Model help:DeltaBW

DeltaBW

This is used to Calculate evolution of long profile of a river ending in a 1D migrating delta, using a backwater formulation.

Model introduction

This program calculates bed surface evolution for a narrowly channelized1D fan-delta prograding into standing water using a backwater formulation, as well as calculating the final water surface of the system and the mass balance of sediment in the system.

Model parameters

Input Files and Directories

Run options

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
Chezy Or Manning, Chezy-1 or Manning-2

Parameter	Description	Unit
Flood discharge (q)		m2 / s
Intermittency (I)	flood intermittency	-
upstream bed material sediment feed rate during flood (Q)		m2 / m
Grain size of bed material (D)		mm
Chezy resistance coefficient (C)	cofficient in the Chezy relation	-
Exponent in load relation (n)		-
Critical Shields stress in load relation (T)		-
Elevation of top of forest (E)		m
Initial elevation of forest bottom (e)		m
Water surface elevation of lake (x)		m
Initial fluvial bed slope (f)		-
Subaqueous basement slope (b)		-
initial length of fluvial zone (s)		m
Maximum length of fluvial zone (m)		m
Slope of forest face (Sa)		-
Submerged specific gravity of sediment (R)		-
Bed porosity (L)		-
Manning-Strickler coefficient (k)	coefficient in the Manning-Strickler relation	-
Manning-Strickler coefficient (r)	coefficient in the Manning-Strickler relation	-
Coefficient in total bed material relation (a)		-
Number of fluvial nodes (M)		-
Time step (t)		days
Number of printouts after initial one		-
Iterations per each printout		-

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

• Water surface elevation

[math]\displaystyle{ \eta = \eta_{f}[s_{s} \left (t\right ), t] - S_{a}[x - s_{s}\left ( t \right )] }[/math]

(1)

• Exner equation for shock condition

[math]\displaystyle{ \left ( 1 - \lambda_{p} \right ) \int _{s_{s}\left (t\right )} ^ \left ( s_{b} \left (t\right ) \right ){\frac{\partial \eta}{\partial t}} d x = I_{f} \{q_{t}[s_{s}\left (t \right ), t] - q_{t} [s_{b}\left (t\right ),t] \} }[/math]

(2)

[math]\displaystyle{ \dot{s_{s}} = {\frac{1}{\left (S_{a} - S_{s} \right )}}[{\frac{I_{f} q_{ts}}{\left ( 1 - \lambda_{p}\right ) \left (s_{b} - s_{s} \right )}} - {\frac{\partial \eta _{f}}{\partial t}}|_{s_{s}}] }[/math]

(3)

[math]\displaystyle{ \left (S_{a} - S_{b} \right ) \dot{s}_{b} = \left (S_{a} - S_{s}\right ) \dot{s}_{s} + {\frac{\partial \eta _{f}}{\partial t}}|_{s_{s}} }[/math]

(4)

• Moving boundary coordinate

[math]\displaystyle{ \hat{x} = {\frac{x}{S_{s}\left (t\right )}} }[/math]

(5)

[math]\displaystyle{ \hat{t} = t }[/math]

(6)

• Exner equation for moving-boundary coordinate

[math]\displaystyle{ \left ( 1 - \lambda_{p} \right ) [\left ({\frac{\partial \eta_{f}}{\partial \hat{t}}} - {\frac{\dot{s}_{s}}{s_{s}}} \hat{x} {\frac{\partial \eta_{f}}{\partial \dot{x}}}\right )] = - {\frac{1}{s_{s}}} I_{f} {\frac{\partial q_{t}}{\partial \dot{x}}} }[/math]

(7)

• Shock condition for moving-boundary coordinate

[math]\displaystyle{ \left (s_{b} - s_{s} \right )[{\frac{\partial \eta_{f}}{\partial \hat{t}}}|_{\hat{x} = 1} + S_{a} \dot{s}_{s}] = {\frac{I_{f} q_{t} \left (1, \hat{t}\right )}{\left ( 1 - \lambda_{p}\right )}} }[/math]

(8)

• Continuity condition for moving-boundary coordinate

[math]\displaystyle{ \dot{s}_{b} = {\frac{S_{a} \dot{s}_{s} + {\frac{\partial \eta _{f}}{\partial \hat{t}}}|_{\hat{x} = 1}}{\left ( S_{a} - S_{b}\right )}} }[/math]

