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CHANNEL EVOLUTION IN JARRELL BOTTOMS, TENNESSEE

Timothy H. Diehl

Jarrell Bottoms is the reach of the South Fork Obion River (SFO) and its associated wetlands from U.S. Highway 79 to just downstream from Christmasville Road, in Carroll County, Tennessee. Channelization of the river isolated sections of the original channel from the newly constructed drainage canal. Drift and sediment filled the SFO drainage canal in two reaches, first at the mouth of Reedy Creek and, later, just downstream from the Louisville and Nashville Railroad bridge. These two blockages created a valley plug and diverted the flow of the SFO across the valley bottom and into sections of its previous meandering channel. The SFO is gradually establishing a single main channel through this valley plug, with most sections of the new channel containing the base flow of the river.

The flow pattern around the more recent upstream blockage includes ponded areas and multiple channels. Just upstream from the railroad bridge, most base flow leaves the canal and flows southwest in the ditch between the railroad and U.S. Highway 79. The remainder of the base flow exits the ditch just downstream from the railroad and flows through a small channel leading northward toward the original channel. At the south edge of the valley bottom, the main flow passes through a relief bridge under the railroad. Sand passing under the relief bridge is building a delta that presently extends about 600 feet westward from the bridge. Below this delta, the SFO flows through a large ponded area, then through a sinuous channel that reenters the drainage canal between the two blockages.

Flow in the reoccupied natural meandering channel bypasses the second, less recent blockage. At the upstream end of the blockage at the mouth of Reedy Creek, several small channels flow northward from the canal to a meandering channel in the open marsh. This channel rejoins the natural channel at the mapped location of the Todd Creek drainage canal, which is filled with sediment. The SFO follows its natural channel from the former location of the Todd Creek ditch to Christmasville Road. Just downstream from Christmasville Road, most flow reenters the canal through a short cutoff that has formed since 1991.

All the sand carried into Jarrell Bottoms by the SFO accumulates within a short distance downstream from the railroad. As a result, the SFO has excess bedload transport capacity in the two short multiple-channel reaches downstream. It will likely widen and deepen the largest of the multiple channels in each of these reaches. The smaller channels may remain open, because little sediment enters them, or woody debris may block them. Throughout Jarrell Bottoms, the apparent trend is toward the formation of a well-defined channel conveying the base flow.

The depth of the reestablished main channel is adequate for small boats even during summer low flow. Hunters and fishermen maintain a boat trail passable by canoes and johnboats through most of Jarrell Bottoms by cutting small gaps in drift that blocks the dominant channel. In multiple-channel reaches, these gaps concentrate flow in the deepest channel. Boat-trail maintenance is contributing to the reestablishment of a single main channel throughout Jarrell Bottoms.


Cite this report as:

Diehl, T.H., 1997, Channel evolution in Jarrell Bottoms, Tennessee, in Gangaware, T., LeQuire, E., Perry, K., and Cordy, T., (eds.), Extended abstracts from Seventh Tennessee Water Resources Symposium: Nashville, Tennessee, American Water Resources Association Tennessee Section, p. 267-268.

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