Waves Over Sand Ripples

Look beneath the waves on a beach or in a bay, and you’ll find ripples in the sand. Passing waves shape these sandforms and can even build them to heights that require dredging to keep waterways passable to large ships. To better understand how the sand interacts with the flow, researchers build computer models that couple the flow of the water with the behavior of individual sand grains. One recent study found that sand grains experienced the most shear stress as the flow first accelerates and then again when a vortex forms near the crest of the ripple. (Image credit: D. Hall; research credit: S. DeVoe et al.; via Eos)

#CFD #computationalFluidDynamics #fluidDynamics #geophysics #granularMaterial #oceanWaves #physics #sandRipples #science #sedimentTransport #sedimentation

A Braided River

The Yarlung Zangbo River winds through Tibet as the world’s highest-altitude major river. Parts of it cut through a canyon deeper than 6,000 meters (three times the depth of the Grand Canyon). And other parts, like this section, are braided, with waterways that shift rapidly from season to season. The swift changes in a braided river’s sandbars come from large amounts of sediment eroded from steep mountains upstream. As that sediment sweeps downstream, some will deposit, which narrows channels and can increase their scouring. The river’s shape quickly becomes a complicated battle between sediment, flow speed, and slope. (Image credit: M. Garrison; animation credit: R. Walter; via NASA Earth Observatory)

#fluidDynamics #geophysics #physics #rivers #satelliteImage #science #sedimentTransport #sedimentation

Smoke Bomb

With a flurry of motion along its pectoral fin, a sting ray lifts the sand nearby and disappears into the turbid cloud. This tactic helps the animal both hide and escape. In a similar move, sting rays and other bottom-dwelling fish can bury themselves in sand.(Image credit: Y. Coll/OPOTY; via Colossal)

#fluidDynamics #fluidsAsArt #physics #science #sedimentTransport #sedimentation #stingray #turbulence

How Particles Affect Melting Ice

When ice melts in salt water, there’s an upward flow along the ice caused by the difference in density. But most ice in nature is not purely water. What happens when there are particles trapped in the ice? That’s the question this video asks. The answer turns out to be relatively complex, but the researchers do a nice job of stepping viewers through their logic.

Large particles tend to fall off one-by-one, which doesn’t really affect the buoyant upward flow along the ice. In contrast, smaller particles fall downward in a plume that completely overwhelms the buoyant flow. That strong downward flow makes the ice ablate even faster. (Video and image credit: S. Bootsma et al.)

#buoyancy #flowVisualization #fluidDynamics #ice #melting #physics #science #sedimentTransport

A Sandy Spine

Where sea and sand meet, Gaia’s spine rises. Photographer Satheesh Nair captured this striking image in western Australia, where wind and wave action have dragged a dune into vertebrae-like cusps. Notice how the size and shape of the curves differs between the under- and above-water sections. Those differences reflect the differing forces that shape them — just water for one set, water and air for the other. (Image credit: S. Nair/IAPOTY; via Colossal)

#beachCusps #fluidDynamics #fluidsAsArt #oceanWaves #physics #science #sedimentTransport #sedimentation

South Island Sediments

In April and May late autumn storms ripped through Aotearoa New Zealand. This image shows the central portion of South Island, where coastal waters are unusually bright thanks to suspended sediment. We typically think of storm run-off as water, but these flows can carry lots of sediment as well. Here, the large amount of sediment is likely a combination of increased run-off from rivers and coastal sediment stirred up by faster river flows. (Image credit: W. Liang; via NASA Earth Observatory)

#flowVisualization #fluidDynamics #physics #satelliteImage #science #sedimentTransport #sedimentation

Dams Fill Reservoirs With Sediment

Dams are critical pieces of infrastructure, but, as Grady shows in this Practical Engineering video, they are destined to be temporary. The reason is that they naturally fill with sediment over time. Rivers carry a combination of water and sediment; the latter is critical to healthy shorelines and stable ecology. But while sediment gets carried along by a fast-flowing river, slower flow rates allow sediment to fall out of suspension, as demonstrated in Grady’s tabletop flume. As his river transitions to a deeper, slower-flowing reservoir, sand falls out of the flow, building up colorful strata. The sand and water even create dynamic feedback loops, as seen with the dunes that form in his timelapse and march toward the dam.

Any long-term plan for a dam has to deal with this inevitable build-up of sediment, and, unfortunately, it’s not a simple or cheap problem to address, as discussed in the video. (Video and image credit: Practical Engineering)

#civilEngineering #dams #engineering #fluidDynamics #physics #science #sedimentTransport #sedimentation

#Klimawandel und schmelzende #Gletscher führen zu erhöhtem #Sedimenttransport in #Hochgebirgsflüssen – mit weitreichenden Folgen für #Landwirtschaft, #Wasserqualität und #Infrastruktur.

https://www.doi.org/10.1126/sciadv.ads6196

Eine Studie zeigt, wie #Gletscher, #Vegetation und #Niederschlag diese Prozesse beeinflussen. Besonders betroffen: Regionen rund um das Tibet-Plateau.

#Erderwärmung #Gletscherschwund #Hochgebirge #Umwelt #Wassermanagement