Hydrodynamic and Thermal
Dispersion Modelling of the Effluent
in a Coastal Channel
Ahmad Sana, sana@squ.edu.om
Sultan Qaboos University, Oman
Contents
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Motivation
Study area
Numerical model
Results and discussion
Conclusions
Motivation
• Various types of industrial plants discharge
effluents to the sea. Generally an outfall structure is
designed to keep minimum possible impact on the
ambient water quality.
• In the present situation the industrial plant is
located in the proximity of a natural wadi channel
connected to the sea forming a lagoon-like water
body.
• The high discharge of effluent with higher than
the ambient temperature may cause thermal
pollution along-with erosion in the channel
(Q=13,500m3/hr =3.75m3/s, T = 40oC).
Study Area
Numerical model
Delft3D-FLOW is the module of Delft3D suite that
provides the hydrodynamic basis for water quality
computations.
The main purpose is the two-dimensional (2D, depth
averaged) and three-dimensional (3D) simulation of
tidal and wind-driven flow by solving the unsteady
hydrodynamic equations.
Numerical model
The main physical phenomena, which are accounted
for in Delft3D-FLOW, are:
• Coriolis force.
• Turbulence model to account for the vertical
turbulent viscosity and diffusivity
• Shear stress exerted by the turbulent flow on the
bottom based on a quadratic Chézy or Manning
formula.
• Simulation of the thermal discharge intake
(advective-diffusion module).
• Simulation of drying and flooding of inter-tidal
flats (moving boundaries)
Computational Parameters
ITEM
CONDITION
Simulation period
August 7 to 21, 2009
Initial condition
Constant water temperature (25.6 oC)
Computational
domain
Horizontal orthogonal curvilinear 206x21
with one layer (depth-averaged condition)
Boundary condition
Meteorological data
Predicted water level at open boundary
(eastern boundary)
Uniform wind, air temperature, solar
radiation and humidity from historical
weather data
Bottom stress
Colebrooke Equation
Model domain
Bathymetry
Tidal elevation at sea boundary
Tidal elevation close to outlet
Thermal dispersion
Bottom shear stress
Possibility of sediment movement
According to Shields Criterion for uniform
bed material sizes, the sediment movement
will be initiated if
In the present case, τb<0.03 N/m2, ρs-ρ=1650kg/m3,
g = 9.81m/s2, Dmin = 0.075mm
No sediment movement will occur
Conclusions
• Detailed information regarding water level, temperature,
depth averaged velocity and bed shear stress is available
within the model domain.
• During the period of prediction, the effect of effluent
discharge on the seawater temperature remains confined
within the lagoon area.
• Seawater quality by virtue of temperature meets the
MECA requirements since the zone of influence of the
effluent is confined within the lagoon area where the
discharge point is located.
• Extremely low values of bed shear stress in the model
domain suggest that the possibility of erosion and therefore
accretion of eroded material is remote.
Thank You