Environmental Engineering Reference
In-Depth Information
Short Exercise 4: Calculation of Discharge from Tracer Data
Tracer dilution methods were used to estimate the discharge of two small streams
flowing into a wetland. The constant injection method was used in the first stream,
where chloride solution having a concentration of 60 g L
1
was injected at a rate of
12 L min
1
. The tracer concentration in the stream reached a steady value of
100 mg L
1
by 150 s after the start of injection (Fig.
3.35
). The background chloride
concentration in the stream was 1 mg L
1
.
1. Using Eq.
3.23
, estimate the stream discharge from concentration data.
The slug injection method was used in the second stream, where 10 L of tracer
solution containing 3 kg of chloride mass was instantaneously injected in the
stream. The tracer concentration reached a peak about 40 s after the release and
declined quickly afterwards (Fig.
3.35
). The background chloride concentration
in the stream was 2 mg L
1
.
Concentration data are listed in Table
3.5
.
2. Using Eq.
3.25
with
Δ
t
¼
10 s, estimate the integral in the denominator of
Eq.
3.24
.
3. Using Eq.
3.24
with
C
1
V
1
¼
3 kg, estimate the stream discharge.
100
slug injection
400
80
300
60
200
40
100
20
constant rate injection
0
0
0
40
80
120
160
0
40
80
120
time (s)
time (s)
Fig. 3.35 Concentration of chloride tracer in streams.
Left
: constant-rate injection test.
Right
: slug
injection test
Table 3.5 Data for slug injection test
t
(s)
C
(mg L
1
)
(
C C
b
)
Δt
(kg m
3
s)
C
(mg L
1
)
(
C C
b
)
Δt
(kg m
3
s)
t
(s)
0
2
______
70
80
______
10
2
______
80
50
______
20
100
______
90
30
______
30
370
______
100
20
______
40
420
______
110
10
______
50
240
______
120
4
______
60
130
______
Total
¼
______
