Floods on the River Barwon. 83 



been instituted and all facts carefully compared, that an 

 engineer is justified in feeling sure that he has proper data 

 to work upon. At sudden contractions, sharp bends, and 

 wherever obstructions occur in the stream, single flood- 

 marks should be accepted with caution. It will be seen 

 further on that much discretion is required in making use of 

 levels obtained at such places. 



3. Two or more series of levels were taken to ascertain 

 the relative heights of various points.- The datum to which 

 all these have been reduced is mean low-water level of 

 Hobson's Bay, obtained through the railway engineers, it is 

 understood. Several cross-sections of the river were also 

 taken at suitable points. Without these cross-sections, 

 calculations of the quantities of water and velocities at 

 various places could not have been made, nor could the 

 action of the flood have been properly investigated. The 

 omission of this part of the inquiry by some engineers has 

 led to erroneous views having been put forward as to the 

 action of the flood. Some of the data on which calcula- 

 tions have been based are, for convenience, given in a tabular 

 form in an appendix to this paper. The main results of the 

 calculations made by the author are shown in the accom- 

 panying diagram, forming a longitudinal section of the 

 portion of the river where the action of the floods has been 

 complicated by the two embankments formed since the 

 great flood of 1852. The upper embankment is the Colac- 

 road causeway, forming the approaches to the iron bridge, 

 also known as the Moorabool-street bridge. The other, a 

 mile and a-half lower down the river, is the railway embank- 

 ment, which was formed about the year 1875. 



4. The author is greatly indebted to Mr. T. B. Muntz, city 

 surveyor of Prahran and a member of this Society, for per- 

 mission to make use of the cross-sections and of the levels, 

 and much other information collected and arranged by him : 

 also for the loan of a plan* of the river showing the course of 

 the flood of 1880. The author has also to acknowledge the 

 receipt of much valuable information from Mr. Robert 

 Watson, the Avell-known railway engineer; and from Mr. W. 

 C. Kernot, of the University. 



5. The catchment basin of the River Barwon, with its 

 tributaries — the Moorabool, Yarrowee (or Leigh), and several 

 small creeks — is estimated to have an area of about 1500 



* The plan has not been printed. 



