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

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

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

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

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

LISTING OF WATER LEVEL DATA (REFERENCE) Hourly data of series code MAHEMDABAD ZA Year 1998, month 9 Day OHS - 6

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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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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

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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RELATION CURVES (1) FUNCTIONAL RELATIONSHIP BETWEEN TWO SERIES: Y(t) = f(X(t+t 1 ) 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

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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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

RELATION CURVES (4) FLOOD WAVE CELERITY(c) AND TRAVEL TIME (t1) –L is distance between stations –A s and A r are total and conveying area –B s and B r are total and conveying width c = dQ/dA s c.t 1 = L so: t 1 = L/c Q = K m A r R 2/3 S 1/2  K m B r h 5/3 S 1/2 dQ/dA s = dQ/(B s dh) hence: c = 5/3B r /B s K m h 2/3 S 1/2 = 5/3.B r /B s.u OHS - 22

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 K m = 33, B s = B r u = K m h 2/3 S 1/2 = 33 x 5 2/3 x (3.6 x ) 1/2 u = 1.84 m/s, c = 1.67 u = 3.07 m/s = 11 km/hr t 1 = L/c = 33/11 hr = 3 hr OHS - 23

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. R YX (  ) = C YX (  )/(S Y S X ) C YX (  )=1/N.  (Y t -m Y )(X t+  -m X ) OHS - 24

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FITTING OF RELATION CURVE RELATION EQUATION OF POLYNOMIAL TYPE: Y t = c 0 + c 1 X t+t1 + c 2 X 2 t+t1 + c 3 X 3 t+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 (TABULAR OUTPUT) Relation curves Computed time shift interval 1: Used time shift interval 1: Error analysis of relation of MAHEMDABAD ZA with NSB00I7 ZS Period from: to Equations: interval boundaries coefficients E E E-01 Date Obs. Est. Diff. Rel.diff Summary of errors Interval Number of data Standard error Overall error analysis Total number of data: 96 Overall standard error:.30 OHS - 29

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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Shift due to resetting of gauge OHS - 33