PARTICLE ACCUMULATION IN A CYLINDRICAL SEDIMENT TRAP UNDER LAMINAR AND TURBULENT STEADY FLOW - AN EXPERIMENTAL APPROACH

The hydrodynamical, fluid and particle parameters which control flushi ng rates, now cells, and accumulation rates of particulate matter in c ylindrical (MultiPIT) sediment traps were quantified in a flume simula tion using a seeding technique for 25-45 mu m particles. Particle coll ection was found to be a trap- and particle-specific filtering process encompassing advective and gravitational entry of particles over a re duced trap aperture area, and gravitational-turbulent removal of parti cles at the bottom of the internal flow cell. Trapping efficiency incr eased up to 10-fold with increasing horizontal flow velocity (1-30 cm . s(-1)). For given flow velocity, the trap over- and undercollected p articles relative to their weight, i.e. (theoretical) Stokes settling velocity. The trapping efficiency increased with increasing trap Reyno lds number Re-T, changed by the approaching velocity in our experiment s. Opposite findings from earlier experiments using the flume seeding technique and changing Re-T by altering the trap diameter (Butman, 198 6) are discussed. Semi-empirical equations are derived for the accumul ation process of light, heavy and intermediate particles. From these, measured trap fluxes can be converted into in-situ verticle particle f lux except for light particles.