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3.
Gryones or spurs
Sometimes the banks of the rivers are damaged by the velocity of river flow,
often resulting in overtopping and flooding the adjacent lands. Gryones or spurs
are constructed from the banks transverse to the flow of the river to
prevent direct attack by the river flow which is deflected away by the gryones.
The nose of the gryones, below the river bed is subjected to the enormous force
by the flowing river and the needs to be constructed strong to withstand such
pressure. When the gryones are directed slightly to the upstream side, they are
called repelling gryones. However when the length of such gryones are small,
they are called deflecting gryones instead of repelling gryones. When the gryones
direct slightly towards downstream side, they are called as attracting gryones.
4.
Guide Banks
Guide banks are constructed parallel to the river with a view to reduce the width
of the river and channelise the flow so as not to change the direction of flow as
in meandering rivers to protect the engineering structures like weirs, bridges
over the river. The guide banks are generally provided in pairs,
symmetrical in plan and may either be kept parallel or diverge slightly upstream
of works, depending upon local conditions. General layout of guide banks, plan
and sections are shown in Figure 6.4.
Fig. 5.4. Guide Bank details
(After Garg, 1998)
