Estimation of evapotranspiration from a bioretention facility using a lysimeter and six predictive equations

Abstract

Low impact development practices such as bioretention are being used more frequently in stormwater management. The commonly considered aspects of bioretention are its ability for filtration and infiltration, but evapotranspiration is not frequently considered despite its potential to be a significant component of the water balance. A lysimeter study was conducted in Guelph, Ontario to estimate the ET rate from bioretention facilities. The lysimeter was designed to mimic standard bioretention design parameters. The average annual ET rate was 1.30 mm/d, with monthly averages ranging from -0.009-2.90 mm/d. The lysimeter-derived ET was then compared to ET predicted by the Hamon, Hargreaves-Samani, Jensen-Haise, Penman-Monteith, Priestley-Taylor, and Thorthwaite equations to determine their applicability to use in urban bioretention systems. The Jensen-Haise equation was found to perform the best once a coefficient of 0.5 was applied to consider the protected environment of the lysimeter.