102255ltr SMP Iss B

Detention Tank Deemed To Comply Solution

Detention sizing calculation

Site Area                                    A          723 m2
Detention volume rate                        R            90 m3/ha
Detention volume required                    V           6.5 kL

10% AEP pre-development flow (current day)   Qo        0.028 m3/s


Orifice calculation - 10% AEP and below

Total tank height (expected water height)    H.t          0.9 m
Two thirds of height                         2/3 H.t    0.60 m
Outlet pipe diameter                         D         0.225 m

Bottom third
Target flow rate                             Q1.req    0.012 m3/s
Depth of water above centroid of orifice     h          0.56 m       (@ D x 1/6)
Orifice diameter                             Dia       0.086 m
Office Area                                  Ao        0.006 m2
No. of orifices                              No.           1 each
Max. orifice diameter for multiple           Dia          86 mm      ANSWER

Middle third
Target flow rate                             Q2.req    0.014 m3/s
Depth of water above centroid of orifice     h          0.49 m       (@ D x 1/2)
Orifice diameter                             Dia       0.098 m
Office Area                                  Ao        0.008 m2
No. of orifices                              No.           1 each
Max. orifice diameter for multiple           Dia          98 mm      ANSWER

Top third
Target flow rate                             Q3.req    0.002 m3/s
Depth of water above centroid of orifice     h          0.43 m       (@ D x 5/6)
Orifice diameter                             Dia       0.041 m
Office Area                                  Ao        0.001 m2
No. of orifices                              No.           1 each
Max. orifice diameter for multiple           Dia          41 mm      ANSWER