Effect of Hydrologic Data Uncertainties on Constructed Wetland Water Budgets

Abstract

Accurate assessment of treatment performance of constructed wetlands relies on water budget analyses. Developing a closed water budget is not a simple task due to errors associated with the estimation of water budget components, i.e., surface water flows, precipitation, evapotranspiration, change in storage, and groundwater seepage. These hydrological variables are subject to uncertainties from various sources including installation and maintenance of the measurement devices, calibration, and data reduction. In addition to measurement uncertainties, disparity and nonhomogeneity of the temporal and spatial resolutions of the observations also introduce errors. Quantifying these uncertainties in hydrologic variables is not straightforward. In this study, historical records obtained by various methods were used to estimate the spatial and temporal variations in the hydrologic data that were subsequently used as a basis for data uncertainty for a large constructed wetland located in South Florida. Uncertainties for each component were estimated and propagated through the water budget equation for various record lengths. A sensitivity analysis was conducted to evaluate the impacts of the imperfect knowledge of hydrologic data on the understanding of wetland hydrology. Results indicated water budget residuals and contributions from hydrologic variables depend strongly on the selection of time steps and length of period. The results of this study are expected to help identify variables that need improvement to reduce the errors in the water budget residuals and help in the effective operation of constructed wetlands.