2.7.3 Design of Clarifier Effluent Launder

Effluent Launder shall also be designed for the extreme condition i.e closure of one Clarifier for repair. In this condition all the flow shall pass through one clarifier. Design of effluent launder is as follows:


Width of launder (b) = 2.625 (Assumed)
Flow through the Launder = 23.34 Cusecs
Gravity (g) = 32.2 Ft / s2

Depth of Flow at the lower end (h) = (Q2/ b2 x g)1/3
= ((11.67)2/ (2.625)2 x 32.2)1/3
= 0.85 Ft
Circumference of each Clarifier = 3.14 x 91.5
= 287.31 Ft
Half Circumference of each Clarifier = 143.66 Ft

Depth of Flow at the Upper End (H) =√(0.850)2+ 2(0.0789)2((143.67)2/32.2(0.850)(2.625)2 = 1.42 Ft
Friction Losses (Say) = 0.33 Ft
Depth of Flow in the Launder = 1.75 Ft
Free Board (15 %) = 0.2625 Ft
Add 0.15 Ft to ensure Free Fall = 0.15 Ft
Total Depth of Launder (1.75 + 0.2625 + 0.15) = 2.16 Ft
Say = 2.25 Ft

A channel / launder 2’- 7.5” wide and 2’ - 3” deep shall be provided around the Clarifier. Depth of the channel / launder shall be measured 2 - 3” below the crest level of the weir. A 1’-0” vertical space shall be provided between the weir crest and bottom of the beam supporting the bridge.