Contents preface (VII) introduction 1—37

Fig. 12.14 Flexible brick pitching
A riprap paving with a toe trench is preferable to other types of revetments at sites where stone is cheap and available in plenty. Riprap of hard angular rock fragments laid on a thick layer of rubble or quarry chips is considered most durable (5). Concrete blocks can also be used when rocks are not available at reasonable costs. Triangular and tetrahedral types of concrete blocks are more suitable to resist the displacement by flowing water.
Another way of providing bank protection is by means of ‘flexible brick pitching. Bricks for this purpose are manufactured such that each brick has two holes across the full width of a brick at one quarter length from either end. These bricks are then laid on the bank slope and for some distance on the river bed at the toe of the bank to serve as a falling apron. The bricks are laid in such a manner that a GI wire passes through the brick holes as shown in Fig. 12.14. The wires are knotted together at their ends and anchored in concrete blocks at their upper ends. These wires hold the bricks in place and permit small movement of bricks.
The bank revetment and launching apron, considered so useful measures for protection of banks of the alluvial streams, are not considered suitable for the protection of banks of gravel and boulder streams. In case of boulder streams, the bed does not scour much and, therefore, the apron would not be able to launch itself. Further, the concrete blocks forming

432 IRRIGATION AND WATER RESOURCES ENGINEERING
the apron could be damaged and dislodged by the impact of the boulders being transported by the mountainous streams. The boulders, rolling on top of the apron, could hit the bank to cause damage to the bank. In such cases, A RC retaining wall near the toe of the bank may be provided from below the anticipated scour bed to about one metre above HFL. The RC retaining wall not only prevents the movement of its backfill but also resists bank erosion due to impact of boulders rolling along the river bed. The RC retaining wall would be designed for earth pressure, hydrostatic and earthquake forces, and the forces due to boulder impact.