1018 



THE IKEIGATION AGE. 



vpirs in the fall and turn in the muddy flood water from the 

 ditch until the bottom of the reservoir is thoroughly wetted 

 and silted up. 



It is hard to make a just estimate of the extent of the 

 use of artesian water in irrigation, first, because of the fact, 

 before stated, that the water is in many places turned into the 

 ditches to supplement the ditch flow, and, second, because 

 there is a tendency in the valley to underrate the extent of 

 such use, lest an optimistic estimate should unfavorably affect 

 desired legislation for storage reservoirs in the mountains, 

 It is realized locally that further agricultural expansion de- 

 pends on the construction of reservoirs to conserve the flood 

 waters, and there is a concerted movement in that direction. 



With a few exceptions the wells of the valley have been 

 sunk by the hydraulic jet process. The exceptions are those 

 which have been drilled through lava, mostly nonflowing wells. 

 The deepest well in the valley, the No. 1 well of the San Luis 

 Oil Company, 1,283 feet deep, was sunk by the hydraulic proc- 

 ess, as were many others that reach 1,000 feet or more in depth. 

 The individual drillers have their favorite forms of bits, and 

 their own methods of "rotating" or "driving" the casing, but 

 the general method of sinking is the same here as elsewhere. 



When the well has been sunk into the desired aquifer arJ 

 the flow is reached, the pump is kept going for some time, 

 a day or more in deep wells, with the object of stirring up 

 the sand and carrying it up the well bore until a considerable 

 cavity is made at the bottom of the well. Water can be 

 delivered to the well only so fast as it can come through the 

 sand walls of the cavity at the bottom of the well. The 



0*3 



f 



Figure 5 Diagram illustrating flow from vertical and horizontal pipes. 



larger this cavity, the greater the contributing area of sand 

 wall and the greater the volume of water. A new well nat- 

 urally excavates for itself such a cavity and "throws sand" 

 for several days, often with a pronounced increase of flow. 

 But in the process large lumps may cave away from the clay 

 above and entirely shut off the flow. It is -the better plan, 

 therefore, to pump out the cavity while the drill rig is set up 

 over the well, so as to clear away the obstruction if the well 

 chokes up. It is customary in the valley to case only to the 

 first clay bed, through the superficial soil and gravel. This 

 distance varies from 10 to 50 or rarely to 100 feet. Though 

 inevitable, this practice of partial casing is much to be de- 

 plored. 



Owing to the high freight rates, the item of casing in an 

 average well costs more than the drilling. As long as a new 

 well can be put down for the cost of casing the first one, most 

 people of moderate means, at least in districts where the clay 

 resists the cavity fairly well, will prefer to take chances on 

 the caving of the uncased well, especially where the wells are 

 drilled for irrigation purposes as a last resort after suc- 

 cessive failures of the ditch water and when immediate results 

 are needed. Many wells, however, are cased down to the 

 main flow that is used. The flow of such a well is affected 

 only by increase in the number of wells, and can be shut off 

 in winter time with impunity, whereas the uncased well is 

 quite likely to cave within a year or so, particularly if plugged 

 in winter. A large percentage of the wells in the valley have 

 fallen off one-half or more in flow, principally through caving 

 in. If caving takes place as a result of plugging the well, it 

 usually happens when the plug is removed. While the well is 

 open the rapid ascent of the water tends to carry to the 

 surface and clear the well of any caved material as fast, as 



it falls. When the well is plugged, however, the water in 

 the bore and to a certain extent in the different aquifers 

 assumes a uniform pressure. This uniformity of pressure has 

 a tendency to favor the disintegration of the walls of the 

 bore. The material breaking away settles downward through 

 the still water in the bore and packs itself in the bottom, 

 When the well is turned on again the amount of material 

 packed in the bottom may be suffcient to cut off the lower 

 flow. Again, the sudden shock of decrease of pressure when 

 the well is suddenly opened by knocking out the plug has like- 

 wise a tendency to jar off pieces of the clay wall. 



The cost of boring wells, owing to the similarity of the 

 formations, is nearly uniform for similar sizes over the valley. 

 The price of the completed well varies of course with the 

 diameter and depth of the bore hole and the size and length 

 of the casing. The price of casing also varies materially from 

 time to time. The following statement gives the cost of a 

 few typical wells in Alamosa, and the cost of others has been 

 given in preceding pages. 



Cost of typical wells in Alamosa. 

 Two-inch wells: 



230 feet deep, cased about 50 feet $ 55 



460 feet, cased about 50 feet 101 



000 feet deep, 

 735 feet deep, 



Three-inch wells: 

 650 feet deep, 

 730 feet deep, 



Town well, 5 in 

 865 feet deep, 



ased about 50 feet, 

 ased to the bottom. 



135 

 351 



ased about 50 feet 145 



ased about 50 fett 161 



les in diameter: 



ased to 852 feet 1,865 



Approximate Measurement of Flowing Wells. 



Tables for determining the discharge of water from com- 

 pletely filled vertical and horizontal pipes were prepared a 

 number of years ago by Prof. ]. E. Todd, state geologist of 

 South Dakota, who issued a private bulletin describing simple 

 methods of determining quickly, with fair accuracy and with 

 little trouble, the yield of artesian wells. The following tables 

 and explanations relating to vertical and horizontal pipes are 

 taken from this bulletin, with extensions by the present 

 writer. The explanations and tables relating to the measure- 

 ment in the partly filled horizontal and inclined pipes are 

 from a paper by Charles S. Slichter. 



In determining the flow of water discharged through a 

 pipe of uniform diameter all that is necessary is a foot rule, 

 still air, and care in taking measurements. Two methods are 

 proposed, one for pipes discharging vertically, which is par- 

 ticularly applicable before the well is permanently finished, 

 and one for horizontal discharge, which is the most usual way 

 of finishing a well. 



The table No. 1 at the end of this article is adapted to 

 wells of moderate size as well as to large wells. If the well 

 is of a diameter not given in the table its discharge can with- 

 out much difficulty be obtained from the table by remembering 

 that, other things being equal, the discharge varies as the 

 square of the diameter of the pipe. If, for example, the pipe 

 is one-half inch in diameter its discharge will be one-fourth 

 of that of a pipe 1 inch in diameter for a stream of the same 

 height. In a similar manner the discharge of a pipe 8 inches 

 in diameter can be obtained by multiplying the discharge of 

 the 4-inch pipe by 4. 



In the first method the inside diameter of the pipe should 

 first be measured, then the distance from the end of the pipe 

 to the highest point of the dome of the water above, in a 

 strictly vertical directon a to b in the diagram (Fig. 5). 

 Find these distances in Table 1 ; the corresponding figure 

 gives the number of gallons discharged each minute. Wind 

 would not interfere in this case, if only the measurements are 

 taken vertically. 



The method for determining the discharge of horizontal 

 pipes requires a little more care. First measure the diameter 

 of the pipe as before; then from a point (b, Fig. 5) 6 inches 

 vertically below the center of the opening of the pipe, or some 

 convenient point corresponding to it on the side of the pipe 

 (a), measure strictly horizontally to the center of the stream 

 (b to <?). With these data the flow in gallons per minute can 

 be obtained from Table 2. It will readily be seen that a slight 

 error may make much difference in the result. Care must be 

 taken to measure horizontally and also to the center of the 

 stream. Because of this difficulty it is desirable to check the 

 first determination by a second. For this purpose columns 

 are given in the tables for corresponding measurements from 

 a point 12 inches below the center of the pipe. Of course the 

 same result should be obtained in the two measurements of 

 the same stream. Wind blowing either with or against the 



