Fundamentals of Engineering Design
Diversity describes the mixture of vegetation types present. Diversity is directly related to age.
Generally, a mature system has a number of different species.
Density and spacing describe the degree of vegetative cover of the bank face from a visual
inspection. Density refers to the vertical thickness of vegetation. The denser the vegetation the better the
erosion protection and the greater the resistance to flow. Spacing describes the location of vegetation
across the bank. Clusters refer to vegetation with gaps in coverage that flow can attack while continuous
describes complete coverage along the bank.
Age estimates the age of the vegetation. Age estimations are used as a guide to the history of the
bank. Mature vegetation can only develop on a stable bank, while a predominance of young, immature
vegetation gives some insight into the recent history of the area. Estimating the age of vegetation requires
significant experience, but an approximation can often be made based on the size and height of the
Bank toe accumulation characterizes the balance between the sediment supply and sediment
removal at the toe of the bank. Banks that have net toe erosion become less stable with time. Banks that
have neither net toe erosion or deposition continue to erode at about a constant rate as eroded materials
are transported at the same rate as generated. Banks with net deposition generally demonstrate greater
stability. With time, vegetation will colonize sediment deposits at the toe.
Stored bank debris notes the presence and type of material found in storage at the bank toe. The
material should primarily be derived from the bank and not an accumulation of bed sediments, which would
indicate a bar.
Vegetation and the vegetative characteristics at the toe can give a good idea of the toe sediment
balance. A stable sediment shelf will have mature vegetation while a newer deposit may only have young,
immature vegetation. Roots will be exposed on a toe deposit that is eroding and adventitious roots will be
present for depositional zones.
Bank erosion describes the processes that lead to hydraulic failure or the detachment and
transportation of individual grains. The purpose of this section of the form is to identify the processes
responsible for the erosion and the distribution of these mechanisms along the banks of the study reach.
Gray and Sotir (1996), Goldman et al. (1986), Petersen (1986), and Gray and Leiser (1982) give more
complete explanations of surface erosion mechanisms.
Erosion location establishes the position of the eroding section in relation to major channel
features. It is important to note the location of erosion in relation to channel planform, bed features and
engineering structures. The field sketches and surveys are very important in providing this information.
Processes attempt to identify the mechanisms responsible for the hydraulic failure. As mentioned
earlier, bank erosion is controlled by climate, soil type, topography, vegetation, and the stream flow
characteristics (Gray and Leiser, 1982, p. 12). The mechanisms that cause surface erosion can be