C. Hydrometric Survey Equipment
This section describes the basic equipment required to measure water level or stage and velocity, as well as several other equipment items that make measurement systems more efficient and versatile.
This section describes the instrumentation used to collect automatically continuous water level records, and methods of installation. There are two distinctive recording systems common to hydrometric surveys: analogue, or graphic; and digital. The analogue recorder has been in continuous use since early in the 20th century and is still widely used in Canada. The digital system, on the other hand, came into common use for water level recording only in recent years.
The digital recording system has replaced the analogue recorder for many applications, although neither system is foolproof. For particularly sensitive or important sites, it is common to use both; the digital system as the primary and the analogue as a back-up.
All automatic water level recorders require some form of manual reference to the water level at the time of installation, and again at all subsequent visits to the station by the technician. The reference gauge should be installed in close proximity to the recording device. Manual reference gauges are described in Section B.2.3.
A graphic water level recorder is an instrument that provides a permanent and continuous long-term record of water level variation. A clock movement controls the rate at which a strip chart advances. At the same time, a float in contact with the water surface activates a marking stylus or pen which reproduces the float's vertical movement on the strip chart.
Graphic recorders can record a virtually unlimited range of stage. They provide a low cost record of stage when installed at lakes or reservoirs, and they may be used to provide a record of flow rates, for licensing purposes, below diversion structures in rated channels designed to transport water at a near constant rate.
Two types of graphic recorders, Type F and Type A, are manufactured by the Leupold Stevens Company of Beaverton, Oregon. Similar models are manufactured by Sherlock Instruments in Australia and by Ott in Germany.
Graphic or Analogue Recorders are described in Appendix-III which also includes instructions on their installation, operation and maintenance.