Preliminary stage-discharge relations for Tombigbee River at Gainesville Dam, near Gainesville, Alabama

The construction of Gainesville Dam and other related channel alterations, completed in 1979, has resulted in changes to the stage-discharge relations in the vicinity. The lack of current-meter measurements, coupled with backwater conditions, makes definition of a single stage-discharge relation impossible. However, limit curves can be defined that would encompass such a relation. Backwater is defined as water backed up or retarded in its course as compared with water flowing under normal or natural conditions. This results in a rise in stage above normal water level while the discharge remains unaffected. Backwater is usually caused by temporary obstruction(s) to the flow downstream. Backwater at Gainesville Dam is due to large tributary inflow and return of flood plain flows to the main channel during recessions. The discharges obtained from 105 computations of flow through the dam for the tailwater and 59 for the pool were plotted versus stage. These plots illustrate, by the scatter of these data points, the variations in backwater. Curves were drawn to envelope the extreme plot patterns showing possible ranges of several feet in stage for any given discharge for both the pool and the tailwater.