106 FOREST LANDS FOR THE PROTECTION OF WATERSHEDS. 



than in the case of forests in steep mountain regions. It is the preservation of 

 these last forests upon land not suited to agriculture that is believed to be 

 especially important from every point of view. 



The statement of Colonel Chittendeu that the flood of 1908 in the Western 

 States would have been much greater if the region had been forested, is a mere 

 statement of his own opinion, entirely without proof, and undoubtedly incapable 

 of proof; and further, if the gauge records given by him show that it is impos- 

 sible to find evidence in them to support the current theory of forest influence, 

 it may also be stated that there is nothing in them to support his own contention. 



The question will, of course, have occurred to the reader of these remarks, 

 Why it is not possible by long-continued observations of the height of floods 

 on our rivers to settle this question absolutely? With reference to this some 

 explanation is necessary. The flow of a stream is the resultant of a number of 

 elements, chief among which are rainfall, its distribution throughout the year 

 and over the area considered, the slope of the ground, the area of forest, culti- 

 vated land, etc., the number of lakes and reservoirs, the temperature, and other 

 elements. The chief of all of these is undoubtedly the rainfall and its distri- 

 bution. A great fall of rain, long continued, will probably cause a great flood 

 whether there are forests or not, although, as before explained, there is abun- 

 dant evidence for the contention that the action of the forest is to diminish the 

 flood. Meteorological phenomena are admittedly variable and uncertain, and, 

 of course, they are entirely incapable of control. The rainfall varies from year 

 to year in long cycles, the extent of the variation being such that in the United 

 States it has generally proved impossible to determine with certainty whether 

 the rainfall over a given territory which has remained in essentially the same 

 physical condition, is increasing or not. The rainfall at a given place may vary 

 from 30 inches in one year to 50 or 60 inches in the following year, and its dis- 

 tribution is subject to similar variations. These variable elements therefore 

 may mask the influence of forests or of reservoirs, but the important point is 

 that these two are the only elements subject to man's control. 



It is admittedly physically possible, by reforesting and by the construction 

 of storage reservoirs, to make the flow of a given stream practically uniform 

 throughout the year, although to do so would in most cases involve a pro- 

 hibitive cost; and, moreover, it would be physically impossible to regulate a 

 reservoir and allow the water to flow out of it in such a way as to produce 

 this effect, because the future can not be foreseen. Observations of gauge 

 readings on rivers, therefore, are inconclusive in themselves. Fortunately, 

 however, we are not without valuable evidence on this point. Mr. M. O. Leigh- 

 ton, chief hydrographer of the United States Geological Survey, has, during 

 the past summer, made an elaborate study of the floods of tho Tennessee River, 

 in which he has endeavored to eliminate the effect of the rainfall and its dis- 

 tribution by comparing the number of days of flood with the number of indi- 

 vidual rainstorms of sufficient magnitude to produce floods. The record shows 

 that during the last half of the period studied the number of days of flood 

 was actually less than in the earlier part of the period, notwithstanding the 

 deforestation which has recently taken place. The rainfall, however, has also 

 been less in the latter period, and the results of Mr. Leighton's study are that 

 the diminution of the rainfall has been much more than sufficient to account 

 for the diminution of the floods, so that the actual result is that the floods 

 have been increasing, the percentage of increase being 1S.75 in the last seventeen 

 years as compared with the seventeen years previous. This study is the best 

 contribution to the subject which has come to the writer's knowledge, and it 

 seems conclusive. The experience in France also furnishes valuable evidence 

 in this matter. 



In 1857 M. F. Valles, a French government engineer, published a work in 

 which, and in some subsequent papers, he gave almost the identical arguments 

 advanced by Colonel Chittenden, maintaining that forests diminished the rain- 

 fall, increased the floods, and diminished the supply of grain by withdrawing 

 lands from cultivation. He also maintained that floods were beneficial by 

 bringing silt from the mountain sides to the plains. His work, however, seems 

 to have been entirely without influence, for immediately after its publication 

 the French Government entered upon a policy of forest protection and refor- 

 estation, particularly in the mountain regions, which has been continued up to 

 the present time. Up to January 1, 1900, the State had acquired over 400,000 

 acres, or 629 square miles, for the purpose of controlling torrents. Of this area 

 440 square miles are in the Alps, 145 square miles in the central plateau and 



