Analysis of constructed treatment wetland hydraulics with the transient storage model OTIS

Abstract The model one-dimensional transport with inflow and storage (OTIS) was calibrated to results from tracer experiments conducted in the Orlando Easterly Wetland in order to quantify short-circuiting of the treatment volume and temporary storage of tracer in isolated, low-flow regions. OTIS was found to fit experimental data very well for both steady and unsteady flow conditions. The model calibrations indicate the presence of three different hydraulic ‘zones’ of the wetland. The first zone is the actively flowing main channel; the second, a temporary storage zone where water and constituents are exchanged with the main flow channel; and the third, completely isolated, ‘dead’ water. The uncertainty of storage zone parameters was determined to be low due to the experimental Damkohler number that quantifies intra-zone mass transfer processes. The appropriateness of the use of a one-dimensional model for treatment wetlands is also addressed.