FLOOD SILT OF THE HUNTER AND HAWKESBURY RIVERS. 195 



later paper by one of the authors, 1 and (2) the modern flood 

 loams and sands, with coarse river gravels. There is also 

 a development of an older coarse river gravel probably of 

 Tertiary age, like that seen between Windsor and Richmond 

 and in the railway cutting east of St. Mary's, and also near 

 Lapstone Hill between Glenbrook and Emu Plains. 



IV. — Volume of Flood Water. 

 The flood quantities for the flood' water of the Hunter 

 Delta have been estimated at 150,000 cubic feet per second 

 above the Paterson, 171,000 cubic feet below the Paterson 

 and above the Williams, and 193,000 cubic feet below the 

 Williams. 2 Mr. R. T. McKay has kindly called our attention 

 to a difficulty in accepting Mr. O. Napier Bell's estimates. 

 If the discharge of the Hunter River when in full flood 

 below the junction of the Williams River be 193,000 cubic 

 feet per second, this amounts to over 11 \ million cubic feet 

 per minute, and the water is derived from a drainage area 

 of 9,127 square miles. Now the big flood in the Murray in 

 1870, coming from a drainage area of about 200,000 square 

 miles discharged at Mildura only about 6 million cubic feet 

 per minute, and it is probable that even this estimate is 

 too high. 3 In 1890 the Murray River when in flood was 

 discharging at Morgan, at the rate of 4 million cubic feet 

 per minute. These figures are fairly correct. This water 

 came from an area of, in round numbers, 400,000 square 

 miles. Is it therefore likely, that even after allowance is 

 made for the greater relative evaporation and percolation 

 of rainfall in the Darling-Murray basin, as compared with 

 the Hunter basin, that the Hunter River with less than ^V 

 of catchment area, should discharge nearly three times as 



1 On an important Geological Fault at the Kurrajong Heights, Journ. 

 Roy. Soc. N.S. Wales, Vol. xxxvi., p. 359, pis. 16, 17. 



8 Report by C. Napier Bell, M. Inst. C.E., op. cit., pp. 20, 21. 



3 The Murray River Irrigation and Navigation, by Robert T. McKay, 

 Sydney University Engineering Society, 1903, pp. 25, 26. 



