Environmental Engineering Reference
In-Depth Information
TABLE 9.10. Stratification Classification of Estuaries
V
K
j
=
(1
−
α
)
(9.90)
2
r
River
Discharge
2
L
Type
Example
V
K
j
=
(1
+
α
)
(9.91)
Highly stratified large
Mississippi River (louisiana)
Mobile River (Alabama)
1
a
2
L
Partially mixed Medium
Chesapeake Bay (Maryland,
Virginia)
James River Estuary
(Virginia)
Potomac River (Maryland,
Virginia)
V
K
j
=
(1
−
α
)
(9.92)
2
a
2
L
Values of
α
r
and
α
a
contain important dimensionless
groups that can be used to measure the relative impor-
tance of dispersion and advection, where
Vertically
homogeneous
Small
Delaware Estuary (Delaware,
Pennsylvania, New Jersey)
Biscayne Bay (Florida)
Tampa Bay (Florida)
San Francisco Bay
(California)
San Diego Bay (California)
k K
V
k K
V
r
L
a
L
(9.93)
,
>
20
dispersion predominates
2
2
and
k K
V
k K
V
Source
: USEPA (1984).
r
L
a
L
(9.94)
,
<
0.05
advection predominates
2
2
Equations (9.85) and (9.86) require prior estimation of
the aeration constant,
k
a
, which can be done using field
measurements (e.g., gas tracer method) or any of the
appropriate formulas in Table 4.5. However, the appro-
priate velocity to be used in these formulas must be
selected according to the following guidelines (Thomann
and Mueller, 1987):
k
d
is the BOD decay constant associated with dissolved
organics (T
−1
),
L
is the BOD remaining (Ml
−3
),
k
a
is the
reaeration constant (T
−1
), and
k
r
is the BOD decay con-
stant associated with both the consumption of dissolved
organics and the removal of BOD by sedimentation.
Equations (9.83) and (9.84) are similar to the classical
Streeter-Phelps equations, with the only difference
being that the diffusion terms
K
l
d
2
D
/
dx
2
and
K
l
d
2
L
/
dx
2
are included here. The solution of Equations (9.83) and
(9.84) are given by
•
When the net nontidal velocity,
V
0
, is greater than
the average tidal velocity,
V
T
, use the net nontidal
velocity.
•
When the average tidal velocity,
V
T
, is greater than
or equal to the net nontidal velocity,
V
0
, use the
average tidal velocity.
j x
L e
x
≤
≥
0
0
1
r
0
L x
( )
=
(9.85)
j x
L e
x
2
r
0
j x
j x
The average tidal velocity,
V
T
(lT
−1
), is given by
k L
k
α
e
e
1
r
1
a
d
0
r
−
x
≤
0
−
k
α
α
a
r
r
a
D x
( )
=
(9.86)
2
2
π
t
2
T
/2
∫
k L
k
α
e
j x
e
j
x
(9.95)
V
=
V
sin
dt
=
V
2
r
2
a
d
0
r
T
max
max
−
x
≥
0
T
T
π
0
−
k
α
α
a
a
r
r
for a sinusoidally varying tidal velocity with period
T
(T) and amplitude
V
max
(lT
−1
).
where
L
0
is the ultimate BOD after initial mixing at the
source location (i.e., at
x
= 0), and the other parameters
in Equations (9.85) and (9.86) are defined as
EXAMPLE 9.8
4
k K
V
(9.87)
r
L
α
r
=
1
+
A tidal river has a mean velocity of 5 cm/s, a reaeration
constant of 0.75 d
−1
, and a longitudinal dispersion coef-
ficient of 120 m
2
is Wastewater is discharged into the
river, and after initial mixing, the river has an ultimate
BOD of 10 mg/l and a BOD decay constant of 0.4
day
−1
. If the temperature of the river is 20°C, determine
the oxygen deficit 200 m downstream of the outfall.
2
4
k K
V
(9.88)
a
L
α
a
=
1
+
2
V
K
j
=
(1
+
α
)
(9.89)
1
r
2
L
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