i6o GEOLOGICAL SURVEY OF NEW JERSEY. 



We have investigated also the lowest reported heights of the 

 Delaware since 1831, and these seem to indicate that the least 

 flow was recorded in September, 1881, but this is accounted for 

 by the fact that the droughts occurring in 1880 and 1881 were 

 the severest of which we have any record in the rain-fall during 

 this period, but we are disposed to think that the evidence 

 points to a greater prevalence of low stages during the last half 

 of the century. 



EFFECT IN EQUALIZING THE DISCHARGE OF STREAMS. 



In the foregoing we have spoken of the extreme stages of the 

 rivers, and we have called attention to these because it may be 

 attempted to show from such records the effect of forests. Our 

 experience is that this cannot be done, but that the real benefit 

 appears in the shorter periods of low water and the smaller 

 number of floods. This is an effect of greater economic value, 

 because the extreme stages are not of frequent occurrence. 

 Thus on the Passaic river, during seventeen years, a rate of 24 

 cubic feet per second per square mile was reached only once 

 and lasted only about three hours, while the lowest rate of flow 

 of .19 cubic feet per second per square mile was reached only 

 two or three times for a few days in each case, whereas the 

 stream stood at stages between .4 and 1.34 cubic feet per second 

 per square mile an average of 112 days yearly, and between 1.34 

 and 3.35 cubic feet also an average of 112 days during each year. 

 It is evident, therefore, that what would be really of importance 

 on the Passaic would be a cause affecting these stages of the 

 river. It is in those stages which prevail during six months of 

 an ordinary dry period that we believe the benefits are most felt. 

 The soil and sub-soil of a catchment hold in storage a large 

 amount of water, which is fed out to the streams in the form of 

 springs and seepage during dry periods. It is a matter of com- 

 mon observation that at such times rivers continue to flow when 

 the rain-fall is very much less than the evaporation, and, indeed, 

 for many days when there is no rain-fall at all. Anything 

 which tends to increase this amount of water held in the ground, 

 and to regulate its discharge to the streams, tends to give a 

 larger dry-season flow and to shorten the periods of very low 



