Calibration of hydraulic parameters for large-scale vertical flow constructed wetlands

Constructed wetlands for water cleanup have been in use for several years and are promising for cost-efficient remediation of large scale contamination. Within this study, flow conditions in layered vertical soil filters used for remediation of contaminated groundwater were investigated in detail by special discharge experiments and an attuned modeling study. Unsaturated water flow was measured in two vertical flow constructed wetlands for contaminated groundwater treatment at a site in eastern Germany. Numerical simulations were performed using the code MIN3P, in which variably saturated flow is based on the Richards equation. Soil hydraulic functions based on Van Genuchten coefficients and preferential flow characteristics were obtained by calibrating the model to measured data using self-adaptive evolution strategies with covariance matrix adaptation (CMA-ES). The presented inverse modeling procedure not only provides best fit parameterizations for separate and joint model objectives, but also utilizes the information from multiple restarts of the optimization algorithm to determine suitable parameter ranges and reveal potential correlations. The sequential automatic calibration is both straightforward and efficient even if different complex objective functions are considered.