Time evolution of gap depths measured in hydrodynamic simulations, defined as the ratio between the gas surface density at the gap center (Σ_gas) to the initial surface density at that location (Σ_gas,0). The color curves show the depth of the three gaps for the α = 5 × 10⁻⁵ model: (blue) the primary gap at 20 au, (green) the secondary gap at ∼8 au, and (red) the tertiary gap at ∼4 au. The black curve shows the depth of the primary gap (at 20 au) for the α = 5 × 10⁻⁴ model.