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Summary of articles for River and Delta Systems (GEO4-4436)
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Lecture Intro: repetition flow, sediment transport, morphodynamicsFlow discharge and sediment transport models for estimating a minimum timescale of hydrological
activity and channel and delta formation on Mars – Kleinhans
Flow discharge = volume flux in m3/s = Q=hWu. The channel width can be derived from images, the
velocity has to be estimated using a friction law and a measure depth from altimetry data.
Wetted perimeter: Rh = Wh/(W+2h).
The depth- and width- averaged flow velocity from Darcy-Weisbach is: u = sqrt((8ghS)/f)
Roughness predictor is defined by the White-Colebrook function:
or
Reynolds shear velocity number. <3.5 is laminar flow, > 70 is turbulent flow and = 11.63 is transition.
V is 4 x 10^-5/(20+t)
Reynolds number of flow. Turbulent > 500.
Froude number: from subcritical (F<1) to supercritical (F=1)
Bed shear stress
Grain size Bonnefille number:
Shields parameter: nondimensionalized shear stress
Meyer Peter and Mueller equation; einstein parameter
, Sediment transport is divided into rolling and saltating bed load, and suspended load diffused upward
into the flow by the turbulence. If there is barely any sediment exchange between the bed and
suspended sediment, then it is called wash load. Wash load is limited by the amount of upstream
supply.
The sensitivity of grain size varies widely. A good description of sediment is necessary for reliable
sediment transport predictions
Stratification: large sediment concentrations are present in the lower part of the flowing water. In
stratification, the sediment grains in the settling process collide with each other, hindering their
downward movement.
Hyperconcentration: when there are extremely large sediment concentrations. In hyperconcentrated
flows, hindered settling becomes dominant, and the sediment behaves as if it is well mixed
throughout the water depth, behaving somewhat like a pure liquid. Hyperconcentration is unlikely for
Martian channel sediments, except for the fine mode of the grain size distribution.
The minimum timescale of formation of a channel or delta and flow (w) can be estimated as
Estimating timescales for channel formation on Mars is challenging because the nature of Martian
channels varies. Larger channels are often catastrophic and show signs of collapse features, while
smaller channels may have groundwater sapping valleys upstream, indicating a more moderate
discharge regime.
There are complex challenges and uncertainties involved in estimating flow dynamics, sediment
transport, and the timescales for the formation of Martian channels and deltas. It emphasizes the
need to consider multiple factors, including grain size distribution and sediment conditions, when
making these estimations and underlines the role of uncertain factors in determining the true
timescales.
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