downstream direction. When open, the valves produce solid circular jets
and can also be used in submerged conditions. The valves may suffer from
cavitation damage and produce unstable jets at small openings, and are
expensive as they have to withstand full reservoir pressures.
Most of those disadvantages are overcome in the hollow-jetvalve
(Fig. 6.7), which closes in the upstream direction (when closed the valve
body is at atmospheric pressure); because of this the valve is, of course,
not suitable for use in submerged conditions. The discharge coefficient of
the fully open valve is about 0.7.
6.4 Tidal barrage and surge protection gates
Due to the large spans and heads to be controlled the design of tidal bar-
rages often built for flood control and surge protection purposes provides
a special challenge in the design, installation and operation of gates. The
following text gives just some parameters of gates used in a few of these
works.
The main storm-surge protection barrage of the Delta works on the
Western Scheldt in the Netherlandscompleted in 1986 has 62 lift gates of
heights 5.9–11.9 m and 42 m span. The storm surge Maeslant barrier in the
navigation way (Nieuwe Waterweg) to Rotterdam, completed in 1997 and
forming part of the same overall scheme has two floating horizontal
radial/sector gates capable of closing the 360 m wide channel. Each gate is
21.5 m high, 8 m wide and 210 m long; the two horizontal arms of each gate
TIDAL BARRAGE AND SURGE PROTECTION GATES 277
Fig. 6.7 Hollow-jet valve (after Smith, 1978)