Assessing The Effect Of Substrate Porosity Layering On The Water Detention Efficiency Of A Bioretention Cell: A CFD Study

Urbanization has drastically increased sealed surfaces, leading to higher stormwater runoff and subsequent associated risks such as flooding and water quality degradation. Nature-based solutions such as bioretention cells are a sustainable approach to manage stormwaters. The present work studies the effects of soil layer porosity on water detention efficiency of a bioretention cell, using computational fluid dynamics (CFD). Three porosities (0.34, 0.40, and 0.43) and multiple soil layering configurations were analyzed under two inflow rates (1 l/s and 1.5 l/s). Results reveal that higher porosity layers reduce bypass runoff compared to lower porosity layers. Configurations with porosity increasing from bottom to top in order from 0.34, 0.40 and 0.43 achieved the lowest runoff, reducing it by up to 22.14\% for 1 l/s. Configurations with low-porosity layers at the top produced the highest runoff, emphasizing the importance of layer arrangement.