Lock exchange experiments with particle-driven gravity currents
CEDA Dredging Days 2017 - Sustainable Dredging - Continued Benefits
Stovers M.P.J., Goeree J.C., van Rhee C.
Abstract: Gravity currents often occur in natural or industrial settings. Common examples are pyroclastic flows, saline wedges within estuaries or slurry flows due to dredging activities. In dredging, small particle sizes can travel large distances. These small fractions, in turn, can cover parts of the seabed burying sea life. Gravity current is a horizontal flow driven by a density difference of two fluids. Gravity or density currents have been well-studied with so-called lock exchange experiments. Where a lock is placed in a rectangular tank separating two fluids with different densities. Releasing the lock causes the two fluids of different densities to flow. However, the understanding of hydro dynamical behavior of particle driven gravity currents is still lacking. For instance, the traveling distances of small particles and the separation of settled particles need to be determined. In this work the influence of the initial volume concentration, of suspended sand, on the run out length and the flow velocity is investigated. This has been done with lock exchange experiments. Furthermore, the particle size distribution (PSD) of settled sediment along the bottom of the tank has been determined. The lock exchange experiments show that, at a higher initial volume concentration, no separation of particles sizes, along the settled bottom of the tank, did occur. This is in contrast with the experiments with lower initial volume concentrations. In these experiments the smaller particles traveled further than the bigger particles. Moreover, it was shown that the run out length is proportional to the initial mixture/water level of the experiment.
Key words: Lock exchange experiment, particles, sediment, gravity currents