THE IRRIGATION AGE. 



45 



ing wells in such sand arises from the tendency of the 

 sand to move with the water; "since the specific grav- 

 ity of sand is only about 2.65, just as soon as a pres- 

 sure greater than three feet is developed to force the 

 water out of the sand, the sand must move with it." 

 In sinking an open well, it is usually necessary to re- 

 move the water as fast as it accumulates. The effort 

 must, therefore, be to minimize the movement of the 

 sand which is forced upward into the bottom of the 

 well by the pressure from without. 



There are two principal methods used where sand 

 forms the bulk of the under-stratum. The first of 

 these is to sink the well only a few feet below the 

 water level, and then sink several perforated pipes or 



strainers in the bottom of 

 the well. These pipes will 

 usually flow when the 

 head of water in the open 

 well is pumped off. The 

 second method, and the 

 one by which probably the 

 most permanent well can 

 be secured, but at a com- 

 paratively high cost, is by 

 building a circular wall of 

 masonry, say two feet 

 thick, upon a platform 

 supported by a wooden 

 curb some two inches 

 thick, and from four to 

 six feet long. (See Fig. 1.) 

 The weight of the wall 

 causes the curb to sink 

 deep into the sand, con- 

 siderably in advance of the 

 excavation within. The 

 pressure of the sand and 

 water within the curbing thus tends to equalize the 

 pressure from without and therefore to greatly expedite 

 the work. In making an open well of this type, it is 

 usually desirable at the finish to have the curbing pene- 

 trate a short distance into the gravel stratum so as to 

 shut off further entrance of sand into the well from 

 without the wall. In sinking the water is usually kept 

 down by a centrifugal or other kind of pump capable 

 of handling a large quantity of water. 



PIPE WELLS. 



Pipe wells are frequently sunk by drilling. Under 

 the conditions existing in the Rio Grande Valley, how- 

 ever, in which sand or sand and gravel, form the water 

 bearing stratum beneath the surface of the soil, they 

 are either driven or sunk by means of a sand-bucket, 

 in which case some form of strainer is common. With 

 small wells three inches or less in diameter, the strainer 

 or point, as it is frequently termed, is fastened to the 

 lower end of the pipe and driven with the pipe to the 

 desired depth. Large wells of this type have been 

 driven, but it is customary with such large wells to 

 sink the open pipe first and lower the strainer inside 

 to the bottom. The pipe is then jacked up until the 

 entire length of the perforated part of the strainer is 

 exposed. 



STRAINERS. 



There are three types of strainers: The common 

 strainer, consisting of a perforated pipe covered with 

 brass gauze or closely wrapped with brass wire: the 



MASONRY CURB ON WOODEN 

 PLATFORM. 



"Cook's"' (a strainer consisting of a pipe cut with 

 horizontal slots, wider on the inner side) ; and the 

 slotted strainer. The first two are too well known to 

 require special mention here. They are used largely 

 to secure water from sand. The last named strainer, 

 which is illustrated in Fig. 12, consists of a pipe per- 

 forated by round holes or oblong slots, and is used in 

 drawing water from a gravel, or a gravel and sand, 

 stratum. 



INFLUENCE OF CAPACITY. 



An increase in the capacity of a well means that 

 more water can be secured by pumping off the same 

 head, or that the same amount will be supplied when 

 pumping off a somewhat less head. In the latter case, 

 the water would stand nearer the surface of the ground 

 while pumping, and for this reason the lift would be 

 less, thus reducing the cost of pumping. It is evident, 

 therefore, that the cost of pumping a given volume of 

 water diminishes with the increase in the capacity of 

 the well. It naturally follows that a saving in the cost 

 of pumping will soon compensate for the relatively 

 larger expenditure for the construction of a well of 

 greater capacity. The size of the well, and the length 

 of the strainer both affect the capacity of the well, if 

 the water enters from the bottom or through -the sides 

 near the bottom. 



SIZE OF THE WELL. 



The area of the bottom, as well as that of the sides 

 of the well, increases as the well grows larger, and it 

 is thus evident that the greater the area the greater 

 the space through which water can enter the well. 

 From this we conclude that the capacity of a well, other 

 things being equal, increases with its size. 



LENGTH OF STRAINER. 



Under equal conditions, and within the limit of 

 the carrying capacity of the pipe, it may be said that 

 the longer the strainer the greater its capacity. This 

 increase in capacity is brought about in much the same 

 way as the increase in the capacity of the well with its 

 size. King says : "Leaving the bottom of the well out 

 of consideration, it is clear that doubling the depth of 

 the well in the water bearing beds doubles the area for 

 water to enter. * * * This capacity increases in a 

 somewhat slower ratio than the depth." * * * This 

 statement also applies to the increase in capacity of a 

 well through its increased size. 



DEPTH OF WELL. 



So long as the head of water while pumping is 

 above the strainer, the depth of the well does not affect 

 the capacity, unless the conditions differ. This state- 

 ment refers to pipe wells with strainers. 



THE STATION WELL. 



The experiment station well is forty-eight feet deep 

 and consists of an open well dug to water level, in the 

 bottom of which is sunk a six-inch pipe, 21 1 /^> feet long, 

 with a 12-foot strainer below the pipe, located in a 

 water-bearing gravel stratum. To facilitate the attach- 

 ment of pumps, the pipe was allowed to project six 

 inches into the open portion of the well. 



The following equipment and materials were used 

 in sinking the well : 



(To Be Continued.) 



Somebody asks: Is the Weather Bureau man re- 

 sponsible for bad weather ? To give an evasive answer : 

 We should say not; the bad weather is responsible for 

 the weather bureau man. 



