In Gibb’s module the above conditions can be complied with. The module is placed outside the bank of the distributary. The water is drawn off from the distributary by a pipe, whose lower edge is at the bed level of the distributary, and delivered from the module into the watercourse through a rectangular aperture at a higher level than that of the pipe. It is possible that, owing to the high level of the aperture, some rolling silt which would otherwise have passed out of the distributary may remain in it. The height of the aperture also prevents the watercourse from drawing off any water at all when the water level of the distributary falls below a certain level, but this objection is not important. An escape weir or notch is provided so that when the water level in the distributary rises to the maximum limit some water overflows into the watercourse. On the whole it appears that all difficulties can be got over, though a good deal of care and precision is necessary in fixing the exact height of the maximum and minimum limits. The difficulties under consideration will all be reduced if some of the outlets on a distributary are left unmoduled, and this is desirable on other grounds. When the supply is normal, _i.e._ between the maximum and minimum limits, and all modules are working, the supply entering the distributary must be regulated with great precision. The outlets draw off a certain supply. If less than this enters the distributary the tail outlets must go short. If more enters there will be a surplus at the tail, though it can probably be disposed of, because the tail water will rise above the maximum limit. For short periods, say an hour or two, no trouble arises because the distributary acts as a reservoir, the water level rising to take in any excess supply, and falling to allow for a deficiency. At the tail the rise and fall may be hardly perceptible. But if the supply were deficient for a whole night the tail outlets would certainly go short. This could theoretically be remedied to some extent by letting in an excess supply for a short time and causing the water level at the tail to rise above the maximum limit, but in practice no such system of compensation could be worked. The very fact of the tail outlets having gone short for a night would not be known. The proper method of preventing any such troubles as those under consideration is to leave some of the outlets on the distributary un-moduled.