Model help:AgDegNormGravMixPW
AgDegNormGravMixPW
This is the calculator for aggradation and degradation of sediment mixtures in gravel-bed streams.
Model introduction
This program computes the time evolution of the long profile of a river of constant width carrying a mixture of gravel sizes, the downstream end of which has a prescribed elevation. In particular, the program computes the time evolution of the spatial profiles of bed elevation, total gravel bedload transport rate and grain size distribution of the surface (active) layer of the bed. The river has constant width. The upstream point, at which sediment is fed, is fixed in the horizontal to be at x = 0. The vertical elevation of the upstream point may change freely as the bed aggrades or degrades. The reach has constant length L, so that the downstream point is fixed in the horizontal at x = L. This downstream point has a user-specified initial elevation hdI.
Gravel bedload transport of mixtures is computed with a user-specified selection of the Parker (1990), or Wilcock-Crowe (2003) surface-based formulations for gravel transport. Sand and finer material must first be excluded from the grain size distributions, which then must be renormalized for gravel content only, in the case of the Parker (1990) relation. In the case of the Wilcock-Crowe (2003) relation, the sand is retained in the computation.
Model parameters
Uses ports
This will be something that the CSDMS facility will add
Provides ports
This will be something that the CSDMS facility will add
Main equations
A list of the key equations. HTML format is supported; latex format will be supported in the future
| Symbol | Description | Unit |
|---|---|---|
| q | water discharge / width | m2 / s |
| T | gravel input | m2 / s |
| I | intermittency | - |
| e | base level | m |
| S | initial bed slope | - |
| L | reach length | m |
| t | time step | days |
| M | no. of intervals | - |
| p | no. of prints | - |
| i | no. of iterations per print | - |
| k | factor by which Ds90 is multiplied for roughness height | - |
| n | factor by which Ds90 is multiplied for active layer thickness | - |
| r | coefficient in Manning-Strickler relation | - |
| R | submerged specific gravity of gravel | - |
| l | bed porosity, gravel | - |
| u | upwinding coefficient for load spatial deviations in Exner equation (> 0.5 suggested) | - |
| a | coefficient for material transferred to substrate as bed aggrades | - |
| C | coefficient, Cf, in the Chezy formulation | - |
Output
| Symbol | Description | Unit |
|---|---|---|
| x | downstream coordinate | m |
| Sl | slope of the bed surface | - |
| H | water depth | m |
| u* | shear velocity | m / s |
| τsg | shear stress on the bed surface | N / m2 |
| η | bed surface elevation | m |
| qbT | bedload transport rate | m2 / s |
| qbf | upstream feed rate | tons / year |
| dsg | geometric mean grain size on the bed surface | mm |
| d90s | the diameter such that 90% of the bed surface is finer | mm |
| pfeed | GSD of the feed | tons / year |
| Ffs | GSD of the substrate | - |
| Ff | GSD of the final surface | - |
Notes
The grain size distributions of the sediment feed, initial surface material and substrate material must be specified. It is assumed that the grain size distribution of the sediment feed rate does not change in time, the initial grain size distribution of the surface material is the same at every node, the grain size distribution of the substrate is the same at every node and does not vary in the vertical. These constraints are easy to relax.
The program does not store the vertical and streamwise structure of the new substrate created as the bed aggrades. It is assumed that the grain size distribution of the sediment feed rate does not change in time, the initial grain size distribution of the surface material is the same at every node, the grain size distribution of the substrate is the same at every node and does notvary in the vertical. These constraints are easy to relax.
The program does not store the vertical and streamwise structure of the new substrate created as the bed aggrades. As a result, is cannot capture the case of aggradation followed by degradation. Again, the constraint is easy to relax, but at the price of increased memory requirements for storing the newly-created substrate.
The flow is calculated using the normal flow (local equilibrium) approximation.
The river is assumed to be morphologically active only intermittently (during floods); this condition is specified in terms of an intermittency If < 1 expressing the fraction of time the river is in flood.
In performing the calculation, the following control parameters must be specified: M = number of spatial intervals, so that the spatial step length = L/M; dt = time step length; Ntoprint = number of time steps to a printout; Nprint = number of printouts in the calculation.
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
