Colloids are widely distributed in the aquatic environment, both in groundwater and surface water. The mechanisms related to colloid transport in porous media are intensively investigated because colloids can facilitate contaminant migration in soils and groundwater. However, the migration of colloids in overland flow is not clear. In this dissertation, laboratory runoff experiments were designed to examine the migration dynamics of colloids and tracer (bromide) in overland flow and soil drainage. On a first laboratory experiment on bare ground (rainfall-runoff sand box of 153 cm length under 64 mm/hour rainfall and 0.31 L/min inflow 80 min -30 min bromide/colloid injection and 50 min flushing- events), the surface transport of a colloid (kaolinite, 0.4 ìm diameter, inflow concentration of 179 mg/L, zeta potential -33 mV) showed no statistical difference to that of bromide, although colloids were filtered effectively through the sand in the subsurface flow in agreement with existing colloid filtration theory. In a second experiment with dense vegetation (Bahia grass implanted in the same rainfall-runoff box), colloids (carboxylated polystyrene latex microspheres, 0.3 ìm diameter, zeta potential -28 mV, inflow concentration 10 mg/l) were removed from the surface runoff on the surface of the plant stems and leaves, or by the soil particles and vegetation roots when infiltrated into soil profile, with a total removal rate of 67% of the colloids compared to 26% in the previous experiment. Through the batch adsorption experiments, we also found that plant parts (leave, stem and root) showed different colloid adsorption capacity (highest for roots). The roles of ionic strength, colloid size, inflow rate, and vegetation type on the removal of colloids by dense vegetation were investigated in a smaller scale runoff experiment through two types of dense vegetation (Bahia and Rye grasses). The Vegetative Filter Strip Modeling System-Transport and Reaction Simulation Engine (VFSMOD-RSE) was used to explore the experimental bromide and colloid transport data. In addition to deposition to vegetation, diffusion driven exchange between colloids in the soil pore water and surface runoff was also considered in the model. Factors identified by porous media classic filtration theory were also found important (and following the same trends) in our surface vegetation studies. The deposition of colloids on the vegetation increased with increases in solution ionic strength and particle size, and with decreases in flow rate. We also found vegetation type played an important role on colloid transport with more deposition onto Rye grass than onto Bahia grass under the same experimental conditions. This dissertation showed that dense vegetation can be an effective pollution control practice effectively reduce the colloid concentration in surface runoff and identified some of the key elements governing the effectiveness of the removal process.