Sometimes the curtain wall which runs across the bed at the downstream end of the pitching is carried into the banks and built up so as to form a profile wall (Fig. 21). This is not very suitable, because the pitching of the sides is apt to settle and leave the profile wall standing out. It is better to lay a row of blocks on the slope. If a hole tends to form in the bed downstream of the curtain wall, blocks of masonry or concrete can be laid and left to take up their own positions (Fig. 22). [Illustration: FIG. 21.] [Illustration: FIG. 22.] When scour of the bed or sides occurs downstream of pitching, it is sometimes said that any extension of the pitching downstream is followed by extension of the scour. This may happen if the cross section of the stream downstream of the pitched section has become greater than the pitched section. In this case there is eddying, due to abrupt enlargement of the stream where the pitching ends. The increased width and lowered bed level (not counting mere local hollows) of the stream should be adhered to in the pitching. Where the masonry of the regulator ends and the pitching begins, there will be an abrupt or tapered enlargement, but the eddies--at very low supplies there may be a fall--cannot do harm. This principle of enlarging the pitched cross section can be followed, even in a new channel, if the soil is light and scour is feared, and for this reason the matter is mentioned in the present Chapter instead of in Chapter III. It was once the custom to splay out the sides of a channel, downstream of a regulator or weir, so as to form a sort of pool in which the eddies exhausted themselves, but this gives curved banks and requires extra land and is not a very convenient or neat arrangement. Where scour of the sides is likely to occur, or has occurred, immediately downstream of the pitching the latter may be turned in as shown in Fig. 23. [Illustration: FIG. 23.] Pitching has constantly to be replaced or extended owing, generally, to failure to pitch a sufficient length or to ram well the earth under the pitching, or to use properly rammed ballast or flat brick, or to give proper bed protection, or to the use of dry brick pitching when a stronger kind is needed. The side slopes of pitching should be 1 to 1. They can be ¹⁄₂ to 1 in rare cases, _e.g._, when there is no room for 1 to 1, or in continuation of existing ¹⁄₂ to 1 pitching. No absolute rule can be laid down as to the length to be pitched, but in a Punjab distributary it is often about 5 times the bed width.