(9)

• Sediment transport relation

1) Total bed material transport

[math]\displaystyle{ q_{t} = \sqrt{R g D} D q_{t} ^* }[/math]

(10)

[math]\displaystyle{ q_{t}^* = \alpha_{t}[\tau^* - \tau_{c}^*]^ \left (n_{t}\right ) }[/math]

(11)

• Backwater formula

[math]\displaystyle{ {\frac{dH}{d \hat{x}}} = s_{s} {\frac{S - S_{f}}{1 - Fr^2}} }[/math]

(12)

[math]\displaystyle{ S = - {\frac{1}{s_{s}}} {\frac{\partial \eta _{f}}{\partial \hat{x}}} }[/math]

(13)

[math]\displaystyle{ Fr^2 = {\frac{q_{w}^2}{g H^3}} }[/math]

(14)

[math]\displaystyle{ S_{f} = C_{f} Fr^2 }[/math]

(15)

[math]\displaystyle{ H \left (1,t\right ) = \xi_{s} \left (\hat{t} \right ) - \eta_{f} \left (1,\hat{t} \right ) }[/math]

(16)

[math]\displaystyle{ \tau^* = {\frac{\tau_{b}}{\rho R g D}} = {\frac{C_{f} U^2}{R g D}} = {\frac{C_{f} {\frac{q_{w}^2}{H^2}}}{R g D}} }[/math]

(17)

• Boundary conditions

[math]\displaystyle{ s_{s} \left ( \hat{t} + \Delta \hat{t} \right ) = s_{s} \left (\hat{t}\right ) + \dot{s}_{s} \Delta \hat{t} }[/math]

(18)

[math]\displaystyle{ s_{b} \left ( \hat{t} + \Delta \hat{t} \right ) = s_{b} \left (\hat{t}\right ) + \dot{s}_{b} \Delta \hat{t} }[/math]

(19)

[math]\displaystyle{ \eta_{b} \equiv \eta [S_{b} \left (\hat{t} \right ), \hat{t}] = \eta_{d} - S_{s} \left ( s_{b} - s_{s}\right ) }[/math]

(20)

• Calculation of derivatives

[math]\displaystyle{ {\frac{\partial \eta}{\partial \hat{x}}}|_{i} = \left\{\begin{matrix} {\frac{\eta_{i+1} - \eta_{i}}{\Delta \hat{x}}} & i = 1 \\ {\frac{\eta_{i+1} - \eta_{i-1}}{2 \Delta \hat{x}}} & i = 2...M \\ {\frac{\eta_{i} - \eta_{i-1}}{\Delta \hat{x}}} & i = M+1 \end{matrix}\right. }[/math]

(21)

[math]\displaystyle{ {\frac{\partial q_{t}}{\partial \hat{x}}}|_{i} = \left\{\begin{matrix} {\frac{q_{t,i} - q_{tf}}{ \Delta \hat{x}}} & i = 1 \\ {\frac{q_{t,i} - q_{t,i-1}}{ \Delta \hat{x}}} & 1 \lt i \lt = M+1 \end{matrix}\right. }[/math]

(22)

