RECONSTRUCTING FLUVIAL MORPHOLOGY FROM SET THICKNESS STATISTICS (Invited Presentation)

Preservation is the link between fluvial surface morphodynamics and what is recorded in the fluvial sedimentary. Reconstruction of the original channel morphology from stratification can provide important information about paleoflow conditions. To infer the original dimensions of paleomorphological features such as river channels from the fluvial record, a detailed understanding of the relation between morphodynamics and preservation is needed. So far, theories to reconstruct the original morphology from preserved stratification have not been tested for meandering river channels for lack of detailed bathymetry.

We report on a series of controlled flume experiments and Delft3D physics-based numerical model runs with the objectives to i) test the prediction of set thickness as a function of the morphology formed by a meandering river channel, and ii) explore and explain spatial and temporal set thickness variations in the resulting channel belt. High-resolution measurements of time-dependent surface elevation were used to quantitatively relate the preserved stratification to the river morphology. Experimental design corresponds to the predicted hydraulic geometry for a non-cohesive gravel-bed river, and the width-depth ratio is chosen such that alternate bars form.

We find that the mean set thickness agrees well with the theoretical prediction from channel morphology. The mean preserved set thickness is 30% of the mean channel depth. Finally, there is much systematic spatial variation in set thickness related to repetitive point bar growth and chute cutoff. We find undisturbed and thick sets close to channel belt margins and more irregular stratification with stacked thinner sets in the channel belt center. We conclude that set thickness statistics can be used to provide quantitative error bounds for the reconstruction of paleochannel dimensions.