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XXV
STANDARD OF STREAMFLOW DATA PROCUREMENT
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Ne twor k des i gn
The location o f stream gauging stations is primarily based upon the urgent need at various dam sites
which is accessible. By the time of expansion of the network at later date, the area or basin of "blind spot" is
put at first priority backing up by the following conditions:
(a)
Accessibility.
(b)
Geographical location.
(c)
Mean annual rainfall.
(d)
Vegetation cover determined from Army Map Service topographic map with
1:50,000 or 1:250,000 scale.
(e)
Basin soil type.
( f ) Type of surface rock.
Field work
The minimum standard of basic hydrologic data for observations and measurements are equal to
those recommended in the United Nations ECAFE Flood Control series No.6.
Water stage data are obtained by staff gage and by water stage recorder. Normally a vertical section
staff gage is installed for manual observation with usual frequency of reading varies from 1 to 5 times of equal
interval during the daytime. At some specific station where stream flow measurement camps are situated, the
reading of water stage by night is also made, in addition, usually 1 to 3 times of equal interval. The standard
bench mark is also established near the gage site. The 1.00 - m standard enameled staff gage section with 1
cm graduation are used with zero reading, in most cases, referred to Mean Sea Level (M.S.L.) Ko Lak datum,
otherwise the assumed datum begin used. Few wire - weight gages are also adopted on highway bridges.
In some mountainous headwater area as well as in the estuary, additional installation of water stage
recorder is made. A continuous record of water stage is obtained at such station. The German A. Ott type X
has so for been adopted as our standard equipment. Some pneumatic recorder is also being used. Weekly
visit to the gage for inspection and changing chart paper by the crew or gage observer is under practice.
At the stream flow gauging station, flow measurement by a current meter is periodically performed so
that the calibration of stream section related to flow can be made through the development of stage - flow
relationship or simply called " rating curve ". Two types of the stream flow gauging station are under operation:
with and without crew camp. Those without crew camp are under moving team and are capable for flow
measurements of several stations. Those with crew camp are subject to less accessibility.
At station operated by a moving crew, at least twice a month during the monsoon period and once a
month during the low flow period are expected for flow rating performance. The moving crew frequently fails
to reach the stations while at their crest stages because of road damage and time available. At station with