EQUIPMENT AND SUPPLIES--Equipment for the measurement of flow under ice

In Reply Refer To:                                         January 9, 1984
EGS-Mail Stop 415


Subject:  EQUIPMENT AND SUPPLIES--Equipment for the measurement of flow under

Reference is made to the Hydrologic Instrumentation Facility (HIF) Memorandum
No. 82.06 on the subject "Winter Equipment."  Studies of equipment for the
measurement of flow under ice are continuing.  This memorandum therefore
is for the purpose of stating interim policy on this subject.

                                Current Meters

Vertical-vane ice meters are individually rod rated.  Meters which were rated
prior to December 1, 1981, are rated only between 0.5 and 8.0 ft/s.  If, for
some reason, this meter with such a rating is used beyond these limits,
especially at the low end, the measurement uncertainty will be increased and
consideration must be given to reducing the indication of the measurement
accuracy.  If low velocities are common in the measurement section, type AA
or pygmy meters are to be used if possible.  The use of a pygmy meter under
ice for all depths and velocities is acceptable.

Vertical-vane ice meters are normally rod rated.  If this meter is to be
used with a cable suspension, it must be submitted to HIF for rating using
cable suspension conditions, if the meter has not been thus rated previously.

                                 Ice Weights

The use of the double spherical weights as a sounding-weight assembly for ice
conditions is no longer an acceptable practice.  Laboratory studies show this
assembly to be unstable at all velocities and especially for velocities greater
than 1.5 ft/s.  The use of conventional weights and meters with a collapsible
hanger assembly (sometimes referred to as a "slush-n-all" assembly) is recom-
mended.  All locally fabricated assemblies are to be rated by HIF.

If you have questions concerning equipment for the measurement of flow under
ice, call HIF.  If your questions have to do with the policies associated
with the measurement of flow under ice, please call the Surface Water Branch.

                                       Arthur L. Putnam
                                       Acting Chief, Surface Water Branch

WRD Distribution:  A, FO