R1.35P/cos 40°1.75P. (11.21)
For safety, the permissible tension is limited by
RperD/600 (11.22)
whereDis the displacement of the vessel (in tons). In Eastern Europe the
relationship
RperD3/5/20 (11.23)
is used (Cˇábelka, 1976). The force Phas three main components: P 1 , the
resistance of the vessel; P 2 , the force due to the longitudinal slope of water
surface in the lock; P 3 , the force due to translatory wave action caused
mainly by ‘sudden’ changes of inflow into (outflow from) the lock. P 1 and
P 2 act against each other and, to a great extent, cancel each other out (for
further details, see also Jong and Vrijer (1981)).
The value of P 3 , which is about 80% of P, is mainly influenced by the
value of dQ/dt. Thus the force acting on the vessel during lockage can be
limited by imposing a permissible limit on dQ/dtduring the filling (empty-
ing) operation (Sections 11.8.2 and 11.8.3). This is best achieved by con-
trolling the rate of opening of the valves of the filling system and/or by the
shape of the culverts at the valves. The limiting value of the transverse
component of the horizontal forces acting on the vessel should not exceed
50% of the longitudinal component P.
11.9 Thrift locks
On canals where there is water shortage, high heads may be overcome by
lifts (Section 11.10) or by locks with thrift basins; the latter have the
advantage that they permit simultaneous handling of large tows but
require greater land use than lifts. In thrift locks, considerable reduction of
water consumption is achieved by conveying, by gravity, part of the water
during lock emptying to thrift basins, to be returned again by gravity to the
lock during its subsequent filling (Fig. 11.15).
Thrift basins are usually constructed next to the lateral lock wall, either
as open or as superimposed closed reservoirs. Every basin is connected with
the lock by its own conduit, provided with two-way gates. By increasing the
number of basins to more than four, only a very small additional reduction of
water consumption can be achieved, and the handling time increases dispro-
portionately in comparison with simple locks. Locks with thrift basins are
used for heads of up to 30 m. For these heads they can still be designed so
that their efficiency is comparable with standard types of boat lifts.
486 INLAND WATERWAYS
