A few years ago the question of the desirability of using modules for the outlets of distributaries in India was raised. The opinions of a large number of the senior canal engineers were called for and considered, and since then the subject has been thoroughly discussed. There are certain inherent difficulties in the way of moduling the outlets of a distributary. Owing, for instance, to rain further up the canal, or to the closure of a distributary owing to a breach in it, the canal supply may increase, and it may be necessary to let more water into the distributary under consideration. Under the present system any excesses of water are automatically taken by the outlets. If all outlets were rigidly moduled they would discharge no more than before the excess supply came in, and the excess supply would all go to the tail of the distributary, and, most likely, breach the banks. To get over this difficulty, the module has to be so arranged that when the water level in the distributary rises to a certain “maximum limit” the module ceases to act as such, and the discharge drawn off from the distributary increases as the water level rises. Again, the discharge of the distributary may at times be considerably less than its full supply. In order that, in such a case, the outlets towards the tail of the distributary may not be wholly deprived of water, it has to be arranged so that when the water level in the distributary falls below a certain “minimum limit” the modules cease to act as such, and draw off supplies which are less the lower the water level. Such supplies are not in proportion to the full supplies of the outlets. It will, however, be shown presently that low supplies need seldom be run. When a distributary, say the upper reach, contains silt, the water level corresponding to a given discharge is higher than before, and care has to be taken that the maximum limit is high enough. At the same time the minimum limit must be so low that it will not be passed when the silt scours out. The difference between the maximum and minimum limits is called the “range” of the module.