Evapotranspiration Crop Coefficients for Cattail and Bulrush

Accurate estimates of evapotranspiration from constructed wetlands are required to establish design flow estimates and to assess the effectiveness of wetland water quality amelioration. Water consumption by two wetland plant species, Typha latifoilia (broadleaf cattail) and Scoenoplectus acutus (hardstem bulrush), was measured in a greenhouse for eight months. Measurements of actual evapotranspiration $\left({\mathrm{ET}}_C\right)$ from replicates of both plant treatments were related to potential evaporation $\left({\mathrm{ET}}_0\right)$ as approximated by evaporation from saturated gravel beds. Ratios of ${\mathrm{ET}}_C$ to ${\mathrm{ET}}_0$ were used to develop crop coefficients $\left(K_c\right)$ for each plant species. The relationship between cattail ${\mathrm{ET}}_C/{\mathrm{ET}}_0$ and the ratio of vegetative to open water surface area $(S_V/S_0)$ agreed with previous investigations. A linear relationship was used to account for advective energy fluxes due to peripheral canopy area. Cattail crop coefficients were scaled according to this relationship. The resulting scaled crop coefficient curve may be transferable to constructed wetlands of a known $S_V/S_0\text{.}$