Numerical modeling of Martian gully sediment transport: Testing the fluvial hypothesis

[1] Using a stereo pair of HiRISE images of a pole‐facing crater slope at 38°S, 218°E, we measure topographic profiles along nine gullies. Typical slopes of the interior channel region (above the depositional apron) are ∼20°. We test the hypothesis that sediment transport on gully slopes occurs via fluvial transport processes by developing a numerical sediment transport model based on steep flume experiments performed by Smart (1984). At 20° slopes, channels 1 m deep by 8 m wide and 0.1 m deep by 3 m wide transport a sediment volume equal to the alcove volume of 6 × 10 m in 10 h and 40 days, respectively, under constant flow conditions. Snowpack melting cannot produce the water discharge rates necessary for fluvial sediment transport unless long‐term (kyr) storage of the resulting meltwater occurs. If these volumes of water are discharged as groundwater, the required aquifer thicknesses and aquifer drawdown lengths would be unrealistically large for a single discharge event. More plausibly, the water volume required by the fluvial transport model could be discharged in ∼10 episodes for an aquifer 30 m thick, with a recurrence interval similar to that of Martian obliquity cycles (∼0.1 Myr).