Integration of Submerged Aquatic Vegetation Motion Within Hydrodynamic Models

Abstract

Aquatic models used for both freshwater and marine systems frequently need to account for submerged aquatic vegetation (SAV) due to its influence on flow and water quality. Despite its importance, parameterizations are generally adopted that simplify feedbacks from SAV, such as canopy properties (e.g., considering the deflected vegetation height) and the bulk friction coefficient. This study reports the development of a fine‐scale non‐hydrostatic model that demonstrates the two‐way effects of SAV motion interaction with the flow. An object‐oriented approach is applied to capture the multiphase phenomena, whereby a leaf‐scale SAV model based on a discrete element method is combined with a flow dynamics model to resolve stresses from currents and waves. The model is verified through application to a laboratory‐scale seagrass bed. A force balance analysis revealed that leaf elasticity and buoyancy are the most significant components influencing the horizontal and vertical momentum equations, respectively. The sensitivity of canopy‐scale bulk friction coefficients to water depth, current speeds, and vegetation density of seagrass was explored. Deeper water was also shown to lead to a smaller decrease in vegetation height. The model approach can contribute to improving assessment of processes influencing water quality, sediment stabilization, carbon sequestration, and SAV restoration, thereby supporting an understanding of how waterways and coasts will respond to changes brought about by development and a changing climate.

Influence of patch size on hydrodynamic flow in submerged aquatic vegetation

“…The elastic modulus of high-density polyethylene is about 1.0 GPa, and silicone foam has an elastic modulus of about 0.5 GPa. Nakayama et al (2020b) demonstrated that the density and the elastic modulus of Zostera marina were 970 kg m -3 to 995 kg m -3 and about 1.0 GPa. Thus, superficial comparisons suggest that high-density polyethylene is similar to Zostera marina.…”

“…We used the SAV model developed by Nakayama et al (2020b) to investigate the interactions between the flows and the flexible motion of SAV (Figure 2). Dividing each leaf into segments and nodes enables us to properly include the drag, friction, buoyancy, lift, and elastic forces.…”

“…However, their models require a high-capacity computer, and cannot be applied using an ordinary PC. Nakayama et al (2020b) proposed an SAV model that can be used on an ordinary PC. Their SAV model considers drag, lift, friction, buoyancy, and elastic forces, as well as the interaction between flows and SAV, by dividing each blade into segments, resulting in good agreement with the results of laboratory experiments.…”

Breaking of Internal Kelvin Waves Shoaling on a Slope

“…A three-dimensional nonhydrostatic model, Fantom, was used to analyze the breaking of internal Kevin waves shoaling on the uniform slope. Fantom is an object-oriented parallel computing model that has been applied to investigate not only real scale phenomena (Maruya et al, 2010;Nakamoto et al, 2013;Nakayama et al, 2014Nakayama et al, , 2016 but also laboratory-scale phenomena (Nakayama et al, 2012(Nakayama et al, , 2020Nakayama, Kakinuma, and Tsuji, 2019). Fantom is based on Direct numerical simulation (DNS) as well as a generic length scale (GLS) equation model (Jones & Launder, 1972;Umlauf & Burchard, 2003), with a partial cell scheme used here to represent the uniform bottom slope in the z coordinate bathymetry (Adcroft et al, 1997).…”

Integration of submerged aquatic vegetation motion within hydrodynamic models

“…Restoration of submerged aquatic vegetation (SAV) in aquatic ecosystems has been suggested as a potential mitigation strategy (Nellemann et al, 2009). For example, while shallow coastal areas have often been assumed to release carbon dioxide to the atmosphere due to inputs of organic matter from rivers (Adiyanti et al, 2016;Cai, 2011), well-vegetated aquatic environments have recently been shown to absorb and capture carbon dioxide-a potential sink of anthropogenic carbon as sedimentary organic carbon, termed "blue carbon" (Duarte et al, 2013). Nellemann et al (2009) report that coastal blue carbon ecosystems accumulate approximately 55% of the total carbon dioxide captured from the Earth's atmosphere due to photosynthesis.…”