On the Effect of Gaps on the Dynamics of Canopy Flows: From Seagrass to Wildfires

Submerged aquatic vegetation (SAV) canopies are found prevalently in coastal, fluvial, lake and other natural aquatic systems. By exerting drag on the flow, such vegetative structures lead to the formation of “canopy flows,” characterized by hydrodynamics analogs to the canonical mixing layer By altering the flow around them, canopies such as seagrass meadows provide numerous and varied ecological services. However, due to both natural and anthropogenic impacts, global canopy formations such as seagrass meadows have been greatly diminished. Many seagrass meadows display patchiness or gaps that persist for several years. Interruptions of canopies by gaps and patchiness alter the type of canopy flow that characterizes these systems. The interrupted systems observe increases in flow velocity and local erosion, and other modifications to mean and turbulent flow characteristics. Because disruptions in turbulence are known to persist and impact downstream flow conditions, we examine how local, gap-induced perturbations evolve and propagate downstream to effectively impact mean and turbulent flow properties in a nonlocal fashion.

Research and developments in wildfire management in terrestrial canopies formed by trees has focused a great deal on large synoptic and terrain scale and plume/scale aspects of wildfire spread. There is little work done on understanding the fluid mechanics of the flow and plumes at the canopy scale. In our study we focus on the canopy scale dynamics of wildfires by examining the intersection between turbulent, buoyancy driven plumes and canopy dynamics. Specifically, in a manner related to the study of submerged aquatic vegetative canopies we will examine how various heterogeneities in the canopies (as found in nature or via fuel breaks) can alter plume behavior.

Speaker: Jeffrey Koseff, Stanford Woods Institute for the Environment