Environmental Engineering Reference
In-Depth Information
10
6
10
5
10
4
10
3
10
2
0
10
20
30
40
50
60
70
80
90
100
exceedance percentage (%)
Figure 4.13.
Load duration curve.
EXAMPLE 4.23
mine the LDC for FC. If most of the water-quality viola-
tions occurred under moist conditions, with 10-40%
flow-rate exceedances, estimate an allowable midrange
FC load under moist conditions.
Ranked daily flow measurements at a section of the
Lower Kansas River between 1970 and 2007 are as
follows:
Solution
Flow
(m
3
/s)
Flow
(m
3
/s)
Flow
(m
3
/s)
Rank
Rank
Rank
From the given data:
N
= 13,655 and
c
std
= 200 CFU/
100 mL. Using the given ranks,
m
, the exceedance per-
centages,
P
e
, can be calculated using Equation (4.158) as
1
4728
4780
170
9559
61
341
1172
5121
158
9901
57
683
903
5462
145
10,242
54
m
N
m
1024
722
5804
133
10583
50
P
e
=
×
100
=
×
100
(4.159)
1366
600
6145
123
10,925
46
+
1
13 656
,
1707
495
6487
114
11,266
42
2048
422
6828
105
11,608
39
The FC load,
L
(CFU/d), corresponding to any given
flow,
Q
(m
3
/s),
2390
368
7169
97
11,949
36
is calculated using the following
2731
331
7511
90
12,290
33
relationship
3073
294
7852
84
12,632
31
3414
262
8194
78
12,973
29
8.64 10
8
(4.160)
L Qc
=
×
×
3755
235
8535
74
13,315
25
std
4097
210
8876
69
13,655
11
where
c
std
is in CFU/100 mL, and 8.64 × 10
8
is a conver-
sion factor to ensure that
L
is in CFU/d. Using Equation
(4.159) to transform the given ranks and using Equation
(4.160) to transform the given flows yields the LDC that
is tabulated as follows:
4438
188
9218
65
There were 13,655 measurements during this period.
The Lower Kansas River has been found to be impaired
relative to a FC standard of 200 CFU/100 mL. Deter-
Exceedance (%)
Load (×10
12
CFU/d)
Exceedance (%)
Load (×10
12
CFU/d)
Exceedance (%)
Load (
×
10
12
CFU/d)
0.0
817
35.0
29.4
70.0
10.6
2.5
203
37.5
27.3
72.5
9.88
5.0
156
40.0
25.0
75.0
9.30
7.5
125
42.5
22.9
77.5
8.71
10.0
104
45.0
21.3
80.0
8.02
12.5
85.6
47.5
19.7
82.5
7.34
15.0
72.9
50.0
18.2
85.0
6.75
17.5
63.6
52.5
16.8
87.5
6.21
20.0
57.2
55.0
15.6
90.0
5.77
22.5
50.9
57.5
14.5
92.5
5.38
25.0
45.3
60.0
13.5
95.0
4.94
27.5
40.6
62.5
12.7
97.5
4.39
30.0
36.2
65.0
11.9
100
1.86
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