Model help:GravelSandTransition
GravelSandTransition
This model is used to calculate evolution of long profile of river with a migrating gravel-sand transition and subject to subsidence or base level rise.
Model introduction
This model calculates the long profile of a river with a gravel-sand transition. The model uses two grain sizes: size Dg for gravel and size Ds for sand. The river is assumed to be in flood for the fraction of time Ifg for the gravel-bed reach and fraction Ifs for the sand-bed reach. All sediment transport is assumed to take place when the river is in flood. Gravel transport is computed using the Parker (1979) approximation of the Einstein (1950) bedload transport relation. Sand transport is computed using the total bed material transport relation of Engelund and Hansen (1967).
In this simple model the gravel is not allowed to abrade. Both the gravel-bed and sand-bed reaches carry the same flood discharge Qbf.
Gravel is transported as bed material in, and deposits only in the gravel-bed reach. A small residual of gravel load is incorporated into the sand at the gravel-sand transition. Sand is transported as washload in the gravel-bed reach, and as bed material load in the sand-bed reach.
The model allows for depositional widths Bdgrav and Bdsand that are wider than the corresponding bankfull channel widths Bgrav and Bsand of the gravel-bed and sand-bed channels. As the channel aggrades, it is assumed to migrate and avulse to deposit sediment across the entire depositional width. For each unit of gravel deposited in the gravel-bed reach, it is assumed that Lamsg units of sand are deposited. For each unit of sand deposited on the sand-bed reach, it is assumed that Lamms units of mud are deposited.
The gravel-bed reach has sinuosity Omegag and the sand-bed reach has sinuosity Omegas.
Bed resistance is computed through the use of two specified constant Chezy resistance coefficients; Czg for the gravel-bed reach and Czs for the sand-bed reach.
Model parameters
Uses ports
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Provides ports
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Main equations
A list of the key equations. HTML format is supported; latex format will be supported in the future
| Symbol | Description | Unit |
|---|---|---|
| Qbf | bankfull water discharge at flood | m3 / s |
| Ifg | flood intermittency, gravel-bed reach | - |
| Ifs | flood intermittency, sand-bed reach | - |
| Qgravel,feed | feed rate of gravel | - |
| Qsand,feed | feed rate of sand | - |
| Bc,grav | gravel-bed channel width | m |
| Bc,sand | sand-bed channel width | m |
| Bd,grav | depositional or floodplain width, gravel-bed reach | m |
| Bd,sand | depositional or floodplain width, sand-bed reach | m |
| Ωg | sinuosity of gravel-bed reach | - |
| Ωs | sinuosity of sand-bed reach | - |
| Λsg | fraction of sand deposited per unit gravel in depositional zone of gravel-bed reach | - |
| Λms | fraction of mud deposited per unit sand in depositional zone of sand-bed reach | - |
| Dg | grain size of gravel | mm |
| Ds | grain size of sand | mm |
| Czg | dimensionless Chezy resistance coefficient gravel-bed reach | - |
| Czs | dimensionless Chezy resistance coefficient sand-bed reach | - |
| L | reach length | m |
| sgsl | initial position of gravel-sand transition (must be < L) | m |
| Sgl | initial slope of gravel-bed reach | - |
| σ | subsidence rate | mm / year |
| ξdo | initial water surface base level | m |
| ξd | rate of base level rise | mm / year |
| Δt | time step | years |
| λpg | bed porosity, gravel-bed reach | - |
| λps | bed porosity, sand-bed reach | - |
| R | submerged specific gravity of sediment | - |
Output
| Symbol | Description | Unit |
|---|---|---|
| Ss,feed,n | normal slope associated with sand feed rate | - |
| Hs,feed,n | normal depth associated with sand feed rate | m |
| Ss,feed,n | normal slope associated with gravel feed rate | |
| Hs,feed,n | normal depth associated with gravel feed rate | m |
Notes
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Numerical scheme
Examples
An example run with input parameters, BLD files, as well as a figure / movie of the output
Follow the next steps to include images / movies of simulations:
- Upload file: http://csdms.colorado.edu/wiki/Special:Upload
- Create link to the file on your page: [[Image:<file name>]].
See also: Help:Images or Help:Movies
Developer(s)
Name of the module developer(s)
References
Key papers
