DRAINAGE BASINS
Drainage Basin or Watershed - land area from which water drains toward a common
water course in a natural basin; the basin of one is separated from another by an
imaginary line called a divide (ex: Continental Divide).
All drainage systems are made up of an interconnected network of streams which
together form particular patterns.
Types of Drainage Patterns
1) dendritic - tree-shaped, irregular branching of
tributary streams that resembles the branching
pattern of a tree, most common; controlled by
direction of slope of the land, found in areas
lacking strong contrasts in bedrock resistance
(i.e. underlying material is relatively uniform),
ex: flat-lying sedimentary rocks
2) trellis - a rectangular pattern in which tributary
streams are nearly parallel & have the appearance of a garden trellis, found in areas where
inclined layers of sedimentary rock of varying
resistance to erosion are exposed
3) rectangular - has many right angle bends, develops
when bedrock is crisscrossed by a series of
joints &/or faults with the streams along the
joint/fault planes
4) radial - streams diverge from a central area like
spokes from a wheel hub, found on isolated
mountains, such as volcanoes & domal uplifts;
the opposite is centripetal
5) annular - produced by structural domes with
concentric patterns of rock strata
6) parallel-pinnate - found in areas having long
parallel ridges, the short parts drain the sides
of the ridges & the long parts drain the troughs
7) deranged - has no geometrical pattern or constant
direction & usually includes a number of lakes,
it is indicative of the destruction of prior drainage
patterns by icesheets