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SECONDARY VALIDATION OF WATER LEVEL DATA (1)

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

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SECONDARY VALIDATION OF WATER LEVEL DATA (1)

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  1. 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 OHS - 1

  2. 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 OHS - 2

  3. 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) OHS - 3

  4. 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: • INFLOW/OUTFLOW BETWEEN STATIONS • FLOW/STAGE REGULATION • LAG BETWEEN STATIONS VARYING WITH RIVER FLOW OHS - 4

  5. 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 OHS - 5

  6. LISTING OF WATER LEVEL DATA (REFERENCE) Hourly data of series code MAHEMDABAD ZA Year 1998, month 9 Day 0 1 2 3 4 5 6 7 8 9 10 11 1 .09 .09 .09 .09 .09 .09 .09 .09 .09 .09 .09 .09 2 .02 .02 .02 .02 .02 .02 .02 .02 .02 .02 .02 .02 3 .02 .02 .02 .02 .02 .02 .02 .02 .02 .02 .02 .02 4 -.01 -.01 -.01 -.03 -.03 -.03 -.03 -.04 -.04 -.04 -.05 -.05 5 -.06 -.06 -.06 -.06 -.06 -.06 -.05 -.05 -.05 -.05 -.05 -.05 6 -.07 -.07 -.07 -.07 -.07 -.07 -.07 -.07 -.08 -.08 -.08 -.08 7 -.08 -.08 -.08 -.08 -.08 -.08 -.08 -.09 -.09 -.09 -.09 -.09 8 -.10 -.10 -.10 -.10 -.10 -.11 -.11 -.11 -.11 -.11 -.12 -.12 9 -.12 -.12 -.12 -.12 .00 .33 .35 .38 .39 .40 .40 .40 10 .33 .75 .80 .80 .77 .79 .83 .84 .85 1.10 1.10 1.11 11 .33 .95 .90 .86 .83 .80 .85 .70 .65 .61 .58 .56 12 .33 .31 .30 .30 .29 .28 .27 .27 .26 .25 .25 .24 13 .15 .14 .14 .14 .12 .12 .10 .10 .10 .09 .09 .09 14 .03 .03 .03 .03 .03 .03 .03 .03 .03 .03 .02 .02 15 .00 .00 .00 .10 .23 .28 .30 .35 .37 .30 .28 .25 16 .50 .48 .47 .46 .45 .40 .38 .36 .45 .60 .80 .85 17 .74 .72 .70 .68 .65 .60 .60 .55 .55 .55 .55 .55 18 5.30 5.15 5.00 4.90 4.60 4.35 4.00 3.80 3.75 3.35 3.25 3.20 19 2.05 2.00 1.95 1.90 1.85 1.80 1.80 1.75 1.70 1.68 1.66 1.65 20 1.68 1.65 1.62 1.60 1.57 1.55 1.55 1.50 1.45 1.42 1.40 1.40 21 1.80 1.70 1.67 1.60 1.57 1.50 1.47 1.47 1.45 1.42 1.39 1.37 22 1.19 1.19 1.18 1.17 1.17 1.15 1.15 1.10 1.10 1.09 1.08 1.07 23 1.56 1.55 1.54 1.53 1.47 1.40 1.34 1.31 1.28 1.24 1.20 1.21 24 1.01 .98 .95 .94 .89 .88 .88 .87 .87 .87 .87 .86 25 3.00 2.80 2.75 2.70 2.50 2.40 2.30 2.25 2.20 2.17 2.13 2.10 26 1.61 1.58 1.55 1.52 1.50 1.47 1.44 1.43 1.39 1.37 1.35 1.32 27 1.15 1.15 1.14 1.14 1.13 1.13 1.12 1.12 1.09 1.08 1.07 1.06 28 1.25 1.43 1.48 1.51 1.53 1.51 1.49 1.47 1.43 1.39 1.35 1.25 29 .95 .94 .92 .90 .89 .88 .87 .86 .85 .85 .84 .84 30 .87 .86 .83 .81 .81 .81 .80 .80 .80 .74 .71 1.25 OHS - 6

  7. OHS - 7

  8. OHS - 8

  9. 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

  10. OHS - 10

  11. OHS - 11

  12. OHS - 12

  13. OHS - 13

  14. 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

  15. 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

  16. OHS - 16

  17. RELATION CURVES (1) • FUNCTIONAL RELATIONSHIP BETWEEN TWO SERIES: Y(t) = f(X(t+t1) • APPLICATION CONDITIONS TO ARRIVE AT ONE-TO-ONE RELATION: • 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 OHS - 17

  18. 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

  19. OHS - 19

  20. OHS - 20

  21. 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

  22. 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

  23. 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

  24. 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

  25. OHS - 25

  26. OHS - 26

  27. 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

  28. OHS - 28

  29. 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 ZS 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

  30. 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

  31. OHS - 30

  32. OHS - 31

  33. OHS - 32

  34. Shift due to resetting of gauge OHS - 33

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