We infer that the morphology of the Ravi Vallis channel system is consistent with it having been eroded by water in a single flood event, and we have used the topography of the channel system to estimate the depth of water in the channel at various stages during its development. Values lie in the range 50--150 m. Measured bed slopes, estimated water depths, and corresponding channel widths are used to obtain mean water flow speeds and volume flow rates. Water flow speeds are found to lie in the range ~10--25 m s-1, and the discharge estimates vary from a maximum volume flux of ~30 ¿ 106 m3 s-1 just after the start of the flood to less than 10 ¿ 106 m3 s-1 in the late stages. Using assumptions about the sediment-carrying capability of the water, estimates are obtained for the minimum duration of the water release event, the minimum total volume of water involved, and the crustal erosion rate. The duration is inferred to have been between 2 and 10 weeks, and the minimum total water volume was between 11,000 and 65,000 km3. The corresponding bed erosion rate was possibly as much as ~100 but more likely ~20--50 m/d. It is estimated that during the early stages of the flood event, flow conditions were supercritical, with maximum Froude numbers between 1.4 and 2 depending on the bed roughness.