COMPUTATION OF DISCHARGE DATA GENERAL DISCHARGE CANNOT BE
COMPUTATION OF DISCHARGE DATA GENERAL: – DISCHARGE CANNOT BE MEASURED DIRECTLY AND CONTINUOUSLY – STAGE MEASUREMENTS h(t) ARE MADE CONTINUOUSLY OR AT FIXED INTERVALS – h(t) IS CONVERTED INTO DISCHARGE Q(t) BY USING THE Q-h RATING CURVE – COMPUTATION OF Q(t) IS DONE MONTHLY ON THE STAGE DISCHARGE OF THE PREVIOUS MONTH NOTE: OHS - 1 – Q(t) REVIEWED ANNUALLY BEFORE TRANSFER TO THE ARCHIVE – TRANSFORMATION DONE AT DDPC AND REVIEWED AT SDPC
STATION REVIEW • BEFORE COMPUTING Q(t): – A SUMMARY OF ALL RELEVANT INFORMATION FOR THE STATION SHOULD BE AVAILABLE, INCLUDING: * STAGE RECORD * LISTING OF ALL RATING CURVES WITH VALIDITY PERIOD TO AVOID OVERLAP OF OR GAPS BETWEEN RELATIONS * ANCILLARY INFORMATION FROM THE FIELD RECORD BOOK AND RATING RELATIONS OHS - 2
TRANSFORMATION OF STAGE TO DISCHARGE AVAILABLE PROCEDURES IN HYMOS: – SINGLE CHANNEL RATING CURVE – COMPOUND CHANNEL RATING CURVE – RATING CURVES WITH UNSTEADY FLOW CORRECTION – RATING CURVES WITH CONSTANT FALL CORRECTION – RATING CURVE WITH NORMAL FALL CORRECTION – RATING CURVES FOR HYDRAULIC STRUCTURES OHS - 3
SINGLE CHANNEL RATING CURVE • USE: – WHEN A ONE-TO-ONE RELATIONSHIP BETWEEN STAGE AND DISCHARGE EXISTS: * WHEN UNSTEADY FLOW EFFECTS ARE NEGLIGIBLE * WHEN BACKWATER EFFECTS ARE NON-EXISTING * WHEN NO SIGNIFICANT FLOOD PLAINS ARE AVAILABLE OR * NO EXTRA RELATION IS REQUIRED FOR THE FLOOD PLAIN FLOW • TYPES: – POWER TYPE EQUATION – PARABOLIC TYPE EQUATION OHS - 4
SINGLE CHANNEL RATING EQUATION POWER TYPE EQUATION – MAXIMUM 5 WATER LEVEL SEGMENTS – CHECK VALIDITY PERIOD – PREFERRED ABOVE PARABOLIC EQUATION PARABOLIC TYPE EQUATION – MAXIMUM 5 WATER LEVEL SEGMENTS – CHECK VALIDITY PERIOD OHS - 5
COMPOUND CHANNEL RATING CURVE MAIN RIVER FLOOD PLAIN TOTAL FLOW OHS - 6
RATING CURVE WITH UNSTEADY FLOW CORRECTION PROCEDURE: – Qst FROM STEADY STATE RATING – COMPUTE THE FACTOR 1/S 0 c – COMPUTE h/ t FROM THE HYDROGRAPH – COMPUTE Q(t) BY JONES FORMULA OHS - 7
RATING CURVE WITH CONSTANT FALL CORRECTION PROCEDURE: – REFERENCE Qr(t) IS COMPUTED FROM h(t) – WITH SIMULTANEOUS READING AT SECOND STATION FALL Ft IS COMPUTED – Fr AND p ARE READ FROM THE RATING PARAMETER DATABASE – ABOVE EQUATION IS APPLIED OHS - 8
RATING CURVE WITH NORMAL FALL CORRECTION PROCEDURE: – REFERENCE Qr(t) IS COMPUTED FROM h(t) – WITH SIMULTANEOUS READING AT SECOND STATION FALL Ft IS COMPUTED – Fr IS DETERMINED FROM LEFT EQUATION AS FUNCTION OF h(t) AND p ARE READ FROM THE RATING PARAMETER DATABASE – ABOVE EQUATION IS APPLIED OHS - 9
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