Geoscience Reference
In-Depth Information
The pattern formed in a landscape by a network of rivers is a familiar way of distinguishing
between different types of river system. There are several common variations on the es-
sentially treelike pattern of a drainage network, and various descriptive terms are used, in-
cluding dendritic, radial, trellis, parallel, and rectangular. The primary influence on these
patterns is the geology of the landscape.
2. This satellite image of the Central Siberian Plateau illustrates a typical drainage
network.Snowathigheraltitudescontrastswiththesnow-freevalleys,helpingtoac-
centuate the drainage pattern
An obvious way of categorizing different types of river is by their types of flow. A river
channel that carries water at all times throughout the year is described as 'perennial', but
this does not describe all rivers by any means. Some channels have water flowing in them
only in particular seasons. These seasonal, or 'intermittent', rivers may be in regions with
a severe winter in which river water completely freezes, or in regions with a distinct wet
season. A river with an even less permanent flow of water is described as 'ephemeral'
and consists of channels that flow only for hours or days following individual rainstorms.
Rivers that arise and flow in deserts are typically ephemeral rivers. A fourth category is
the 'interrupted' river, one that has permanent flow over short reaches throughout the year
while most of the river is dry. While these distinctions are undoubtedly real, like most clas-
sification schemes in the natural world, the boundaries between different classes are better
