PRIMARY VALIDATION OF WATER LEVEL DATA OBSERVED DATA

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 OHS - 1 * ELEVATION OF WATER SURFACE W. R. T CERTAIN DATUM * BASIC DATA REPRESENTING THE STATE OF A WATER BODY * USED FOR COMPUTATION OF DISCHARGES USING STAGEDISCHARGE RELATIONSHIPS * QUALITY OF STAGE DATA INFLUENCES RELIABILITY OF DISCHARGE DATA DIRECTLY * OTHER USES - NAVIGATION, INUNDATION, RESERVOIR LEVELS ETC.

• 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

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 OHS - 3 * STAFF GAUGE * AUTOGRAHIC RAINGAUGE * DIGITAL RECORDER

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

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

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 OHS - 6 – PARTIAL BLOCKAGE IN STILLING WELL * SERIOUS SYSTEMATIC ERRORS

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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