Outlet Structure


The discharge characteristics for a basin can be represented by the following discharge equations:


1. Orifices


Q : The orifice flow rate (m3/s)
Cd : Orifice discharge coefficient (0.40-0.62)
Ao : Area of orifice (m2)
Do : Orifice diameter (m2)
Ho : Effective head on the orifice measured from the centre of the opening (9.81 m/s2)


2. Weirs

a) Sharp-Crested Weir

where :

Q : Weir discharge (m3/s)
Cscw : 1.81 + 0.22 (H/Hc), sharp crested weir discharge coefficient
B : Weir base width (m)
H : Head above weir crest excluding velocity head (m)
n : number of end contractions

b) Broad-Crested Weir


Q : Weir discharge (m3/s)
Cbsw : Broad crested weir coefficient
B : Weir base width (m)
H : Effective head above weir crest (m)

c) V-Notch Weir


Q : Weir discharge (m3/s)
θ : Angle of V-notch (m)
H : Head on apex of V-notch (m)


d) Spillway




Qs : The spillway discharge in m3/s.
c : The weir coefficient for the spillway (ranging from 1.45 m0.5/s for a broad crested weir to 2.15 m0.5/s for an ogee crested weir)
L : The effective length of the spillway (m)
H : The water level (m)
Hs : The spillway crest elevation (m)


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