In this simulation the initial conditions are a pseudo-fractal landscape, but impact cratering occurs during the progress of the simulation.  The processes in this simulation differ from the previous case in that all the runoff producing fluvial erosion is water that has infiltrated, flowed laterally, and seeped into the developing valleys.  There is no critical shear stress for fluvial erosion, but the valley development is limited to a relatively few widely spaced valeys, and that crater rims and inter-valley flats remain largely undissected.  Also, dissection is limited to the base of inner crater walls.  Several large impacts wipe out much of the valley network.