Transcript Hydrology Project Training Module

SECONDARY VALIDATION OF WATER
LEVEL DATA (1)
• PRIMARY VALIDATION:
– BASED ON KNOWLEDGE OF INSTRUMENTATION
AND METHODS OF MEASUREMENT WITH
ASSOCIATED ERRORS
• SECONDARY VALIDATION:
– EMPHASIS ON COMPARISONS WITH
NEIGHBOURING STATIONS AND/OR RELATED
PHENOMENA TO:
* IDENTIFY SUSPECT VALUES
* IDENTIFY AND QUANTIFY SHIFTS (TIME-SHIFTS AND
SHIFT IN REFERENCE LEVEL)
– REQUIREMENT IS SIGNIFICANT SPATIAL
CORRELATION
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SECONDARY VALIDATION OF WATER
LEVEL DATA (2)
• ACTIVITY INCLUDES:
– COMPARISON BETWEEN WATER LEVEL SERIES AT
SUCCESSIVE POINTS ON THE SAME RIVER
* TIME SERIES
* RELATION CURVES
– COMPARISON WITH OTHER SOURCES IN CASE OF
DOUBT ON STATION AT FAULT:
* E.G. COMPARISON BETWEEN INCIDENT RAINFALL AND
LEVEL HYDROGRAPHS
– FOR ROUTINE MONTHLY VALIDATION:
* PLOT SHOULD INCLUDE TIME SERIES OF AT LEAST THE
PREVIOUS MONTH
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SCRUTINY OF MULTIPLE HYDROGRAPH
PLOTS (1)
• FIRST STEP:
– A HARD COPY IS MADE OF THE WATER LEVEL DATA
FOR REFERENCE PURPOSES
• SECOND STEP:
– GRAPHICAL INSPECTION OF COMPARATIVE PLOTS
OF TIME SERIES. THIS PROVIDES A RAPID AND
EFFECTIVE MEANS TO DETECT ANOMALIES:
* INDIVIDUAL OUTLIERS
* FABRICATION
* SHIFTS (TIME AND REFERENCE LEVEL)
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SCRUTINY OF MULTIPLE HYDROGRAPH
PLOTS (2)
• ERROR TYPES:
– PEAKS ARE OBSERVED AT ONE STATION BUT NOT
AT ITS NEIGHBOUR
– LAG TIME BETWEEN STATIONS IS WIDELY
DIFFERENT FROM THE NORM
– SUDDEN SHIFTS AT A STATION OFTEN VISIBLE
HYDROGRPAH TAILS OF DIFFERENT PERIODS
• RESEMBLANCE OF HYDROGRAPHS AFFECTED
BY:
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– INFLOW/OUTFLOW BETWEEN STATIONS
– FLOW/STAGE REGULATION
– LAG BETWEEN STATIONS VARYING WITH RIVER
FLOW
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EXAMPLE OF SCRUTINY OF TIME SERIES
PLOTS
• TWO STATIONS ON WATRAK RIVER
(TRIBUTARY OF SABARMATI) ARE
CONSIDERED:
– MAHEMDABAD (SSW-GUJARAT), AND
– NSB00I7 (CWC)
• STATIONS ARE DISTANCED SOME 33 KM APART
• LATERAL INFLOW BETWEEN THE STATIONS IS
SMALL COMPARED TO RIVER FLOW
• U/S AS WELL AS D/S ADDITIONAL
HYDROMETRIC STATIONS ARE BEING
OPERATED
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LISTING OF WATER LEVEL DATA (REFERENCE)
Hourly data of series code MAHEMDABAD
Day
OHS - 6
0
1
2
3
4
5
ZA
Year 1998,
6
7
month
9
8
9
10
11
1
2
3
4
5
.09
.02
.02
-.01
-.06
.09
.02
.02
-.01
-.06
.09
.02
.02
-.01
-.06
