EW/FS/WW/AT5
Waste Water Treatment
Ocean outfalls: Principles of the hydraulic design
The hydraulic design is based on the hydraulic energy balance for the complete system by
comparing the specific energy between any two points in the system and taking into
account all friction and fitting losses between two adjoining points. This balance ensures
continuity of flow.
The energy principle is represented by the Bernoulli equation for pipe flow:
v11/2g + p1/ρg + z1 = v22/2g + p2/ρg + z2 + hf + hL
where:
v = Q/A average velocity
p = intensity of pressure at centre-line
ρg = specific weight
z = centre line elevation
hf = frictional head loss (in terms of Chezy or Manning or Darcy Weisbach Colebrook White)
hL = local head loss (losses occurring where the flow velocity changes
in magnitude or
direction)
A T-port configuration (Sappi Saiccor outfall at
Umkomaas)
The continuity equation for steady incompressible flow is of use for effluent discharge:
ΣQIN = ΣQOUT
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