Hydraulic modeling of a distributary channel of Athabasca Valles, Mars, using a high-resolution digital terrain model

Estimating magnitudes of flow rates in outflow channels has a central role in developing understanding of the paleohydrology of Mars. The typical approach to flow estimation is to identify geomorphic features, which indicate bankfull levels, and then use a hydraulic model to convert these levels into flow rates. Data constraints have meant that important assumptions about model equations, boundary conditions and parameter values have been necessary. In this paper, we use a high-resolution digital terrain model derived from NASA's Mars Reconnaissance Orbiter Context Camera stereopair imagery to develop a finer resolution step backwater hydraulic model than previously attempted. Furthermore, the data facilitate a more critical, more formal and broader assessment of this type of model than has previously been attempted. A distributary channel of Athabasca Valles is used as a case study. The median bankfull flow estimate was 39,000 m(3) s(-1), although estimates range up to 140,000 m(3) s(-1) depending on the assumptions employed. The principal uncertainties stem from assumptions about bankfull levels and downstream boundary conditions; and assumptions about the friction coefficient, criticality of flow, expansion and contraction losses, and geometric details of the channel are also important under certain conditions. Examination of additional DTMs further downstream would permit the analysis to be extended to hydraulic control sections that provide better-known boundary conditions, hence improving flow estimates. It is concluded that new-generation DTM data provide opportunity for deeper insight into the challenges and opportunities for modeling the paleohydrology of Mars, although further work is needed to achieve satisfactory levels of confidence.