CHANNELIZATION EFFECTS ON OBION RIVER FLOODING,WESTERN TENNESSEE1

ABSTRACT: Much of the Obion River in western Tennessee was channelized into the 1960s. Stage data from three stream-flow gaging stations on the Obion were used to determine how channelization affected flood frequency and annual maximum stage. Channelization affected the upper and lower Obion River differently. Flooding has become infrequent on the upper Obion River since channelization, even during the winter and spring which is the wettest time of year. In contrast, except for the winter months, there has been little effect on flood frequency on the lower Obion River where stage is highly dependent on the Mississippi River. The Mississippi River often backs up and floods the Obion River more than 50 km above its mouth and may contribute to flooding at an even greater distance upstream by reducing the water-surface gradient and slowing discharge. Channelization on the upper section of the river and many of the small tributaries has increased flow efficiency, but has also caused channel erosion and downstream deposition, reducing the cross-sectional channel area and possibly contributing to downstream flooding. Maximum annual stages at the upper and lower Obion River changed little. Therefore, the maximum surface area, submerged at least once each year, has been unaffected by channelization.