24 EAINFALL AND FLOODS. 



it seems to me) be without practical advantage. And when 

 the question is asked (as it sometimes is asked), Avhat pro- 

 portionate deduction for absorption should be made from 

 the total rainfall as the first step in calculating its effect 

 upon the river? I am disposed to reply, that if at the com- 

 mencement of the rainfall the soil and strata were in an 

 average state of moisture, then the whole of the rainfall 

 (or an equivalent quantity of water) would be sooner or later 

 discharged by the river ; if the soil and strata were below 

 their average state of moisture, the discharge would be less 

 than the total rainfall by the proportion which would suffice 

 to supply what was wanting in the soil and strata ; if, on the 

 other hand, the soil and strata held at the commencement of 

 the rainfall more than their average amount of water, then 

 the total extra discharge by the river which would follow 

 the rainfall would be equal to the total amount of the rain- 

 fall plus the superabundant moisture of the soil and strata. 

 In other words, the extra discharge following a particular 

 rainfall will be equal to the rainfall, less than the rainfall, 

 or more than the rainfall, according to the previous con- 

 dition of the soil and subjacent strata in regard of mois- 

 ture. 



I very much doubt whether the question admits of a more 

 precise general answer than this, nor do I believe that in any 

 particular case the attempt to express numerically the ad- 

 dition or the deduction that should be applied to the total 

 rainfall in consideration of the previous state of the soil 

 and strata would be otherwise than vain. Further, I am 

 disposed to maintain that if in any particular case the 

 question I have asked could be answered precisely, nothing 

 would be gained. The question of the occurrence of a flood 

 will have been determined one way or the other long before 

 the whole effect of the rainfall upon the river has passed 



