Environmental Engineering Reference
In-Depth Information
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Erosion
Transportation
Deposition
Size of particles (mm)
FIGURE 7.15
Relationship between water velocity and particle size, and transportation, erosion, and deposition of a stream.
(From Hjulström, F.,
Uppasala Geol. Inst. Bull
., 25, 1935. With permission.)
The materials in the stream depend on the source materials. Silts and clays, causing
muddy waters, result from shales and chemically altered rocks in the drainage basin. Clear
waters, under normal flow conditions, are common to mountainous regions composed of
predominantly sialic crystalline rocks.
Stream Classification and Deposition
General
Streams are classified by geomorphic development and shape, and are associated with
characteristic soil deposits, modified by stream velocities, flood conditions, source materi-
als, and climate.
Shape:
Streams have been classified by shape (Tanner, 1968) as either straight, crooked,
braided, or meandering. These classes relate in a general manner to the classes based on
geomorphic development.
Geomorphic classes:
Several classifications can be found in the literature:
•
Boulder zone (also headwater tract, young or early stage)
•
Floodway zone (also valley tract, mature or middle stage)
•
Pastoral zone (also plain tract, old age or late stage)
•
Estuarine zone (at the river's mouth,
Section 7.4.2)
Rejuvenated streams have been uplifted by tectonic movements that change their char-
acteristics.
The terms boulder zone, floodway zone, etc., describe river morphology based on the
criteria of Bauer (Palmer, 1976) for tectonically stable areas. All are illustrated in
Figure
7.16,
an aerial mosaic of a 5-mi-long river flowing over crystalline rocks in a tropical
climate.
