stream stability and sediment transport environmental hydrology lecture 21

Stream Stability andSediment Transport

Environmental Hydrology

Lecture 21

Geomorphic work expressed in channel characteristics

Winooski Falls, Photo by Jim Westphalen

• Channel dimensions (cross-section)

• Channel profile (longitudinal view)

• Channel pattern (plan view)

Channel Pattern

Meandering Stream Braided Stream

Plan (aerial) view of channel geometry

Ward & Trimble, Fig 6.10

Channel Pattern

Sinuosity (S) = Lc / Lv

where Lc = channel lengthLv = valley length

Helical flow induces meander formation

Cut banks

Meander Geometry

Ward & Trimble, Fig 6.11

How do these concepts scale?

Graphic from A. Ward

How do these concepts scale?

Ward & Trimble, Fig 6.15

“Hydraulic Geometry” of stream channels

Sediment Transport

Upper White River, VermontPhoto courtesy K. Donna

Stream Load

Estimating Suspended Load Export

Source: V. Axelsson, Uppsala Univ.,Sweden

Estimating Bedload Transport

Mean boundary shear stress (o)

o = g R S

Where: = density of water g = gravitational constantR = hydraulic radiusS = bed slope

= R S

= specific weight of water

Estimating Bedload Transport

Tractive Force (T)

T= d S

Where: = specific weight of water (kg/m3)d = flow depth (m)S = water surface slope (m/m)

Estimating Bedload Transport

Particle size at incipient motion (d*)

d*= c T

Where: T = tractive force (kg/m2)c = conversion factor [ f(T) ]d* = particle size (cm)

Estimating bedload transportLittle River

0.000.200.400.600.801.001.201.401.601.80

0 5 10 15 20 25 30

distance from left bank, (looking upstream (m)

elev

atio

n ab

ove

datu

m (

m)

Little River

0%

20%

40%

60%

80%

100%

1 10 100 1000

particle size (mm)

Per

cent

of

part

icle

s eq

ual t

o or

fin

er t

han

T= d S

d*= c T

Channel Migration

Ora

nge

Co.

Add

ison

Co.

010 10 20 Miles

Win

dsor

Co.

Add

ison

Co.

ROCHESTER

Rt. 125

HANCOCK

ROCHESTER

Rt.

100

RIPTON

GRANVILLE

BRAINTREE

Upper White River basin, VermontFigure courtesy K. Donna

1990

1975

Date ofphotography

Negativescale

Daily meanDischarge1

(cfs)

Oct. 16, 1939 1:31,680 178

July 19, 1956 1:15,840 805

July 1, 1975 1:15,840 415

Sept. 5, 1982 1:12,000 162

May 3, 1990 1:15,840 1220

1 Refers to mean daily discharge recorded at USGS Station #01144000 on the date that air photos were taken.

From: Kathleen Donna, Assessing Channel Change on the Upper White River, VermontUniversity of Vermont, M.A. Thesis, Dept of Geography, 2002

Reach 3 Reach 4