al., 1977) to appreciate that the protective facing of banks must reach
down below the water surface to a sufficiently low level, and its bottom
edge must be flexible enough to ensure permanent contact with the
subsoil. A good filter adapted to suit the subsoil is essential, as is drainage
of sufficient capacity (Section 8.7.3). For further details see also PIANC
(1987).
The height of the waves at the bank generated by navigation in con-
strained waterways depends primarily on the ship’s speed and its relation-
ship to the dynamic wave velocity, size, and form of the vessel, and its
position relative to the bank. The effect of waterway cross-section is
implicitly contained in the wave velocity. The boat speed is the most
important factor, and the generated wave height rises quite steeply with
the speed until a maximum is reached, corresponding to the speed at
which the sailing motion becomes a gliding one with the bow above the
water surface (on a medium-sized waterway fast boats moving downstream
at speeds of 20–25 km h^1 typically generate waves 0.2–0.3 m high (Novak,
1994)). This speed corresponds to the surge velocity and is rarely attained
476 INLAND WATERWAYS
Fig. 11.7 Bank protection of navigable waterways (Hydro Delft, 1985)
