SEASONAL VARIATION IN THE STAGE-DISCHARGE RELATIONSHIP OF THE MIDDLE MISSISSIPPI RIVER
The maximum seasonal variation in stage for the tested discharge condition (generally just above bankfull) ranged from 0.3 to 1.1 m. The gaging stations located along the alluvial section of the MMR generally showed the greatest seasonal variation. The maximum and minimum stages for these stations generally occurred during the summer and winter to early spring, respectively. In contrast, the bedrock-floored section showed no or an inverse trend.
Current river gaging and flood forecasting methods utilize averaged annual rating curves, in which stage-discharge relationship is assumed invariant throughout the year. The results of this investigation suggest this is not a valid assumption. The observed systematic variations in the stage-discharge relationship have been most commonly attributed to one of two mechanisms: (1) intra-annual variations in vegetation along channel banks and on the floodplain, and (2) variations over time in bedforms and bedform-induced roughness. The results suggest one or both of the mechanisms may be resulting in the seasonal variation along the MMR.