AbstractHigh urbanization adversely affects the hydrological behavior of watersheds. Therefore, different stormwater management strategies have been put forward to mitigate these negative effects. Grass swales are one of the environmentally friendly practices that are widely used today as an alternative to traditional infrastructure systems to reduce the peak flow rates, increase infiltration, and the time of concentration. The determination of the effective parameters on the hydrological characteristics of grass swales plays an important role in identification of proper design criteria. To this end, hydrological experiments were conducted by designing a grass swale module and integrating it into a large-scale rainfall-watershed-swale (RWS) experimental setup. The potential effective parameters (rainfall, soil, grass type, drainage area, and grass height) on the hydrological performance of the grass swales were tested with six different swale configurations by the controlled laboratory experiments. Experimental results show that swales decrease the peak flow significantly. In addition, hydrological performance of swales decreases with the increase in rainfall intensity or rainfall duration. Moreover, the soil and grass type have a significant effect on the peak flow reduction and drainage performance of the swales.