Discussion of “Artificial roughness standard for open channels”

The need of fundamental studies on the resistance to flow in open channels is becoming more generally recognized, and this paper is a valuable contribution to the problem. The fact that each paper that has appeared in the last few years comes to somewhat different conclusions points up the need for still further research in this field. At any rate it has been pretty well proved that the formula proposed by the writer in 1950 is not the final answer. On the other hand, the eminent authority Thijsse [1951] has agreed that these efforts are in the right direction. It is only at a few minor points that the writer would criticize this excellent paper. It would seem that 14 ft was much too short a length for an experimental channel of this sort, even when the six-foot entrance section is taken into account. It is very difficult in so short a flume to be sire that uniform flow has been established, and it is hard to determine the slope accurately.