CORRECTION AND COMPLETION OF WATER LEVEL DATA (1)

1
CORRECTION AND COMPLETION OF WATER LEVEL DATA (1)

• WHERE
• DIVISIONAL OFFICES
• WHEN
• AS A CONTINUOUS PROCESS WITH VALIDATION
• WHAT
• INCORRECT AND MISSING VALUES WILL BE REPLACED
  USING INTERPOLATION OR RELATIONS
• SUSPECT (FLAGGED) VALUES WILL BE INSPECTED AND
  CORRECTED (IF NECESSARY) OR FLAG REMOVED IF FOUND
  ACCEPTABLE

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CORRECTION AND COMPLETION OF WATER LEVEL DATA (2)

• NOTE
• VALUES ESTIMATED FROM OTHER GAUGES ARE INHERENTLY
  LESS RELIABLE THAN VALUES PROPERLY MEASURED
• HENCE IF STANDARD ERROR IN RELATION CURVE IS
  SUBSTANTIAL, THEN
• EITHER DOUBTFULL VALUES ARE RETAINED WITH A FLAG,
  OR
• VALUE IN RECORD IS SET TO MISSING

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CONDITIONS FOR CORRECTION AS LEVEL

• LEVEL RECORD COMPLETE BUT RECORDER OUT OF
  ADJUSTMENT AND CHECK OBSERVATION IS AVAILABLE
• RECORD CORRECT BUT SHIFTED IN TIME
• PRIMARY RECORD (dwlr-record) IS MISSING BUT
  ALTERNATIVE AVAILABLE AT THE SAME SITE
• PART MISSING BUT DURATION IS SHORT DURING A
  PERIOD OF LOW FLOW OR RECESSION

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CORRECTION USING RIVER LEVEL OR DISCHARGE ?

• CORRECTIONS AND COMPLETION AS WATER LEVEL
• SMALL GAP INTERPOLATION ACCEPTABLE
• STANDARD ERROR OF STAGE-RELATION CURVE SMALL
• CORRECTION AND COMPLETION AS DISCHARGE
• STANDARD ERROR OF STAGE-RELATION CURVE TOO LARGE
• ONE OR BOTH STATIONS ARE AFFECTED BY BACKWATER
• RAINFALL-RUNOFF MODEL REQUIRED FOR COMPLETION

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COMPARISON OF STAFF GAUGE AND AWLR/DWLR RECORD (1)

• IF MORE MEASUREMENTS OF THE SAME VARIABLE ARE
  MADE AT A STATION, ONE RECORD MAY BE USED TO
  CORRECT OR REPLACE THE OTHER WHEN MISSING
• ERROR CLASSIFICATION
• OBSERVER ERRORS
• RECORDER TIMING ERRORS
• PEN LEVEL ERRORS
• ERRORS ARISING FROM STILLING WELL AND INTAKE
  PROBLEMS
• MISCELLANEOUS INSTRUMENT FAILURES

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COMPARISON OF STAFF GAUGE AND AWLR/DWLR RECORDS
(2)

• OBSERVER ERRORS
• IDENTIFICATION
• DISPLAY OF STAFF GAUGE AND AUTO-GRAPHIC OR
  DIGITAL RECORD IN ONE GRAPH
• DISPLAY OF DIFFERENCES
• TRANSCRIPTION ERRORS (E.G. 6.57 FOR 5.67)
• CORRECTION
• REPLACEMENT BY CONCURRENT MEASUREMENT AT THE
  RECORDING GAUGE

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COMPARISON OF STAFF GAUGE AND AWLR/DWLR RECORDS
(3)

