EQUIPMENT AND SUPPLIES--Equipment for the measurement of flow under ice In Reply Refer To: January 9, 1984 EGS-Mail Stop 415 SURFACE WATER BRANCH TECHNICAL MEMORANDUM NO. 84.05 Subject: EQUIPMENT AND SUPPLIES--Equipment for the measurement of flow under ice 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