Empirical test of filtering theory: Particle capture by rectangular-mesh nets

Theoretical equations predicting particle capture by rectangular-mesh nets were evaluated empirically. Flow was measured through and around silk caddisfly nets and model nets (made of steel mesh) with a thermistor flowmeter. Measured speeds through nets were compared to theoretically predicted speeds based on net morphology and ambient water velocity. The median absolute percent difference between measured and predicted speeds was 20%, while the median absolute difference was 0.013 m s−1(ambient speed range 0–0.60 m s−). Analysis of published distributions of particle sizes caught in caddisfly nets verified that larger particles in the water were more likely to be caught by the nets than smaller particles, but not by as great a factor as predicted. An adhesion probability of about 0.2% is necessary to make the theory agree with particle capture data.