624 PROCEEDINGS OP SECTION J, 



waters reach, in a comparatively short distance, a level very little 

 above tliat of the sea. Tlie sides of these gorges are thickly 

 covered with timber. 



From Pheasant's Nest, which is a gorge of the character above 

 described, just below the junction of the Cordeaux with the ISTepean, 

 the waters of the united streams are held back and raised to a 

 height of 439.5 feet above the sea level by means of a dam about 

 ten feet high, which is constructed across the Nepean. 



The Nepean Tunnel which unites the waters of the rivers 

 referred to with those of the Catai^act River, commences at the 

 dam, with an invert level of four hundred and thirty feet above 

 the sea. It is 23,507.25 feet long, nine and a-half feet wide and 

 seven and a-half feet high, driven through the sandstone rock and 

 inclined on a gradient of two and a-half feet per mile, having a 

 discharging capacity of ninety-seven millions of gallons daily. 



At Broughton's Pass another similar dam is constructed, about 

 twelve feet in height, across the Cataract River, by means of 

 which the combined waters of the Nepean, Cordeaux, and Cataract 

 are raised to a level of four hundred and twenty-six feet above 

 the sea, and are then conveyed by the Cataract Tunnel, which 

 commences with an invert level of four hundred and sixteen feet 

 above the sea, being a drop of about two feet below the invert 

 level of the Nej)ean Tunnel at this point ; it is 9,724.33 feet long, 

 ten and a-half feet wide, and eight and a-half feet high, driven 

 through the sandstone rock on a grade of three and a-half feet 

 per mile, and having a discharging capacity of one hundred and 

 tifty-live millions of gallons per day. 



On leaving the Cataract Tunnel, the outlet of which is a little 

 over six and a-quarter miles from the Pheasant's Nest, the water 

 is conveyed for several miles through very rugged country, inter- 

 sected by deep creeks. 



From the mouth of the tunnel, and for a lengths of 1,133 

 feet, the three and a-half feet per mile gradient is continued, the 

 canal being cut out of the rock and having a width of nine feet, 

 it then gradually widens to twelve and a-half feet, with vertical 

 sides, and a fall of twenty-one inches per mile, the depth of 

 water being eight feet when runming full. 



In excavating the canal over this portion and for some distance 

 on, where the formation is sandstone, every endeavour was made 

 to save the rock in places where it appeared that lining could be 

 dispensed with. When it became necessary to protect the sides 

 the lining is composed for the most part of dry rubble masonry, 

 in places where the cutting was shallow, or the ground very bad, 

 walls of concrete or of rubble in cement were built. 



The creeks are spanned by large wrous;ht-iron pipes or syphons, 

 on stone piers or bearers, with concrete abutments. 



