8.6.2.3. Canal Falls When the desired bed slope is flatter than the ground slope, as is usually the case, a canal fall has to be provided well before the channel bed comes into filling and the FSL becomes too much above the ground level. The location of a fall depends on a number of factors. It may be combined with a regulator or a bridge for economic benefits.
The alignment of another smaller offtaking channel may require that the fall be provided downstream of the head of the offtaking canal. This will ensure that the FSL of the offtaking channel is sufficiently high to irrigate its command area by flow irrigation. One may provide either a larger number of smaller falls or a smaller number of larger falls. Relative economy of these two possible alternatives should be worked out and the location of falls will be, accordingly, decided. The distributaries and watercourses offtaking from the upstream of a fall may easily irrigate some areas downstream of the fall. As such the FSL in the channel may be allowed to remain below ground level for about 200-400 m downstream of a fall.
