are 220 m long. The gates have a unique ball (pivot) joint 10 m in diameter.
Under normal conditions the gates are ‘parked’ in two dry docks (one on
each bank). To operate the gates the docks are flooded, the gates are
floated and swivelled into position in the waterway. When contact
between the gates is established, they are flooded and sink to the bed
closing the channel. After the flood danger has passed the whole process is
reversed and the gates are towed back to their ‘parking’ position.
Large vertical lift gates need a high superstructure required to lift the
gate clear and to allow sufficient room for navigation. This high super-
structure is not only expensive but also environmentally intrusive; further-
more the gate in its raised position may be subjected to high wind loads. A
solution to these problems adopted, e.g. in the single gate tidal barrier on
the River Hull(UK), is to rotate the gate through 90° to a horizontal plane
when ‘parked’ in the raised position. Another possibility of course is the
use of different types of gates as, e.g., on the tidal barrage on the River
Tees(UK) completed in 1994 where 4 buoyant fish-belly gates 13.5 m long,
8.1 m high and 2 m thick (Norgrove 1996) have been used.
TheThames barrierprotecting London against flooding from tidal
surges completed in 1982 uses a novel concept of a rising sector gate (see
Fig. 6.8). The 20 m high gates are attached at both ends to discs (about
278 GATES AND VALVES
2.830 m. M.L.W.S.
6.900 m. SURGE
64900
9.250 m.
UPRIVER
GATE ARM.
TRUNNION
ASSEMBLY.
FIXED END.GATE SPAN.HINGED END.
DOWNRIVER
SECTIONTHROUGH RISING SECTOR GATE
10 5 0 10 m.
SECTION OF GATE LOOKING
DOWNRIVER
Fig. 6.8 Thames barrier gates
