This approach has the potential to solve a number of the problems of fish passage through culverts. Figure 6 is a drawing of such an artificially rough culvert bottom. Based on the literature review, the study concluded that the maximum flow velocities for anadromous fish are much greater than those of Virginia's nonanadromous trout. These factors all depend on culvert slope. One solution to the fish passage problem would be to increase the roughness coefficient of culvert bottoms, which in turn would allow installing culverts at steeper slopes without affecting fish passage.
Culverts can be the best way to cross trout streams in Virginia, provided certain actions are taken.
The culvert should be on the same slope as the streambed. The slope of the stream should be less than 3 percent. The culvert barrel should be properly countersunk at the outlet. In addition, newly installed culverts should not use baffles to control stream flow, and concrete aprons should not be used at culvert outlets. If these actions are not possible or feasible, then bridges should be constructed.