A scaling approximation of equilibrium timescales for sand-bed and gravel-bed rivers responding to base-level lowering

The timescale required for a river channel to reach new equilibrium conditions following a disturbance presumably depends on channel substrate size, and previous field studies have suggested that gravel-bed channels should reach equilibrium more quickly than sand-bed channels. To estimate the relative timescale difference between sand-bed and gravel-bed rivers responding to base-level lowering, we developed a simple scaling approximation. Equilibrium timescales derived from these equations for sand-bed rivers were found to be approximately half of those for gravel-bed rivers. While gravel-bed channels do not need to transport as much sediment to reach equilibrium conditions as sand-bed channels, transport of sediment is more rapid in sand-bed channels leading to quicker equilibration.