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Coastal Engineering: Theory and Practice
develop. This is called scour hole. Scour is generally classified into different
types based on flow field, bed materials, and bed levels and also type of
obstruction. The different types of scour are discussed in detail below.
7.4.2 General scour
General scour is usually defined as the bed lowering observed in rivers or
channels as a response to increasing water discharge. General scour which
occurs irrespective of the existence of the structure. Another aspect to take
into account is the fact that general scour occurs in a river in its natural
State, i.e., without the presence of structures, which in turn generate other
types of scour, called local scour. Normally, the time scale for general scour
is longer than the time scale for local scour.
7.4.3 Local scour
Local scour which occurs when water flows around obstructions in channels,
generating complex flow patterns, increased flow velocities, turbulence and
due to any local obstruction to flow in océan e.g. step-sided scour pits
around structures.
The intermittent structures tend to amplify the flow velocities and turbulence levels depending upon their geometry. It can also generate vortices and exert erosive forces on bed sédiments, owing to which, the local
enhancement of sédiment movement rates and érosion are attained. The
phenomenon of local scour around an obstruction is shown in Fig. 7.4.
Local scour has received wide attention from researchers, mainly because it
is easier to rig the model test set-up as well as to carry out the tests, in the
Recirculating
surface vortex
(clockwise to right of
pier. anticlockwise to
left of pier)
Fig. 7.4 Local scour.
Coastal Engineering: Theory and Practice
develop. This is called scour hole. Scour is generally classified into different
types based on flow field, bed materials, and bed levels and also type of
obstruction. The different types of scour are discussed in detail below.
7.4.2 General scour
General scour is usually defined as the bed lowering observed in rivers or
channels as a response to increasing water discharge. General scour which
occurs irrespective of the existence of the structure. Another aspect to take
into account is the fact that general scour occurs in a river in its natural
State, i.e., without the presence of structures, which in turn generate other
types of scour, called local scour. Normally, the time scale for general scour
is longer than the time scale for local scour.
7.4.3 Local scour
Local scour which occurs when water flows around obstructions in channels,
generating complex flow patterns, increased flow velocities, turbulence and
due to any local obstruction to flow in océan e.g. step-sided scour pits
around structures.
The intermittent structures tend to amplify the flow velocities and turbulence levels depending upon their geometry. It can also generate vortices and exert erosive forces on bed sédiments, owing to which, the local
enhancement of sédiment movement rates and érosion are attained. The
phenomenon of local scour around an obstruction is shown in Fig. 7.4.
Local scour has received wide attention from researchers, mainly because it
is easier to rig the model test set-up as well as to carry out the tests, in the
Recirculating
surface vortex
(clockwise to right of
pier. anticlockwise to
left of pier)
Fig. 7.4 Local scour.