Gravity currents in aquatic canopies

Abstract

Abstract. A lock exchange experiment is used to investigate the propagation of gravity currents through a random array of rigid, emergent cylinders which represents a canopy of aquatic plants. As canopy drag increases, the propagating front varies from the classic profile of an unobstructed gravity current to a triangular profile. Unlike the unobstructed lock exchange, the gravity current in the canopy decelerates with time as the front lengthens. Two drag-dominated regimes associated with linear and non-linear drag laws are identified. The theoretical expression for toe velocity is supported by observed values. Empirical criteria are developed to predict the current regime from the cylinder Reynolds number and the array density.

Exchange flow between open water and floating vegetation

“…Tanino et al [20] identified a transition from inertial to drag-dominated flow within an array of cylinders that filled the water depth. They showed that the array drag became dominant over inertia when C D aL > 7.…”

“…Following from (18), each case was classified by the non-dimensional drag parameter, C D aL (see also [20]). For simplicity, we let L = L 3 = L g , the distance to the center of the visualization window (Fig.…”

“…With the following simplifying assumptions, we can estimate α from the equations of linear momentum. First, when vegetation is present, the viscous drag is negligible compared to the vegetative drag [20,23]. Second, initially the exchange flow is dominated by inertia (following the classic evolution), but within the root layer the vegetative drag exceeds inertia for C D aL 3 > 7 [20].…”

“…First, when vegetation is present, the viscous drag is negligible compared to the vegetative drag [20,23]. Second, initially the exchange flow is dominated by inertia (following the classic evolution), but within the root layer the vegetative drag exceeds inertia for C D aL 3 > 7 [20]. The initial inertia-dominate regime is discussed in the results, but here we consider only the drag-dominated limit, so that within the root layer the inertia term is negligible compared to the drag term.…”

Wind effect on diurnal thermally driven flow in vegetated nearshore of a lake

“…Since floating and rooted emergent vegetation is extensively present in nearshore, several studies [16][17][18][19] included their impacts on exchange flows. Unlike floating vegetation, rooted vegetation inherently imposes resistant forces to significantly reduce the circulation and volumetric flowrate of exchange flow, and increase flushing time [16,17].…”