Kyle Strom

Civil and Environmental Engineering, Virginia Tech

Title: Vertical flux rates of muddy sediment in coastal waterways and plumes

Abstract:

Rivers deliver significant loads of fine muddy sediment eroded from upstream landscapes to coastal regions. Upon arrival, mud can deposit in or move through the rivers, bays, estuaries, marshes, and deltas of the region. Being able to forecast the movement and eventual resting spot of this sediment has important implications for society. For example, evaluating the effectiveness of river diversion projects aimed at using sediment deposits to build deltaic landscape is dependent on being able to accurately model the movement of mud from a high-energy river to a low-energy embayment. The same is true for developing water quality models of coastal waterbodies and evaluating how mud deposits shoal waterways and impede vessel navigation. While its importance is known, modeling mud movement through coastal waters is complex and difficult. The outcome of this complexity is that the predictive power of current methods remains poor. Part of the complexity is due to the flocculation process whereby mud particles form aggregates, or flocs, which grow or shrink in size and density depending on turbulence levels and other water column properties (see figure below). When flocs grow or shrink in size, the rate at which they settle out of the water changes, creating dynamic settling speeds that are difficult to model. Furthermore, estuarine zones and river mouth plumes can be stratified, with positively buoyant freshwater suspensions of mud flowing over clearer saltwater (see figure below). This talk highlights work designed to better understand the vertical flux of muddy cohesive sediment in the fluvial to marine transition. The talk specifically focuses on: (1) the response of flocs sizes to changing shear and concentration conditions; (2) improvements to simple modeling of floc size in turbulent flows; and (3) the effective settling rate of mud in the presence of settling-driven interfacial instabilities and shear at the contact point between overlying muddy freshwater suspension and underlaying clear saltwater.

Biography:

Kyle Strom is an associate professor in Civil and Environmental Engineering at Virginia Tech where he teaches and conducts research in the field of environmental hydraulics and sediment transport. Dr. Strom received his B.S. and M.S. degrees from Washington State University and a Ph.D. from the University of Iowa. His research focuses on fluid and sediment dynamics of natural systems such as rivers, estuaries, fans, and deltas over a range of spatial and temporal scales. The underlying motivation for his group’s work is the understanding of fundamental processes for better forward and backward prediction of river and landscape system evolution in time under natural and anthropogenic influences. For more information see www.strom.cee.vt.edu.