Formation of Mangala Valles outflow channel, Mars: Morphological development and water discharge and duration estimates

The morphology of features on the floor of the Mangala Valles suggests that the channel system was not bank-full for most of the duration of its formation by water being released from its source, the Mangala Fossa graben. For an estimated typical 50 m water depth, local slopes of sin alpha = similar to 0.002 imply a discharge of similar to 1 x 10(7) m(3) s(-1), a water flow speed of similar to 9 m s(-1), and a subcritical Froude number of similar to 0.7-0.8. For a range of published estimates of the volume of material eroded from the channel system this implies a duration of similar to 17 days if the sediment carrying capacity of the similar to 15,000 km(3) of water involved had been 40% by volume. If the sediment load had been 20% by volume, the duration would have been similar to 46 days and the water volume required would have been similar to 40,000 km(3). Implied bed erosion rates lie in the range similar to 1 to similar to 12 m/day. If the system had been bank-full during the early stages of channel development the discharge could have been up to similar to 10(8) m(3) s(-1), with flow speeds of similar to 15 m s(-1) and a subcritical Froude number of similar to 0.4-0.5.