RIVERS OF NEW SOUTH WALES. 395 



Creeks re-form at the opposite side of Brookong Plain, the former 

 at the phice where it flows into Lake CuUivel, and the latter at the 

 point where it joins Urana Creek. 



As already pointed out, the coastal rivers of New South Wales 

 differ in an important degree from those of the interior, in their 

 silt-carrying capabilities. A brief examination of the nature of 

 the catchment areas on the opposite sides of the Dividing Range 

 is suflicient to aftbrd an explanation of this fact. Between the 

 coast line and the summit of the Dividing Range is inclosed an 

 area of 50,000 square miles. As the length along the coast from 

 the border of Victoria to that of Queensland is nearly seven hun- 

 dred miles, the mean distance from the coast to the summit of 

 the Dividing Range is little over seventy-one miles. On the 

 other hand, the distance measured along the centre of the valley 

 of the Murrumbidgee from the source of its head waters to its 

 confluence with the Murray, is three hundred and ninety miles ; 

 and the corresponding distance in the case of the Lachlan 

 three hundred and eighty-two miles ; while the distance from the 

 source of the Macquarie to the point were that river is lost in the 

 Marshes is about two hundred and forty-two miles, and to the 

 Darling three hundred miles. Measured in the same way, that is 

 taking the general direction of the river while avoiding its wind- 

 ings, the extreme length of the course of the Hunter is about 

 one hundred and forty miles, and the corresponding lengths for 

 the Clarence and Hawkesbury, each about one hundred and thirty 

 miles. These figures place in a clear light the high rates of fall 

 on the coast river basins as compared with those on the western 

 basins. That the average I'ate of fall of the former is absolutely, 

 as well as relatively great, is apparent when we consider that the 

 height of the Dividing Range varies generally from 2,300 to 

 5,0U0 feet ; so that a straight line drawn from the summit to the 

 coast would have, on an average, a slope of about fifty feet per 

 mile. In reality almost the whole of the descent is accomplished 

 in a comparati\'ely short length of the river. The natural conse- 

 quence of this, is that when the foot of the mountains is reached 

 and the velocity of the rivers is suddenly checked, a remarkable 

 rise of the surface level occurs during floods and frequently 

 results in the inundation of the alluvial lands. Whilst this great 

 rise of the surface level at the points where the rivers emerge from 

 the hills generally represents the heaping up of the waters conse- 

 quent on the sudden dimunition of tiie rate of fall, it is often due 

 in an important degree to the narrowness of the channels where 

 these points are reached. In the instance of the Clarence at 

 Copmanhurst, the great erosive power of the current at that place 

 has resulted in the formation of a deep and narrow chaniiel ; so 

 that when floods occur, their discharge is obstructed both by the 

 diminution of tlie rate of fall and by the comparatively small 

 section of the channel. Owino: to these causes the rise of tlie 



