66 



In giving an account of this work in the Annuales forestieres, M. A. F. d' H6ricourt com- 

 bats these assertions in a victorious manner, and proves conclusively that the reforesting 

 of a portion of the upper basin of the Loire would have prevented the inundation of 

 1846. 



"Accepting," says he, "the data of M. Valles, who has analyzed with much care the 

 various phenomena which characterized the flood of October, 1846, in the upper basin of 

 the Loire, I will admit with him, that if we could have held back 175,000,000 cubic 

 meters of water, the inundation which proved so sad a calamity to France would not have 

 presented so painful an event. The upper basin of the Loire, as far as Roanne, comprises 

 an area of 640,000 hectares, (158,080,000 acres) of which at least a third say 213,000 

 hectares (52,693,000 acres) might be profitably reforested. This inundation was caused 

 by a rain which lasted sixty hours, and poured upon the soil a sheet of water 153 millimeters 

 (about six inches) in depth. This portion of the basin of the Loire, therefore, received 

 979,200,000 cubic meters of water. On the hypothesis of M. Vall6s, 244,800,000 cubic 

 meters were absorbed. There accordingly remained for superficial flow 734,400,000 cubic 

 meters. 



"But, let us suppose that in 1846, the 213,000 hectaries above mentioned to have 

 been covered with massive woods, and then let us calculate what would have happened. 

 These 213,000 meters would have received as their share 290,000 cubic meters. The ab- 

 sorbent qualities of the soil are increased forty per cent, by reforesting, and this operation 

 would have withdrawn 130,116,000 cubic meters from the superficial flow, which would 

 have reduced the amount upon the retimbered portions to 195,174,000 cubic meters. But 

 this liquid mass would have been hindered in its course down the valley, as we have 

 above explained, by the passive resistances of every kind which the forest presents, and 

 a half, at least, would not have arrived until the other half, which had fallen in other 

 parts of the basin had passed off. We may, therefore, conclude that the superficial flow 

 would not have exceeded 500,000 cubic meters, and that the calamities occasioned by the 

 inundation of 1846 would have been completely prevented by reforesting." 



" Snows Retard the Flow of Waters : — This hindrance in the flow is very apparent 

 at a time when the snow is on the ground. When a part of a valley is wooded, the snows 

 that fall there lie much longer than in other parts, and while diluvial rains, which ordin- 

 arily cause inundations, would be quickly followed by a rise of waters in the cleared region, 

 and suddenly augment the liquid mass in that portion, the same rains would affect but 

 slowly the snows that lie in the wooded portions. The swell would come by slow degrees, 

 and the flood would give no special cause of alarm. 



" Mountain Torrents : — But it is especially upon mountains formed of slaty or marly 

 rock that the utility of forests is shown in a remarkable degree. When the slopes of 

 these lands, which have but slight powers of resistance, are denuded, the rains wear them 

 into ravines with the greatest facility, forming partial excavations which extend from 

 below upward, and end by forming a vast ravine, into which the lateral rills enter and 

 which are themselves ramified in every direction. At every shower the waters plunge 

 from every part of the mountain into the channels they have worn, producing a torrent 

 that brings down with it masses of rock and scatters them over the plains. When the 

 slopes are wooded, nothing of this kind can happen, for the trees protect the soil from 

 the shock of the flood and by retaining it with their roots they guard it against erosions. 

 They, moreover, break up the waters and hinder them from flowing too rapidly toward 

 the valley, and thus, by this double effect, they oppose an invincible obstacle to the for- 

 mation of these devastating torrents. The most effectual obstacle that can be opposed to 

 these inundations is, therefore, reforesting, and of all preventive measures this is the 

 cheapest, besides offering, above all others, the inestimable advantage of maintaining and 

 of multiplying itself. We need not think that these effects will require a long time to be 

 felt, for it is not necessary to wait until the woods have come to their full size, and in 

 four or five years their efiects will begin to be observed. Every replanting on these slopes 



