Developing engineering design criteria for ecologically sound road crossings for endangered fish in Georgia

Research was carried out to determine the extent to which road crossings, especially culverts, act as barriers to the passage of the Cherokee darter (Etheostoma scotti) and other small weak-swimming fish in small streams of the Etowah River Basin, in north Georgia. Barriers to fish passage include excessive velocities, scouring and drops at culvert outlets, low depths and excessive turbulence. Physical parameters of 70 small stream road crossings (less than 50 km2 drainage area) were measured and assessed for fish passage suitability against literature criteria. Statistical analysis indicated that most pipe and box culverts in the Etowah River Basin impact fish passage. For passage of weak-swimming fish, a natural streambed or similar should form in culverts. This requires bridges, bottomless culverts or adequately sized, embedded culverts, resulting in larger culvert spans, especially for the smallest streams studied. Costs of road crossing options were compiled and engineering design criteria were developed.