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 pa rticles by a momentum jet discharging from below into a conical basin. The work was motivated by its relevance to Lake Banyoles, where sediments are s uspended in different conical basins by bottom jets fed by a groundwater ka rstic system. Two different flow regimes were identified: a "Jet Flow" regi me (JF) and a "Lutocline Flow" regime (LF). In the LF regime, the particles were resuspend ed, forming a well-established interface along the entire c ross-sectional ara of the cone. This regime occurs when the particle Reynol ds number 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 d iameter of that particles and nu is the kinematic viscosity of water) is be low a critical number Re-c that depends on the slope of the basin. The maxi mum 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 tan beta (where h(o) is the height of the particle bed, M-o is the kinematic momentum flux of the jet and tan beta is the slo pe of the basin). Application of the results to the basins of Lake Banyoles showed a good agreement provided that the aggregate properties of the susp ensions are used. It is also shown that, in the LF regime, inflows to the b asins 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.