Suppose two parallel distributaries to be 4 miles apart, each of them being an average Indian one, say sixteen miles long with a gradient of one in 4,000, and side slopes of ¹⁄₂ to 1, the bed width and depth of water at the head being respectively 13·5 feet and 2·9 feet, and at the tail 3 feet and 1 foot. The discharge of the distributary, with N = ·0225, will be 72 c. ft. per second. The discharge available for the 2 mile strip along one bank will be 36 c. ft. per second. If the duty is 300 acres per c. ft. the area irrigated in this strip will be 10,800 acres, or 1,350 acres for each of the eight squares like ACDB. Each main watercourse would then have to discharge 4·5 c. ft. per second. Supposing its gradient to be 1 in 4,000 and its side slopes ¹⁄₂ to 1 and N to be ·0225, its bed width would be 3 feet and depth of water 1·45 feet. Its wet border would be 6·3 feet, and its average length 5280√2 + 5280 - 200 or 12,546 feet. Its wetted area would be 79,040 square feet, and the total wetted area of the 16 watercourses--on the two sides of the distributary--would be 1,264,640 square feet. The wetted border of the distributary itself is 19·5 feet at the head and 5 feet at the tail, average 12·25 feet, and its wetted area is 5,280 × 16 × 12·25 or 1,034,880 square feet. If the distributaries were two miles apart, there would be twice the number of distributaries, and each square would be one square mile instead of four. Each watercourse would have to discharge 1·125 c. ft. per second. It would have a bed width of 2 ft., depth of water ·8 ft., wet border 3·8 feet, length 6,173 feet, and wetted area 23,457 feet. The total wetted area of the 64 water courses would be 1,501,248 square feet, or 18 per cent. more than before. Each distributary would discharge 36 c. ft. per second, the bed width and depth at the head being 10 feet and 2·24 feet, and at the tail 2 feet and ·75 feet. The wet border at the head and tail would be 14·5 and 3·5 feet, mean 9 feet, and the wetted area of the two distributaries would be 1,520,640 square feet or 50 per cent. more than before. Supposing that, in the case of the larger distributary considered above, the 2-mile square was considered too large, and that rectangles 1 mile wide were adopted, so that the watercourses were a mile apart, their number would be doubled and their length and size reduced. Their total wetted area would not be greatly affected, but the difference in the wetted areas of the two small distributaries as compared with the one large one, would be the same as before. In practice, of course, distributaries are not always parallel, nor are the blocks of irrigation all squares, and frequently, owing to peculiarities in the levels of the ground or the features of the country, or the boundaries of villages, it is necessary to align the watercourses in a particular manner, or to construct more than one watercourse where one would otherwise have sufficed, but the above