.09
.02
.02
-.03
-.06
.09
.02
.02
-.03
-.06
.09
.02
.02
-.03
-.06
.09
.02
.02
-.03
-.05
.09
.02
.02
-.04
-.05
.09
.02
.02
-.04
-.05
.09
.02
.02
-.04
-.05
.09
.02
.02
-.05
-.05
.09
.02
.02
-.05
-.05
6
7
8
9
10
-.07
-.08
-.10
-.12
.33
-.07
-.08
-.10
-.12
.75
-.07
-.08
-.10
-.12
.80
-.07
-.08
-.10
-.12
.80
-.07
-.08
-.10
.00
.77
-.07
-.08
-.11
.33
.79
-.07
-.08
-.11
.35
.83
-.07
-.09
-.11
.38
.84
-.08
-.09
-.11
.39
.85
-.08
-.09
-.11
.40
1.10
-.08
-.09
-.12
.40
1.10
-.08
-.09
-.12
.40
1.11
11
12
13
14
15
.33
.33
.15
.03
.00
.95
.31
.14
.03
.00
.90
.30
.14
.03
.00
.86
.30
.14
.03
.10
.83
.29
.12
.03
.23
.80
.28
.12
.03
.28
.85
.27
.10
.03
.30
.70
.27
.10
.03
.35
.65
.26
.10
.03
.37
.61
.25
.09
.03
.30
.58
.25
.09
.02
.28
.56
.24
.09
.02
.25
16
17
18
19
20
.50
.74
5.30
2.05
1.68
.48
.72
5.15
2.00
1.65
.47
.70
5.00
1.95
1.62
.46
.68
4.90
1.90
1.60
.45
.65
4.60
1.85
1.57
.40
.60
4.35
1.80
1.55
.38
.60
4.00
1.80
1.55
.36
.55
3.80
1.75
1.50
.45
.55
3.75
1.70
1.45
.60
.55
3.35
1.68
1.42
.80
.55
3.25
1.66
1.40
.85
.55
3.20
1.65
1.40
21
22
23
24
25
1.80
1.19
1.56
1.01
3.00
1.70
1.19
1.55
.98
2.80
1.67
1.18
1.54
.95
2.75
1.60
1.17
1.53
.94
2.70
1.57
1.17
1.47
.89
2.50
1.50
1.15
1.40
.88
2.40
1.47
1.15
1.34
.88
2.30
1.47
1.10
1.31
.87
2.25
1.45
1.10
1.28
.87
2.20
1.42
1.09
1.24
.87
2.17
1.39
1.08
1.20
.87
2.13
1.37
1.07
1.21
.86
2.10
26
27
28
29
30
1.61
1.15
1.25
.95
.87
1.58
1.15
1.43
.94
.86
1.55
1.14
1.48
.92
.83
1.52
1.14
1.51
.90
.81
1.50
1.13
1.53
.89
.81
1.47
1.13
1.51
.88
.81
1.44
1.12
1.49
.87
.80
1.43
1.12
1.47
.86
.80
1.39
1.09
1.43
.85
.80
1.37
1.08
1.39
.85
.74
1.35
1.07
1.35
.84
.71
1.32
1.06
1.25
.84
1.25
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Water level time series (2) (2 months)
6
5.5
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
-0.5
05/09/98
12/09/98
19/09/98
26/09/98
03/10/98
10/10/98
17/10/98
24/10/98
31/10/98
Time
ZA_MAHEMDABAD
OHS - 7
ZS_NSB00I7
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Water level time series (2) (detail)
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
27/09/98
28/09/98
29/09/98
30/09/98
01/10/98
02/10/98
03/10/98
04/10/98
05/10/98
06/10/98
07/10/98
Time
ZA_MAHEMDABAD
OHS - 8
ZS_NSB00I7
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DATA VALIDATION
• OBSERVATIONS:
– OCCURRENCE OF PEAKS TOO REGULAR TO BE
NATURAL, LIKELY DUE TO RELEASES FROM
RESERVOIR(S)
– TIME SERIES PLOTS SHOW TWO TYPES OF ERRORS:
* SPURIOUS ERRORS DUE TO READING OR ENTRY ERRORS
* ERRORS IN THE OCCURRENCE OF THE PEAKS
