Model help:BedrockAlluvialTransition

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BedrockAlluvialTransition

This is used to calculate aggradation and degradation with a migrating bedrock-alluvial transition at the upstream end.

Model introduction

This program calculates the bed surface evolution at predefined nodes relative to moving boundary nodes for a transition from bedrock to allvium.

Model parameters

Input Files and Directories

Run Parameters

About

Parameter	Description	Unit
Input directory	path to input files	-
Site prefix	Site prefix for Input/Output files	-
Case prefix	Case prefix for Input/Output files	-

Parameter	Description	Unit
Flood discharge (q)	water discharge per unit width during floods	m2 / s
Intermittency	flood intermittency (I)	-
Upstream bed material sediment fed rate during floods	volume sediment feed rate per width at upstream end during flood	m2 / s
Grain size of bed material (D)		mm
Chezy resistance coefficient (Cf)	coefficient in Chezy relation	-
Subaqueous basement slope (b)	slope of bedrock basement	-
Slope of forest face (S)	initial slope of alluvial region	-
Submerged specific gravity of sediment		-
Bed porosity (L)		-
Position of downstream end of the reach (d)		m
Number of spatial steps (M)		-
Time step (t)		days
Number of iterations before printing (i)		-
Number of printouts (p)		-

Parameter	Description	Unit
Model name	name of the model
Author name	name of the model author	-

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

Nomenclature

Symbol	Description	Unit
x	downstream coordinate (0 = initial bedrock - alluvial transition)	-
η	bed elevation	m
Sl	bed slope	-
qb	volume bedload transport per unit width	-
H	water depth	mm
qw	water discharge per unit width during floods	m2 / s
If	flood intermittency (0 < I <= 1)	-
Q	volume sediment feed rate per width at upstream and during flood	m2 / s
D	grain size of alluvium	mm
Cz	coefficient in Chezy relation, Cf	-
b	slope of bedrock basement	-
Sinit	initial slope of alluvial region	-
L	bed porosity	-
k	coefficient in Manning-Strickler relation	-
a	coefficient in Manning-Strickler relation	-
d	position of the downstream end of the reach	m
M	number of spatial intervals	-
t	time step	year
i	number of interations per print	-
p	number of prints	-
sd	position of the downstream end of the reach, equals to initial length of alluvial region	-
qtf	volume sediment feed rate per width at upstream end during floods	m2 / s
Sb	slope of bedrock basement	-
dt	time step	years
Mtoprint	number of steps to printout	-
Mprint	number of printouts	-

Output

Symbol	Description	Unit
x	downstream coordinate	m
η	bed surface elevation	m

Notes

This program computes fluvial aggradation/degradation with a bedrock-alluvial transition. The bedrock-alluvial transition is located at a point s_ba(t) which is free to change in time. A bedrock basement channel with slope S_b is exposed from x = 0 to s_ba(t); it is covered with alluvium from x = s_ba(t) to x = s_d, where S_d is fixed. Initially s_ba = 0. The bedrock basement channel is assumed to undergo no incision on the time scales at which the alluvial reach responds to change. In computing bed level change on the alluvial reach, the normal (steady, uniform) flow approximation is used. Base level is maintained at x = s_d, where bed elevation h = 0. The Engelund-Hansen relation is used to compute sediment transport rate, so the analysis is appropriate for sand-bed streams. Resistance is specified in terms of a constant Chezy coefficient C_z.

• Note on model running

The water depth is calculated using a Chézy formulation, when only the Chézy coefficient is present in the inputted file, and with the Manning-Strickler formulation, when only the roughness height, k_c, value is present. When both are present the program will ask the user which formulation they would like to use.

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)

Gary Parker

References

Key papers

Links

• Model:BedrockAlluvialTransition