1905 



FORESTRY AND IRRIGATION 



313 



basin, but the rock itself from its 

 dense texture and resistant character 

 does not tend to absorb precipitated 

 water but rather to shed it immediate- 

 ly as surface run-off. 



In the bearing of geological condi- 

 tions upon stream flow then, the Wall- 

 will would seem to possess a marked 

 advantage over the Esopus in its deep 

 soil and large area of porous lime- 

 stone. It is, of course, impossible to 

 define closely the limits of such in- 

 fluence. In general, however, it is 

 evident that, as far as the single factor 



hand, the forests have been reduced, 

 in the main to small, scattered wood- 

 lots occupying less than 15 per cent, 

 of the entire basin. If forest cover 

 exerts any real influence in equaliz- 

 ing stream flow, the forested Esopus 

 should in this respect possess a mark- 

 ed advantage over the deforested 

 Wallkill. 



As between these two streams then 

 the question limits itself to whether 

 forest cover on the one hand or mod- 

 erate topography, extensive natural 

 reservoirs, and favorable geological 



The Upper Esopus Basin 



of geology is concerned, the flow of 

 the Wallkill should be more constant 

 and equable than the flow of the 

 Esopus. 



5. The marked difference between 

 these two basins in the extent and uni- 

 formity of forest cover has already 

 been noted. The headwaters of the 

 Esopus and of all of its principal trib- 

 utaries are covered by continuous and 

 unbroken forest, including 85 per cent, 

 of the total catchment area. In the 

 valley of the Wallkill, on the other 



conditions on the other exert the 

 greater relative influence in storing 

 precipitation and equalizing stream 

 discharge. 



This question can be answered by 

 a comparative study of the behavior 

 of the two streams under daily meas- 

 urement. The discharge mcasutv- 

 ments of the two basins, made by the 

 Division of Hydrography of the Geo- 

 logical Survey, were computed by 

 weekly means for the three yrars 

 from 1901 to 1903 inclusive. The 



