Physical modelling of the removal of Glines Canyon

Dam & Lake Mills

By

Chris Bromley, Gordon Grant, Colin Thorne

University of Nottingham / Oregon State University

Source: National Park Service

Elwha River Project

“…the full restoration of the Elwha River ecosystem and the native anadromous fisheries…’

Elwha River Ecosystem and Fisheries Restoration Act, 1992 (P.L. 102-495)

Lake Aldwell ~ 2.98 million m3

Lake Mills ~ 11.85 million m3

Image courtesy of National Park Service

Baselevel

2.29 m =

2.8 cm

Research hypotheses The greater the magnitude of the drop in

baselevel,

a. The greater the incision and lateral adjustment that will occur within the original delta area

b. The more rapidly sediment will erode from the delta surface

c. The greater the total volume of original delta sediment will be eroded

Dam

Horizontal scale = 1 : 310

Vertical scale = 1 : 81.7

Vertical distortion = 3.79

3.3 km = 10.65 m

1.067 km = 3.44 m

45.72 m = 0.56 m

•Similitude of Froude No. & Shields No.

•Assume uniform steady flow

Qm = Qp * HV1.5

Qm growth = 110 l/min → Qp = 420 m3/s (14,825 cfs)

Amount of original delta eroded by different channel positions under the single and triple

notch scenarios

0

10

20

30

40

50

60

70

80

0 2,000 4,000 6,000 8,000 10,000Run time (minutes)

Per

cen

tag

e er

od

ed

1x L

3x L

3x C

3x R

Amount of original delta eroded by increasing incrementsof removal starting

from the central channel position

0

10

20

30

40

50

60

70

80

0 1,000 2,000 3,000 4,000 5,000

Run time (minutes)

Perc

en

tag

e e

rod

ed

3x C

6x C

12x C

21x C

Erosion rates of the original delta for the single and triple notch scenarios in

different channel positions

0

50

100

150

200

250

300

350

400

450

500

0 2,000 4,000 6,000 8,000 10,000

Run time (minutes)

Ero

sio

n r

ate

(cm

3/m

in) 1x L

3x L

3x C

3x R

Erosion rates of the original delta for increasing increments of dam

removal in the central channel position

0

100

200

300

400

500

600

700

800

0 2,000 4,000 6,000

Run time (minutes)

Ero

sio

n r

ate

(c

m3/m

in)

3x C6x C12x C21x C

R113x - center

R73x - left

0 - 21 0 - 21

R113x - center

R73x - left

3 - 21 3 - 21

R113x - center

R73x - left

6 - 21 6 - 21

R113x - center

R73x - left

9 - 21 9 - 21

R113x - center

R73x - left

12 - 21 12 - 21

R113x - center

R73x - left

15 - 21 15 - 21

R113x - center

R73x - left

18 - 21 18 - 21

R113x - center

R73x - left

21 - 21 21 - 21

Total dimensionless incision along initial delta topset

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

100 200 250Distance downstream along delta topset (cm)

Dim

ensio

nles

s inc

ision

(T

otal

inci

sion

/ in

itial

sed

imen

t dep

th)

1x Left 3x Left 3x Centre 6x Centre 12x C 21x C

Thalweg lengths for the different removal scenarios

200

400

600

800

1,000

1,200

1,400

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

Run time (Minutes)

Th

alw

eg le

ng

th (

cm)

1x L 3x L 3x C 6x C

12x C 3x R 21x C

Run From

(mins.)

To

(mins.)

Prototype

Sediment-transporting

time

(Weeks)

% total sediment volume

passing

Downstream

Yrs-worth of

Sediment

Transport

1x Left

7345 7765 7.0 8.41 6.6

3x Left

3430 3730 5 14.57 11.5

3x

Centre

3470 4360 14.8 32.69 25.8

3x

Right

2790 2940 2.5 3.72 2.9

Run From

(mins.)

To

(mins.)

Prototype

Sediment-transporting

time

(Weeks)

% total sediment volume

passing

downstream

Yrs-worth of

Sediment

transport

1x Left

7345 7975 10.5 13.54 10.7

3x Left

3430 4035 10.1 26 20.5

3x

Centre

3470 4720 20.8 40.08 31.7

3x

Right

2790 3430 10.7 15.54 12.3

Conclusions 1

• Volumes and rates of original delta erosion increase with,

-central incisional channels

-increasing magnitudes of removal

Conclusions 2• Beyond 3x C, relationships less clear,

-peak rates and volumes very high

during very early stages of removal

-increasing channel lengths d/s of original delta may represent negative feedback between original delta erosion and delta progradation

Acknowledgements • St. Anthony Falls Laboratory & NCED• Dianna Smith, Jason Lundheim, Mike

Plante, Dick Christopher, Ben Erickson, Jeremy Schultz, Josh Brand, Matt Leuker

• Brett Otteson, Ben Freisen, Corey Markfort• Alessandro Cantelli, Gary Parker, Chris

Paola, Greg Stewart, Tim Randle, Gordon Grant, Colin Thorne

• Brian Winter, Bill Jackson, Reclamation