force of the stream. The change of slope may require narrowing (for
increasing slope) or widening of the river which, if left to self-adjustment,
may take decades to be achieved.
The combination of the stage duration curve with a sediment rating
curve (established by direct measurement (Section 8.4) or by computation
(Section 8.3) can be used as shown in Fig. 8.9, to estimate the annual sedi-
ment run-off; the comparison of sediment duration curves corresponding
to different stage–discharge curves in turn then gives an estimate of the
increase or decrease of sediment transport due to a change in width of a
river channel (Fig. 8.10) (UNECAFE, 1953).
After the selection of alignment and cross-section river training
should proceed from upstream taking into account the requirements of
‘high’, ‘mean’ and ‘low’ water training.
A suitable arrangement for this type of water river training is shown
in Fig. 8.11, and the use of the above guidelines for the improvement of a
confluence of two rivers is illustrated in Fig. 8.12 (Schaffernak, 1950).
A special case of river training is the junction or crossing of a river
and navigation canal (or harbour entrance from a navigable river).
Because the canal usually requires a fairly wide entry for navigation pur-
poses, support for the river flow is lost and unwelcome sediment deposi-
tion may occur in the canal mouth. A solution to this problem is provided
by specially formed circular enlargement of the canal (‘Thijsse egg’
developed in the Netherlands) with a circulation that prevents or at least
reduces the sedimentation in the canal mouth (Fig. 8.13); for further par-
ticulars see Jansen et al.(1979).
RIVER IMPROVEMENT 345
Fig. 8.9 Determination of annual sediment run-off