Fluidization of sediments in a conical basin by subterranean springs: relevance to Lake Banyoles.

An experimental study was carried out to investigate the resuspension of particles by a momentum jet discharging from below into a conical basin. The work was motivated by its relevance to Lake Banyoles, where sediments are suspended in different conical basins by bottom jets fed by a groundwater karstic system. Two different flow regimes were identified: a "Jet Flow" regime (JF) and a "Lutocline Flow" regime (LF). In the LF regime, the particles were resuspended, forming a well-established interface along the entire cross-sectional ara of the cone. This regime occurs when the particle Reynolds number $ {\bf Re_p = (u-w_s)d_p/ \nu} $ where u is the mean velocity of the flow at the jet entry, w _s is the settling velocity of particles, d _p is the diameter of that particles and $ {\bf \nu} $ is the kinematic viscosity of water) is below a critical number Re _c that depends on the slope of the basin. The maximum height to which particles rise in the LF regime was also determined as a function of four non-dimensional variables: D ₁ = h _o /(M _o ^1/2 /w _s ), D ₂ = h _o /d _p , Re _p and $ {\bf tan \, \beta} $ (where h _o is the height of the particle bed, M _o is the kinematic momentum flux of the jet and $ {\bf tan \, \beta} $ is the slope of the basin). Application of the results to the basins of Lake Banyoles showed a good agreement provided that the aggregate properties of the suspensions are used. It is also shown that, in the LF regime, inflows to the basins can be estimated by a simple technique based on a balance between the sedimentation flux and the upward advection of sediments by the mean flow. [ABSTRACT FROM AUTHOR]