14 SEWER DESIGN 



old map must always be regarded with suspicion, however, 

 and its accuracy questioned until proved. Since it will in no 

 case be possible to scale horizontal distances from such a map 

 with sufficient exactness for the statement of the lengths of 

 pipe required for the proposal of the bidders, it is better to 

 chain the lengths of all the streets, and for the preliminary 

 study of grades use the true distances. These distances can be 

 recorded at the street intersections, as stations starting from the 

 centre of some street assumed as zero, and then the profiles 

 which are made will require no correction, and the first state- 

 ment of quantities made will be true until the pipe is laid in 

 the ground. This map will show (see Plate I) the location of 

 the lines of pipe, their sizes and grades, and the location and 

 character of the outfall. The sizes and grades are generally 



marked by figures, thus: , indicating a 1 2-inch pipe on a 



.6 per cent grade, or a grade of .6 feet in a hundred feet. It 

 has been suggested that the size of the pipes might be expressed 

 by the thickness of broken lines, making the width of the lines 

 in inches equal the diameter of the pipe in feet, and the length 

 of the dash five times the diameter of the pipe, the spaces between 

 the dashes being the length of the dash, all being drawn to the 

 scale of the map. The advantage claimed is that on a map 

 reduced by photography, or otherwise, the sizes can be read 

 in this way when figures would be illegible. (Proc. Phila. 

 Engrs, Vol. XII, p. 105). 



If no plans are available, a survey must be made on which 

 the preliminary studies can be based. A most economical 

 and satisfactory method of collecting approximate data is 

 described by J. H. Fuertes in the Transactions of the American 

 Society of Civil Engineers * as practised by him in connec- 

 tion with investigations made of the New York water supplies 

 and in a survey for a report on an improved sewerage system 

 for Harrisburg, Pa. The method involves the use of two 

 aneroid barometers with vertical scales in feet and adjusted 



* Summarized in Engineering Record, Vol. XLIII, p. 349. 



