Gully characteristics.
Gully characteristics and/or erosional features observed in the study area can be used to
infer surface materials and soil profiles. This inferred information can be used to identify
an unknown landform. Natural features such as forests, however, can obscure gully
characteristics, such as cross section and profile, and thereby reduce the usefulness of this
landform indicator. Also, climactic conditions can complicate the interpretation of the
erosional features; therefore, the analyst will rarely use the erosional features alone to
predict the identity of the landforms. For this reason, the collective photo pattern data
elements are needed for identifying landforms.
There are four general cross-section classes for gullies. Each class is associated with a
certain surface material and profile. V-Shaped gullies with short, steep gradients are
associated with granular materials such as found in glacial outwash terraces. Loessial
landforms have a U-shaped cross section near the headward portions of gullies. Coastal
Plain landforms have sand/clay erosional features with flat-bottomed gullies; sharp, steep
side-slopes; and low, flat gradients. Cohesive soils have softly rounded, saucer-shaped
gullies with long gradients that often indicated shale uplands. There is no specific gully
classification for landforms consisting of layered soils with strong profiles. The analyst
should be aware that the gully cross section and profile characteristics can be misleading.
An example is a gully within or near the boundary of a terrace or a valley wall, where
cross section and profile exceptions do occur.
The gully characteristics are described in general terms such as “broad U-shaped or Vshaped with steep gradients.” As the gully characteristics are observed stereoscopically,
the information is recorded on a photo pattern data element table for each unknown
landform.
Source: Terrain analysis procedural guide for surface configuration, US Army engineer
topographic laboratories, 5-10