A large culvert in a small stream can be good news for water flow but bad news for fish movement. That was the case a few years ago at a stream culvert along State Route 53 in Pickens County, Georgia. When the culvert was extended to a four-barrelled structure to accommodate seasonal high flows, the improvement changed the width of the stream inside the culvert from 4 feet to 40 feet. During periods of low and normal water flow, the resulting water depth was predicted to be 1/2-inch or less--far too shallow for the stream's tiny, federally-listed as threatened, Cherokee darter. Even if the darters managed to swim through the culvert they would not get far because of a shallow silt-filled "lake" below. Georgia Department of Transportation (GDOT) biologists solved both problems by installing a vertical wall in the middle of one outside barrel. The construction also included a low sill across the inlet in front of the remaining 3-1/2 barrels which diverts water to the outside barrel during low-water flows. During higher flows, the water spills over into the entire culvert. Thanks to the partition and the sill, the Cherokee darters have the stream conditions they need to move freely and to travel to Long Swamp Creek and into smaller streams for spawning and rearing their young. The easy solutions saved time, too, allowing GDOT crews to complete willow staking, native-grass planting, and other on-site environmental tasks.
--Aug 21, 2006
|Photo by Wesley King|
|During low flows, water is channeled into only one of the box culverts.|