– ADDITIONAL INFORMATION REQUIRED FROM U/S
OR D/S STATIONS TO EVALUATE STATION(S) AT
FAULT
OHS - 9
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Water level time series (4) (2 months)
8
7.5
7
6.5
6
5.5
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
-0.5
05/09/98
12/09/98
19/09/98
26/09/98
03/10/98
10/10/98
17/10/98
24/10/98
31/10/98
Time
ZA_AMBALIYARA
OHS - 10
ZA_DABHA
ZA_MAHEMDABAD
ZS_NSB00I7
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Water level time series (4) (detail)
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-0.2
27/09/98
28/09/98
29/09/98
30/09/98
01/10/98
02/10/98
03/10/98
04/10/98
05/10/98
06/10/98
07/10/98
Time
ZA_AMBALIYARA
OHS - 11
ZA_DABHA
ZA_MAHEMDABAD
ZS_NSB00I7
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Water level time series (4) (detail)
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-0.2
27/09/98
28/09/98
29/09/98
30/09/98
01/10/98
02/10/98
03/10/98
04/10/98
05/10/98
06/10/98
07/10/98
Time
ZA_AMBALIYARA
OHS - 12
ZA_DABHA
ZA_MAHEMDABAD
ZS_NSB00I7
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Water level time series (4) (detail)
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
- 0.2
27/09/98
28/09/98
29/09/98
30/09/98
01/10/98
02/10/98
03/10/98
04/10/98
05/10/98
06/10/98
07/10/98
Time
ZA_AMBAL IYARA
OHS - 13
Z A_DABHA
ZA_MAHEMDABAD
ZS_NSB00I7
T
ee
cc
h
n
ic
a
lA
sssista
sistan
ccee
T
h
n
ic
a
lA
n
H
Y
R
O
L
G
YP
EC
H
YD
D
R
O
LO
O
G
YPR
RO
OJ
JE
CT
T
DATA VALIDATION
• ACTION AFTER EACH STEP:
– FLAG ANOMALIES ON THE GRAPHS AND IN THE
TABULAR OUTPUT OF THE SERIES
– ADJUST ANOMALIES WHEN SOURCE AND SIZE OF
ERROR IS EXACTLY KNOWN
– CORRECTION SHOULD ONLY BE CARRIED OUT
WHEN NO BETTER OPTIONS ARE AVAILABLE (TO
ALLOW MORE POWERFUL APPLICATION OF
SUBSEQUENT TESTS)
– IF IN DOUBT OR CORRECTION INCLUDES HIGH
UNCERTAINTY AWAIT VALIDATION AS DISCHARGE
OHS - 14
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COMBINED HYDROGRAPH AND RAINFALL
PLOTS
• OBJECTIVES:
– TO ASSESS TIMING ERRORS
– TO OBTAIN EVIDENCE OF LATERAL INFLOW
• OFTEN:
– RISE IN RIVER STAGE PRECEDED BY A RAINFALL
EVENT IN THE BASIN
• EXCEPTIONS (E.G):
– NOT EVERY STORM CAUSES RUNOFF
– SPILL FROM RESERVOIRS ALSO CAUSE RISING
LEVELS
– ONE OR BOTH SITES AFFECTED BY BACKWATER
OHS - 15
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Time Series
7
32
6.5
30
6
28
5.5
26
5
24
4.5
22
4
20
3.5
18
3
16
2.5
14
2
12
1.5
10
1
8
0.5
6
0
4
-0.5
2
-1
30/07/94 31/07/94
0
01/08/94 02/08/94
03/08/94 04/08/94 05/08/94
