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Table 2‑2: The Particle Tracking Module troubleshooting guide.
+---------------------+-----------------------+-----------------------+
| **Error** | **Cause** | **Solution** |
+=====================+=======================+=======================+
| Particle paths | The selection of | Make sure the |
| appear as | input magnitude | correct magnitude |
| vertical or | and direction | and direction |
| nearly vertical | layers have been | raster are |
| lines. | reversed. | selected. |
+---------------------+-----------------------+-----------------------+
Particle paths may travel through a water body, depending on the value
of the **W.B. Raster Resolution** parameter and the **Step Size**
parameter. This phenomenon is related to the **Step Size,** as explained
in Figure 2‑2a, which shows a small creek that is 6 m wide. The thin
blue lines represent flow paths. Note that the leftmost line crosses the
creek while the other four exhibit the expected behavior and do not
cross it. This behavior is because the leftmost particle path does not
“see” the creek, as demonstrated in Figure 2‑2b when the creek is
converted from a polygon to a raster with a 1 m cell size. The particle
tracking algorithm detects whether the path has reached the water body
by checking whether the starting or ending point of the flow path
segment overlaps a raster cell that represents a water body. The red
feature in Figure 2‑2b shows the segment “skips” over the creek because
the segment length is too large and is positioned so that neither the
starting nor ending points coincide with the creek's location. This
situation may be remedied by selecting a smaller value for the **Step
Size** parameter.
.. figure:: ./media/particletrackingMedia/media/image5.png
:align: left
:alt: A screenshot of a computer Description automatically generated
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Figure 2‑2: Possible scenarios of the particle paths crossing a thin
waterbody. The paths pass the water body (Figure 2‑2a (left)). The cell
sizes of (Figure 2‑2b(center)) and (Figures Figure 2‑2c(right)) are 1
meter and 5 meters, respectively.
Another possible reason for a flow line to cross the creek is that the
**W.B. Raster Resolution** is too large to represent the creek
accurately. This scenario is shown in Figure 2‑2c in the area indicated
by the red box. In Figure 2‑2c, the creek is illustrated with a raster
resolution of 5 m. In this case, because of the coarse resolution, there
may be a gap in the water body's raster representation, enabling the
flow path to “leak” through the gap indicated by the region within the
red box. This situation may be remedied by selecting a smaller value of
the **W.B. Raster Resolution** parameter or by increasing the width of
the narrow creek (if it is reasonable).
Another potential problem of the particle tracking function is that the
flow path may be trapped in a sink or pit close to the water body. A
sink can exist very close to the water body, even if sinks have been
filled. The sinks are due to converting the water body from a polygon to
a raster format in conjunction with the superposition of the smoothed,
unfilled DEM in areas overlain by the water body (see Section 2.2.2,
**Fill Sinks** parameter). The DEM raster cell containing the sink may
lie slightly outside of the polygon representation of the water body but
is contained within the raster representation of the water body. In this
case, flow may become trapped in the sink before reaching the water
body. This scenario may be treated by manually modifying the boundary of
the water body to extend over the sink.