PRIMARY VALIDATION OF WATER LEVEL DATA

1. PRIMARY VALIDATION OF WATER LEVEL DATA • OBSERVED DATA MAY BE SUBJECTED TO ERRORS • RANDOM, SYSTEMATIC AND SPURIOUS • AIM OF VALIDATION IS TO DETECT SYSTEMATIC ERRORS & SPURIOUS VALUES • WATER LEVEL DATA • ELEVATION OF WATER SURFACE W.R.T CERTAIN DATUM • BASIC DATA REPRESENTING THE STATE OF A WATER BODY • USED FOR COMPUTATION OF DISCHARGES USING STAGE-DISCHARGE RELATIONSHIPS • QUALITY OF STAGE DATA INFLUENCES RELIABILITY OF DISCHARGE DATA DIRECTLY • OTHER USES - NAVIGATION, INUNDATION, RESERVOIR LEVELS ETC. OHS - 1

2. PRIMARY VALIDATION - AT SUB-DIV. DPCs • DATA COMPARISON AT SINGLE STATION • INDIVIDUAL OBSERVATION & PRE-SET DATA LIMITS • MAXIMUM & MINIMUM • UPPER & LOWER WARNING LEVELS • MAXIMUM RATE OF RISE AND FALL • TWO MEASUREMENTS OF A VARIABLE • MANUAL OBSERVATIONS & AUTOMATICALY RECORDED OHS - 2

3. EQUIPMENT & OBSERVATION METHODS • SOURCES OF ERRORS • METHOD OF MEASUREMENT • TYPICAL ERRORS IN EQUIPMENT OR TECHNIQUE • DATA VALIDATION EXERCISE • NOT TO BE PURELY STATISTICAL • FIELD PRACTICES MUST BE CLEARLY UNDERSTOOD • AWARENESS ABOUT THE DISTURBANCES ALONG RIVER SIDES • THREE BASIC EQUIPMENT • STAFF GAUGE • AUTOGRAHIC RAINGAUGE • DIGITAL RECORDER OHS - 3

4. STAFF GAUGE • INSTRUMENT & PROCEDURE • PRIMARY MEANS OF MEASUREMENT • ZERO OF GAUGE FORMS THE DATUM AT STATION • OTHER AUTOMATIC GAUGES ARE CALIBRATED & CHECKED AGAINST STAFF GAUGE • TYPICAL ERRORS • MISPLACEMENT OF DECIMAL POINTS • 0.01, 0.10 • 4.12, 4.10, 4.9, 4.6, 4.3, 4.1, 3.99 • 4.12, 4.10, 4.09, 4.06, 4.03, 4.01, 3.99 OHS - 4

5. DATA “ESTIMATED” BY OBERVERS • ESTIMATION BY FABRICATION • WITHOUT VISITING THE STATION • MAY SHOW UP AS INCONSISTENT HYDROLOGICAL SEQUENCES • ABRUPT FALL OR CHANGE IN SLOPE OF A RECESSION CURVE • LARGE PERIODS OF UNIFORM LEVEL FOLLOWED BY DISTINCT FALL • UNIFORM MATHEMATICAL SEQUENCES - FALL BY 0.05 TO 0.10 OHS - 5

6. AUTOMATIC WATER LEVEL RECORDER • INSTRUMENT & PROCEDURES • VAST MAJORITY OF AGR • FLOAT & PULLEY WITH STILLING WELL • CHART IS CHANGED - DAILY/ 7-DAILY • TYPICAL ERRORS • INSTRUMENT MALFUNCTION • CHART TRACE GOES UP WHEN THE RIVER GOES DOWN • FLOOD HYDROGRAPH TRUNCATED • STAFF GAUGE AND CHART DISAGREE • CHART TIME & CLOCK TIME DISAGREE • PARTIAL BLOCKAGE IN STILLING WELL • SERIOUS SYSTEMATIC ERRORS OHS - 6

7. DIGITAL WATER LEVEL RECORDER • FLOAT TYPE • MECHANICAL LINKAGE REPLACED BY SHAFT ENCODER • ELIMINATES MECHANICAL LINKAGE ERRORS • PEN TRACE ERRORS • IN STILLING WELLS • PRESSURE TRANSDUCER TYPE • WITHOUT STILLING WELL • ERRORS ASSOCIATED WITH STILLING WELL ARE AVOIDED • DATA CORRUPTION IS POSSIBLE DUE TO OTHER ELECTRONIC OR SENSOR’S MALFUNCTIONING • STAFF GAUGE DATA IS USED AS BASE OHS - 7

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