24 SEWER DESIGN 



the pipe and is alternately raised and dropped. The material 

 is collected in the bucket, and at intervals the bucket is lifted 

 entirely out and emptied. This is repeated; the pipe gradually 

 sinks, a man standing on the top if necessary. Other sections 

 of the pipe are added from time to time. It becomes necessary 

 sometimes to pour water into the pipe to aid in the cutting and 

 flow of the material into the bucket. The bucket should be 

 connected by a rope passing over a sheave connected with a 

 frame or shears above. Great depths can be reached by this 

 method with reasonable rapidity and at no great cost. 



Levels should be run and frequent benches established and 

 checked along all the streets. For the preliminary study on 

 the large map the levels are best expressed as contours show- 

 ing on flat ground differences of i foot. The profiles on the 

 separate sheets will require a vertical scale different from the 

 horizontal, depending on the grade of the street, and it is better 

 to hold to one vertical scale through all, rather than change 

 it for each sheet. Ten feet to the inch will generally serve, 

 though 4 feet to the inch is not too large for flat country. Levels 

 should be read at the bottom, and at the surfaces of all creeks 

 or brooks crossed by the sewer. Such points may serve for 

 outfalls or for flushing-gates, so that the high- and low-water 

 elevations should be found if possible. 



Of late years, particularly through the experience of the 

 U. S. Geological Survey, much data has been collected on the 

 value of various methods of running levels, particularly as 

 those methods affect accuracy and cost. On the long aqueduct 

 lines now under construction, as for Los Angeles and for New 

 York City, similar valuable data has been acquired.* 



The most common practice is to use two rodmen and to 

 read more than one wire on the level rod. On the Los Angeles 

 work the average number of miles run per day was 5.2 and the 

 cost including that involved in establishing frequent bench- 

 marks was $13.20 per mile. On the Catskill Aqueduct work, 

 with the same force, but with the addition of a note-keeper, 

 * See Engineering News, Vol. LX, p. 311, and Vol. LIX, p. 186. 



