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XXVI I
It is noted that the daily mean flow are mostly subject to upstream diversion. Headwater utilization of
water by people diversions and state-owned diversions are expected in many river basins in this country.
Consequently, the virgin flow is hardly determined. Daily mean values may be replaced by the monthly mean
in the case of flow measured at tail waters of existing reservoirs.
Time basis used for daily mean flow is from midnight to midnight.
Review of procedure for stream flow data processing.
Following are steps used for review the overall data before finalizing the process:
1) Checking of gage height data which are obtained either from staff gage or from water stage
recorder, for the following cases:
a) Representability of daytime observation for the daily mean value, if the data are from staff
gage reading.
b) Discrepancies of recording charts, if any.
c) Desirability of hourly-basis process for daily mean flow.
d) Datum’s of gage observation and of the rating curve used.
e) Location of gage from which data are taken and location of gage at which the rating curve
is developed.
2) Checking of availability and goodness of field measurement notes.
3) Checking of differential magnitude of gage height during discharge measurement as to which
arithmetic average or weighted average is desirable.
4) Checking stability of rating curve used.
5) Review of shifting control sample and design shifting, if any.
6) Adjustment of backwater, flood wave, etc., by rate of change of falls as index, if any.
7) Overall review of daily mean flow data as an end product.
8) Checking consistency of runoff volume among those observed at the upstream and downstream
stations, taking into account intervening diversions of flow, if any.
Classification of stream flow data
The station description states the degree of accuracy of the records. “Excellent” indicates that, in
general, the error in the daily records is believed to be less than 5 percent; “good”, less than 10 percent; ‘fair”,
less than 15 percent; “poor”, probably more than 15 percent.