Channelization effectiveness in the Obion River Basin, West Tennessee

Channelization, the straightening and enlargement of a stream channel, was implemented for flood control and land drainage and reclamation purposes on the Obion River, a tributary of the Mississippi River in West Tennessee. I establish two hypotheses to investigate the effectiveness of channelization: (1) that shortened river lengths and increased surface water gradients may have increased flooding downstream, and (2) that low gradients and poor drainage, not overbank flooding, may be the primary causes of lowland wetness that inhibits crop production on the floodplain. Gage height and water budget analyses, topographic map interpretation, interviews with farmers, and soil surveys were used to determine whether or not channelization has significantly helped farmers on the Obion River watershed. Comparing overbank flooding events before and after channelization on the middle reaches of the Obion River revealed that the number of growing season flood days has been reduced, but the increased hydraulic efficiency has resulted in more dramatic river level increases in the downstream reaches during growing season floods following channelization. Lowland wetness that follows major precipitation events in the Obion River basin appears to be a consequence of poor surface water drainage on the floodplain and soil characteristics such as low gradients and low soil permeability. Channelization was intended to improve agricultural conditions by reducing flooding, but the wetness problem on croplands is a result of natural topographic and soil conditions and not of overbank flooding. The justification to use channelization as a means of reducing lowland wetness for cropland reclamation in the Obion River basin has been shown to be inappropriate.