Measurement of local bed shear stress in streams using a Preston-static tube. (Notes)

Local bed shear stress ([[tau].sub.w]) is a fluid dynamic parameter of importance in determining the physical and biological characteristics of stream-bed environments. Unfortunately, it is often difficult to measure ([[tau].sub.w]) under field conditions. Herein we describe the use of a Preston-static tube, which is essentially a surface-mounted Pitot-static tube, to measure [[tau].sub.w] in mountain streams. Our results indicate that it is possible to measure local shear stress quickly, consistently, and inexpensively in the field. This technique also provides high spatial resolution, which should allow for detailed in situ studies of local shear stress at scales relevant to lotic organisms. Such information will be invaluable in studies of benthic organisms and hydraulically relevant phenomena in the near-bottom zone of lotic systems.