51. If a culvert length of 139 ft is too long for this secondary con- 

 tainment area, the next step is to design for a shorter culvert length with a 

 15-in.-diam culvert. Designing for a Gt value of 8,000, the culvert length 

 is then reduced to 100 ft. The final step is to determine if the head loss 

 will provide enough energy for adequate mixing through the culvert. Using the 

 head loss equation and the new culvert diameter and length , the maximum head 

 loss is 0.94 ft. The head difference between the primary and secondary con- 

 tainment areas is 1.7 ft. 



52. Inlet baffle. An inlet baffle at the end of the culvert will 

 reduce the effects of short-circuiting and turbulent flow and assist in dis- 

 tributing the flow laterally (Schroeder 1983). The inlet baffle should be 

 placed 3 to 4 ft directly in front of the culvert discharge with a width of 

 twice the distance from the baffle to the culvert discharge. The height 

 should be approximately 2 ft above the bottom of the containment area. A 

 slotted baffle may be made of 4- by 4-in. wooden posts spaced 6 in. apart 

 (Figure 18). 



6' 



-4"x4" WOODEN POST 



6" 



\ 



3~: 



6 



V 









V 





V 





\) 





V 





V 





V 





V 



4 





V 





'1 



2D 



D - DISTANCE FROM THE CULVERT TO THE BAFFLE 

 Figure 18. Slotted baffles 



Secondary containment area 



53. The secondary containment area has to be sized to provide adequate 

 retention time for good settling and sufficient volume for storage of settled 

 material. The total volume of the containment area is the sum of the ponded 



36 



