My dissertation research is focused on understanding how emergent (sub-aerial) macroform sandbar geometry varies with channel morphology and flow variability in wide, sandy-bed Great Plains Rivers. The image below shows large, emergent sandbars in the unchannelized reach of the Missouri River, along the Nebraska-South Dakota border. These bars were formed during the 2011 flood.
Work done by myself and others has shown that emergent sandbar geometry varies substantially along-stream, but this variation is unexplained. I am testing the hypothesis that variation in bar geometry reflects the spatial variation in bed-material sediment transport gradient. An alternative hypothesis is that variation in bar random or weakly dependent on channel morphology. The hypothesis is relevant to both geosciences and ecology. In geosciences we typically want to constrain reservoir geometries, or better understand feedbacks between bedforms, channel hydraulics, and morphologic adjustment of river channels. The image below shows an emergent macroform sandbar (background) and submerged, migrating macroform (foreground...with sticks marking the location of the slipface) in the Niobrara River, northern Nebraska
Macroforms are also an important component of riverine ecosystems. The tops of sandbars are nesting and brooding habitat for turtle and bird species, and the margins of sandbars provide a mosaic of aquatic habitat for macroinvertebrates, amphibians, reptiles and fish. Sandbar geometry, specifically sandbar height, is directly relevant to probabilities of nest and brood success for migratory bird species. Understanding spatial variability in bar height thus crucial to population simulation models for species of concern. The photo below shows a nest and two eggs of an interior least tern (Sterna antillarum) on the top of macroform sandbar in the lower Platte River, eastern Nebraska.
