Turbidity variation analysis of Nilwala River at
Kadduwa NWSDB Intake
By Tissa Ramavikrama
MSc(GIS&RS),BSc(science), NDES
Data source
Daily turbidity records at NWSDB pumping station
Kadduwa(Regional chemist- Matara)
Objective
To Identify the most probable turbidity values for design
considerations of new water treatment plant Matara stage
iv project
Summary Statics of Raw Water turbidity records at Kadduwa
Intake
Mean
Standard Error
Median
Mode
Standard Deviation
Sample Variance
Kurtosis
Skewness
Range
Minimum
Maximum
Sum
Count
38.32
1.14
18.10
11.30
56.65
3208.75
22.40
4.03
642.20
2.80
645.00
94777.36
2473.00
• This is the Recoded maximum turbidity
value of the day
• This data 1 st January 2011 to 30 th
October 2017.
Tubidity
Range(NTU)
Histogram
Frequency
0 - 25
1520
25 - 50
470
50 - 75
169
75 - 100
113
1200
100 - 125
52
1000
125 - 150
33
150 - 175
29
175 - 200
21
200 -225
14
225 - 250
13
250 - 275
8
275 - 300
9
300 - 325
4
325 - 350
3
350 -375
3
375 - 400
4
400 - 425
2
425 - 450
2
450 -475
1
475 - 500
1
500 - 525
0
525 - 550
0
550 - 575
1
575 - 600
0
600 - 625
0
625 - 650
1
Total
2473
1520
1600
Frequency
1400
800
600
470
400
169
200
0
0
113
52 33 29 21 14 13 8
9
4
3
3
4
2
2
1
1
0
0
1
0
0
1
0 25 50 75 100125150175200225250275300325350375400425450475500525550575600625650
Bin
Frequency
•
•
•
•
This distribution is not a normal distribution.
Turbidity variations of river depend on rainfall and other seasonal factors.
Consider the Average or modal value of turbidity at risk for WTP design.
Analysis of Monthly turbidity variations is better
Recorded Maximum Turbidity per Month
Month
January
February
March
April
May
June
July
August
September
October
November
December
2011
2012 2013
255
80
325
325
127
350
279
263
97
404
172
122
309
108
371
180
151
95
22
391
79
124
71
46
153
118
56
171
186
181
370
645
350
450
251
458
Year
Standard
2014 2015
2016
2017
Average Diviation
294
145
92
88
183
106
97
493
273
76
249
155
83
165
131
91
158
82
89
390
57
210
206
140
47
210
183
225
208
111
402
70
50
55
143
124
155
70
73
47
120
126
185
71
25
81
86
53
30
105
21
248
105
80
211
297
53
201
186
72
215
393
237
368
154
231
361
140
315
129
Monthly Variation Pattern of Maximum Turbidity recorded
700
600
Max: Turbodity
500
400
300
200
100
0
0
2
4
6
8
10
Month
2011
2012
2013
2014
2015
2016
2017
12
14
Summary statistics of Monthly Turbidity variations
Mean
Standard Error
Median
Mode
Standard
Deviation
Sample Variance
Kurtosis
Skewness
Range
Minimum
Maximum
Sum
Count
Octomb
Decem
January
February March
April
May
June
July
August September er
November ber
182.64
248.73 158.39 206.27
207.56 143.11 119.54
86.10
104.50 185.73
368.33 315.17
39.98
58.55
30.98
52.82
41.87
46.99
47.80
20.16
30.07 27.20
62.78 52.46
145.00
273.00 131.00 172.00
210.00
94.70
72.80
70.80
105.30 186.00
360.00 306.00
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105.77
154.91
81.97
139.75
11187.62 23997.27 6719.67 19531.37
-2.21
-1.07
-1.27
-1.23
0.38
0.35
0.81
0.71
245.40
417.20 195.90 346.80
79.60
75.80
83.10
57.20
325.00
493.00 279.00 404.00
1278.50
7.00
1741.10 1108.70 1443.90
7.00
7.00
7.00
110.78
124.31
126.47
53.33
12273.31 15453.92 15994.06 2844.23
-0.49
3.72
4.75
1.20
0.05
1.87
2.13
1.11
324.10 352.20 368.70 160.10
46.90
49.80
22.30
24.90
371.00 402.00 391.00 185.00
1452.90 1001.80
7.00
7.00
836.80
7.00
602.70
7.00
79.56
71.98
6329.00 5180.48
0.59
2.65
0.91
-0.59
226.80 243.90
21.20 53.10
248.00 297.00
731.50 1300.10
7.00
7.00
153.79 128.50
16513.
23650.27
37
2.15 -1.73
1.26 -0.11
430.00 318.00
215.00 140.00
645.00 458.00
1891.0
2210.00
0
6.00
6.00
• If N (No of month have data) become a large value this distribution
is Normal Distribution
Maximum Expected Turbidity values of each Month
Month
January
February
March
April
May
June
July
August
September
October
November
December
Annual Average
Standard
Average Diviation
183
106
249
155
158
82
206
140
208
111
143
124
120
126
86
53
105
80
186
72
368
154
315
129
194
111
Probable Maximum Turbidity
50%
183
249
158
206
208
143
120
86
105
186
368
315
60%
209
288
179
242
236
175
152
100
125
204
407
348
70%
238
330
201
280
266
208
186
114
146
223
449
383
80%
272
379
227
324
301
248
226
131
171
246
498
423
90%
318
447
263
385
350
302
282
154
206
278
565
480
95%
357
504
293
436
390
348
328
174
235
304
621
527
99%
429
609
349
531
465
432
414
210
290
353
726
614
194
222
252
287
336
376
452
Conclusion
• Better to get annual average turbidity vale of the most probable
turbidity of the design considerations.
• Minimize the failures of the Water treatment plant consider the
probability values and probable maximum turbidity values according
to the requirements.
Thankyou