from the river or the branching of canals may create special traffic and
construction problems – see also Section 8.7.1.
Sections of canals which are either temporarily or permanently
above the surrounding groundwater table need (apart from erosion pro-
tection) some means of protection against loss of water by seepage; proper
underdrainage and protection of the impermeable or seepage-resistant
layer (e.g. clay, concrete, plastics, etc.) against back pressure in the event
of an increase of the groundwater level are essential. Bank protection on
canalized rivers and canals is of the same type and variety as on trained
rivers (Chapter 8).
Adequate canal depth and width are required, just as on regulated
rivers and, because of the drift of tows passing through bends, a greater
width is required there.
The minimum width, B, of a waterway in a straight section with
simultaneous navigation in both directions is B 3 b or B 2 b 3 ∆b,
wherebis the width of a barge (or a group of barges) and ∆bis the side
clearance, with ∆b'5 m. If navigation is in one direction only, B
(1.5 2)b.
The minimum radius, r, of a curved waterway is given by the length,
L, of a typical barge multiplied by a constant which is about 3 for push
boats and 4.5 for towed barges. The width of the waterway in a bend with
a two-way traffic has to be increased to B 0 B∆B(Fig. 11.5(a)), where
∆B
2 r
L
2
B
L
2 r
2
. (11.1)
The drift (deflection) angle, , is the inclination of the tow to the tangent
of the radius of curvature passing through the centre of the tow
(Fig. 11.5(b)). The drift depends on the radius of the bend, the speed,
power, and design of the tow (tug), loading of the tow, wind forces, and
the flow pattern. The drift angle is larger for tows travelling in the down-
stream than the upstream direction.
The US Army Corps of Engineers (1980) extrapolated German drift
angle data from the Rhine up to a tow length of 180 m and obtained, for
the downstream direction, values of 2°15° for radii of curves of
400 mr2500 m (the larger the radius the smaller the value of ). For
the upstream direction the values of are halved.
According to the US Army Corps of Engineers, the following equa-
tions apply for the channel width B 0 in bends: for one-way traffic,
B 01 L 1 sindb 1 2 c, (11.2)
and for two-way traffic,
B 02 L 1 sindb 1 L 2 sinub 2 2 cc, (11.3)
472 INLAND WATERWAYS
