RIVER IMPROVEMENT 349
their location are best determined by model studies or experiments in situ.
Deflectors rely in their action on the induced spiral flow and secondary
currents as well as on the rectified main direction of flow. An example of
the use of a series of floating vanes to rectify the flow and protect a bank in
a large river is shown in Fig. 8.17.
Channel beds liable to substantial erosion can be stabilized by
ground sillsor – more extensively (and expensively) – by a series of drop
structures. Ground sills usually span the whole width of the river channel,
with the greatest height at each bank and a gentle slope to the stream
centre. Rubble mounds, cribs filled with rubble, and concrete are some of
the materials more frequently used for ground sills.
Fig. 8.15 Groyne construction