XLIV. J. I. HAYCROPT. 



zero, increasing to a maximum, providing the rainfall is constant 

 and of sufficient duration to permit the water from the farthest 

 point to reach the outlet, whilst it continues. As long as the 

 rain continues, and the absorption is supposed constant, the 

 volume at the outlet will be constant, and a maximum. When, 

 however, in this case the rain does not continue sufficiently long 

 for the water from the farthest point to reach the outlet, whilst 

 it still rains, the maximum quantity will not be experienced. 



When the slope of a catchment is not uniform, suppose a case 

 where a railway runs practically parallel to a hilly range : the 

 upper portion of such a catchment would be steeper than the 

 lower portion, and the water would run off quicker from such 

 steeper portions, thereby increasing the volume on the natter 

 portion, so that in such a case the maximum quantity might 

 arrive at the outlet, though the rain did not continue to fall 

 whilst the water from the farthest part of the catchment was 

 travelling thereto. 



The consideration of this question, from a theoretic point of 

 view, as dealt with in the Encyclojiedia Brittannica, would lead 

 one to believe that the maximum flood at the outlet of a catchment 

 will be continued when the rain continues long enough for the 

 waters from the farthest point to reach the outlet while it still 

 rains. This maximum volume will be the product of the number 

 of acres in the catchment, by the rainfall in inches per hour, by 

 the coefficient of run off. This is no doubt true as an abstract 

 fact, and can be demonstrated mathematically on a suitably 

 shaped catchment, but if the fetch of a catchment be so great, 

 that no rainfall of such duration can be experienced, the slopes 

 thereon are of the utmost importance, as may be seen on con- 

 sideration of two catchments, one, " A," : of uniform slope through- 

 out its length, and another, " B," of gradually increasing slope 

 from its outlet to its farthest point. If the fetch and nature of 

 soil in both cases be equal and similar, " A " may never 

 experience the maximum volume, whilst " B " would probably 

 do so, both being subjected to a rainfall of equal intensity, but 

 the duration of which would not be sufficiently long to permit 



