74 



THE IRRIGATION AGE. 



and recorded are even more meager than 

 in the portions already referred to, and as 

 a consequence the formulae in use for de- 

 termining the maximum flood discharges 

 of streams are even less accurate. 



In the Southern States the best results 

 have been obtained by the use of the form- 

 ula already given, but in the following 

 form : 



and in the portion of the United States 

 lying west of the Mississippi River, with 

 the exception of a few localities, the fol- 

 lowing form of the formula has met the 

 greatest approval: 



Q = 160(M), 



in both of which the values of the letters 

 are the same as already given. 



Results obtained by the use of any of 

 the formulse given above are not claimed to 

 be exact, and can only serve to give some 

 idea of the rates of flow which may be 

 expected from maximum floods in the dif- 

 ferent localities. In making rough pre- 

 liminary estimates these formulae are use- 

 ful for determining the maximum flood 

 discharges of rivers as well as the approxi- 



mately safe proportions of structures in- 

 tended to span the streams, to divert water 

 from them or to provide spillways for 

 dams. But before any final plans and es- 

 timates are made or contracts entered into, 

 the nature and history of the particular 

 locality should be carefully ascertained 

 and studied, and such measurements and 

 observations made as time and opportunity 

 will allow, in order that the formula may 

 be modified to suit the particular locality 

 and conditions involved. For making ex- 

 act and reliable determinations of the max- 

 imum flood discharges from any watershed, 

 topographical, geological and meteorolog- 

 ical characteristics must be known and 

 used to modify an existing formula o'r to 

 construct a new one for use in making the 

 necessary calculations. 



The general formulae already given, 

 when used intelligently, can easily be mod- 

 ified so as to take into consideration the 

 extreme precipitousness or flatness, pervi- 

 ousness or imperviousness of the surface, 

 and the particular degree of precipitation 

 which characterizes the particular basin in 

 question. 



(To be continued. ) 



THE ART OF IRRIGATION/ 



CHAPTER IX. IRRIGATING WITH FURROWS. 



BY T. S. VAN DYKE. 



A SSUMING that the ground is fine 

 f\ enough to hold up the small streams 

 of water mentioned in Chapter VII with- 

 out letting them drop through too quickly, 

 you will generally find it best for all or- 

 chard and garden work to irrigate with 

 furrows instead of flooding. You will 

 find this true whether working the ground 

 for pleasure or profit and whether on a 

 large or small scale. Furrows do better 

 and cleaner work and when everything is 

 arranged as it should be the labor is 

 generally reduced to a minimum. The 

 results are those of a long, slow, soaking 

 rain, whereas flooding at the very best has 

 too much of the effect of a short and pour- 

 ing shower. As flooding is sometimes the 

 cheaper way of irrigating large fields, as 

 in alfalfa, so is the use of furrows general- 

 ly cheaper in orchard and garden work of 

 any magnitude. To handle a flooding 



"Copyright 1895, by T. S. Van Dyke. 



head on ten acres will take from two to 

 four men according to its size, whereas 

 one man can manage the furrows on ten 

 acres if the delivery flume is fixed as it 

 should be. I have known five acres of 

 lemons furrowed, irrigated and cultivated 

 by a boy of sixteen who lost not an hour 

 from school, and the whole was well done. 

 It was all in the arrangement being per- 

 fect at the start. 



The first requisite for good irrigation 

 from furrows is an irrigating head of from 

 twenty to fifty inches of water for at least 

 twenty- four hours for each ten acres. The 

 head will vary with the nature of the soil, 

 the product and the length of time you 

 can run the water. Where the soil is 

 quite close in texture and you can have 

 the head for three days at a time twenty 

 inches will do good work. I have seen 

 fine work done with fifteen inches for ten 

 acres, but it was with a four days' ran, 

 which gave plenty of time for the smallest 



