Research on the Dynamic Mechanism of Water-Suspended Sediment Pits Based on Gravitational Flow of Particle Clouds

Abstract

When particulate matter is released into a water body and settles to the bottom, it often forms a special landform with a central
depression and peripheral bulge, known as an underwater crater. This paper systematically studies the dynamic mechanism of water subsurface sedimentation forming craters based on the gravity flow of particle clouds. The entire process is divided into four stages: formation and
accelerated sinking of the particle cloud, impact and radial expansion at the bottom, continuous deposition and accumulation growth, and
final stable form. By introducing the negative buoyancy entrainment model, wall radial jet theory, and particle initiation criteria, a theoretical
framework for the evolution from single particle sedimentation to collective dynamics is constructed. The study shows that the formation of
underwater craters is essentially the vertical momentum of the particle cloud converting into radial wall jet at the bottom, which then exerts
shear stress on the bed and causes the particles to be pushed outward. Combining the constraint of the underwater static angle and the law
of volume conservation, this paper reveals the variation law of crater characteristic sizes, finding that the crater radius is proportional to the
square root of the released sediment volume and inversely proportional to the square root of the particle size, and shows weak dependence on
water depth in the far-field approximation. The research results of this paper can provide important theoretical support for the evolution of water subsurface sediment gravity flow, seabed scouring in marine engineering, and environmental assessment of deep-sea mining.