The time development of an arbitrary sea bottom configuration driven by tidal currents is computed assuming that the bottom topography is characterized by a small amplitude. In particular, a sand pit of small depth is considered. The bottom configuration is decomposed into its spatial Fourier components, which develop each independently from the other. The flow and sediment transport in the tidal environment are evaluated using the model formulated by Blondeaux and Vittori (2005), which considers both the bed and the suspended loads and the presence of wind waves. The model for the pit development is supported by a comparison of the predicted time development of a trench dredged in front of the Scheveningen (Netherlands) beach with field measurements. The effects of the residual current, the tidal asymmetry, the wind waves, and the grain size distribution of the sediment on the time development of large-scale sand pits are discussed. The model shows that for particular values of the parameters the pit can trigger the formation of large-scale bed forms.