Nomenclature

Symbol	Description	Unit
qw	water discharge / width	L2 / T
Cz	dimensionless Chezy resistance coefficient	-
R	submerged specific gravity of sediment	-
λp	bed porosity	-
nt	exponent in load relation	-
ηd	water surface elevation of the lake	L
Sfl	initial fluvial bed slope	-
sfl	initial length of fluvial zone	L
Sa	slope of foreset face	-
Δt	time step	T
Mtoprint	number of steps until a printout is made	-
Mprint	number of printouts after the initial one	-
x	downstream coordinate	L
η	bed surface elevation	L
qb	volume bedload transport per unit width	L2 / T
H	water depth	L
τ	shear stress	-
sU	location of the upstream coordinate	L
sbb	reach of the alluvium bottom	L
sss	reach of the alluvium top	L
ηup	upstream bed surface elevation	L
ηtop	bed surface elevation of the top of the forest	L
ηbot	bed surface elevation of the bottom of the forest	L
q	flood discharge	L2 / T
If	flood intermittency	-
Q	upstream bed material sediment feed rate during floods	L2 / T
D	grain diameter	L
E	elevation of the top of the forest	L
e	initial elevation of the bottom of the forest	L
f	initial fluvial bedslope	-
b	subaqueous basement slope	-
s	initial length of the fluvial zone	L
L	bed porosity	-
k	coefficient in the Manning-Strickler relation	-
a	coefficient in the total bed material load relation	-
r	coefficient in the Manning-Strickler relation	-
M	number of fluvial nodes	-
t	time step	T
p	number of prints	-
i	number of iterations per print	-
ηs(t)	bed elevation at the topset-foreset break	L
ηb(t)	bed elevation at the foreset-bottomset break	L
ss(t)	coordinate corresponds to the topset-foreset break	L
sb(t)	coordinate corresponds to the foreset-bottomset break	L
qt	volume total bed material transport rate per unit width	L2 / T
qtf	upstream sediment feed rate	L2 / T
ηf(x,t)	bed elevation on the fluvial region	L
dot{s}s	prograding rate of the delta at the topset-foreset break	L / T
dot{s}b	prograding rate of the delta at the foreset-bottomset break	L / T
Ss	bed slope of the fluvial region at the topset-foreset break	-
x^	dimensionless downstream coordinate	-
t^	dimensionless time	-
qt *	Einstein number for total bed material	-
αt	coefficient in generic relation for total bed material load	-
τ*	Shields number	-
τc *	critical Shields number at the threshold of motion	-
Cf	bed friction coefficient	-
S	down-channel bed slope	-
qts	volume rate of supply per unit width of total bed material load used in study of bedrock rivers	-
g	acceleration due to gravity	L / S2
Sf	down-channel friction slope	-
Fr	Froude number	-
τb	bed shear stress	M / L / T2
ρ	water density	M / L3
ξs	elevation of standing water	-

Output

Symbol	Description	Unit
qbT	total volume gravel bedload transport rate per unit width summed over all sizes	L2 / T
v	flow velocity	L / T
τsg	shield stress	-

Notes

This module is a calculator for 1D Subaerial Fluvial Fan-Delta with Channel of Constant Width. This model assumes a narrowly channelized 1D fan-delta prograding into standing water. The model uses a single grain size D, a generic total bed material load relation and a constant bed resistance coefficient. The channel is assumed to have a constant width. Water and sediment discharge are specified per unit width.The channel is assumed to have a constant width. Water and sediment discharge are specified per unit width. The fan builds outward by forming a prograding delta front with an assigned foreset slope. The code employs a full backwater calculation.

In the normal flow formulation, for any given time t = t^: a) Specify the downstream bed elevation η_d

b) Calculate the backwater curve upstream from x^ = 1.

c) Use this to evaluate q_t everywhere, including q_ts at x^ = 1.

d) Implement the shock condition to find dot{s}_s. This shock condition requires knowledge of the term d η_f / d t^ |x^ = 1 . It is sufficient to evaluate this term using the current bed profile and that obtained one step earlier, at t^ = 0, this term can be ignored.

e) Solve Exner everywhere to find new bed elevations at time Δt^ later.

f) Use continuity condition to find dot{s}_b.

• Note on model running

A uniform grain size is assumed, and the same choice of Manning Strickler or Chézy is posed to the user.

The fan builds outward by forming a prograding delta front with an assigned foreset slope.

If the flow becomes supercritical, the backwater calculation will fail, so the program automatically alerts the user and exits.

The initial depth at the top of the foreset must be greater than the critical water depth H_crit; if it isn't the program will alert the user and exit

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: https://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

• Grover, N.C., and Howard, C.L., 1937, The passage of turbid water through Lake Mead, Transactions, American Society of Civil Engineers, 103, 720-732.

• Kostic, S. and Parker, G., 2003a, Progradational sand-mud deltas in lakes and reservoirs. Part 1. Theory and numerical modeling, Journal of Hydraulic Research, 41(2), 127-140.

• Kostic, S. and Parker, G., 2003b, Progradational sand-mud deltas in lakes and reservoirs. Part 2. Experiment and numerical simulation, Journal of Hydraulic Research, 41(2), 141-152

• Swenson, J. B., Voller, V. R., Paola, C., Parker G. and Marr J., 2000, Fluvio-deltaic sedimentation: a generalized Stefan problem, European Journal of Applied Math., 11, 433-452.

Links

• Model:DeltaBW