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

Abstract

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 now 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 0.2 N (setup A) or 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.

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