U.S. Department of the Interior U.S. Geological Survey Modeling sand transport and sandbar evolution along the Colorado River below Glen Canyon Dam

U.S. Department of the InteriorU.S. Geological Survey

Modeling sand transport and sandbar evolution along the Colorado River below Glen Canyon Dam

OUTLINE:

• Available and unavailable data• Kees’ model of the entire reach• Our model of Eminence• STEP 1: calibrating models hydrodynamically• STEP 2: running morphodynamically

• Experiments adjusting sediment transport

• STEP 3: Repeat for several types of models

Available data

1. Multibeam • Topo• Water-surface

2. ADCP velocity3. Total station

• HWM4. Sediment

Concentration5. Bed D506. Bar grain size

Stage-Q Data

Stage-Q Data

Extent of HWM data

Sediment Concentration

Unavailable data:

1. Topo in rapids2. Stage-Q at likely

model boundaries

3. Composition of bed sediment

4. Change in suspended concentration through reach

Stage-Q Data

Stage-Q Data

Extent of HWM data

Sediment Concentration

Available water-surface data:

Multibeam sonar based water-surface elevations

High-water marks surveyed post HFE

Longitudinal water-surface profiles:

840.80

840.85

840.90

840.95

841.00

841.05

841.10

841.15

841.20

0 100 200 300 400 500 600 700

HIGHWATER MARK- ALL DataKriged multibeam data extracted at surveyed ws pts

EminenceHigh-water marks are very noisy

Only present info along the edge of river left

Multibeam data provide spatial structure

Kees’ Model

• 3D using 12 layers• Compressed hydrograph• Bed-evolution on• Roughness: Zo=0.01 m• 2D Turbulence: HLES on• 3D Turbulence: K-Epsilon• Incoming sediment concentration is 50% of measured• Thickness of sediment on bed is 1m everywhere

Kees’ 3D Model: Eminence Reach

• Modeled ws is much lower than measured

• Not able to match measured ws without:• Lowering the

downstream boundary AND

• Increasing the roughness significantly

840.60

840.70

840.80

840.90

841.00

841.10

841.20

840.85 840.90 840.95 841.00 841.05 841.10 841.15 841.20

Multibeam water surface (m)

Mo

del

ed w

ater

su

rfac

e (m

)

1:1 Line Kees Model

Kees’ 3D Model: Eminence Reach

840.600

840.700

840.800

840.900

841.000

841.100

841.200

0 100 200 300 400 500 600

Distance downstream (m)

Wa

ter-

su

rfa

ce

ele

va

tio

n (

m)

Interpolated multibeam points along thalweg

T40 zo=0.05 and 0.001

Kees Model

• Thalweg shows a similar problem

• BUT, water-surface is too high in lower eddy…..

• Points to problems with topography in rapid between, boundary conditions and roughness

Eminence Models

• 2D model and 3D (12 layers)• Compressed hydrograph• Roughness: variable• 2D Turbulence: HLES on • 3D Turbulence: K-Epsilon• Incoming sediment concentration is 100% of measured• Thickness of sediment on bed is based on min surface• Composition of bed sediment is based on D50 eyeball and σ

from composited bar measurements

Eminence Model

STEP 1: Calibrate the models hydraulically based on measured topo near end of peak (no bed evolution)

STEP 2: Run model with bed evolution on with the HFE hydrograph and measured sediment

• Run model without bed evolution for topography at end of the peak using a range of possible z0 values• Using Ks=30* z0 for 2D model runs (White-Colebrook)

• Compare to multibeam measured water surface points for same time period.

• Compare ADCP velocity vectors and magnitude for similar time period.

• Select z0 that provides the best hydraulic calibration

STEP 1: Calibration Strategy

3D HLES: water surface

• WS is reasonably well calibrated- although not very sensitive to zo

• RMS=0.028 m840.85

840.90

840.95

841.00

841.05

841.10

841.15

841.20

840.85 840.90 840.95 841.00 841.05 841.10 841.15 841.20

Multibeam water surface (m)

Mo

del

ed w

ater

su

rfac

e (m

)

1:1 Line T40 ave ws, zo=0.05 and 0.001

3D HLES: Water surface along thalweg

840.900

840.950

841.000

841.050

841.100

841.150

0 100 200 300 400 500 600

Distance from upstream

ws

ele

va

tio

n

Interpolated multibeampoints along thalwegT38 zo=0.01

T33 Zo=0.001

T34 zo=0.0001

T40 zo=0.05 and 0.001

T41 zo=0.1 and 0.001

Variable zo improves ws to a point, but increasing the upstream zo further doesn’t seem to change the ws much

3D HLES: Difference between modeled and measured water surface

Z0=0.01

Z0=0.001 Z0=0.0001

Z0=0.05 and 0.001

The variable roughness case seems to improve results in the eddy eye

3D HLES: vectorsEddy-eye is shifted upstream slightly

3D HLES: velocity magnitude

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Measured velocity (m/s)

