under average flow conditions. Assuming a 3-cfs flow rate, a head difference 

 of 2 ft between the primary and secondary containment areas, a head loss 

 through the culvert of 1.25 ft, and culvert lengths of 10, 50, and 100 ft 

 based on the containment area design, the culvert design may proceed as 

 follows: 



If 



D = culvert diameter, ft 



Q = maximum flow rate, cfs 



L = culvert length, ft 



g = 32.2 ft/sec 



H = maximum head loss through the culvert, ft 



N = number of parallel culverts 



then, 



,2^4/3 . 



D _ ] 8Q"Ll.5D" T/ " + 185(0. 025)"l] 

 gTT 2 HN 2 



3/16 



H = 



1.5 + 



185(0.025) L 



D 



4/3 



8Q 



2 2 4 

 ,gT7 N D ; 



L = 



>tt 2 HN 2 D 4 

 8Q 2 . 



I- 1.5 



D 



4/3 



185(0.025)' 



b. 



The calculated minimum diameters for the following numbers and 

 lengths of culverts are 



L, ft 



D, ft 



D, in. 



10 



0.85 



10.2 



50 



1.06 



12.7 



100 



1.18 



14.2 



10 



0.64 



7.6 



50 



0.80 



9.7 



100 



0.90 



10.8 



1 



1 

 1 



2 

 2 

 2 



The selected commercial sizes and calculated lengths are 



N D, in. L, ft 



12 

 15 

 8 

 10 

 12 



35 



139 



14 



62 



178 



34 



