180 



THE IRRIGATION AGE. 



a region where the precipitation of water in the form 

 of rain or snow is much greater than can be utilized, 

 or the underlying water plane is supplied from the per- 

 ennial flow of large rivers or streams fed from a never- 

 failing watershed. 



It is essential to artesian water that it be confined 

 under pressure beneath a cover. All water in porous 

 soils, if the pores are to be filled to saturation, must 

 rest upon a floor of practically impervious material. 

 Underground water has a slow motion on account of 

 the resistance of friction, and accumulates, assuming a 

 nearly horizontal position along its upper surface, as 

 it does in an open pond or reservoir. This is its na- 

 ture. Now, if an overlying impervious bed has an in- 

 clination steeper than the inclination of this water 

 plane, its dip may bring it into contact with the water. 

 Down grade from the line of meeting of the water 

 plane with the under surface of the more steeply in- 

 clined impervious cover, the conditions of confinement 

 under pressure exist, and beyond this line of contact 

 or meeting the ground water will be artesian that is, 

 when it finds an outlet it will rise, seeking to attain 

 the portion or level its surface would have were it not 

 for the obstacle in the shape of the overhanging rock 

 or impervious bed in its way. 



When this impervious covering is perforated by 

 boring a well, the question whether there will result 

 a flowing well, or a mere rise to some higher level with- 

 in the bore hole, will depend on what the level of the 

 ground surface may be. If at that point the ground 

 surface happens to be above the grade plane of the 

 confined underground water, there can not be a flowing 

 well. 



TAKING WATER FROM STREAMS AND RIVERS. 



There are four varieties of natural water courses, 

 the waters of which, when used for the purpose of irri- 

 gation, require different machinery or appliances to 

 control. 



First The slow current, to control the water of 

 which all that is necessary is a simple sluice gate that 

 may be opened or closed by any contrivance which can 

 be raised or lowered or moved to and fro sideways to 

 admit or stop the flow of water or regulate its quantity. 

 At a point above the level of the land to be irrigated a 

 three-sided box is sunk, the bottom of which is below 

 the regular surface of the water and the top above the 

 surface of the leveled bank. 



The end toward the water is fitted between two 

 uprights on each side of the box, which form grooves 

 to permit the slide to be moved or pushed down to con- 

 trol the supply of water. Or, the "gate," as it is proper 

 to call the sliding end of the box, may be in two parts 

 hinged at each side and swinging open in the middle 

 like the gates of a transportation canal, care being 

 taken to have the two wings of the gate open up stream 

 so that the pressure of the water will not throw them 

 open automatically. 



These two simple principles of an intake and 

 shutoff gate is the basis of all contrivances for admit- 

 ting water from a slow moving stream, whether the land 

 to be irrigated consist of 100 or 1,000 acres. There 

 are many varieties of them, some in iron and steel and 

 constructed of massive masonry to accommodate an 

 enormous flow of water, but all of them are substan- 

 tially based upon the idea given above. 



Second Rapid current streams, or mountain tor- 

 rents, require a dam to reduce the current before it en- 

 ters the water gate, or else the latter would be soon 



torn out or undermined by the swirl of the waters. 

 This is the object of the dam : to create a smooth, 

 placid sheet of water, similar to the surface of a pond 

 or reservoir, and from it admit water in through the 

 water gate. This dam, if the current is very swift, 

 may be constructed at right angles with the bank, that 

 is, straight out into the stream. This will form a 

 breakwater, a quiet harbor, so to speak, and the water 

 wil become still inside of it. 



Third Dry rivers. Dry river beds are common 

 everywhere in the arid and semi-arid regions. They 

 are often alluded to as "rivers with their bottom on 

 top," being dry nearly always except during the rainy 

 season, when a greater or less body of water flows in 

 their channel, according to the quantity of rainfall 

 within reach of the watershed which supplies them. 



Although surface-dry for eight or nine months of 

 every year, there is in most cases an underground sup- 

 ply of water sufficient to supply an enormous quantity 

 of water by sinking cribbed reservoirs and pumping. 

 For the ordinary purposes of irrigation these streams 

 must be dammed to create a reservoir which will retain 

 the water when it flows, and back it up high enough 

 to reach the head gates of the irrigating ditches along 

 its banks. These streams are not always as peaceable 

 as they seem, for they are often converted into raging 

 torrents that carry away every obstacle in their path. 

 Hence the damming of them requires the highest en- 

 gineering skill and the most substantial material to 

 dam up the water, for no one can tell whether the 

 stream will run a. small quantity of water or inundate 

 the country around about. 



An arroyo is the Spanish for a small cut or open- 

 ing between low hills, and refers to a small stream or 

 rivulet that sometimes flows through it. These water 

 courses are not streams, properly speaking, but rather 

 waterways, for they have no subterranean or under- 

 ground water, and what does flow in or through them 

 is adventitious or accidental, depending upon the quan- 

 tity of rainfall. 



These arroyos are quite common in all hilly land 

 in the West and Southwest, and sometimes reach the 

 dignity of mountain torrents, but in a few days they 

 run dry and the water is lost. Much of this water may 

 be saved for irrigating pxirposes in a variety of ways. 

 Damming is not advisable generally, for the dry stream 

 may become an irresistable torrent and sweep every- 

 thing out of its path. A partial or wing dam in most 

 cases will hold the water for several weeks, perhaps 

 three months, and permit it to slowly seep down into 

 the soil for the benefit of the land below, or, where the 

 lay of the land on the hillsides is favorable, running 

 deep furrows parallel with the slope will restrain the 

 water from flowing too rapidly down the watershed, 

 and thus also permit it to seep slowly into the soil, 

 and if followed up will eventually result in creating a 

 water table into which shallow wells may be sunk for 

 pumping purposes. 



Where the land is sloping below a hill or series 

 of hills deep furrowing with a sidehill plow at inter- 

 vals of say six feet from the top to the bottom of the 

 hill with a succession of rough furrows at the bottom 

 will save up or store enough water to irrigate by infil- 

 tration many acres of land for corn, potatoes, melons 

 and vines generally. Experiments demonstrate that 

 this process will equal two irrigations of an inch each, 

 and by careful, constant cultivation a good crop of 

 r-orn or potatoes, even melons, pease and beans, may be 