Mo

del

ed v

elo

city

(m

/s)

1:1 Line

T40 z0=0.001 and 0.05

2D HLES: water surface

• Modeled using similar range in zo (ks=30z0)

• 3 sets of ks values give similar water-surface elevations 840.85

840.90

840.95

841.00

841.05

841.10

841.15

840.85 840.90 840.95 841.00 841.05 841.10 841.15 841.20

Measured wate surface (m)

Mo

del

ed w

ate

surf

ace

(m)

2DH_T8 ks=0.03 and 1.5

2DH_T10 ks=0.003 and 1.5

2DH_T11 ks=0.0003 and 1.5

1:01

2D HLES: Difference between modeled and measured water surface

T8 ks=0.03 and 1.5

(zo=0.001 and 0.05)

RMS=0.043

Extremely similar looking, very difficult to tell any difference based on ws. RMS for lower ks seems to be lower because the ws in the eddy-eye is lower. I don’t think RMS is reliable in this case…….

T11 ks=0.0003 and 1.5 (zo=0.00001 and 0.05)

RMS=0.039

T10 ks=0.003 and 1.5 (zo=0.0001 and 0.05)

RMS=0.040

2D with HLES: velocity vectors

• Vectors are also essentially the same……

T8 ks=0.03 and 1.5T10 ks=0.003 and 1.5T11 ks=0.0003 and 1.5

Minor changes in vectors…..

2D HLES: velocity

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 0.5 1 1.5 2 2.5 3

Measured velocity (m/s)

Mo

de

led

ve

loc

ity

(m

/s)

2DHLES T8 ks=0.03 and 1.5

1:01

2DHLES T10 ks=0.003 and 1.5

2DHLES T11 ks=0.0003 and 1.5

Still only minor differences between all 3 roughness cases…..

STEP 1: Summary

• 3D HLES: Looks reasonably well calibrated based on:• WS elevations look quite good• Velocity magnitude looks good• Velocity vectors are on the right track

• 2D HLES: Not clear which z0 combination is best—probably fine to use similar values to the 3D case.

STEP 2: Morphodynamics

• Once models are hydrodynamically calibrated, run with bed evolution using:• Pre-HFL topography• Measured suspended sediment concentration• Measured thickness of bed material• Estimated composition of bed material

Based on average D50 from Eyeball assuming log-normal distributions with =1.6 estimated from composited samples from the Eminence bar

STEP 2: 3D HLES Morphodynamics

Measured change: Modeled change:

•Bar extends too far upstream and is too high•Significant deposition in eddy eye, rather than the measured scour•Return channel is not strongly defined•Large bar develops on river right just above the downstream rapid. This occurs where velocity is lower than measured (no eddy develops in the model)•Too much scour through the thalweg


Measured change: Modeled change (Liz):

See similar trends in model from Liz, although her model develops a stronger return channel, deposits more sediment in the eye and less on the rest of the bar. Liz’s model uses similar thickness and bed composition, but 50% the suspended sand concentration and different sediment transport relation.


Measured change: Modeled change (ks=0.001 and 1.5): Modeled change (ks=0.0001 and 1.5): Modeled change (ks=0.00001 and 1.5):

STEP 2: Cross-sections Pre-peak Topo

Post-peak Topo

3DHLES (z0=0.001 and 0.05)

2DHLES (ks=0.03 and 1.5)


2DHLES (ks=0.0003 and 1.5)

2D models build bars further into the main channel

3D model builds a reasonable bar, but scours bed


Post-peak Topo

3DHLES (z0=0.001 and 0.05)



2DHLES (ks=0.0003 and 1.5)

Both models build a bar in the eddy eye rather than scouring

2D models also appear to deposit sediment in the thalweg


Post-peak Topo

3DHLES (z0=0.001 and 0.05)



2DHLES (ks=0.0003 and 1.5)

Both models build a higher elevation bar further in the main channel than measured

2D models also appear to deposit sediment in the thalweg


Post-peak Topo

3DHLES (z0=0.001 and 0.05)



2DHLES (ks=0.0003 and 1.5)

Both models build the river right bar too far into the main channel

2D models deposits material in the thalweg, 3D model erodes.


Post-peak Topo

3DHLES (z0=0.001 and 0.05)



2DHLES (ks=0.0003 and 1.5)

3D and 2D models over build bars on channel margins and scour the bed

2D models build a larger river left bar

STEP 2: Summary

• 2D and 3D models over build the bars in terms of elevation and spatial extent into the main channel.

• 3D HLES appears somewhat better than 2D HLES• 2D HLES build bars further into the channel• 2D HLES deposits material in the thalweg, rather than

scouring

• Model Time comparisons:• 3D HLES model runs take 1+ hrs• 2D HLES model runs take ~2-3 minutes

What can improve bed evolution prediction?

