61st Annual Report on Research 2016

This research is concerned with developing a theoretical model for the formation of fluvial levees and testing that model with field data collected on local rivers in Indiana, USA. This research will address two key questions about levees: 1) Under what geomorphic and hydrodynamic conditions will levees form?; and 2) What process-related variables control their evolution and profile shape?

Upon tackling question 1 with data, we discovered something unsuspected this year. We started the process by mapping levees along various river systems using elevation data. The high-resolution LiDAR data of Indiana floodplains contains a surprising number of secondary channels (TOC, left image). These secondary channels tend to form on parts of the river where levees are small and not consistently present. We mapped the occurrence and controls on these secondary channels as a proxy for understanding why some systems do not produce levees and to provide a clear view of Indiana Rivers. We mapped 3064 km2 of floodplain and found that 37.3% of floodplains contain floodplain channels that form long, coherent down-valley pathways with bifurcations and confluences, and they are active only during overbank discharge. Upon further analysis we discovered that these floodplains channels form on rivers with high migration rates and oxbow production rates tend to produce floodplain with secondary channels. Indeed the secondary channels are formed by connecting together oxbow lakes (TOC, right image). This is supported by an analysis that shows our mapped oxbow lakes are wider and deeper channel segments compared to the secondary channels. In fact, the oxbows have a width more similar to the main river channel, supporting the interpretation that they are genetically linked to the main channel.

These results underscore the importance of how the morphodynamics of the fluvial system influence levee formation. Highly active rivers cannibalize their own levees during lateral migration, in turn limiting their formation. Moreover, rivers without levees have markedly different floodplain compared to leveed rivers which tend to have smoother floodplains with less topography (TOC, top of left image).

These results have been published in a peer-reviewed journal with acknowledgments to PRF:

David, S., Edmonds, D.A., Letsinger, S., (2016) Controls on the occurrence and prevalence of floodplain channels in meandering rivers, Earth Surface Processes and Landforms, doi: 10.1002/esp.4002