A submersible device for measuring drag forces on aquatic plants and other organisms

Fraser M. Callaghan, Glenn G. Cooper, Vladimir Ivanovich Nikora, Nicolas Lamouroux, Bernhard Statzner, Pierre Sagnes, John Radford, Emmanuel Malet, Barry J. F. Biggs

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)


This paper describes a device, the submersible drag gauge (SDG), that can be used for drag measurements in studies of flow-biota interactions at low (setup A) and high (setup B) load applications. The device is designed so that solely drag forces acting on a test object in a boundary layer flow are measured. The SDG can measure drag on organism(s), such as macrophtyes, crayfish or mussels, as well as a combination of such organisms and sediments assembled in a variety of arrangements in both laboratory and field conditions. Laboratory calibrations over the range of 0 to 4 N showed that setup A registered forces as low as 0.02 N, whereas setup B often did not register forces up to c. 0.15 N. The relative standard error of drag measurements was < 3% for forces > 0.2 N (setup A) or < 4% for forces > 1 N (setup B). Using a rigid cylinder, and natural and artificial (plastic) Egeria densa as examples, showed how the SDG can serve in studies of flow-biota interactions such as drag-velocity relations, assessments of drag coefficients, or the frequency spectrum of macrophyte drag.

Original languageEnglish
Pages (from-to)119-127
Number of pages9
JournalNew Zealand Journal of Marine and Freshwater Research
Issue number1
Publication statusPublished - Mar 2007


  • drag gauge
  • plant dynamics
  • flow-biota interactions
  • boundary layer flow
  • experimental flume
  • fresh-water macrophytes
  • shear-stress
  • circular-cylinders
  • flow resistance
  • cross-flow
  • reconfiguration
  • adaptations
  • vegetation
  • BED


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