HISTORY OF CIVIL ENGINEERING IN NEW SOUTH WALKS. G41 



brick arch were then carefully filled and pointed from the inside, 

 and the invert bricks were taken up and I'elaid to the correct 

 level after <;routina: tlie crack in the concrete. Two courses of 

 bricks were then taken out along the springing level and relaid in 

 short lengtlis, and this portion of the sewer rendered afresh. No 

 further settlement occurred, and the repairs carried out make this 

 portion of the sewer as strong as any other. 



One of the pumping engines employed was a twenty-five horse- 

 power one, which also worked a stone-breaker and a saw-mill. 

 Two ten horse-power and one sixteen horse-power winding engines 

 were used at the rock tunnel shafts, and steam winches were used 

 at the sand-tunnel mouths for hoisting purposes, and there were 

 ten miles of tramline laid in connection with the work. At two 

 hundred feet from the cliffs in the line of the sewer a shaft was 

 sunk about thirteen feet by six feet in plan. The invert level of 

 the sewer at this shaft is six feet above high water. From the 

 eastern or sea end of the shaft a heading was driven out thi-ough 

 the clifi" in a direct line with the sewer, and the action of the 

 waves watched for a considerable period before designing the 

 outlet work. The conditions to be met as regards the action of 

 the waves are indicated in the following extracts from the final 

 report of the board before referred to: — "During southei'ly, south- 

 easterly or eastei'ly gales the waves on the coast attain enormous 

 magnitude and strike the coast line and the clifls with extra- 

 ordinary force." "No person who has not actually 



witnessed it can form an idea of the magnitude of the waves 

 which roll on this coast, or of the overwhelming force with which 

 they strike the cliffs in heavy storms." After that careful con- 

 sideration of the subject which its importance demanded, the 

 outlet work was designed and executed. A large chamber was 

 excavated at the bottom of the shaft beforementioned, the finished 

 inside dimensions of which are thirty-two feet in line of sewer, 

 eighteen feet across line of sewer, and twenty-five feet in height. 

 The floor of this chamber at the middle of its length is two feet 

 three inches above high-water level. From tlie eastern or down- 

 stream end of the chamber there are two circular outlet channels of 

 four feet diameter, with a fall of one in thirty -nine. One of these 

 outfall channels is in a direct line with the main sewer, and the other 

 channel is driven in a straight line from the north-east corner of 

 the chamber, making an angle of 31° with the former. Midway 

 in the chamber and at right angles to the line of the sewer 

 there is a massive weir curved in plan on the downstream face, 

 and supported on the upstream face by the back of a massive 

 tongue or cut-water, and at either end of the weir there is a four 

 feet diameter circular opening, the bottom of which is at the floor 

 level. The sewage from the main sewer enters the chamber on an 

 ogee fall of three feet six inches, is diverted by the cut-water into 

 two channels passing round the sides of the chamber in suitable 

 Pi 



