THE WATER SUPPLIES IN THE ARID REGION. 



65 



storms occur that swell it beyond the capacity of its 

 banks. In such floodplains accumulations of sand 

 and gravel are found irregularly distributed among 

 soils and clays. These sand and gravel deposits 

 become natural reservoirs for water, which comes 

 down in part from the adjacent hills, but in larger 

 part from the great floods. Now, these floodplain 

 waters can be secured for irrigation, either by tapping 

 them with canals that lead to lower ground, or by 

 sinking wells and pumping out the water. In actual 

 practice both the gravity method and the pump 

 method are used, but in general the pump method is 

 found more economical. 



The irrigable area of the arid region can therefore 

 be increased from these three sources, but the quan- 

 tities cannot be exactly defined without most thorough 

 geological research. Some districts will afford much, 

 some little, by reason of varying geological condi- 

 tions, but actual experience proves that the amounts 

 are considerable and worthy of notice in such an ac- 

 count of water supply as we are now giving. It seems 

 probable from the general experience of other lands 

 that three or three and a half million acres may be 

 added to the total for the arid region by the use of 

 pump waters, artesian waters and floodplain waters. 

 This, then, will give to*practical irrigation in the arid 

 lands where 20 inches of rainfall or less is found a 

 total area of forty million acres. 



AMOUNT OF LAND UNDER CULTIVATION. 



In no civilized country is all the land cultivated. 

 Denmark has the greatest amount, where 75 per cent, 

 is under the plough. The accompanying table ex- 

 hibits the proportion cultivated in different states and 

 territories of this country. Denmark, Great Britain, 

 Canada and the total for the United States are in- 

 terpolated in appropriated places for comparison. 

 When these 40 million acres are cultivated by 

 methods of irrigation they will be found wonderfully 

 productive, and their products will support a popula- 

 tion as great as that found in the United States at the 

 present time. It must be many decades before it is 

 all redeemed. As from district to district farmers 

 come nearer to the realization of the practical catch 

 as here represented more refined methods of catch will 

 be adopted and the practical catch will be increased; 

 but this will not result in increasing the acreage cul- 

 tivated, for at the same time better methods of irriga- 

 tion will be developed, from which a greater produc- 

 tion will result and which will require a greater prac- 

 tical duty of water. In fact, it seems probable that 

 intensive agriculture by increasing the product will 

 decrease the acreage, so that the total amount here 

 estimated will never be realized. 



A word must be aid about the character of this 



investigation and the degree of probability which 

 inheres in its results. 



In measuring rainfall and runoff, only averages can 

 be given. A farmer sells a field of corn standing in 

 the shock. In order that he may establish its value, 

 he husks and measures a few shocks and derives 

 therefrom an average which controls the quantity in 

 the terms of the sale. The average thus obtained 

 will never, except by accident, be exactly that of any 

 one shock of corn, and yet an approximation to 

 accuracy will be reached sufficient for practical pur- 

 poses of trade. In like manner, the statements made 

 in this paper are rarely if ever absolutely accurate for 

 any one small district of country, and the quantities 

 must always be taken as mean quantities, which only 

 approximate accuracy. The investigations have been 

 carried on but for a few years, and to be complete by 

 small districts it would be necessary greatly to 

 multiply the stations for rainfall gauging and stream 

 gauging. Notwithstanding all this, the general aver- 

 ages may be taken as approximately safe. 



Most of the lands now irrigated are watered by 

 streams and irrigating works that do not require the 

 most expensive plants; that is, the small streams are 

 nearly all taken out upon the land, and a small stream 

 irrigates a small area at a correspondingly small total 

 cost. As irrigation is extended, larger and still 

 larger plants are generally, though not always, neces- 

 sary, and for this purpose aggregated capital is 

 necessary. This capital will sometimes be secured 

 by cooperation among the irrigators themselves, and 

 sometimes capital will itself lead the way, for the 

 purpose of increasing the value of lands and selling 

 the same with water-rights to the farmers. Whatever 

 method is pursued, aggregated capital must be em- 

 ployed. Therefore the farmer and the capitalist 

 alike are interested in these results. Before money 

 or labor is to be invested in irrigating works, it be- 

 comes necessary to consider the water supply. Is 

 there land? is the first question raised; Is there water? 

 is the next question; and Can the water be carried to 

 the land with reasonable economy? is the third. 

 Many canals have been constructed without a proper 

 consideration of these three questions, and already 

 capital has been wasted, and we have now reached a 

 time in arid America when these three primary 

 questions relating to irrigation enterprises should be 

 properly answered, before lands are bought and sold, 

 homes established, labor organized and capital in- 

 vested. Without these precautions bonds are 

 worthless. 



In the next annual report of the Geological Survey 

 the subject of this article will be treated at length 

 and the facts arrayed in a more elaborate manner. 



