Global sensitivity analysis of bioretention cell design for stormwater system: A comparison of VARS framework and Sobol method

Bioretention cell (BC) design variation significantly changes its hydrological dynamics at unit-scale leading to major changes in its target design goals when designed unit replicated at the catchment-scale. Improved understanding of the behaviors of BC design parameters under different rainfall conditions is critical for effective implementation of BCs to achieve design goals. This paper illustrates and compares two global sensitivity analysis methods (i.e., VARS and Sobol) for the identification of influential parameters and their variations in hydrological dynamics (model responses) under different rainfall conditions and perturbation scales, so as to quantify their uncertainty and reliability for influential factors ranking. From the application results of both sensitivity analysis methods, six parameters out of the total seventeen including conductivity, berm height, vegetation volume, suction head, porosity and wilting point were indicated for their significant sensitivities to surface infiltration, surface outflow and peak flow. In addition, soil thickness, conductivity slope and field capacity (in a total of nine) were categorized as influential to storage outputs. Conductivity and vegetation volume were ranked as the most influential parameters, followed by berm height and suction head, porosity and wilting point. The results analysis also demonstrated that the behavior of design parameters towards model response significantly changes with different rainfall conditions and perturbation scales, as well as the used sensitivity analysis methods. In particular, it is indicated from this study that the VARS is preferred over other sensitivity analysis approaches including the Sobol method (i.e., variance-based method) because of its higher accuracy, reliability, and computational efficiency.