IRRIGATION AND DRAINAGE 149 



orchard as shown in Plate V. The method is familiar where- 

 ever irrigation is practiced, but there are still many unsolved 

 questions connected with it. For example, the best length 

 of furrow depends on the character of soil; a light soil requires 

 a relatively short furrow, while the reverse is true with a 

 clay or adobe soil. Frequency of irrigation is another 

 unsettled question, the interval varying from a week or ten 

 days to one or even two months. The amount of water to 

 be applied is another serious problem. Much investigation 

 must still be done before these questions will finally be 

 answered to the best interests of the horticulture of 

 America. 



244. Water measurement. Quantity of water may be 

 designated in a variety of ways; it is most frequently given 

 in cubic feet, gallons, acre-inches, acre-feet, cubic feet a 

 second (called second-feet), and miner's inches. Cubic feet 

 and gallons are units commonly employed to designate the 

 amount of water in a storage reservoir. An acre-foot sig- 

 nifies the water on an acre of land if it be a foot deep ; since 

 an acre contains 43,560 square feet, an acre-foot is, there- 

 fore, equivalent to 43,560 cubic feet. The acre-inch is the 

 most convenient measure of an irrigation. An application 

 of 2% acre-inches means that the piece of land in question 

 received water equivalent to a rainfall over the entire piece 

 of 2^4 inches. To change acre-inches to acre-feet, divide 

 by 12; vice versa, to change acre-feet to acre-inches, mul- 

 tiply by 12. One acre-inch equals 3630 cubic feet or 27,150 

 gallons. This weighs 226,392 pounds, or 113.2 tons. To 

 change acre-inches to cubic feet, multiply the number of 

 acres in question by 3630, and multiply this by number of 

 acre-inches. 



245. Miner's inch. The common measure of stream 

 flow is the miner's inch. This unit varies somewhat in dif- 

 ferent states; but is commonly accepted to mean the amount 

 of water flowing through an opening 1 inch square, with the 



