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An undertow model calibrated for regular waves on plane beaches is applied to predict the irregular wave induced undertow for both plane and barred beaches and for both laboratory and field data sets. The model combines a logarithmic profile in the bottom boundary layer witha conventional parabolic profile in the interior. The height and period of the irregular waves are represented by the local root-mean-square wave height and spectral peak period and the measured mean volumeflux below trough level is used as input to the model. The model is capable of predicting the undertow profiles both inside and outside the surf zone, provided that the empirical coefficient associated withthe mean bottom shear stress is adjusted at each measuring line. Themodel appears to give reasonable predictions of the bottom boundary layer thickness and shear velocity, although these predictions could not be verified due to a lack of data. To develop a predictive undertow model, a simple relationship with an adjustable coefficient is applied to predict the measured volume flux below trough level using thelocal wave height and water depth. The calibration coefficients involved in the predictive model are not universal among the lab and field conditions possibly due to the effects of wave directionality and longshore currents in the field measurements, which are neglected in this paper. [ABSTRACT FROM AUTHOR]