Abstract
In an effort to obtain a better understanding of the resistance characteristics of a flow passing through a foot protection construction of a diversion weir, the effects of a submerged overflow were researched. The following facts were obtained.
1. The energy loss due to flow passing through a foot protection construction was affected by the extent to which the overflow of the weir was submerged and this energy loss was smaller than the loss of a protective device of the same construction which was set up in an open channel flow with the same discharge and depth. The difference between these energy losses increased as the flow state approached the boundary of the free and submerged overflow, and decreased with an increase in depth, with both the losses reaching the same value. It was considered that this phenomenon was due to the difference in the velocity distribution of the flow coming into the protective construction of each channel.
2. The ratio, nr, of nw to n0 for the flow state is the same (where nr=nw/n0, nw is Manning's roughness coefficient for the foot protection construction of the weir, and n0 is the roughness coefficient for the case in which the same construction is set up in an open channel flow) is related to the degree of submerged overflow, Hr and Hrc (where Hr=H2/H1: H1 and H2 are the total energy in the upstream or downstream of the weir based on the crest, respectively; and Hrc is Hr at the boundary of the free and submerged overflow of the weir).
The relationship is represented by the equation,
nr=1-0.6001-Hr/1-Hrc.
