THE EFFECT OF THE FOREST UPON WATERS 



157 



fifty years it has been admitted as a 

 scientific dogma that forests, by reason 

 of their capacity to retain rainfall, have 

 the power to diminish great floods in 

 the rivers, and that deforestation is the 

 main cause of inundations ; it is like- 

 wise to deforestation that progressive 

 diminution in water-levels and in low 

 water-flow is attributed, both so notice- 

 able in recent years. In a word, we 

 look upon the forests as regulators of 

 stream-flow, as immense sponges gath- 

 ering up the precipitation, however 

 abundant it be, and restoring it after- 

 ward gradually. 



"According to reports presented by 

 the hydraulic engineers at the tenth 

 meeting of the permanent association 

 of the congress of navigation, held at 

 Milan in 1905, we must discount to a 

 large degree the influence of the forest 

 upon stream-How and upon springs." 



So far as the eminent secretary of 

 the Geographical Society is concerned, 

 the statements made by those who pre- 

 sented the reports establish clearly that 

 the influence of the forest on the run- 

 off from rainfall is nothing in times of 

 flood; that it has nothing to do with 

 the existence of springs, but that it is 

 able to hold the soil on slopes, to dimin- 

 ish the volume of matter carried away 

 by streams, to lessen erosion, and to 

 prevent land slips, except in cases of 

 glacial formations. Mr. Charles Rabot 

 adds that at the congress at Milan the 

 partisans of the forest presented no 

 facts and no observations in support of 

 their theory, limiting themselves to 

 affirmations without furnishing proofs. 



The conclusions drawn from the pa- 

 pers referred to above by Mr. Rabot 

 seem to us to be much too arbitrary ; 

 the reading of the same documents has 

 not left with us the same impression. 

 We would like to present to our read- 

 ers at the very beginning the most strik- 

 ing parts of the papers presented at 

 the congress ; we will discuss them 

 afterwards. 



Mr. Wolfschiitz has undertaken to 

 show that the retentional power of the 

 forest fails after an extraordinarily 

 abundant rainfall of long duration. He 



says in his report: "We must recognize 

 that man is powerless against the prin- 

 cipal causes of floods and of abundant 

 rainfall." 



According to Mr. Wolfschiitz, there 

 fell in the basin of the Rhine 209 milli- 

 meters of water in three days, in No- 

 vember, 1882; 215 millimeters in eight- 

 een hours, August 2, 1888, in the Ries- 

 enwald ; 187 millimeters in twenty-four 

 hours, in July, 1897; 184 millimeters in 

 forty-eight hours in 1897, in the basin 

 of the Traun ; 208 millimeters in two 

 days in 1899; 242 millimeters in twenty- 

 four hours at Riechenhall and at Alt- 

 Ausse, September 12, 1899. In 1882, 

 at the time of the Rhine floods, accord- 

 ing to Honsell, it was the most heavily 

 wooded watersheds (the Black Forest, 

 the Hardt, the Spessart, the Fichtelge- 

 birge, and the Odenwald) that contrib- 

 uted most to swelling the waters of the 

 Rhine. According to statements of the 

 central bureau of hydrography, Vi- 

 enna, the most heavily wooded water- 

 sheds have often experienced the most 

 disastrous floods, and it was thus in 

 1897 on the watersheds of the tribu- 

 taries of the Elbe, in 1897, and in 1899, 

 on the watersheds of the Enns, of the 

 Traun, and of the Ybbs. Even the very 

 dense covering of the Riesenwald had 

 no influence on the floods in the streams 

 of Silesia that occurred, following tor- 

 rential rains, in August, 1888 ; July. 

 1897, and July, 1903. 



The powerlessness of man in the 

 case of such an unusually heavy rain- 

 fall is apparent to all, but if he is en- 

 tirely unable to prevent its occurrence, 

 he can, at least, lessen its disastrous 

 effects. Mr. Wolfschiitz recognizes, 

 moreover, that the reforestation of 

 some square kilometers "exerts a pro- 

 tective influence on the stream-flow of 

 certain areas adjoining the forests in 

 question or on cleared lands," but that 

 this local and restricted influence can- 

 not extend far. 



The report of Mr. Lauda, director of 

 the central bureau of hydrography, 

 Vienna, is one of the most remarkable 

 of those that were presented at the con- 

 gress of Milan. He takes pains to tell 



