Construction, Calibration and Use of Flush Mounted Wall Shear Stress Probes

As part of an investigation into the response of pool-riffle sequences in rivers to variations in the flow rate, a method measuring the local bed shear stress on a fixed sinusoidal bed form was required. This paper describes the development and use of suitable bed shear stress probes. The direct measurement of boundary shear stress in open channel flows is notoriously difficult, since the associated velocity gradient occurs in an extremely thin layer adjacent to the surface. In the present study, the range of shear stress required to be measured was 0.1 – 8 N/m2. Measurement of boundary shear stress was required in at least 27 positions in the experimental rig. Sufficient accuracy was required to develop a coherent profile of shear stress and allow the positions of maximum and minimum shear stress to be determined.