The correct estimation of conveyance water losses from an irrigation system is vital for the proper management for the system. Seepage is the most dominant process by which water is lost in the canal. Thus, for the effective operational planning and management of an irrigation system, a dependable forecasting of the seepage is very important. Seepage rates are obtainable either by direct measurement or by estimation. This study investigated the usefulness of the equations of Moritz and Davis-Wilson in estimating the seepage losses of concrete-lined canals. Seepage losses of the concrete-lined trapezoid canals of the Menemen irrigation system at the end of the Gediz basin were measured by the inflow-outflow method and the results were compared with the estimates of seepage losses given by the use of these two equations. Average seepage losses were measured as 107.6 l s(-1) km(-1) for the main canal, 32.1 l s(-1) 100 m(-1) for the secondary canals, and 11.7 l s(-1) 100 m(-1) for the tertiary canals. Standard deviation and variation coefficients were found to be 79 l s(-1) km(-1) and 73%, respectively, for the main canal, 29 l s(-1) 100 m(-1) and 89%, respectively, for the secondary canals, and 17 l s(-1) 100 m(-1) and 158%, respectively, for the tertiary canals. Actual seepage losses from the main canal, the secondary canals, and the tertiary canals were all much higher than the standards and showed a wide margin of variability. As in the study area, seepage losses in other irrigation systems in Turkey are much higher than the standards, and since the seepage losses estimated by the Moritz and Davis-Wilson equations are much lower than the measured values, the use of these empirical equations in the estimation of seepage losses is not possible. These equations, if used, should be calibrated for existing canal conditions.