# HydroGeoSphere/Subsurface Flow (Initial)

Initial heads should be given for both steady-state and transient problems since the iterative solver uses them as a starting point in achieving a solution. These heads can be assigned or read from a file.

## Initial head

* hval Initial head [L].
Chosen nodes in the currently active media (see Section 5.8.1) are assigned an initial head value.

## Initial head surface elevation

All nodes in the currently active media (see Section 5.8.1) are assigned an initial head value equal to the surface elevation at the same xy-location.

## Initial head from depth-saturation table

Scope: .grok
* depth(1), saturation(1) First entry.
* depth(2), saturation(2) Second entry.
       ...etc.
    n. depth(n), saturation(n) nth entry.
    n+1. end The string 'end'
Paired values of depth $z$ and saturation $S$ should be entered from smallest to largest depth. The last line of the table must be an end card, and the number of entries in the list are counted automatically to determine the table size.
Chosen nodes in the currently active media (see Section 5.8.1) are first assigned a saturation which is interpolated from the depth-saturation table. The nodes depth is calculated relative to the node on ground surface at the same xy-location. The computed saturation is then converted to an initial head value using the constitutive relationships (see Section 5.8.3) for the zone number of the element containing the chosen node. In cases where a node is shared by two elements with different zone numbers, then the zone number of the lowest numbered element is used.

## Initial head from file

* fname Name of the file which contains the initial head data.
All nodes in the currently active media (see Section 5.8.1) are assigned an initial head value which is read from a free-format ascii file. The heads must be listed in the file in order from node 1 to node NN. Each line can contain one or more values.

## Initial head from output file

* fname Name of the file which contains the initial head data.
All nodes in the currently active media (see Section 5.8.1) are assigned an initial head value which is read from a previously generated output file with a name of the style prefixo.head.suffix, where suffix is a 3-digit number identifying the output file. Since it is applied to the current media type you can use, for example, prefixo.head.003 for the porous media and prefixo.head_overland.003 for the surface domain. This can be useful, for example, when a run crashes (since you don’t have to start simulation from scratch) or if you want to use separate solutions of groundwater and surface flow to start a coupled surface-subsurface simulation.

## Initial head subsurface from surface output file

* fname Name of the file which contains the initial surface domain head data.
All nodes in the currently active media (see Section 5.8.1) are assigned an initial head value equal to the surface domain head at the same xy-location. The surface heads are read from a previously generated output file with a name of the style prefixo.head_overland.suffix, where suffix is a 3-digit number identifying the output file.

## Function x initial head

* x1,h1 The x-coordinate and initial head value for the first point.
* x2,h2 The x-coordinate and initial head value for the second point.
Using linear interpolation, chosen nodes in the currently active media (see Section 5.8.1) are assigned initial head values, based on their x-coordinate and given heads at two points.

## Function z initial head

As above but as a function of z.

## Initial head raster

* rasterfile Name of the raster file containing the initial head data. This is a string variable. The file should be formatted as outlined in Section H.
All nodes in the currently active media (see Section 5.8.1) are assigned an initial head value equal to the raster value at the same xy-location.

## Map initial head from raster

* rasterfile Name of the raster file containing the initial head values. This is a string variable. The file should be formatted as outlined in Section H.
For each node in each element in the set of currently chosen zones, a value for the initial head will be interpolated from the raster file data.
This instruction currently only generates initial head values for the porous medium.

## Restart file for heads

* flow_restart_file_name Name of the file which contains the results of the previous flow solution.
All nodes are assigned an initial head value which is read from the file. This allows heads from a previous run to be used as initial conditions for a subsequent simulation, for example, if one wants to carry on the simulation further in time without restarting from time zero.
Since, by default, head values for the last time step are output in BINARY format to a file with the suffix prefixo.hen, these are always available for restarting a flow run. It is recommended that this file be renamed in order to avoid accidentally overwriting it and changing the restart conditions for a later run.

## Compute velocity field from head

* v_head_file Name of the file which contains the results of the previous flow solution.
A flow solution is not performed. Instead, the velocity field is computed from the previous flow solution, a steady-state flow field is assumed, and the transport solution proceeds.
The heads are read from a previously generated output file with a name of the style prefixo.head.suffix, where suffix is a 3-digit number identifying the output file.

## Compute velocity field from head and conc.

* v_head_file Name of the file which contains the results of the previous flow solution.
* v_conc_file Name of the file which contains the results of the previous transport solution.
* vrhomax, vcmax Assumed maximum density and concentration.
A flow solution is not performed. Instead, the velocity field is computed from the previous flow solution and transport solution, a steady-state flow field is assumed, and the density-dependent transport solution proceeds.
The heads are read from a previously generated output file with a name of the style prefixo.head.suffix, where suffix is a 3-digit number identifying the output file.
The concentrations are read from a previously generated output file with a name of the style prefixo.concentration.species.suffix, where suffix is a 3-digit number identifying the output file.