Temporal estimation of hydrodynamic parameter variability in stormwater constructed wetlands – The hysteresis effect during multi-rainfall events

Abstract

Constructed wetland (CW) systems are increasingly implemented as appropriate water treatment facilities, the efficiency of which varies with time due to possible malfunctions such as clogging related to excessive loads of suspended solids or inadequate CW sizing. Numerical flow modeling was used to evaluate filtering performance and to improve the design of CWs. Such modeling usually involves the so-called van Genuchten-Mualem (vGM) soil hydrodynamic parameters which are difficult to measure. This paper focuses on the sensitivity of the model with respect to the vGM parameters revealing a predominant influence of the shape parameters and the saturated conductivity of the filter on the piezometric heads, during feeding and drainage. A simple, robust and low-cost inverse modeling approach, deterministic and stochastic, for the identification of the soil hydrodynamic properties from piezometric heads measured during successive storm events is also presented. The temporal variability of hydrodynamic parameters was assessed and analyzed with regards to modeling efficiency. Principal component analysis showed that the estimated hydrodynamic parameters from the feeding and drainage sub-periods were significantly different.