2D hydraulic modelling of the ancient paleolake in Gusev Crater, Mars.

The application of hydraulic models on Mars is still a scarcely discussed topic in the scientific literature, despite the interest of  these models to study paleofloods and to understand the geological past of the planet. In this work, we present the application of a 2D-hydraulic model (using HECRAS) in Gusev crater aiming to study the hydrodynamics of a paleolake that would have been formed in the crater about 3,5 Ga ago.

Using a corrected and optimized 100m resolution Digital Elevation Model derived from MOLA ( Mars Orbiter Altimeter) data, we first identify and map the different evidences of water marks. Different flow rates and commonly used friction values were combined to obtain several flow hypotheses, which in turn were simulated with the 2D model. Our main aim was to study the flow patterns inside the crater and the inlet and outlet conditions in order to check if the water levels obtained with our simulations correspond to what the mapped benchmarks may suggest.

The Ma’adim valley feeding Gusev crater ends in a fluvial-lake delta. The flat top morphology  of this delta suggests that streamflow processes must have occurred on its top during its formation. Then, one of our major research assumptions is based on finding flow rates consistent with a fully submerged. In this regard, model outcomes obtained with flow rates covering the whole delta are consistent with previous discharge estimations compiled from the scientific bibliography.

Moreover, we also took advantage of the last capabilities of the hydraulic modeling software to go further than just simulating water flows. That said, we varied the concentration of sediments within the fluid and other fluid parameters such as internal shear stress and dynamic viscosity to model a hyperconcentrated flow, which has been already proposed  as forming flow conditions for the delta. At the same time, we also analyzed turbulence and flow recirculation processes trying to stablish a relation with the sediment distribution within the crater.

Based on our work, we conclude that the downstream boundary conditions in the hydraulic model is the main source of uncertainty in the modelling of Gusev crater,while changes in roughness has a minor influence on model outcomes. Finally, we raised the question on how low gravity in Mars may have affected sediment transport by water and how the nature of this process may have been different than in the Earth.