Geoscience Reference
In-Depth Information
Contaminant transport modeling
This chapter presents models for the fate and transport of water-quality constituents,
such as temperature, salinity, dissolved oxygen (DO), nitrogen, phosphorus, carbons,
and toxicants, in aquatic systems. In particular, heat exchange across the water sur-
face, interactions among DO, nitrogen, phosphorus, carbons and phytoplankton in
the eutrophication system, and sorption of contaminants on sediment particles are
discussed.
12.1 HEAT AND SALINITY TRANSPORT MODEL
Water temperature and salinity are among the key environmental conditions that
significantly affect the physical, chemical, and biological processes in aquatic sys-
tems. Thus, the simulation of heat and salinity transport is essential to water quality
modeling.
12.1.1 Governing equations
The presence of heat and salinity may induce stratification and density currents. To
adequately model these effects, the most preferable approach is the 3-D hydrody-
namic model, coupled with heat and salinity transport calculations. As described in
Section 2.4.4, the 3-D hydrodynamic equations are (2.112)-(2.115) with the water
density
varying with temperature and salinity. Under the hydrostatic pressure
assumption, the momentum equations (2.113)-(2.115) are simplified to Eqs. (2.117)
and (2.118). A further simplification may be made by assuming the temporal and
spatial variations of water density in the continuity equation (2.112) to be negligible,
yielding (Sheng, 1983; Blumberg and Mellor, 1987)
ρ
+
∂
u
y
∂
∂
u
x
∂
+
∂
u
z
∂
=
0
(12.1)
x
y
z
g
z
s
x
dz
u
x
)
∂
x
+
∂(
u
y
u
x
)
∂
u
x
∂
t
+
∂(
+
∂(
u
z
u
x
)
1
ρ
ρ
0
g
∂
z
s
z
∂ρ
1
ρ
∂τ
xx
=−
x
+
+
∂
y
∂
z
∂
∂
∂
x
1
ρ
∂τ
1
ρ
∂τ
xy
xz
+
+
+
f
c
u
y
(12.2)
∂
y
∂
z
