FLOOD SILT OF THE HUNTER AND HAWKESBURY RIVERS. 201 



The construction of levees, which except in cases of very 

 high floods restrict the area covered by the flood water 

 very considerably, further complicates the question of 

 estimating the amount of silt deposited by each flood. 



It is interesting to note that as there are 2*463 parts per 

 1000 of solid residue in the flood water of the Hunter, and 

 its specific gravity is assumed to be about 2*, this would 

 obviously prove that if all this residue were deposited from 

 a sheet of water 10 feet in depth, it would yield '0123 foot 

 in thickness of silt, or in round numbers '15 inches. At 

 this rate as much of the Hunter Delta silt is at least 30 

 feet thick, this would have taken 2,400 years to form on the 

 assumption that there is a flood every year. If the aver- 

 age be taken at one flood every five years the time for the 

 delta formation would be extended to 12,000 years. This 

 is probably less than the actual time needed, and is less 

 than the 30,000 years assumed as necessary for the forma- 

 tion of the delta of the Nile. It serves, however, to show 

 something of the order of the time needed for the building 

 of a delta like that of the Hunter. 1 



Appendix. — The following letter from Mr. R. Bailey to 

 Mr. J. Hall, dated on October 28th, 1904, at the "Mercury 

 Office," West Maitland, and read to the Society when our 

 paper was being discussed, by Mr. J. Hall is of such interest, 

 on the economic side of the question, that by Mr. Hall's 

 kind permission we quote it in full : — 



" In reply to yours re floods in the Hunter, I beg to state that 

 having questioned a number of farmers in the district on the 

 matter, they are unanimously against floods despite the value of 



1 If Mr. Gordon's estimate of 24,500 millions of cubic feet of flood water 

 be assumed to be the correct amount for the flood water over and above 

 what would be discharged by the river while flowing between its banks, 

 the weight of the silt brought down by it would be over 1% millions of 

 tons, and over 5 millions of tons on Mr. Moriarty's flood estimates, viz., 

 88,000 millions of cubic feet of water. 



