Biological Systems Engineering


Date of this Version



Published in JOURNAL OF IRRIGATION AND DRAINAGE ENGINEERING 119:5 (September/October 1993), pp. 912-914.


The writers appreciate the interest expressed by the discussers in this manuscript, and are pleased to have the opportunity to further discuss this material. The discussion states that the writers have generally examined a condition already investigated in other previous studies. Reynolds number values and roughness element size for the articles referenced by the discussers are shown in Table 5. Since flow rate and Reynolds number values were not given by Ferro and Giordano (1991), data from this study are not included in Table 5.
It can be seen from Table 5 that the roughness element sizes examined by Bathurst (1978) were much larger than those used by the writers. Each of the other studies was conducted to obtain information for use on river systems. The focus of this paper, in contrast, was upland areas. Thus, Reynolds number values employed by the other authors were substantially larger than those used in this investigation.
The discussers reference material presented by Colosimo et al. (1988) to characterize flow conditions occurring in this study. It can be seen from Table 5 that the smallest Reynolds number value used by Colosimo et al. (1988) was 25 times greater than the largest Reynolds number value employed in this investigation. Certainly for river systems, with flow depths much greater than roughness element heights, Reynolds number may have a minimal effect on friction factor. However, for upland areas with much smaller water depths, friction factors may be substantially affected by Reynolds numbers. This influence is clearly shown in Figs. 2, 3, and 4.