User's guide of Proceessing Modflow 5.0

190 Processing Modflow
size of the time marks is defined by Size (in pixels). The default value of Size is 10 for
the top view window and 3 for the cross-section windows. The sizes can be ranged from
1 to 2,147,483,647.
- Simulation Mode: PMPATH can be used to calculate flowlines or pathlines. Flowlines
indicate the instantaneous direction of flow throughout a system (at all times of a
steady-state flow simulation or at a given time step of a transient flow simulation).
Pathlines map the route that an individual particle of water follows through a region of
flow during a steady-state or transient condition. In a steady-state flow system pathlines
will coincide with flowlines. In this case, only the option Flowline, use the flow field
from the current time step is available. In the case of a transient flow simulation that
groundwater flow varies from time step to time step, the flowlines and pathlines do not
coincide. Use the option Pathlines, use transient flow fields to calculate transient
pathlines.
- Stop Conditions: In general, particles will stop when the allowed travel time defined in
Tracking Step is reached or when the particles reach specified head cells. In addition to
these conditions, two stop conditions are available:
1. Particles stop, when they enter cells with internal sinks:
The flow model MODFLOW includes the options to simulate wells, drains, rivers,
general-head boundaries, streams, evapotranspiration and recharge. Except the last
two options, they are treated as internal distributed sources or sinks by PMPATH. If
the internal sink of a cell is sufficiently strong, flow will be into the cell from all cell
faces. In that case, every particle that enters the cell will be discharged. If the sink is
weak, flow will be into the cell from some cell faces and a part of flow will leave the
cell through another faces. A particle entering such a cell may be discharged or may
leave the cell again. In the finite-difference approach, however, it is impossible to
determine whether that particle should be discharged or pass through the cell. If this
option is selected, particles will be discharged when they enter cells with internal
sinks, regardless of the flow condition.
2. Particles stop, when the simulation time limit is reached.
This option is only available, if the simulation mode Pathlines, use transient flow
fields is selected. In PMPATH, the starting time of each particle is always the
beginning of the time step defined in Current Time. For the forward particle tracking
scheme, the simulation time limit is the end of a transient flow simulation. For the
backward particle tracking scheme, on the other hand, the simulation time limit is the
beginning of the simulation. Backward particle tracking will not work, if this stop
option is checked and particles are started from the beginning of a transient flow
4.3 PMPATH Options Menu