d. The mean velocity (v) and friction factor (f) at average flow 

 are 



N D, in. v, fps 



1 12 



1 15 



2 8 

 2 10 

 2 12 



2.86 



0.1156 



1.83 



0.1073 



3.22 



0.1324 



2.06 



0.1229 



1.43 



0.1156 



Also, 



Gt = 



= 42- 



V 2 



ttD 



where 



3 

 Y = specific weight, 62.4 lb/ft 



f = friction factor 



= 185n 2 /D (n = Manning's coefficient, 0.025 for 

 corrugated metal pipes) 



v = mean velocity at average flow, fps 



-5 2 

 u = absolute viscosity, 2.36 * 10 lb-sec/ft at 60 c 

 s 

 Q = average flow rate, cfs 



= Q x (production ratio, 0.75) 



Mixing at average flow: 



D, in. L, ft 



1 



12 



35 



1 



15 



139 



2 



8 



14 



2 



10 



62 



2 



12 



178 



G,sec 



t,sec 

 12.1 



Gt 



334 



4,043 



147 



76.2 



11,195 



519 



4.5 



2,333 



230 



30.1 



6,924 



118 



124.4 



14,656 



f . Generally, a Gt of about 8,000 provides adequate mixing for 

 ~ flocculation. Either one 15-in.-diam, 139-ft-long culvert or 

 two 12-in.-diam, 178-ft-long culverts could be used. However, 

 one 15-in.-diam culvert would be the best design since it would 

 provide shorter culvert length. 



35 