06/08/94 07/08/94
08/08/94 09/08/94
Time
ZA_AMBALIYARA
OHS - 16
PH_RAHIOL
PH_VADAGAM
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RELATION CURVES (1)
• FUNCTIONAL RELATIONSHIP BETWEEN TWO
SERIES:
Y(t) = f(X(t+t1)
• APPLICATION CONDITIONS TO ARRIVE AT
ONE-TO-ONE RELATION:
–
–
–
–
OHS - 17
STATIONS LOCATED ALONG THE SAME RIVER
NO MAJOR TRIBUTARY JOINS IN BETWEEN
NO BACKWATER EFFECTS
TIME OF TRAVEL OF FLOOD WAVE BETWEEN
STATIONS IS TAKEN INTO CONSIDERATION
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RELATION CURVES (2)
• APPLICATION:
– TO IDENTIFY INDIVIDUAL OUTLIERS
– TO IDENTIFY SHIFTS IN THE RELATIONSHIP
BETWEEN TWO STATIONS, WHICH MAY BE CAUSED
BY:
* SHIFT IN GAUGE SETTING
* CHANGE IN THE CONTROL SECTION(S)
– TO FILL IN MISSING DATA
OHS - 18
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Water level time series (2)
12
11
10
9
8
7
6
5
4
3
2
1
0
27/07/97
28/07/97
29/07/97
30/07/97
Time
ZA_MAHEMDABAD
OHS - 19
ZS_NSB00I7
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Scatter plot (no time shift)
10
9
8
7
6
5
4
3
2
1
0
-1
-2
0
1
2
3
4
5
6
7
NSB00I7 - H(t)
OHS - 20
8
9
10
11
12
TechnicalAssistance
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RELATION CURVES (3)
• TO ELIMINATE THE LOOPING IN THE SCATTER
PLOT A TIME SHIFT HAS TO BE APPLIED TO
ACCOUNT FOR TRAVEL TIME OF THE FLOOD
WAVE
• TRAVEL TIME IS DERIVED FROM:
– HYDRAULIC CALCULATION OF FLOOD WAVE
CELERITY
– CROSS-CORRELATION ANALYSIS
OHS - 21
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RELATION CURVES (4)
• FLOOD WAVE CELERITY(c) AND TRAVEL TIME
(t1)
– L is distance between stations
– As and Ar are total and conveying area
– Bs and Br are total and conveying width
c = dQ/dAs
c.t1 = L
so:
t1 = L/c
Q = KmArR2/3S1/2  KmBrh5/3S1/2
dQ/dAs = dQ/(Bsdh)
hence: c = 5/3Br/BsKmh2/3S1/2 = 5/3.Br/Bs.u
OHS - 22
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RELATION CURVES (5)
• NOTE:
– CELERITY AND HENCE TRAVEL TIME VARIES WITH
RIVER-CROSS-SECTION AND FLOW CONDITION
• TRAVEL TIME COMPUTATION FROM
HYDRAULICS:
L=33 km, h= 5 m, S = 3.6x10-4
Km = 33, Bs = Br
u = Kmh2/3S1/2 = 33 x 52/3 x (3.6 x 10-4)1/2
u = 1.84 m/s, c = 1.67 u = 3.07 m/s = 11 km/hr
t1 = L/c = 33/11 hr = 3 hr
OHS - 23
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RELATION CURVES (6)
• TRAVEL TIME FROM CROSS-CORRELOGRAM:
– CORRELATION COMPUTED FOR INTEGER VALUES
OF TIME-LAG T
– FIND TIME-LAG WHICH GIVES MAXIMUM LINEAR
CORRELATION BETWEEN THE RECORDS AT THE
TWO SITES; THIS TIME-LAG IS OPTIMISED.
