8 DIMINISHED FLOW OF ROCK RIVFE. 



While the changes thus far observed in the flow of the Rock River 

 appear not to have been so great as to cause serious apprehension, the 

 interests affected are sufficiently important to give to the question of 

 the conditions on which the river flow depends and the possible means 

 of preventing further decrease a decided local significance. It was 

 in consequence of an expressed desire on the part of citizens of the 

 parts of Wisconsin and Illinois involved that the investigation of this 

 question was originally undertaken by the Bureau of Forestry. 



The special problem in stream flow presented by the Rock River 

 watershed is rather simple in character, and the main facts can be 

 compassed in a brief report. But in view of the general interest that 

 attaches to the subject of water flow, that part of the report dealing 

 with the influence of the forest cover has been extended so as to include 

 certain suggestive results of recent observations made in Europe. In 

 the light of the facts thus established it is also possible to draw more 

 deflnite conclusions than could be arrived at by any study of local 

 conditions which it was practicable to make. 



The writer wishes to express his obligations to the following gentle- 

 men who have rendered assistance in this investigation: The Hon. 

 R. R. Hitt. Representative in Congress for the Ninth district of Illi- 

 nois, at whose request the investigation was undertaken; Prof. Thomas 

 C. Chamberlin. of the University of Chicago, and Prof. C. R. Yan 

 Hise and Mr. C. K. Leith. of the University of Wisconsin. 



SUMMARY. 



The results of this study may be summarized as follows: 



The geological formation and topography of the Rock River water- 

 shed are favorable to a sustained water supply. 



Since the settlement of the region the forests have been much 

 reduced in area, while the conditions of growth in those that remain 

 have changed for the worse. Cultivated land and woodlots have been 

 largely converted to pasturage, thus interfering with the waterflow. 

 In some districts the swamps and fields have been artificially drained. 



Since 1SS5 the rainfall has decreased. This loss has probably lessened 

 slightly the volume of the river'flow. The fluctuations in the flow, 

 however, have been caused by artificial drainage and by changes in 

 the forest conditions of the region. Of these the latter is probably 

 the more important cause. 



Forests diminish the loss of water by evaporation from the ground. 

 At Nancy. France, it has been found that in the summer months five 

 times as much water is evaporated outside of the forest as within it. 

 Against this must be set off the slight loss of water which is inter- 

 cepted in falling by the leaves of the trees and evaporated without 

 ever reaching the ground, and the consumption of water by the trees 



