* 



AND PROTECTION OF AGRICULTURAL LAND. 15 



between 5 o'clock on the morning of the 4th and 5 o'clock on 

 the morning of the 5th of August. Various formulae have been 

 suggested for calculating the flood discharge due to a given area 

 of land, but the information as to the amount of flood water said 



have been discharged from different districts of country is so 

 discordant, due no doubt to the varied physical conditions above 

 noticed, that it seems to me to be impossible with elements so 

 variable to found any formula that can be generally useful. 



It may not be uninteresting to state, however, that the quan- 

 tity of water passing off during high floods is variously given 

 by different authorities at from 1 foot to nearly 100 cubic feet 

 per minute per acre for the districts in which the observations 

 were made. The highest gauging I have ever got was ] 5 cubic 

 feet per minute per acre from a town district of 630 acres, 

 after three days of nearly continuous rainfall. Thunderstorms, 

 however, discharge a very much greater amount during their 

 short duration, and it is stated that, in August 1846, during 

 a thunderstorm in London, 3'3 inches fell in two hours and 

 twenty minutes, being 85 cubic feet per minute per acre. I 

 think that, with our present information, the only general 

 result to be gathered from records of floods is, that the flood 

 discharge bears a higher ratio to the ordinary discharge in small 



n in large rivers. This is due to the fact that in a small 

 iver a rainfall may affect and swell every one of its drains 



d feeders at the same time, whereas, in a larger river the 



infall may be confined to one district only, and thus the 

 flooding is modified in its amount. It follows, therefore, that 

 the smaller streams or burns intersecting a property at a place- 

 far removed, it may be, from the main stream, may, especially 



