6.4.2 Bendway Weirs
Bendway weirs, also referred to as stream barbs, bank barbs, and reverse sills, are low
elevation stone sills used to improve lateral stream stability and flow alignment problems at
river bends and highway crossings. Bendway weirs are used for improving inadequate
navigation channel width at bends on large navigable rivers. They are used more often for
bankline protection on streams and smaller rivers. Design guidelines for bendway weirs are
presented in HEC-23 (Lagasse et al. 2001).
Hardpoints are an erosion control technique consisting of stone fills spaced along an eroding
bank line (Figure 6.3). The structures protrude only short distances into the river channel and
are supplemented with a root section extending landward into the bank to preclude flanking,
should excessive erosion persist. The majority of the structure cannot be seen as the lower
part consists of rock placed underwater, and the upper part is covered with topsoil and seeded
with native vegetation. The structures are especially adaptable in long, straight reaches not
subject to direct attack.
Figure 6.3. Perspective of hard point with section detail (after Brown 1985a,b,c).
Retards are devices placed parallel to embankments and river banks to decrease the stream
velocities and prevent erosion (Figures 6.2 and 6.4).
Pile retards can be made of concrete, steel or timber. The design of timber pile retards is
essentially the same as timber pile dikes shown in Figure 6.6. They may be used in
combination with bank protection works such as riprap. The retard then serves to reduce the
velocities sufficiently so that either smaller riprap can be used, or riprap can be eliminated.