THE EFFECT OF FOREST COVER 

 UPON STREAM FLOW 



PART II. 



A STUDY OF DRAINAGE CONDITIONS IN THE CATSKILL MOUNTAINS 



BY 



W. B. GREELEY 



Forest Assistant, U. S. Forest Service 



I N the preceeding paper upon this 

 * general subject 1 it was strongly 

 emphasized that forest cover must not 

 be considered as an independent or 

 isolated factor in its bearing upon 

 stream flow ; that it is rather but one 

 of a number of far reaching, inter- 

 related factors whose combined in- 

 fluence makes a stream's discharge 

 regular or irregular; and that before 

 any influence can justly be attributed 

 to the forested or denuded character 

 of a drainage basin the bearing of 

 all of these other factors, precipita- 

 tion, topography, geological condi- 

 tions, must be carefully weighed. An 

 attempt to approach the question in 

 this manner was made by the writer 

 in a study of two small tributaries 

 of the Hudson, Esopus Creek and 

 Wallkill River, under the direction of 

 Mr. Newell, of the Reclamation Ser- 

 vice. With the object of getting at 

 the influence of all the factors which 

 affect stream flow, a detailed com- 

 parison of the two drainage basins 

 was made, covering the following 

 points : 



1. Precipitation, by weekly means. 



2. Prevailing temperatures, by sea- 

 sonal and annual means. 



3. Topography. 



4. Geological conditions. 



5- The extent of forest cover and 

 general forest conditions. 



6. The character of flow of the two 

 streams as shown by continuous dis- 

 charge measurements made by the 

 Division of Hydrography of the Geo- 

 logical Survey. 



These two catchment areas were 

 chosen for the study because they dif- 

 fer widely in the extent and density 

 of their forest cover. Esopus Creek 

 is well timbered, with not more than 

 15 per cent, of cleared land upon its 

 entire basin. In the basin of the Wall- 

 kill, on the other hand, fully 85 per 

 cent, of the land is cleared and under 

 tillage, the remaining forest cover be- 

 ing confined to small, scattered wood- 

 lots. The object of the detailed com- 

 parison of the two streams, then, in 

 the various respects noted above, was 

 to determine first, as closely as pos- 

 sible, the probable effect of all the 

 other factors, geology, topography, 

 temperature, and rainfall, upon reg- 

 ularity of stream flow. Then, by di- 

 rectly comparing the flow of the two 

 streams under daily measurement in 

 the light of such influence, we should 

 be able to judge whether or not the 

 marked difference in the forested con- 

 dition of the two basins has any ef- 

 fect upon stream discharge. 



The results of this comparative 

 study may be summarized briefly. 



i. With regard to precipitation, 

 practically no difference exists be- 

 tween these two drainage basins, 

 either in total amount or in regular- 

 it}' of distribution throughout the 

 year. As shown by records of the 

 Ignited States Weather Bureau, the 

 mean weekly precipitation upon the 

 KSOJHIS basin for the period of three 

 years covered in this study is one inch, 

 and upon the Wnllkill basin .<)J inches. 

 In each case the average deviation 



I The Effect of Forest Cover Upon Stream Flow, Part I, Grneral Factors Governing 

 Stream Flow, FORESTRY AND IRRIGATION for June. 1905. 



