Particle size segregation of turbidity current deposits in vegetated canopies

Abstract

Interactions between ecology, hydrodynamics and sediments play central roles in the evolution of coastal and freshwater ecosystems. We set out to characterise interactions of a specific hydrodynamic phenomenon -turbidity currents -with vegetation and sediment dynamics. We measured hydrodynamics and sediment deposition rates when turbidity currents flowed into plant canopies in a lockexchange flume experiment, using simulated vegetation and three real plant species, and varying the turbidity current's initial sediment concentration in the range 1.0-6.0 gL -1 . The natural sediment used had an essentially bimodal size distribution, with coarse (6.2-104 μm) and fine (2.2-6.2 μm) fractions. In all cases, on entering the vegetation canopy, the turbidity current was initially inertially-dominated, but subsequently became drag-dominated. In the inertial regime, there was no size segregation in the deposited material. In the drag-dominated regime, the deposited material became increasingly dominated by fine sediment, at a rate dependent on the vegetation type. The transition between these two regimes occurred at a distance equivalent to 5.1 to 7.6 times the total water depth downstream of the lock gate. The size segregation of deposited sediment is posited to have important consequences for substrate evolution, which in turn may affect vegetation growth. Thus, our findings point to a non-linear feedback mechanism between the spatial heterogeneity of vegetation canopies and that of the substrate they help to engineer.

The influence of physicochemical environment on the distribution and abundance of mangrove gastropods in Ngurah Rai Forest Park Bali, Indonesia

“…The study site at station 1 and station 4 which were on the coastal area so that the influence of sea current can affect the substrate fraction composition. According to Eddy and Roman (2016); Gao et al (2018);Soler et al (2020), which the stronger current will be found coarse granules. Conversely, in waters with the weak current will be found smooth granules will be deposited.…”

Particle segregation within bidisperse turbidity current evolution

“…2019, 2020; Soler et al. 2020) and numerical simulations (Salaheldin et al. 2000; Huang, Imran & Pirmez 2007, 2008; Abd El-Gawad et al.…”

“…Turbidity currents (TCs) are multiphase flows driven by the horizontal pressure gradient which is induced by the suspended load (Meiburg, Radhakrishnan & Nasr-Azadani 2015) and is usually a complex polydisperse particulate flow. These flows, natural or human-triggered events, occur everywhere in rivers, estuaries and submarine environments, and they have an important impact on the safety and stability of underwater buildings (Middleton 1993;Simpson 1999;Meiburg & Kneller 2010;Delannay et al 2017;Liu & Zhang 2019). The upper interface of the TC experiences entrainment and detrainment with the ambient fluid during propagation, while the lower interface of the TC interacts strongly with the bed materials regarding erosion and deposition (Ismail, Viparelli & Imran 2016).…”

“…To fully characterize the process and mechanism within a multigrain TC system, laboratory experiments (Gladstone, Phillips & Sparks 1998;Baas et al 2005;Ezz, Cantelli & Imran 2013;Ismail et al 2016;de Leeuw, Eggenhuisen & Cartigny 2018;Pohl et al 2019Pohl et al , 2020Soler et al 2020) and numerical simulations (Salaheldin et al 2000;Huang, Imran & Pirmez 2007Abd El-Gawad et al 2012;Ezz & Imran 2014) were employed to provide convenience for comprehensively monitoring the morphological evolution and current characteristics. In the streamwise direction, both experimental studies (Kubo 2004;Felix, Sturton & Peakall 2005;Alexander et al 2008) and numerical simulation researches (Steenhauer, Tokyay & Constantinescu 2017;Lee 2019;Ouillon, Meiburg & Sutherland 2019) visualized that the highest concentration is at the head during the current evolution.…”

Hydrodynamics and Sediment Transport of Downslope Turbidity Current Through Rigid Vegetation

“…For this real scenario, Testik and Yilmaz (2015) proposed parameterizations for the required propagation distance of turbidity currents fully controlled by vegetation drag, and also the convergency-slope values of the current-ambient fluid interface. Soler et al (2020) found that the deposited material became increasingly dominated by fine sediment as turbidity currents propagate into the vegetation region. In addition, the resistance forces exerted by vegetation stems reduce the bulk velocities of turbidity currents, as well as degrade the level of bed shear stresses, thus further mitigating sediment erosion and transport (Montakhab et al, 2012;Zhang & Nepf, 2011).…”