• RECORDER TIMING ERRORS
• IDENTIFICATION
• FAST OR SLOW RUNNING CLOCK CAN BE IDENTIFIED BY
  COMPARISON WITH STAFF GAUGE READING
• CORRECTION
• WHEN DIGITAL RECORD IS PRODUCED BY DIGITISER FROM
  ANALOGUE RECORD CONTRACTION OR EXPANSION USING
  DIGITISER
• WHEN DIGITAL RECORD IS EXTRACTED MANUALLY ADD
  RECORDS (WHEN CLOCK IS FAST) OR ELIMINATE RECORDS
  (WHEN CLOCK IS SLOW)
• (CLOCK 4 HOURS FAST IN 8 DAYS ONE DATA POINT IS
  REMOVED AT 2 DAY INTERVALS)

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COMPARISON OF STAFF GAUGE AND AWLR/DWLR RECORDS
(4)

• PEN LEVEL ERRORS
• IDENTIFICATION
• GRADUALLY DRIFTING PEN DETECTED BY DEVIATION FROM
  STAFF GAUGE OBSERVATIONS
• CORRECTION
• ERROR ?X OBSERVED AT TIME t i k WHICH HAS
  COMMENCED k INTERVALS BEFORE
• X corr,j X meas,j - (j - i)/k?X
• for j i,
  i1, ., i k

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COMPARISON OF STAFF GAUGE AND AWLR/DWLR RECORDS
(5)

• ERRORS FROM STILLING WELL AND INTAKE PROBLEMS
• INDENTIFICATION
• TRUNCATED HYDROGRAPHS
• LAGGED RECORDS
• FLAT TRACES
• CORRECTION
• IF FLUCTUATIONS ARE SMALL REPLACEMENT BY STAFF
  GAUGE RECORD
• OF FLUCTUATIONS ARE LARGE USE OF RELATION CURVE
  IS PREFERRED

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COMPARISON OF STAFF GAUGE AND AWLR/DWLR RECORDS
(6)

• MISCELLANEOUS INSTRUMENT FAILURES
• (LIKE SILTING OF STILLING WELL, BLOCKING OF
  INTAKES, HUNG FLOAT, ETC.)
• IDENTIFICATION
• STEPPED TRACES
• FLAT TRACES
• CORRECTION
• INTERPOLATING A SMOOTH CURVE ON THE HYDROGRAPH
  PLOT

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FILLING IN MISSING DATA

• SHORT GAPS
• SIMPLE LINEAR INTERPOLATION WHEN LEVEL DIFFERENCE
  AT BEGINNING AND END OF GAP IS SMALL
• GAPS IN RECESSION CURVE
• EITHER INFILL AS DISCHARGE, OR
• AS WATER LEVEL BUT USING THE EXPONENTIAL DECAY IN
  DISCHARGE AND Q-H RELATION
• LONGER GAPS
• USE OF RELATION CURVE
• STANDARD ERROR SHOULD BE SUFFICIENTLY SMALL
• ADJUSTMENT MAY BE REQUIRED TO GET PROPER
  CONNECTION AT BEGINNING AND END OF GAP

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FILLING IN MISSING DATA

• GAP IN RECESSION CURVE
• RECESSION CURVE
• Qt2 Qt1 exp- ?(t2-t1)
• STAGE-DISCHARGE RELATION
• Q c(h a)b
• COMBINING
• ht2 (ht1 a)exp-?(t2-t1)/b - a

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USE OF RELATION CURVE WITH ADJACENT STATION

• FILLING IN MISSING RECORDS
• APPROPRIATE TECHNIQUE IF THE STANDARD ERROR IN
  THE RELATION IS SMALL
• IDENTIFYING AND CORRECTING MISREADINGS
• IDENTIFYING AND CORRECTING SHIFT IN
• GAUGE ZERO, THEN CORRECTION ONLY REQUIRED IF
• DISCHARGE RATING CURVE WILL NOT BE CHANGED
• LEVEL INFORMATION ITSELF IS OF IMPORTANCE
  (COASTAL ZONE)
• CHANGE IN CROSS-SECTION
• ESTABLISH NEW DISCHARGE RATING CURVE

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