Drainage System.
There are numerous drainage patterns. Six patterns are basic, and they include dendritic,
trellis, radial (centrifugal), parallel, annular, and rectangular. These basic types are
described below.
Dendritic patterns are generally associated with landforms composed of flat-lying rocks
and impervious soils. Folded, tilted, and faulted rocks often created landforms that are
identified from a trellis drainage pattern. Cones, peaks, and domes of igneous materials
create centrifugal (radial) drainage patterns. Gently sloping landforms such as eolian
plains are associated with a parallel pattern. Annular patterns are associated with domes
of layered rock with variable resistance to weathering. Landforms with rock joints or
angular changes in rock materials are associated with a rectangular drainage pattern.
The regional characteristics of terrain surfaces are often indicated by the drainage pattern.
The drainage pattern may provide a clue concerning dip, strike, or type of bedrock and
the general depth of the surface materials. The type of surface material is reflected in the
landform drainage system. For example, the complete absence of surface drainage
indicates pervious materials such as sand. A highly integrated system with branching
tributaries indicates an impervious soil with poor internal drainage, such s clay or silt.
Source: Terrain analysis procedural guide for surface configuration, US Army engineer
topographic laboratories, p. 5-8