9. =Design of a Distributary.=--A distributary is a canal in miniature and, like a canal, it may have branches. It has masonry bridges, falls and drainage syphons. It has, as already mentioned, a masonry regulator at its head. At the off-take of any branch or distributary there is a regulator in the head of the branch. If the branch takes off a large proportion of the water there is a double regulator. A distributary gives off watercourses as a canal gives off distributaries. The watercourses belong to the people and not to Government and they are cleared and maintained by the people. Each watercourse has a masonry head known as an “outlet” (Fig. 11). The outlet is the point where the water passes from the hands of Government officials to those of the cultivators. The outlet is of masonry and its opening is not adjustable but is fixed in such a way that its discharge, when the distributary is full, bears, as nearly as can be arranged, the same ratio to the F.S. discharge of the distributary as the area intended to be irrigated by the watercourse bears to that intended to be irrigated by the distributary. [Illustration: FIG. 11.] The floor of the outlet is level with the bed of the distributary. It thus draws off rolling sand which might otherwise accumulate in the distributary. Small outlets are made of earthenware pipes, about ·4 feet in diameter, laid in concrete. Two pipes, or three, may be laid side by side. If more than three would be required, a masonry opening is adopted. The discharge through an outlet, is generally 2 to 5 c. feet per second per square foot of outlet area, and the head ·1 to ·5 feet. For the tract of country allotted to any distributary, a contour map is prepared on a fairly large scale, say 4 inches to a mile. On the map the line is laid down and a rough longitudinal section, showing the ground level, is prepared as in the case of a canal. It has already been stated (Art. 4) that a distributary is so designed that its water level, when three-fourths of the full supply is run, shall be well above the level of most of the ground along its course. In other words it should have a good command. A good rule is to allow a fall of ·5 feet from the level of the water in the distributary to that in the watercourse, a slope of 1 in 4,000 for the water flowing along the watercourse, and a fall of ·3 feet for the water at the tail of the watercourse to the level of the ground. This last level is, like the other ground levels, taken from the contour map. This procedure, in short, consists in making the water level of the watercourse at its head govern that of the distributary, just as the water level in the distributary at its head was made to govern that in the canal.