178 SEWER DESIGN 



and where x equals 



1 < 



\/R-S in metric units, 



or 



,, , 1.811 . .00281 

 4I.66H --- 1 -- _ 



v = - - t - - r - Vtf ' s m English units 



or 



The values given for w are as follows: 



I. Channels lined with carefully planed boards or with 



smooth cement ............................... oio 



II. Channels lined with common boards or surfaces care- 



fully plastered with cement-mortar, one-third sand, in 

 good condition, also for iron, cement, and terra-cotta 

 pipes, well jointed and in best order, and for other 

 surfaces equally rough ........................ on 



III. Channels lined with unplaned timber or rough cement- 



mortar ...................................... 012 



IV. Channels lined with ashlar and well-laid brick-work, 



ordinary metal, earthenware, and stoneware pipe in 

 good condition but not new, cement and terra-cotta 

 pipe not well jointed nor in perfect order, plaster, and 

 planed wood in imperfect or inferior condition, and 

 other surfaces equally rough ................... 013 



V. Channels in rubble masonry ...................... 017 



VI. Channels in earth; rivers ....................... 025 



VII. Streams with detritus ......................... 030 



