Fundamentals of Engineering Design
Figure 5.25 Headcuts (after Schumm et al., 1984)
Perched tributaries, which are sharp changes in bed elevation at stream junctions, are an indication
of a degrading streambed. If the main channel is incising while the tributary is not, there will be a sharp
difference in bed elevations where the two channels meet.
The depth of loose sediment deposits on the bed, alternating bars in the channel, and frequent
overbank flows generally indicate an aggrading stream. Degradation of structures and widespread bank
failures are also good indicators of degradation.
5.2.4
BANK CHARACTERISTICS
The bank characteristics analysis examines soil types, vegetation, the presence of bank structures,
erosion processes, and geotechnical failure mechanics. The bank angle and bank height can best be
determined by field survey; however, during field reconnaissance these values can be estimated. The
following terminology is used to describe bank characteristics:
Soil types describe the classification of the bank materials as cohesive, noncohesive, composite
or layered. Sower (1979) describes cohesive soils as soils for which the absorbed water and particle
attraction work together to produce a body which holds together and deforms plastically at varying water
content. Cohesive banks are typically formed in silts and clays while noncohesive banks are formed from
sands, gravels, cobbles, and boulders. Composite banks consist of layers of cohesive soils intermixed by
layers of non-cohesive soils. Streams flowing through alluvial deposits often have composite banks. Non-
cohesive deposits are relics of former channel bars and deposition zones that become covered by silt and
clay deposits. The interface between the cohesive and non-
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