60 SEWER DESIGN 



is about i : 130, and the sewer-grades range from i : 50 to i : 630. 

 At the gages the outlet sewer is of good rubble masonry with 

 flat and somewhat irregular rocky bottom. Length of main 

 and tributary sewers at Gage No. 8 is 4.37 miles. 



Districts IX and X. Discharge measured by Gages Nos. 18 

 and 19, in East Main and Alexander Street sewers respectively. 

 The former serves a small but densely populated area traversed 

 by the principal street, while the latter serves a large and well- 

 developed residential district. In District IX the sewer grades 

 range from i : 54 to i : 400, and the average surface-slopes of the 

 streets is about 1:151; and in District X the sewer-grades range 

 from 1:70 to 1:330, the average surface-slope being 1:172. 

 From its general character this latter district should give the 

 greatest percentage of rainfall-discharge, as the amount of 

 roof -surf ace is here proportionally the greatest. The length 

 of main and tributary sewers at Gage No. 18 is 0.76 mile. 



District XVII. Discharge measured by Gages No. 30 

 and 31 in the Griffith Street sewer. The tributary area is well 

 sewered and developed, and the average density of population 

 may be estimated at about 35 per acre. Every street has an 

 improved roadway, about one-fifth of the total street-surface 

 being asphalt, one-fourth stone block, and the remainder 

 macadam and gravel pavement. Numerous large business 

 blocks and apartment-houses are found on the territory, but 

 the greater portion of it is occupied by residences, standing 

 generally on lots of medium size, although in about twenty- 

 five acres of the area the lots are very deep and afford oppor- 

 tunity for additional streets. The surface-grades in about 

 one-half of the area are of good inclination, while in the remainder 

 they are rather flat, the average being about i : 240 for Gage 

 No. 30 and i: 175 for Gage No. 31. Sewer-grades vary from 

 i: 100 to 1:350. The soil is generally a clayey loam, and much 

 of the rainfall is as yet absorbed into the ground. Length of 

 main and tributary sewers at Gage No. 30 is 2.56 miles. 



In an article on flood-waves by Alvah Grover in the Trans. 

 Am. Soc. C. E., Vol. XXVIII, an apparatus is described for 



