This is a modified version of Mrs. Beukeboom’s M.Sc. thesis research on:

Riverbank Characteristics and Stability along the Upper

Estuarine Reaches of the Moose River, Northern Ontario

Department of Land Resource ScienceUniversity of Guelph

September 26, 2000

(Martini, 1986)

Hudson Bay Lowland - extent of Tyrrell Sea

Goals

1. Determine the factors contributing to bank failure occurrence.

What?

Where?

Why?

When?

How?

silt unit

Tyrrell Sea clay

unit

Riverbank Stratigraphy

Bank Stratigraphy

Dunes

Cut and fill structures

SAND SILT

Laminations

Blocky structure

Rotational slump Translational slide

Examples of Mass MovementsWHAT?

failure surface

linear motion

Translational slide

curved motion

base failure

face failure

toe failure

Rotational slump

failure plane

WHAT?

Rotational slump Translational slide

Earth flow Block fall

WHAT? Examples of Mass Movements

Large rotational slump

Undercutting erosion by high water levels during the spring freshet.

littersilt

sand

ice-raftedcobbles

clay

Erosive River Water

External FactorsWHY?

north mainland

river flow

Ice is forced over the bank crest

Erosive River IceWHEN?

Bulldozing at the toe of the bank

Scars on tree trunksIce pushes the upper silt unit

HOW?

Seasonal Variation in Water TableHOW?

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 5 10 15 20 25 30

Distance from bank crest (m)

Dep

th (

m)

Summer1997

Fall 1997

Spring1998

Welladded inSpring1998

Cree Village - retaining wall -Two Bays cruiser

Freighter canoes at docks

Human activities have some impact on the riverbanks.

Human ImpactHOW?

slumpMoose River flow direction

Store Creek

Human Impact - Stability ProjectsHOW?

Bank Stratigraphy - Tyrrell Sea clayHOW?

10 most critical surfacesMINIMUM BISHOP FOS = 1.70

Ban

k H

eig

ht

(m)

Width (m)

water table

Slope Stability Model

Season Scenario FOS

Spring

Summer

Autumn

May - spring freshet

May - undercut

May - ice jam

Frozen ground

August

October

1.70

1.66

1.80

1.85

1.72

1.73

Slope Stability Model

FOS = Factory of Safety

HOW? Sensitivity of the Tyrrell Sea Clay

Sample ID In-situ Strength(kPa)

Remoulded Strength(kPa)

Sensitivity(S)

NML S15

NML S30

NML T2

SPI T8

NML S17

BI T1

BxI T9

13.1

13.1

14.3

28.7

16.9

11.5

30.3

0.7

0.8

0.9

3.6

2.1

1.6

5.3

18.7

16.4

15.9

8.0

8.0

7.2

5.7

not quick clay (remoulded strength < 0.5 kPa) range from low (S < 8.0) to medium-high sensitivity (S >8.0)

Scanning Electron MicroscopyTyrrell Sea Clay

Tyrrell Sea Clay

Marine diatoms– The presence of these diatoms along a fresh water river prove that this clay was deposited under marine conditions. Most quick clays are deposited under marine conditions.

Open structureThe open structure of this clay is similar to the Leda clay found in Ontario and Quebec. This “card-house” structure is very stable until the bonds that join the edges of the platelets are disturbed (due to flushing out during the spring melt, ice jams, earthquakes etc.)

1. Stratigraphic influence

sand unit on islands aid drainage undercutting erodes sand - block falls silt unit of mainland frequently experience

rotational slumping particularly in the spring

during break up TSC unit involved in deep rotational slumps

and earth flows

Conclusions

2. Subarctic climate

freezing cements sediment together in

winter

spring thaw creates wet conditions for bank

river ice is erosive - undercuts, steepens

loss of support as ice jam passes reduces

stability

Conclusions

3. Fluvial dynamics of estuary

regular inundation and exposure of TSC

cracks, degrades basal unit

erosive effect positively corresponds with

failure occurrence

Conclusions

4. Human Impact

can facilitate failure

deforestation, drainage, excavation

changing bank morphology by grading

Conclusions

5. Tyrrell Sea clay

medium to high sensitivity

open structure

high primary mineral content

high silt content

low liquid limit

high divalent cation adsorption

low sodium content

Conclusions