A method of protection which is suitable when the water contains much silt is what is known in India as bushing. Large leafy branches of trees are cut and hung, as shown in [fig. 18], by ropes to pegs. They must be closely packed so as not to shake. At first they require looking after, but silt rapidly deposits and the branches become fixed and no longer dependent on the ropes. If the work is carefully done, the result is a smooth, regular, and tenacious berm, as per dotted line in the figure.
Fig. 18.
Fig. 19.
Another method, used on canals, is to make up the bank with earth and to revet it with twigs or reeds, as shown in [fig. 19]. The foundation must be taken down well below bed-level, otherwise the work may slip. This kind of work cannot be done except when the canal is dry.
If the bank consists of sand or of very sandy soil, it must in any case have a flat side slope such as 3 to 1. If the sand is in layers alternating with firm soil, it is a good plan to dig out some of the sand and to replace it with clods of hard earth.
Staking ([fig. 20]) may be used, the stakes being one or two feet apart from centre to centre, and long twigs laid horizontally being passed in and out of the stakes, or bushing filled in behind the stakes. But bushing alone is cheaper and nearly as good.
Fig. 20.