10 FORESTS, WOODS, AND TREES 
Russian river in the plain and the American rivers in the 
mountains. Oppokov’s conclusions are as follows: The 
flow of the Dnieper is closely related to the amount of 
rainfall in the whole basin. Rainfall and evaporation are 
the most important factors influencing the level of the 
river. The influence of woods and also of peat-bogs has 
been greatly over-estimated. He even believes that a 
considerable amount of vegetation in a river basin may 
lower the level of a river owing to the amount of evapora- 
tion set up, and says that the best conservers of water are 
not peat-bogs or forests, but beds of sandstone. 
Mr. Cecil H. Roberts, C.E., has made investigations on 
the climate and physical features of the basin of the river 
Dee, in connection with proposals for the extension of the 
Aberdeen Waterworks. These investigations are described 
in a paper as yet unpublished. Mr. Roberts has not been 
able to trace any influence either of forests or of the felling 
of large areas of wood on the maximum or minimum flows 
of the river (10). 
As the results of observation are capable of varied 
interpretation, it is of interest to record that the influence 
of forests on stream-flow is now being experimentally 
studied (11). This important experiment, which will 
probably settle the question, was inaugurated in 1910 in 
the Rio Grande National Forest in the Rocky Mountains of 
Colorado. This experiment involves the careful measure- 
ment for a number of years of two streams flowing out of 
two well-wooded watersheds; and later a comparison of 
the flow of these streams after the forest cover has been 
removed from one of the watersheds. Dams, weirs, and 
recording instruments for measuring the flow of the streams 
have been installed, as well as instruments for measuring 
temperature, rainfall, evaporation, humidity, and other 
atmospheric factors that may affect the flow. All outside 
factors will be eliminated; and the records at the end of 
ten or twenty years are expected to throw much light on 
the relation of the forests on mountain watersheds to the 
flow of the mountain streams. 
