Discussion of "Fluvial gravels on Mars: Analysis and implications" by W.E. Dietrich, M.C. Palucis, R.M.E. Williams, K.W. Lewis, F. Rivera-Hernandez, and D.Y. Sumner

Abstract

Hydraulic geometry offers robust scaling of channels across many orders of magnitude in natural rivers, irrigation canals, and laboratory channels (Ferguson 1986). Although the authors’ analysis focuses on fluvial deposits, it is worth noting that hydraulic geometry relations can be developed for a variety of fluids, which may have relevance for some Martian channels given that differences in gravity and atmospheric conditions (pressure, temperature, and, thus, viscosity) may cause channel hydraulics and flow rheology (Froude and Reynolds numbers) to differ from those on Earth. Data from mountain rivers in Idaho provide an example of how channel width responds to differences in erosional processes, flow rheology, runoff characteristics, and degree of riparian vegetation within a given physiographic region (similar topography, geology, and climate) following fire disturbance (Figure 28.15). In all cases, the exponent of the hydraulic geometry equation is within the range typically observed for terrestrial alluvial and bedrock rivers (0.3-0.6; Montgomery and Gran 2001; Wohl 2004) but systematic differences in width are evident. The debris-flow widths are event-based responses and the postdebris-flow channel widths are transient responses following disturbance, both of which differ from the long-term bankfull conditions examined by the authors, but they nonetheless provide some sense of scaling for different formative processes across a range of rheological and environmental conditions.

Citation

Buffington, John M. 2017. Discussion of "Fluvial gravels on Mars: Analysis and implications" by W.E. Dietrich, M.C. Palucis, R.M.E. Williams, K.W. Lewis, F. Rivera-Hernandez, and D.Y. Sumner. In: Tsutsumi, D.; Laronne, J.B., eds. Gravel-bed Rivers: Processes and disasters. Chichester, UK: Wiley. p. 780-783.