A model for the dynamics of colloid deposition in porous media is developed by combining macroscopic and microscopic theories of particle deposition. The model considers the non-uniform coverage of collector surfaces by retained particles during the deposition process. A flux-correcting function is introduced that enables the determination of the overall colloid deposition rate as a function of surface coverage. A non-linear dependence of particle deposition rate on surface coverage is obtained, in agreement with experimental data of particle deposition. It is shown that the model is successful in describing the blocking (excluded-area) effect in particle deposition dynamics.