Estimating discharges for historic floods along the middle and lower segments of the Mississippi River

Authors: Jonathan W.F. Remo*, Department of Geography and Environmental Resources, Southern Illinois University, Carbondale, Matthew D. Therrell, Department of Geography, University of Alabama
Topics: Water Resources and Hydrology, Hazards, Risks, and Disasters, Coupled Human and Natural Systems
Keywords: Historic Floods, Mississippi River, Hydraulic Modeling
Session Type: Paper
Day: 4/11/2018
Start / End Time: 10:00 AM / 11:40 AM
Room: Napoleon B2, Sheraton 3rd Floor
Presentation File: No File Uploaded

Historic peak-flood elevations for the middle and lower segments of the Mississippi River extend back into the late-18th century (i.e., between the confluence of the Missouri and Ohio rivers and below the confluence with the Ohio River, respectively). We have developed calibrated and validated 1-D unsteady flow models (retro-models) for river conditions during the late 19th century using historical hydrologic and geospatial data to estimate upper and lower discharge bounds for these historic flood events. Retro-modeling has allowed us to extend the quantitative flood record along these river segments by more than 100 years providing valuable insights into the range of natural hydrological variability of the Mississippi River. In addition, using these hydraulic models has allowed us to explicitly take into account changes in levee protected areas and floodplain land cover on peak flood discharges as well as assess the uncertainty in our discharge bounds. For the middle Mississippi River, our modeling suggests at least two large historic floods exceeding the current flood of record by ~20%. (i.e., the 1993 Flood; 30,600 cms). This suggests floods larger than the 1993 Flood are likely along this river segment. Along the lower Mississippi River, we found historic floods (prior to the 20th century) were substantially smaller by discharge (~25%) when compared to the largest floods of the 20th and 21st centuries (~56,600 cms). Our modeling also suggests levees protecting ~ 90% of the natural floodplain from inundation along this segment is mainly responsible for the substantially larger floods during the modern record.

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