Particle contact on flat plates in flow : a model for initial larval contact

Abstract

Patterns and rates of particle contact onto flat plates in steady unidirectional flows were investigated in a laboratory flume. Plates with three leading edge configurations (faired, bluff and split) were used to generate boundary-layer flows that differed in downstream patterns of plate-ward advection, turbulence and shear stress. Particle contact onto the leading edges of all plates was consistently low in 2,5, and 10 cm s-1 along-stream flow speeds. Contact was enhanced under separation eddies that formed over bluff and split plates, but was reduced at reattachment points. High contact rates appeared to correspond to a combination of local plate-ward advection, a thick boundary layer, and reduced shear stress. Surprisingly, particle contact rates in the "non-varying" flow region further downstream on the plates varied only slightly between plate types and between flow speeds. Contact rates did, however, vary strongly with particle abundance in the flume. These results were used to develop a predictive model of passive larval contact rate onto settlement plates in known larval concentrations and free-stream flows. The contact model, when combined with larval behavioral observations, provides the basis for a more objective, quantitative method of interpreting larval settement plates.