Irrigation and water-supply : a practical treatise ... / by John Scott.

  • Scott, John.
Date:
1883
Catalogue details

Licence: Public Domain Mark

Credit: Irrigation and water-supply : a practical treatise ... / by John Scott. Source: Wellcome Collection.

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    watering tliem alternately. Where several small springs occur near eacli other, connecting drains can often be put in, and the waters collected and brought into one channel. Canals w^hich serve for irrigation are frequently only conveyers of water from distant rivers, or from natural lakes. If a canal is formed with the express object of watering a given area of land, the capacity of the canal should be large enough to provide a flow con- siderably in excess of the actual quantity of water required. Where the water has to be carried a long distance, and the soil is porous, the loss by filtration and evaporation may amount to 25 and even 33 per cent. Catch-water Tanks and Reservoivs.—In many cases where irrigation is carried on, the supply of water is obtained by impounding the winter rainfall for use during the dry season. The flood-water, in very dry districts even, when stored and made available at the right season, is found amply sufficient for the pro- duction of good crops. Assuming that an inch of water is the least quantity that should be applied at each watering, this, over one acre of surface, is equal to 3,630 cubic feet, or 27,152 gallons. To irrigate 30 acres once, at this rate, would require a tank capacity of 108,900 cubic feet, or a tank exactly ~ acre in extent and 10 feet deep; and to irri- gate 30 acres four times, or 60 acres twice, would re- quire a tank four times as large, or 1 acre in extent and 10 feet deep. A tank or reservoir can often be formed by merely erecting a dam or embankment to impound the water in a natural basin or ravine. Indeed, it will seldom pay to make a ground-tank where the impounding