THE INFLUENCE OF FORESTS ON CLIMATE AND FLOODS 235 



the cultivated surfaces, until the rain rushes 

 down the hillsides in destructive torrents, 

 gullying the ground and choking the minor 

 lines of drainage with rocks, sand, and gravel, 

 and hurrying into the recipient of the water- 

 shed volumes of water which before reached 

 it in a comparatively quiet flow. 



Colonel Torrelli affirms as the result of 

 careful observations that four-fifths of the 

 precipitation in forests is absorbed by the 

 soil or detained by the surface of the 

 ground, to be gradually given up in springs 

 and gentle rills, and only one-fifth of the 

 precipitation is delivered to the rivers rap- 

 idly enough to create floods. Upon the same 

 slopes and surfaces denuded of their forests, 

 the proportions are reversed. 



That the destruction of the forests in 

 mountainous watersheds is follozued by dis- 

 astrous floods where previously such Hoods 

 were unknozvn is not a matter of theory, 

 opinion, or probability, but it is a well- 

 established physical fact. 



* * * The method of prevention by the 

 maintenance and planting of forests upon the 

 headwaters and upper slopes of the affluents 

 of the basin depends for its efficiency upon 

 the ability of forest-covered slopes to retain 

 for a considerable time a large percentage 

 of heavy rainfall, thereby preventing the sur- 

 charge of the lines of drainage. In France, 

 Italy, Germany, and Austria the systematic 

 planting of mountain slopes as a means of 

 restoring lost fertility and preventing the 

 inundations follozving the destruction of 

 forests, is an established fact follozved by 

 results more satisfactory than the most san- 

 guine anticipations." 



*The following information with reference 

 to the deforesting of the watershed of the 

 West Branch of the Susquehanna was re- 

 ceived after the completion of this report : 



Ltimbering operations were commenced in 

 this region in 1850, but no systematic record 

 of the amounts cut was kept until 1862. In 

 the latter year the cut was 38,000,000 feet 

 board-measure. It rapidly increased until it 

 attained its maximum of 319,000,000 feet in 

 1873, ar >d then fell to about 212,000,000 feet 

 in 1890. The total amount cut since 1862 is 

 about 5,250,000,000 feet board-measure, which 

 represents about 30,100,000 logs. 



In the year 1880 the timber on nearly 

 700,000 acres of land in Pennsylvania was 

 destroyed by fire. 



The above statements are based on the 

 census report for 1880, and on information 

 furnished by Mr. George S. Banger, Secre- 

 tary of the Susquehanna Boom Company. 



There is at least one officer of the 

 United States Corps of Engineers who 

 is acquainted with the teachings of ex- 

 perience. 



Colonel Chittenden himself, the of- 

 ficer who has most recently written on 

 the subject, apparently believes that the 

 sediment carried by the Mississippi 

 River into the Gulf of Mexico comes 

 entirely from the mountain areas at 

 the sources of the tributaries, for he 

 says : 



"It must be clear from the foregoing that 

 the bottom-lands of the Missouri add nothing 

 whatever to the total quantity of sediment 

 that passes out of the mouth of the stream, 

 for these bottoms have been increasing 

 rather than diminishing in quantity. Like- 

 wise, the Mississippi bottoms contribute noth- 

 ing to the volume of sediment that is car- 

 ried into the Gulf of Mexico. It all comes 

 from the uplands far and near, but principally 

 from the more remote and hilly regions. This 

 load is in the nature of through traffic. The 

 local freight picked up from a caving bank 

 is mostly discharged at the next station. It 

 follows, therefore, that if the banks of these 

 streams were revetted from the Gulf to 

 Pittsburg, the Falls of St. Anthony, and the 

 mouth of the Yellowstone, the quantity of 

 sediment passing into the Gulf would not be 

 diminished a particle." 



In my previous discussion of Colonel 

 Chittenden's paper, I have shown, I 

 think, the incorrectness of this state- 

 ment. Any sediment washed into a 

 river, whether from the uplands or 

 from the banks in the lower portions, 

 is gradually carried downstream and 

 adds to the total volume of earthy mat- 

 ter that is being transported or moved 

 by successive floods. But the point is, 

 as indicated in the extract from Major 

 Suters report (and this is perhaps what 

 Colonel Chittenden means) that unless 

 the influx of the earthy material from 

 the uplands and mountain slopes above 

 the navigable portions is prevented, the 

 protection of the banks along the lower 

 navigable portions will not be sufficient 

 to maintain, the navigation, because the 

 channel will be gradually filled up by 

 this sediment coming from above. As 

 Major Suter says: "The influx of ma- 

 terial from above must first be stopped." 



