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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1907 Excerpt: ...principally in cleaning or enlarging the pools or channels above them in order to give the proper contractions and to reduce the velocity of approach and to raise the crests of the weirs so as to provide a free fall for the discharge. To get the necessary fall often required that the crests of the weirs be placed within a foot or less of the level of the water in the main canal at ordinary stages. In order that the supply need not be entirely shut off when only a small head was carried in the canal, provision was made whereby openings could be made beneath the crests of the weirs. It is often necessary to get water into such laterals early in the spring or late in the fall when not enough is in the canal to allow the weir to be used. Here is one of the most serious difficulties encountered in connection with the use of weirs, or for that matter any other practical means of measuring diversions. The farmers wish to irrigate all the land possible and locate their laterals or head ditches just as high as they can and get water into them, which does not leave the fall which a weir requires. The miner's boxes need still a greater margin, and for discharges of only a cubic foot or two per second it is not practicable to use rating flumes, so such diversions will have to be changed or, if continued, be regulated by guess as they have been in the past. In developing new irrigation districts this difficulty should be guarded against by prohibiting the diversion of water from the canal at a height so near the water level in the canal as to make the measurement of the water impossible. In some places where the lands adjoining the canal sloped away more rapidly the weirs had ample fall, but were set so close to the outlet from the canal and so much below the level of t...

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9781377170428

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