• 3D HLES bed evolution needs improvement:• Use van Rijn 1984? • Adjust van Rijn roughness height? • Adjust bed composition? • Avalanching processes? • Change diffusivity?• Other ideas?

Morphodynamics for several transport cases

Measured change: Modeled change: T40 (zo=0.001 and 0.05)Modeled change: T40 Rh=2Modeled change: T40 coarser bedModeled change: T40 vr84 LizModeled change: T40 vr84 KeesModeled change: T40 Diffusivity=0.0001

Morphodynamics for several cases

All fairly similar, except the van Rijn 1984 model with Kees’ low settling velocities. This model builds lower bars, but fills in the thalweg……

Pre-peak Topo

Post-peak Topo

3DHLES (z0=0.001 and 0.05)

3DHLES (z0=0.001 and 0.05)- coarser bed composition

3DHLES (z0=0.001 and 0.05)- Van Rijn 1984—Kees ws

3DHLES (z0=0.001 and 0.05)- Van Rijn 1984—Liz

3DHLES (z0=0.001 and 0.05)- Rh=2, not 1

3DHLES (z0=0.001 and 0.05)- HED=0.0001, not 0.5

Morphodynamics for several cases

Pre-peak Topo

Post-peak Topo

3DHLES (z0=0.001 and 0.05)

3DHLES (z0=0.001 and 0.05)- coarser bed composition

3DHLES (z0=0.001 and 0.05)- Van Rijn 1984—Kees ws

3DHLES (z0=0.001 and 0.05)- Van Rijn 1984—Liz

3DHLES (z0=0.001 and 0.05)- Rh=2, not 1

3DHLES (z0=0.001 and 0.05)- HED=0.0001, not 0.5

Summary effects for different transport cases:

• van Rijn 1984 vs 2000• changing transport relation can produce large changes in the bed

depending on how it is parameterized…..needs more work• Adjust roughness height

• See marginal changes• Adjust bed composition

• Bed evolution appears insensitive to bed composition (actually a plus since we don’t have detailed information about bed composition)

• Adjusting Horizontal eddy diffusivity• Did not see substantial change in morphology…needs more work

• Avalanching processes• Could prevent the bars from developing too far into the main channel.

Need help from Kees to employ• Other ideas?

Morphodynamics for two sediment conditions

Measured change:

Modeled change: 3DHLES- no suspended sediment at input, measured sediment thickness on bed

Modeled change: 3DHLES- measured suspended sediment at input, 10 cm sediment bed thickness

Looks like the majority of the sediment deposited in the bar comes from the suspended sediment, rather than from material available on the bed in the reach

Morphodynamics for two sediment conditionsPre-peak Topo

Post-peak Topo

3DHLES (z0=0.001 and 0.05)


3DHLES (z0=0.001 and 0.05)- no input suspended sed

3DHLES (z0=0.001 and 0.05)- 10 cm thick bed

No input suspended sediment reduces deposition of sediment in eddy eye and scours bed

2 cm of sediment on the bed and the full suspended load changes the results very little.


No input suspended sediment may erode the bar in some places…….

2 cm of sediment on the bed and the full suspended load reduces height of bar somewhat

Pre-peak Topo

Post-peak Topo

3DHLES (z0=0.001 and 0.05)





No input suspended sediment at the input erodes the channel significantly

2 cm of sediment on the bed and the full suspended load looks quite similar to the 2D results, but the bed is prevented from eroding……

Pre-peak Topo

Post-peak Topo

3DHLES (z0=0.001 and 0.05)




STEP 3: Apply 1 and 2 to other models

• Calibrate hydrodynamic calibration for:1. 3D model with HLES—Complete2. 3D model without HLES—in progress

3. 2D model with HLES—Complete4. 2D model without HLES—in progress5. 2D model with Secondary—in progress

Comparisons:

• Velocity vectors • (compared to measured at end of peak 3/8/08_15:00)

• Velocity magnitude• (compared to measured at end of peak 3/8/08_15:00)

• Topography • (compared to measured after peak 3/10/08)

Cumulative erosion/deposition Binned erosion/deposition by elevation Select cross-sections

• Model efficiency• Run time

Ideal info for modeling other sites:

1. Stage-Q relationship at downstream end of reach2. Water-surface profiles at flows of interest3. Topography- need detailed topo entire area of interest. 4. Select reaches with good entrance and exit conditions5. Hydrograph6. Suspended sediment concentration for hydrograph7. Estimate of bed thickness (minimum surface maps)8. Estimate of bed grain size distribution (Average D50 from

eyeball/ from bar grain size analysis)

Documents

U.S. Department of the Interior U.S. Geological Survey Modeling sand transport and sandbar evolution along the Colorado River below Glen Canyon Dam