IRRIGATION 



IRRIGATION 



1683 



In the semi-arid regions west of the 100th meridian, 

 with a rainfall of 20 inches or less, crops ai'e liable to 

 be entire failures three or fom- years out of five; while 

 with an irrigation plant there should not be a failure 

 one year in five. In the arid regions with less than 15 

 inches of rain, irrigation is a necessity on most soils. 

 Here the work has been highly organized and sys- 

 tematized, so that the cost of water deUvered at the 

 field amounts to $2 to $5 an acre each year. Under 

 skilful management, the most abundant yields are 

 secured. The most careful management is required in 

 the application of water to prevent serious injury to 

 the land and to avoid actual injury to the crop in ren- 

 dering the plants tender and hable to disease, and in 

 maintaining the quahty and flavor, both of which are 

 hable to depreciate unless good judgment is displayed 

 in supplying water. 



Sources uf water-supply. 



The principal sources of water-supply are streams, 

 surface wells, artesian wells, and the storage of storm 

 waters. For small irrigated tracts near cities, the city 

 water-supply may often be used to advantage. In 

 other localities the nature of the conditions will deter- 

 mine the most economical source from which to secure 

 the water. Perpetually flowing streams, if situated in 

 such a w'ay that water can be carried to the land by 

 gravity, have the advantage of cheapness of construc- 

 tion and maintenance. On the other hand, if the 

 stream supplies others in the community, there is liable 

 to be trouble and expense in establishing and maintain- 

 ing water-right claims and in securing water when 

 needed for the crop. Questions arising out of the 

 water-rights on streams and rivers in the western 

 states, with the various state laws, the multiplicity of 

 court decisions on the most intricate legal questions — 

 both in different states and different countries along the 

 line of the stream — the absence in most states of ade- 

 quate police or judicial powers vested in the irrigation 

 commissioner, have led to the most perplexing and 

 bewildering state of affairs, and have involved the 

 states and individuals in enormous costs for lawsuits, 

 resulting in many cases in the apportionment of many 

 times the volume of the stream to the settlers along 

 its bank. 



The large planter must seek some perennial and 

 abundant supply of water, as is furnished by streams, 

 but it is safe to say that all streams of any size in the 

 w'estem part of the United States are already appropri- 

 ated to their fullest extent, although the water so appro- 

 priated is not all in present use. Smaller planters are 

 much more independent with some of the other sources 

 of supply mentioned above. Wells from 10 to 20 feet 

 deep, with pumps operated by windmills, or wells of a 

 maximum depth of 50 feet operated by many forms of 

 gasolene, hot-air or port.ible engines, attached to directs 

 acting pumps or centrifugal pumps, form in general a 

 very satisfactorj' means of irrigating small areas. 



Over hmited areas artesian wells have been very suc- 

 cessfully used. If they are flowing wells dehvering a 

 considerable stream, they can be used over small areas 

 without storage reservoirs, or over much larger area.s 

 with reservoirs. They should be capped in all cases, 

 where possible, so that the flow can be stopped when 

 not actually needed. 



In many places it is possible, at a comparatively small 

 expense, to construct a dam to collect the storm waters. 

 The magnitude and expense of such work will depend 

 entirely on the configuration of the surface, the area 

 of the watershed, the volume of the water to be hantlled 

 as well as the nature of the soil, and the material out of 

 which the dam is to be constructed. 



Methods of raising water. 



Various methods are used for raising water from 

 streams, wells, or storage reservoirs which may he 



below the general level of the land to be irrigated. 

 Hydrauhc rams are sometimes used for small areas, 

 but these are not economical when a small volume of 

 water is at hand, as only about one-seventh of the water 

 can be collected. Open buckets carried on an endless 

 belt, operated by either windmills, or steam-power or 

 even horse-power, are used with success and offer the 

 advantage of cheap construction. The ordinary cylinder 

 or plunger pumps are usually employed when the water 

 has httle or no sediment, and are operated by wind- 

 mills or by steam or other form of engine. When the 

 water carries considerable sediment such pumps are 

 hable to wear away rapidly, and the centrifugal pump 

 is the most economical form to use. The relative first 

 cost of equipment for pumping with windmills or with 

 gasolene or hot-air engines of approximately equal 

 horse-power is about the same. The windmill, however, 

 is dependent upon a mean velocity of wind of about 8 

 mUes an hour, whUe the engine may be operated at any 

 time, and is thus more rehable when either form of 

 motive power is taxed to nearly the extreme Umit. 

 There are many kinds of windmills on the market, 

 and many forms of home-made construction are in use. 



Storing and conducting water. 



Storage reservoirs for streams and for storm waters 

 varj' in size and in cost ;is well as in mode of construc- 

 tion according to the character of the land, size of 

 area, volume of water, nature of the material of con- 

 struction, and demand for the water. The construc- 

 tion of such reservoirs sometimes involves engineering 

 problems of the most difficult kind, demanding the 

 ex-penditure of immense sums of money. 



In the use of windmills, it is necessary to have small 

 distributing ponds or tanks, as the direct flow from the 

 pump is usually so small and varies so much with the 

 velocity of the wind that it cannot be depended on to 

 water any considerable area. Where it is stored it can 

 be turned out on the land in large volumes, so that it 

 spreads over the surface and waters the whole area uni- 

 formly. For an ordinary windmill the ponds are from 

 50 to 100 feet square. They can be stocked with fish and 

 thus be a source of some revenue and variety in the 

 family supphes. Unless the pond is situated on a slight 

 elevation, the earth for the embankment must be taken 

 from the outside. The banks are usually made with a 

 slope of 1^ to 1 foot. For a bank 5 feet high and 2 feet 

 across the top, the side would be about 7 J 2 feet and the 

 base about 13 feet wide. If the ground is at all pervious 

 to water, the bottom of the pond should be protected 

 from undue seepage and loss of water by puddUng. 

 This should be done with clay, if this is obtainable. 

 This puddhng is often done by driving horses or cattle 

 in the pond while the surface is wet. A pond of the 

 size indicated above, operated by a windmill where the 

 mean wind velocity is about 8 miles an hour, will 

 irrigate from 3 to 5 acres of land in the semi-arid regions. 

 Such a pond could be counted UfXin to irrigate from 5 to 

 10 acres where, as in the East, only one or two irriga- 

 tions would be required during the season. The size 

 of the reservoirs and the area they will irrigate, when 

 supplied by steam or other kind of engine, will depend 

 upon the available water-supply and upon the size of 

 pump and power used. 



Ditches and flumes. 



The* water is usually carried from the stream or 

 storage reservoir by gravity in open ditches. This 

 involves loss by evaporation from the surface and by 

 seepage through the soil. When the water-supply is 

 hmited and its value is consequently great, tcrra-cotta 

 pipes, uon pipes, cement or wooden [lijx's may be 

 used. When the surface of the countrj' is vmeven and 

 ravines have to be cro.ssed, flumes are used to carry 

 the water on an even grade across the depression. 

 These flumes may be iron pipes, open wooden troughs. 



