Discharge response to channelization of a coastal plain stream

Abstract

The Obion River in western Tennessee was channelized by the U.S. Army Corps of Engineers in the 1960s. The primary purpose was to reduce flooding that inhibits agricultural productivity in the lower bottomlands. Channel enlargement and straightening has improved hydraulic efficiency. The increase in water velocity has effectively decreased flooding in the upper sections of the Obion River. However, runoff from the channelized portion of the drainage basin converges at downstream locations faster than the stream channel can accommodate, resulting in higher peak discharges and an increase in flood frequency. During the growing season months (May–October), the number of floods on the lower Obion River increased 140 percent following channelization. The greater flow efficiency allows water to move rapidly out of the Obion River drainage, decreasing the average duration of flood events. Brief periods of inundation, however, can destroy crops; therefore, the change in flood duration caused by channelization is not a desirable alternative to the higher number of floods that also occur. Conditions for bottomland cultivation have improved in the upper channelized sections of the Obion River. However, the higher flood frequency during the growing season on the lower river segments will limit agricultural productivity, which is contrary to the initial justification for channelization.