The location of average velocity on the vertical free water flow

Summary

• 1. The relative coordinate η_V of the point (measuring from the bottom) where the local velocity is equal to the average velocity on the vertical in free turbulent flow decreases with an increase of the velocity factor C, which corresponds to an increase in η_V with an increase in roughness and a decrease in depth; this is expressed by (8) and (9).

• 2. The directions provided in the norms for the use of the single-point method of measuring the average velocity on the vertical for η_V=0.40 are valid if C>25 m^0.5/sec. For C<25 m^0.5/sec, it is recommended that η_V be determined according to Table 2 in dependence onn andh.

• 3. If we accept an allowance of Δη_V=1% for the placing of the instrument at the point in question, the problem arises of using variable values of η_V also for large values of C (C>48 m^0.5/sec); this problem can be solved by means of (8) and the graph in Fig. 1.