CHAPTER II 

 PREPARATORY MAPS AND DATA 



A PROPER treatment of the subject-matter of the last chap- 

 ter, as well as of many other points to come up in the study of 

 sewer design, will depend upon a thorough knowledge of the 

 physical and topographical conditions affecting the work. 

 It is therefore necessary to obtain certain information before 

 a real consideration can be given to the design proper. The 

 first requisite is a map on which to lay down the desired lines 

 of sewers, locate the mains, and determine the possible posi- 

 tion of the outfall or outfalls. This may be an old city map, pro- 

 vided it covers the ground required and is reasonably accurate, 

 more inaccuracy in the map being tolerated if the grades are 

 all good and the location of the outfall practically determined 

 within a short distance. On the other hand, if the ground is 

 generally level and the location of the outfall undetermined, 

 the need for accuracy in the preliminary study of grades is 

 correspondingly increased. This map should be drawn on a 

 scale of from 200 to 400 feet to an inch; and the area covered 

 should be that of the existing town or city, of the region where 

 the outfall may be located, and of all territory which may 

 ultimately be drained into the system; it should also include 

 any high land which may furnish storm-water to drain into a 

 system of storm- water sewers, should they be contemplated.* 

 It is often easiest to collect these data by taking an old map 

 which covers, perhaps, only a part of the territory desired and 

 extending it where necessary by means of new surveys. The 



* In the regulations of the New York State Department of Health, it is 

 specified that the maps and the designs made, shall include all the territory within 

 the boundary lines of the city, whether the proposed construction covers the 

 entire area or not. 



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