FORESTRY AND IRRIGATION 123 



titanic methods. The use of streams seasons. When wells are sunk through 



is confined simply to the headwaters, the cap rock which confines the water 



and then chiefly on the slope where supply, the water rises to the sea-level 



the heavy rainfall exists. There irri- or a little above it, and to higher levels 



gation finds its best use in preventing further back from the coast. To sup- 



a check in growth during the months ply this water to the plantations, pump- 



which are short of rain. In a few ing plants of an expensive nature are 



instances the waters of this slope have absolutely necessary. A number of 



been diverted around spurs of the moun- types are in use driven by equally varied 



tains to the drier side of the ridge. types of engines. The multi-valvular 



The difficulties connected with this and automatic valve pumps are most in 

 method in such exceedingly rough coun- favor, though centrifugal and direct- 

 try makes the undertaking almost im- acting plunger pumps are used. 

 practicable. Some conception of them The Island of Oahu, the most pro- 

 may be gained from the following de- ductive of the entire group, has five of 

 scription of an engineering feat on the the most progressively managed plant a- 

 island of Maui, taken from a recent tions, and these alone produce one-fifth 

 census report : of all the sugar that comes from the 



"A canal was dug along the slopes Hawaiian group. These all use under- 

 of the great crater Haleakala, and a ground waters for their irrigation sup- 

 large stream of water was brought 22 ply. The Oahu plantation, according 

 miles and distributed through laterals, to the 1902 -report of the irrigation in- 

 Along the route of the canal scores of vestigations, U. S. Department of Agri- 

 gulches and canyons are crossed and a culture, has 4,950 acres of irrigated 

 dozen or more high ridges are penetrated land and produces an average yield of 

 by tunnels, some of them nearly half a ten tons of sugar per acre. The greater 

 mile in length. One of the gulches, on part of this plantation lies above 200 

 the side of a vast crater, is 350 feet deep feet above the sea-level, extending from 

 and nearly a quarter of a mile wide, this to an elevation of 750 feet. Forty 

 with perpendicular sides. The pipe lines 1 2-inch wells of an average depth of 

 used in crossing it were not placed on more than 440 feet, and varying from 

 trestles, but the less expensive and more 350 to more than 800 feet, supply the 

 stable method was followed, of dropping water, and eight pumping stations, \vith 

 them into the gulch, thus forming an a daily capacity of 64,230,000 gallons, 

 inverted siphon, which proved a success lift it from sea-level, to which it rises 

 from the start." in the wells. The approximate cost of 



The waters which find their way to the stations already completed on this 



the sea through underground channels, plantation was $71 1,000, and the entire 



and which appear at some points in the system when completed will cost $1,000,- 



form of springs, discharge themselves ooo. One plant of 10,250,000 gallons 



into the ocean apparently beneath a capacity delivers water to a level of 370 



ledge of rock at a depth of from 300 to feet and costs $175 per day to operate. 



800 feet below sea-level, as is shown by Another of 8,000,000 gallons capacity 



the depth of wells required to reach raises water 150 feet and costs $75 per 



them. day ; another of the same capacity, but 



It seems evident, therefore, that this delivering to an elevation of 650 feet, 



supply of fresh water lies in the form costs $225 per day. The two unfin- 



of a sheet of "sweet" water over the ished stations will elevate the \vater 



denser salt water beneath it, being con- 750 feet. 



stantly replenished and held at this level Ewa plantation, adjoining Oahu on 



by the supply from the rains on the the west, is of particular interest because 



mountains. When too large supplies its fields produce more sugar to the acre 



are drawn from these deep wells the than any other in the world, and its irri- 



water becomes somewhat brackish, and gating wateis are obtained entirely from 



salt in injurious quantities is sometimes coast artesian supply, which becomes at 



pumped on the land in exceptionally dry times rather brackish. That these two 