RYX() = CYX()/(SYSX)
CYX()=1/N.(Yt-mY)(Xt+-mX)
OHS - 24
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OHS - 25
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Scatter plot (shift = 2.8 hrs)
10
9
8
7
6
5
4
3
2
1
0
-1
-2
0
1
2
3
4
5
6
7
NSB00I7 - H(t-2.8)
OHS - 26
8
9
10
11
12
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FITTING OF RELATION CURVE
• RELATION EQUATION OF POLYNOMIAL TYPE:
Yt = c0 + c1Xt+t1 + c2X2t+t1 + c3X3t+t1 + …
• AT MAXIMUM 3 SEGMENTS PER RELATION TO
FIT THE SCATTER PLOT AND TO ACCOUNT FOR
DIFFERENT TIME SHIFTS t1 ARE ALLOWED IN
HYMOS
• ADVISABLE NOT TO GO BEYOND SECOND
ORDER POLYNOMIAL
OHS - 27
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Relation curve fit (period 27-31/7/97)
10
9
8
7
6
5
4
3
2
1
0
-1
-2
0
1
2
3
4
5
6
7
NSB00I7 - H(t-2.8)
OHS - 28
8
9
10
11
12
TechnicalAssistance
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RELATION CURVE (TABULAR OUTPUT)
Relation curves
Computed time shift interval 1: -2.87
Used time shift interval
1: -2.87
Error analysis of relation of MAHEMDABAD ZA with NSB00I7
Period from: 1997 7 27 to 1997 7 30
Equations: interval boundaries coefficients
1
.000 -.113974E+01
12.000 .150284E+01
-.550978E-01
Date
Obs.
Est.
Diff. Rel.diff
1997 7 27 0 1
.34
.31
.03
10.39
1997 7 27 1 1
.37
.31
.06
20.13
1997 7 27 2 1
.37
.31
.06
20.13
1997 7 27 3 1
.37
.31
.06
18.78
1997 7 27 4 1
.37
.34
.03
9.04
1997 7 27 5 1
.37
.37
.00
.78
1997 7 27 6 1
.37
.39
-.02
-5.04
.
. . . .
.
.
.
.
1997 7 30 4 1
2.20
2.15
.05
2.41
1997 7 30 5 1
2.15
2.14
.01
.67
Summary of errors
Interval Number of data Standard error
1
96
.30
Overall error analysis
Total number of data:
96
Overall standard error:
.30
OHS - 29
ZS
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COMPARISON OF RELATION CURVES
• TWO WAYS TO CHECK CONSISTENCY OF
WATER LEVEL RELATION CURVES:
– COMPARE THE CURVE FOR ONE PERIOD WITH THE
SCATTER PLOT FOR A PREVIOUS OR FOLLOWING
PERIOD
– COMPARE THE RELATION CURVES FOR DIFFERENT
PERIODS
• THE TIME SHIFT APLLIED EITHER IN THE
SCATTER PLOTS AND/OR IN THE RELATION
CURVES SHOULD APPROXIMATELY BE THE
SAME FOR A SPECIFIC WATER LEVEL RANGE.
OHS - 29
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Water level time series (2)
10
9
8
7
6
5
4
3
2
1
01/08/97
02/08/97
03/08/97
04/08/97
Time
ZA_MAHEMDABAD
OHS - 30
ZS_NSB00I7
TechnicalAssistance
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Relation curve fit (period 1-5/8/'97)
8
7
6
5
4
3
2
1
1
2
3
4
5
6
NSB00I7 - H(t-3)
OHS - 31
7
8
9
10
TechnicalAssistance
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Comparison of Relation Curves (July vs August '97)
9
8
7
6
5
4
3
2
1
0
-1
0
1
2
3
4
5
6
7
8
9
10
11
NSB00I7 - H(t-3)
First relation
OHS - 32
Second relation
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Comparison of Relation Curves (July vs August '97)
9
8
7
6
5
4
3
2
Shift due to resetting
of gauge
1
0
-1
0
1
2
3
4
5
6
7
8
9
10
11
NSB00I7 - H(t-3)
First relation
OHS - 33
Second relation
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