1 / 17

CORRECTION AND COMPLETION OF WATER LEVEL DATA (1)

A continuous process of validating and correcting incorrect or missing water level data using interpolation or relations. Suspect values will be inspected and corrected if necessary or flagged if acceptable.

rodericki
Download Presentation

CORRECTION AND COMPLETION OF WATER LEVEL DATA (1)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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 OHS - 1

  2. 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’ OHS - 2

  3. 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 OHS - 3

  4. 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 OHS - 4

  5. 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 OHS - 5

  6. 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 OHS - 6

  7. 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) OHS - 7

  8. 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, i+1, …., i + k OHS - 8

  9. 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 OHS - 9

  10. 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 OHS - 10

  11. OHS - 11

  12. OHS - 12

  13. 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 OHS - 13

  14. OHS - 14

  15. 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 OHS - 15

  16. 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 OHS - 16

  17. OHS - 17

More Related