296 



INFLUENCE OF WOODLANDS UPON STREAMS. 



its middle and lower portionB, showing that the lowering of the water at Magdeburg 

 cannot be ascribed to the deepening of the channel at that place. 



3. That the high water does not compensate for the decrease in the ilow at mean and 

 low stages. The author proves from the measurements at Sonderheim, and from 

 others extending through 3-2 years at a gauge in the Danube at Alt-Orsova, that there 

 has been a decrease in the depth of water iu that river at all stages. As for variations 

 in the result of observations in other streams, the author accounts for them by show- 

 ing that high water often occurs in the tributaries. 



The following table from the work of Bergbaus shows the difference 

 of level in the Elbe, at Magdeburg, by mouths, on the general average 

 of half- centuries. 



Were these numbers reduced to a diagram, it would be seen that the 

 curve for thej^rs^ half-century would bo above and nearly parallel with 

 that for the second, a maximum appearing in March and a minimum iu 

 September in both cases. The greatest widening apart would be in 

 December, and next to this iu August. 



In consideration of the facts presented, the commission arrived at the 

 conclusion, that tbe decrease in the depth of mean and low stages, is 

 due to a diminution in the amount of water moved annually. This de- 

 crease points to a lessening in the yield of springs, of which, however, 

 he gives other proofs, derived from the diminution of water iu small 

 streams, and in aqueducts and wells. 



Tbe Commission also agreed with the author in the conclusion, that 

 the decrease iu depth of low water in streams from a failure iu the 

 yield of springs and swamps is well founded. The causes of this de- 

 crease are — 



1. A less amount of watery precipitation per annum, from the clearing and grubbing 

 of forests. 



2. An increase in the amount of evaporation from these causes, 



3. Changes of the earth's surface, which, instead of retaining the water that falls 

 and allowing it to penetrate the soil, cause it to flow off rapidly, thus causing high 

 ■water for short periods, often followed by droughts of long duration. 



This subject being also brought before the Eoyal Academy of Sciences 

 at Saint Petersburg, a paper was read January 27, 187G, substantially con- 

 firming the opinions above expressed. The commission (consisting of 

 Messrs. von Helmerseu and Wild), iu the course of this paper remark : 



As a warning example, the author cites Palestine, Persia, Greece, Sicily, and Spain, 

 which countries are suffering in cousequeaco of the devastation of their forests. To 



