REPORT ON FORESTS. 155 



In this table, wherever the flood has been held back by stor- 

 age reservoirs, the maximum rate of flow is taken to be that of 

 that portion of the catchment not affected by such holding back. 

 Such correction has been made on the Pompton for the storage 

 reservoirs of the East Jersey Water Company and for Green- 

 wood lake, but several other natural lakes upon the catchment 

 have not been allowed for, so that the maximum rate for the 

 Pompton is undoubtedly still reduced by these other lakes. 

 The maximum rate on the Pequannock is taken to pertain only 

 to the portion of the catchment below the East Jersey storage 

 reservoirs. For the Wanaque the catchment has been reduced 

 by throwing out the part controlled by Greenwood lake, 

 although nothing is allowed for Sterling lake. The Musconet- 

 cong maximum is also corrected by throwing out the portions of 

 catchment controlled by lake Hopatcong and Stanhope reservoir. 

 The maximum rates of discharge here given are consequently 

 sufficiently accurate to admit of comparison. The table is con- 

 venient for ready reference and general comparison, but without 

 allowing for local peculiarities no useful lesson can be learned 

 from it as to the effect of forests upon flood-flow. The maxi- 

 munijrale of discharge measured in this way is effected by purely ] 

 local conditions, mainly by the shape of the valley at the point ' 

 where the measurement is taken. The velocity of discharge 

 down the valley is determined by the depth of the water and the 

 slope of the valley above the point of gauging. It is also affected 

 to a less degree by the capacity and slope of all the valleys of the 

 catchment. Where these are flat, so that the water can spread, 

 no great depth can be attained, and the rate of discharge is 

 consequently lower. The retarding effect of forests, if any exist, 

 would be better shown by the rate at which the water comes in 

 to the valleys from the surrounding slopes. Thus, on the Rari- 

 tan, we determine by taking the accumulation of water between 

 the dam below Bound Brook and the mouth of the Millstone, 

 that for six hours the water was discharged into this portion of 

 the valley at a rate which averaged almost as high as the maxi- 

 mum recorded for a short time at the dam, and from this we 

 must infer that the maximum rate of discharge into the valley 

 above the dam was much higher. On two water-sheds exactly 

 similar in topography, the rate of discharge will be greater as 



