Pathlines¶

Pathline starting points are under Output Specification → Pathlines. You can specify a single pathline, pathlines distributed along a line, pathlines spread over a polygon, pathlines around a circle, or pathlines from a well. How a pathline is traced, including across levels and line boundaries, is described under Pathline tracing.

A pathline is drawn when Show is checked for that row and pathlines are turned on in the map display. Changing pathline starting points or pathline settings does not require the model to be solved again. Click Regenerate pathlines, beside the pathline data table, to redraw the pathlines.

The settings that control tracing for every pathline — step size, time markers, and capture — are under Pathline Settings in the map display options, described at the end of this page.

Point¶

Label is a text label that helps you keep track of multiple single pathlines.
Direction is the direction that pathlines are traced from the starting point. It may be either upstream or downstream.
X,Y is the coordinates of the starting point. Type the coordinates, or click the map pin in the cell and then click the map. The map pin is shown when the cell is empty.
Start Level is the level of the pathline at the start point. A value of 1.0 starts a pathline at X,Y at the top of the domain that is level 1 at this location. A value of 2.25 starts a pathline at the elevation where 25% of the saturated thickness is above and 75% of the saturated thickness is below, in the domain that is level 2 at X,Y. A value of 2.99 starts a pathline with 99% of the saturated thickness above and 1% below, very near the base of the level 2 domain at X,Y. Pathlines are drawn for all levels encountered along the path, not just the start level. A single Start Level may be entered, or several levels separated by commas, which starts an array of pathlines with the same x,y coordinates but at different levels. For example, you could enter "2.1, 2.3, 2.5, 2.7, 2.9" to start pathlines at five elevations in level 2.
Show, if checked, includes this pathline.

Line¶

This starts a number of pathlines equally spaced along the segments of a polyline.

Label is a text label that helps you keep track of multiple line pathlines.
Direction is the same as defined for Point.
Coordinates are the coordinates of the polyline along which the pathlines start. Click the edit icon in this cell to open the coordinate editor, and enter one vertex per line, with x and y separated by a comma. To digitise the line on the map, click the draw icon and then click each vertex; double-click to finish.
Number is the number of pathlines to start in each segment of the polyline. The start points are equally spaced along each segment.
Start Level is the same as defined for Point.
Show is the same as defined for Point.

Area¶

This starts pathlines equally spaced within an area defined by a polygon. This can be used to trace pathlines from a source area, or to define capture zones for wells.

Label is a text label that helps you keep track of multiple area pathlines.
Direction is the same as defined for Point.
Coordinates are the coordinates of the polygon. Click the edit icon in this cell to open the coordinate editor, and enter one vertex per line. The polygon is closed from the last vertex to the first. To digitise the polygon on the map, click the draw icon and then click each vertex; double-click to close the polygon.
Nesting Level allows you to nest several area pathline polygons inside each other, with different start-point spacings. If you are not nesting or overlapping these, specify 1 for all. To place a smaller polygon with denser or less dense spacing inside another polygon, use nesting level 1 for the larger polygon and nesting level 2 for the smaller one. You may nest up to 5 levels. The polygon with the higher nesting level overwrites the spacing and other inputs of lower nesting levels.
Spacing is the distance between pathline start points. Start points are spread on a hexagonal array based on this spacing.
Start Level is the same as defined for Point. For example, if the source area spanned level 2, you could enter "2.1, 2.3, 2.5, 2.7, 2.9" to start pathlines at five elevations in level 2.
Show is the same as defined for Point.

Circle¶

Circle pathlines start equally spaced on a circle. For wells, Well is a better choice, because those pathlines stay linked to the well if the well is moved.

Label is a text label that helps you keep track of multiple circle pathlines.
Direction is the same as defined for Point.
X,Y is the coordinates of the centre of the circle. Type the coordinates, or click the map pin in the cell and then click the map.
Radius is the radius of the circle. For a well, make this radius larger than the well radius, otherwise the pathlines terminate before they can start.
Number is the number of pathlines to start. The start points are equally spaced around the circle.
Start Level is the same as defined for Point.
Show is the same as defined for Point.

