Geoscience Reference
In-Depth Information
Tributaries
Drainage
divide
Interfluves
Confluence
Republican River
Smoky Hill River
Confluence
Trunk
stream
Kansas River
Figure 16.4 The concept of drainage basins. Also called
watersheds, drainage basins are separated from one another
by high points on the surrounding landscape called divides.
Each large drainage basin contains numerous tributaries, which
themselves are separated from each other by interfluves.
Figure 16.5 A typical river confluence. The Smoky Hill River
flows into this image from the upper left, whereas the Republican
River enters from the upper right. They join at a confluence in
the center of the photograph to form the Kansas River, which is
the trunk stream of the Kansas River basin, and flows toward the
bottom (east) of the image.
of elevated terrain that forms a kind of high rim around any
given basin (Figure 16.4). Below this rim, the topography slopes
downward into the core of the basin. As a result, all runoff and
groundwater flow into a network of streams that collectively
funnel into the trunk stream , which is the largest stream in the
drainage basin. Each stream that flows into the trunk stream, or
a stream that flows into another stream, is called a tributary .
Tributaries are themselves separated from one another by rela-
tively low topographic rims called interfluves . The point where
a tributary joins the trunk stream, or any stream for that matter,
is referred to as a confluence (Figure 16.4).
Drainage basins range from several hectares to thousands
of square kilometers in size, with numerous watersheds con-
tained within larger ones in a nested fashion, as you can see
in Figure 16.4. Notice, for example, that the small drainage
basin portrayed in light orange is nested within the drainage
basin highlighted in yellow. In other words, water that drains
into the orange basin ultimately flows into the larger stream
contained within the yellow basin at a confluence. This stream
ultimately flows into the trunk stream at another confluence,
like the one pictured in Figure 16.5. This image shows the
confluence of the two major tributaries of the Kansas River,
which is the trunk stream of the Kansas River basin in the cen-
tral United States. To see the geographic relationship of these
streams, refer back to the map in Figure 15.4. In this map note
that the Republican River drains the northern portion of Kansas
and southern Nebraska, whereas the Smoky Hill River drains
western Kansas. These two streams meet in eastern Kansas to
form the Kansas River.
Now put this discussion of drainage basins into the context
of major watersheds in the United States. The map in FigureĀ 16.6
not only shows the geographic position and size of the largest
drainage basins, but also indicates into which ocean the trunk
stream of any particular basin flows. The largest watershed in
North America is the Mississippi River basin (bold outline),
which drains most of the United States (and a small part of
Canada) and funnels water to the Gulf of Mexico. The Missis-
sippi watershed contains several other large basins, including
the Ohio, Arkansas, and Missouri, which are named after their
trunk streams. Another way to describe these trunk streams is
that they are major tributaries of the Mississippi River. Each of
these trunk streams, in turn, contains a number of smaller tribu-
taries. A major tributary of the Missouri River, for example, is
the Kansas River shown in Figure 16.5. In other words, one can
accurately say that the Smoky Hill and Republican rivers are
tributaries not only of the Kansas, but also of the Missouri River
and, ultimately, the Mississippi River.
The western divide of the Mississippi basin is the Rocky
Mountains. This divide is the famous continental divide that
separates the Mississippi watershed and its drainage to the
The primary stream of a drainage basin.
Interfluves Topographic high points in a drainage basin that
separate one tributary from another.
Trunk stream
A stream or river that flows into a larger stream or river.
 
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