stage) and riverbed permeability and thickness are also entered at discrete locations along the centerline.

You may also specify different “default inflow concentrations” for water that enters the aquifer through aquifer boundaries, injection wells, or rivers and lakes. During each time step the program automatically inspects all cells and determines the cells where water enters the simulation domain. For these cells the program automatically assigns fixed-concentration B.C.’s for the transport solution if the user has not already specified a concentration boundary condition at this location. For example, you could have the program automatically assign zero concentration B.C.’s (default) at all upgradient, freshwater inflow cells and not worry about specifying these boundary conditions manually.

The following types of Groundwater Flow boundary conditions are available:

  • Uniform Hydraulic Head – assigned over an area based on a polygon and a user-specified vertical extent. Hydraulic head values may be constant or time-dependent (entered as a head vs. time schedule).
  • Linearly-Varying Hydraulic Head – based on a line or multi-segment polyline (B.C. centerline), a width (plan view), and a vertical thickness over which the B.C. will be applied to individual cells.
  • Hydraulic Head for Aquifer Boundary Faces – a fixed hydraulic head boundary condition is uniformly assigned across the entire depth of a vertical grid boundary (e.g., boundary cells at upgradient and/or downgradient boundaries).
  • Pumping Wells – vertical and horizontal injection and extraction wells with single or multiple screened intervals. Pumping rates may be constant or time-dependent (entered as a flow rate vs. time schedule). Pumping well assignments are made from a “design database” which contains User-created well-screen designs and pumping-rate schedules.
  • Lakes –boundary defined as a polygon. The user defines the lake hydraulic head; the lake bed thickness, elevation, and permeability; and the concentration of dissolved constituents in the lake water (if the lake becomes a discharging B.C.).
  • Rivers – based on polylines. The user defines river segment endpoint heads, elevations, bed thicknesses, widths, permeabilities and concentrations (if a river segment discharges into the aquifer).
  • Recharge – based on polygon-shaped areas or on a cell-by-cell basis. Groundwater recharge with an assigned solute concentration (default is zero) is assigned by the program to cells adjacent to the top boundary of the simulation domain.
Adaptive Groundwater
The following types of Solute Transport boundary conditions are available:
  • Uniform Concentration –assigned over an area based on a polygon and a user-specified vertical extent.  Solute concentrations may be constant or time-dependent (entered as a concentration vs. time schedule).
  • Linearly-Varying Concentration – based on a line or multi-segment polyline (B.C. centerline), a width (plan view), and a vertical thickness over which the B.C. will be applied to individual cells.
  • Constant Concentration for Aquifer Boundary Faces – a fixed solute concentration boundary condition is uniformly assigned across the entire depth of a vertical inflow boundary (e.g., upgradient boundary).
  • Default Inflow Concentrations – You may also specify different “default inflow concentrations” for water that enters the aquifer through aquifer boundaries, injection wells, or rivers and lakes (i.e., “leaky” B.C.’s). Please refer to the above discussion.