3. Use of Current-Meter Gaging Stations

Current-meter gaging stations are permanent or semipermanent stations located along a watercourse where flow conditions permit the establishment of a discharge rating curve based upon multiple current-meter measurements. After the rating curve has been established, the rate of flow is determined from the curve based on the measured depth of flow at the station. If measurements become necessary in existing streams or canals, current-meter gaging stations can be set up with relatively little effort and usually without modification to the channel.

Current-meter gaging stations are often preferred over other means of water measurement when large flows are to be measured and head loss is costly, or when freeboard is not available. They may also be desirable for sediment-laden flows even when discharges are not large. However, excess sediment and seasonal growths of weeds can change head versus discharge relationships, requiring frequent preparation of new rating curves. The frequent rating shifts can become labor intensive, and flumes may be the better choice. Where flow depths are too small for current meters and only small heads are possible, flumes are probably the best alternative measuring method.

The discussion of current meters, gaging stations, and operational procedures presented in this chapter is brief and is intended mainly to stress the more typical irrigation water measurements that may be made by this method. For more detailed information, refer to USGS Water Supply Paper No. 888 (USGS, 1965), Buchanan and Somers (1969), the National Handbook of Water-Data Acquisition (USGS, 1980), and Wahl et al. (1995).