EAINFALL AND FLOODS. 33 



no evidence that these rains were followed by more de- 

 structive floods than those which I have selected ; while 

 the general testimony of the time with reference to the 

 floods of 1882 and 1889 is to the effect that each of these 

 in its turn was the highest that had ever been known. 

 This consideration alone would suffice to justify my selec- 

 tion, even if we were nnable to see any reason why the 

 exceptional rains I have referred to should be differently 

 treated, But I think it is not difficult to discover several 

 reasons why such rains do not produce effects in proportion 

 to their violence. I will name a few which occur to me. 



1. Such rains can scarcely occur but in connection with 

 summer thunderstorms, when the soil and subjacent strata 

 are likely to be in a specially receptive condition. 



2. The time occupied in percolation will be equivalent 

 to a material prolongation of the duration of the rain, the 

 proportional prolongation being greater as the actual dura- 

 tion is less. 



3. Such rains are always very local, and are not likely 

 to be co-extensive with the area of even so small a river 

 basin as that of the Frome. 



4. The amount of flood in Bristol must be limited by the 

 carrying capacity of the river Frome in its upper reaches, 

 and the greater the overflow of these, the greater is the 

 relief to Bristol. 



To conclude, if I am not going beyond my province in 

 pointing the moral of my story, I would say that to my 

 mind it suggests the expediency of waiting =until we see 

 the full effect of the improvements which have been made, 

 or are being made, in the channel of the Frome, before 

 plunging into costly undertakings, the supposed necessity 

 of which is based upon calculations that are at least open 

 to question. 



D 



