Research
Here are some examples of our current research.
Modeling landscape evolution under steady and transient states
Based on a series of controlled laboratory experiments conducted at the St. Anthony Falls laboratory of the University of Minnesota, we study the effect of changing precipitation patterns on landscape evolution at the short and long-time scales. These experiments are designed to develop a complete drainage network by growth and propagation of erosional instabilities in response to external forcings. We focus our study to the investigation of how changes in the frequency and magnitude of large rainfall events might influence landscape evolution. Results suggest that the statistics of topographic signatures, for example, evolution of drainage network, slopes, curvatures, etc., show dependence on both rainfall patterns and uplift rate. The implications of these results for predictive modeling of landscapes and the resulting sediment transport are being explored.
Effect of migrating bed topography on tracer dynamics
Instantaneous, high-resolution bed elevations, velocity fluctuations and
sediment transport rates along with travel distances of tracer particles representing the grain size distribution of bed material were measured, for a range of discharges in a series of recently conducted flume experiments. Here we seek to understand and quantify how statistics of tracer travel distances depend on multi-scale variability of river bed topography. Preliminary results show that bed elevation fluctuations strongly affect the statistics of travel distances. The implications of these results for predictive modeling of sediment transport are also being studied.
Coupled dynamics of turbulence and topography
Simultaneous high resolution measurements of velocity fluctuations, bed elevations and sediment flux were performed in a large scale laboratory flume. Probability density functions (pdfs) of the bed elevation fluctuations and the instantaneous Reynolds stress reveal heavy-tail statistics and a strong feedback between the co-evolution of bedforms and the near-bed turbulence [see, Singh et al., 2012, JGR; Keylock et al., 2013, GRL]. These results complement our previous findings [Singh et al., 2010, WRR] in which the signature of bedform evolution on the near-bed velocity fluctuations was confirmed via the presence of a spectral gap and two distinct power-law scaling regimes in the spectral density of velocity fluctuations. Efforts are underway to further explore and quantify the relation between observed asymmetry in the probability distribution of bed elevation fluctuations and intermittency (multi-fractality), as the result of scale coupling.
