Simulating flows in horizontal subsurface flow constructed wetlands operating in Portugal

Constructed wetlands are wastewater treatment technologies based in natural systems, and their environmental and hydraulic behaviour is influenced by weather conditions like temperature, solar radiation and precipitation. In this paper, a one-dimensional dynamic model applicable to horizontal flow constructed wetlands is presented. The structure of the hydraulic module considers Darcy's law for estimating head losses along the porous media and the boundary condition of the outlet structure. For the water budgets, precipitation and evapotranspiration are considered. The model was calibrated and validated with data from a constructed wetland operating in the South of Portugal, and a good agreement between simulated and measured data was obtained. The relevance of considering evapotranspiration in order to obtain good flow estimations was demonstrated, showing a significant influence of that variable on daily flow reductions, especially during summer months. Better simulation results were obtained when considering an evapotranspiration pattern that describes variations during the day, instead of a constant daily evapotranspiration rate.