stream stability and sediment transport environmental hydrology lecture 21
TRANSCRIPT
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