Chapter II: The Designing of a Canal (3)

Profile walls (Fig. 21, page 92) used occasionally to be built at frequent intervals along a distributary. They will not prevent scour occurring, if the stream is tending to scour, unless very close together. Such walls are of some use as showing whether the channel is altering, but they are expensive and have to be altered if, as often happens, the channel is remodelled. It is a much better plan to lay down blocks--about 1¹⁄₄ foot cubes--of masonry or concrete, along the centre line at every 500 feet, with their upper faces level with the bed. If the bed scours they may be displaced but otherwise they are useful not only for showing what silt, if any, has deposited, but for showing the centre line of the channel. Without them the centre line is liable to be altered in silt clearances or berm cuttings. To enable a block to be readily found and to be replaced in proper position if displaced, there should be two small concrete pillars exactly opposite to it and equidistant from it, one on either bank of the channel. Such blocks and pillars may with advantage be placed at quite short intervals on curves.

The rest houses for the use of officials on tour are generally at intervals of about 8 to 14 miles. There is generally a rest house near to a large regulator and frequently there is one near to a small regulator. This facilitates inspection work and discharge observations and it saves money, because the house can be looked after by one of the regulating staff. Not infrequently the house is placed just too far away from the regulator. Similarly if a rest house is near a railway station it should be within a quarter of a mile of it--always provided that this does not bring it too near to villages or huts--and not a mile or more away as is sometimes the case. It is also a mistake to place a rest house off the line of channel unless perhaps when it is on a district road which crosses the channel.