In Reply Refer To:                              November 20, 1991
Mail Stop 415


Subject:  EQUIPMENT--Current Meters for Measurement of Flow
                     During Ice Conditions

There is considerable confusion about the correct current meter to
use for discharge measurements when ice is present.  The purpose
of this memorandum is to provide guidelines on this subject.

Vane-type meters were developed by WRD in an attempt to find a
meter rotor that did not fill with slush ice as open metal cups
tend to do.  Several vane-type meters, with slightly different
vane and yoke configurations, have been used.  While these meters
are effective at shedding slush, their low-velocity performance is
poor.  In 1988 these meters were discontinued from the Hydrologic
Instrumentation Facility (HIF) warehouse.

Office of Surface Water Technical Memorandum No. 88.18 stated that
the preferred metering equipment for ice conditions is a type AA
current meter built with a Water Survey of Canada (WSC) winter-
style yoke with a polymer rotor.  The WSC winter-style yoke had
proven itself for many years with the conventional metal-cup
rotor.  The polymer rotor had gained popularity with field
personnel for making discharge measurements during ice conditions
because it does not fill with slush as does the metal-cup rotor,
and because ice does not easily adhere to the polymer material.

Office of Surface Water Technical Memorandum No. 90.01 established
policy that meters with polymer rotors, including those for
measuring during ice conditions, should not be used because of
inaccuracies in measured velocities where the flow is noticeably
turbulent.  This policy has now been revised, but only for making
measurements during ice conditions.  The superior ability of the
polymer rotor to shed slush ice and retard freezing is considered
to be more important than turbulent-flow considerations on ice-
covered streams.

This memorandum revises policy to permit the use of polymer rotors
in winter-style AA meters for conditions where slush ice is
present.  The winter-style AA meters with metal-cup rotors are
preferred for slush-free measurements during ice conditions.
Regular AA meters (with metal-cup rotors) are also acceptable for
slush-free conditions, if cutting the required larger holes
through the ice is not a problem.

Winter-style meters with both polymer and metal rotors are
available from the HIF.  Winter rods in both 1/2- and 1-inch
diameters are available for suspending this style of meter.  Where
cable suspension is required, tilting harness assemblies for
30- and 50-pound standard sounding weights are available.  These
harness assemblies are designed to pass the weight and meter
through an 8-inch diameter hole.  Under-ice video taping of
various types of sounding weights by WSC during the winter of 1991
shows this weight-meter assembly to perform acceptably.  All
winter-style meters must be individually rated with the suspension
device that will be used with it.

Winter-style meters and related equipment are available from the
HIF, which will arrange for individual ratings.  The following are
appropriate stock numbers and descriptions

Meter, Winter-Style, Metal Rotor, No Rating            1104001
Meter, Winter-Style, Polymer Rotor, No Rating          1104002
Rod, 1/2-inch, Extension Section                       2102005
Rod, 1/2-inch, Lower Section for Winter Meters Only    2102013
Rod, 1-inch, Extension Section for Winter Meters Only  2103002
Rod, 1-inch, Lower Section for Winter Meters Only      2103003
Foot, fits 1/2-inch or 1-inch rods                     2103001
Harness, Tilting, for 30 lb. weight                    3305001
Harness, Tilting, for 50 lb. weight                    3305002

For special applications, please call Russ Wagner at 494-1580 or
(601) 688-1580, and for special ratings call Bill Kaehrle at
494-1526 or (601) 688-1526.

The Office of Surface Water is currently engaged in an extensive
review and testing of all available current meters.  This study
may provide information on better equipment for all field
conditions, including meters for making measurements during ice
conditions.  However, there is no certainty that a better meter
will be found and stocked in the next several years.  The above
recommendations provide for use of consistent equipment until
improved instrumentation is obtained.

                                  Charles W. Boning
                                  Chief, Office of Surface Water

WRD Distribution:  A, B, PO, FO

This memorandum supersedes parts of Office of Surface Water
Technical Memorandum 90.01.