No gravity transport across a breakline?

Marulke · 2020-12-13 11:47:02

Hi,
i am running a sediment transport model with bed load only.

I feed all the incoming bed load into a rectangular area a short distance from the upper (infow) boundary. I use "external source", "sediment discharge" and an index number too feed the bed load.

To avoid the sediment piling up in the feeding area I have activated "gravity transport" for that area and set all the critical slopes very low, only 5 degrees.

I expected that if the sediment feed was too high gravity transport (slope failure) would prevent excessive bed build up. By limiting slope to 5 degrees i would force bedmaterial slide out of the feeding area.

However, I got tens of meters of sediment buildup in the feeding area and a steep wall of sediment formed along the break line between the feeding area and the surrounding area. Much steeper than the 5 degree limit for slope failure.

So my question is: What happens with gravity transport across the boundary between two regions, when one region has gravity transport activated and not the other region? Gravity transport stops at the boundary?

Thanks,
Marulke

Matteo Facchini · 2020-12-21 12:37:01

Hi marulke,

actually, this should not happen. However, it is hard to help you out without seeing at least your bmc file. Could you copy/paste it here?

Cheers,
Matteo

Marulke · 2020-12-27 10:36:26

Hi,
you find the bmc-file below.

Sediment was fed into region index 4.

Kind regards,
Marulke

PROJECT {
title = Base_case
date = 4 December 2020
}
DOMAIN {
PARALLEL {
number_threads = 0
}
BASEPLANE_2D {
region_name = Big_reservoir
GEOMETRY {
type = 2dm
file = 20201213_A200_short.2dm
STRINGDEF {
name = US_boundary
node_ids = (1 544 421 462 362 419 415 5677 270 472 435 448 431 5678 450 507 2)
upstream_direction = right
}
STRINGDEF {
name = DS_boundary
node_ids = (30 5862 4225 4411 3989 4003 3997 5857 31)
upstream_direction = right
}
STRINGDEF {
name = DS_feeding_area
upstream_direction = right
node_ids = (5 160 106 123 98 253 118 313 107 317 117 245 77)
}
STRINGDEF {
name = US_feeding_area
node_ids = (79 333 104 268 135 279 97 284 122 298 105 297 116 5595 4)
upstream_direction = right
}
STRINGDEF {
name = feed_region
node_ids = (91 267 134 278 109 283 153 119 295 121 324 92 326 241 321 100 258 114 93 124 120 264 113 254 108 5597 115 249 94 248 111 242 99 110 252 91)
upstream_direction = right
}
}
HYDRAULICS {
PARAMETER {
riemann_solver = exact
}
FRICTION {
type = manning
default_friction = 0.025
wall_friction = on
}
INITIAL {
type = continue
file = nosed_4000m3s__restart.cgns
restart_solution_time = -1.0
}
BOUNDARY {
type = hydrograph
string_name = US_boundary
slope = 1
file = Inflow_4000_m3s.txt
}
BOUNDARY {
name = DS_boundary
type = hqrelation
file = DS_HQ_boundary_Q_4000m3s_WL575masl.txt
string_name = DS_boundary
}
}
TIMESTEP {
total_run_time = 5000000
start_time = 0
ignore_wave_celerity = off
CFL = 0.975
morph_cycle = constant
cycle_step = 50
}
OUTPUT {
console_time_step = 1000
restart_time_step = 10000
SPECIAL_OUTPUT {
type = node_centered
output_time_step = 100000
values = (depth velocity wse grain_bedload tau deltaz)
format = sms
}
SPECIAL_OUTPUT {
output_time_step = 1000
type = BASEviz
}
SPECIAL_OUTPUT {
type = stringdef_history
output_time_step = 100000
stringdefs = (DS_feeding_area US_feeding_area feed_region)
stringdef_values = (Q Qsed)
}
SPECIAL_OUTPUT {
type = balance
output_time_step = 100000
balance_values = (sediment)
}
}
MORPHOLOGY {
PARAMETER {
control_volume_type = constant
control_volume_thickness = (0.1 0.1 0.1 0.1)
control_volume_thickness_index = (1 2 3 4)
}
BEDMATERIAL {
GRAIN_CLASS {
diameters = (13.3)
}
MIXTURE {
name = Unigrain_13mm
volume_fraction = (100)
}
SOIL_DEF {
name = Reservoir_bed
LAYER {
mixture = Unigrain_13mm
bottom_elevation = -5
}
}
SOIL_ASSIGNMENT {
index = (1 2 3 4)
soil = (Reservoir_bed outer_feeding_area Reservoir_bed Reservoir_bed)
}
SOIL_DEF {
name = outer_feeding_area
LAYER {
mixture = Unigrain_13mm
bottom_elevation = -0.1
}
}
}
INITIAL {
type = initial_mesh
}
BEDLOAD {
FORMULA {
bedload_formula = mpm
bedload_factor = 0.61625
bedload_exponent = 1.6
theta_critical_approach = theta_critical_vanrijn
}
DIRECTION {
lateral_transport_type = lateral_bed_slope
lateral_index = (1 2 3 4)
}
DIRECTION {
lateral_transport_type = curvature_effect_dynamic
lateral_index = (1 2 3 4)
radius_calculation_type = velocity_vectors
min_abs_radius = 100.0
min_abs_radius_use = min_value
}
BOUNDARY {
type = IODown
string_name = DS_boundary
}
PARAMETER {
}
}
SOURCE {
EXTERNAL_SOURCE {
type = sediment_discharge
file = US_bedload_inflow_831.5kg_per_sek_tilsv_1,375kgmin i modell.txt
mixture = Unigrain_13mm
index = (4)
}
}
GRAVITATIONAL_TRANSPORT {
index = (4)
angle_failure_dry = (5)
angle_failure_wetted = (5)
angle_failure_deposited = (5)
}
}
}
}

Matteo Facchini · 2021-03-08 09:54:52

Hi marulke,
I think that what happens to you is quite "normal": you are imposing some strong conditions in your region "4", with very low failure angles, while outside this condition does not hold. Therefore, you have a lot of sediment flushed out of your region 4, that cannot move at the same "pace" outside this region.
You could try to use the gravitational transport everywhere on your domain (with different angles) or to feed the sediment from the upstream cross-section and setting a short gravitational transport area at the upstream end of your domain.
Best
Matteo

User Forum of Software BASEMENT

#1 2020-12-13 11:47:02

No gravity transport across a breakline?

#2 2020-12-21 12:37:01

Re: No gravity transport across a breakline?

#3 2020-12-27 10:36:26

Re: No gravity transport across a breakline?

#4 2021-03-08 09:54:52

Re: No gravity transport across a breakline?

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