Well¶

Well pathlines are like circle pathlines, but they are linked to a specific well. When you move a well, the pathlines stay with it. The circle that the pathlines start on is centred on the well and has a radius 1.2 times the well radius. Tracing is upstream if the well is extracting and downstream if the well is injecting.

Well Label is the pumping well to trace from. Choose the well from the list in this cell.
Number is the number of pathlines to start. The start points are equally spaced around the circle centred on the well.
Start Level is the same as defined for Point.
Show is the same as defined for Point.

Pathline settings¶

These settings are in the map display options, under Pathline Settings. They control the tracing of all pathlines entered above.

In steady simulations, pathlines are traced through a steady flow field. In transient simulations, pathlines are generally traced through the simulated transient flow field, and time along a pathline is synchronized with the simulation time. The exception is Freeze Transient, described below. The rest of this discussion of transient pathlines assumes Freeze Transient is not checked. Each time step in a transient model has a flow solution that, for pathline tracing, applies from the start to the end of the time step. Transient pathlines are only traced during the simulated time window. Transient pathlines terminate when one of the following occurs:

the simulation time along the pathline is less than 0 or greater than the total simulation time (the sum of the time period lengths),
the total elapsed time exceeds Total Time, or
the pathline exits the model or enters a well or linesink.

Steady pathlines terminate when condition 2 or 3 is reached.

Step Size defines the size of steps used in the algorithm that traces pathlines. Pathlines are composed of many small straight line segments. The length of these segments equals Step Size times the largest dimension (x or y) of the plot window. A smaller Step Size causes smoother, more accurate pathlines, at the cost of more computation.
Time Markers, if checked, draws arrows at specific time intervals along the pathlines. This is useful for defining the capture zone of a well within a time limit, or for simulating solute transport times. When you move the cursor over an arrow, the elapsed time, domain, and elevation of the pathline at the arrow are shown.
Time Marker Increment is the elapsed time between arrows, when Time Markers is checked.
Total Time is the total amount of time allowed on pathlines. This can be set to show, for example, the limit of a 2 year capture zone for a water supply well.
Start Time is the simulation time at the starting points for pathlines in a transient simulation. Simulation time starts at zero at the beginning of a transient simulation. For example, in a 300 day simulation, the starting time for well pathlines could be 300 days and the pathlines traced upstream, so the simulation time decreases along the pathline. Pathlines traced downstream have increasing simulation time along the pathline.
Freeze Transient, if checked in a transient simulation, traces pathlines through a frozen snapshot of the flow field at Start Time, as though that flow field existed indefinitely, like a steady flow field. This is generally not recommended, because the frozen flow field does not exist for longer than an instant. This option is offered because capture-zone delineation rules in some states (for example, Massachusetts) require such an analysis.
Capture Constrain, if checked, plots only the pathlines that are captured by the wells or internal line boundaries selected in the next two inputs. Capture constrain applies only to pathlines traced downstream. This can help define the capture zone of a well, stream reach, or drain. For example, to define the zone of contribution to a well, start numerous pathlines at the water table within a polygon, and constrain the displayed pathlines to those captured by the well. The starting points of those pathlines define the zone of recharge captured by the well.
Capture Wells is the well or wells the capture constraint applies to. Choose one or more wells from the list. All three well types are included: discharge-specified, discharge-specified (multi-domain), and head-specified. Do not mix well pathlines that start at a well with a capture constraint on that same well. Pathlines that start at the well are not treated as captured, because the trace starts at the well and does not end there.
Capture Lines is the internal line boundary or boundaries the capture constraint applies to. Choose one or more from the list. The list includes head-specified lines that are internal, discharge-specified lines, rivers, and drains/fractures.