giles wiggs sheffield centre for international drylands research aeolian dune processes and dynamics...
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Giles Wiggs Sheffield Centre for International Drylands Research
Aeolian dune processesand dynamics
2004 Joint AssemblyMontreal, Canada
Dunes in equilibrium….
Best 1993
Measurements of mean windspeed and sediment transport
McKenna-Neumann et al 1997Wiggs 2001
windspeed
sand flux
Lancaster et al 1996
Measurements of shear velocity
U*
Wiggs 2001
mean shear velocity
shear stress
turbulence
-20
-15
-10
-5
0
5
10
15
20
0 20 40 60 80 100 120 140 160 180 200
Distance (m)
Hei
gh
t (m
) / A
ng
le (
deg
)
-0.014
-0.012
-0.01
-0.008
-0.006
-0.004
-0.002
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
-uw
b/u
rs
Measurements of Reynolds turbulent stress
0
1
2
3
4
5
6
7
0 240 480 720 960 1200 1440 1680 1920 2160 2400 2640
Time (seconds)
Ve
locit
y (
m/s
)
0
10
20
30
40
50
60
70
80
90
100
San
d t
ran
sp
ort
(p
art
icle
co
un
t)
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8
Velocity (m/s)
San
d t
ran
sp
ort
(p
arti
cle
co
un
t)
Reynolds stress
Streamline angle
Calibration of numerical models
He
igh
t(c
m)
-150 -100 -50 0 50 100 150 200 250 300 350 400 450 5000
20
40
60
Distance from dune crest (cm)-150 -100 -50 0 50 100 150 200 250 300 350 400 450 500
0
20
40
60 7-150 -100 -50 0 50 100 150 200 250 300 350 400 450 500
0
20
40
60 6
-150 -100 -50 0 50 100 150 200 250 300 350 400 450 5000
20
40
60 2
5
-150 -100 -50 0 50 100 150 200 250 300 350 400 450 5000
20
40
60
Streamwise Velocity (m/s): -4.8 -2.4 0 2.4 4.8 7.2 9.6 12 14.4
1
Parsons et al 2004
x/h from dune crest
z/h
-20 -15 -10 -5 0 5 10 15 200
2
4
6
8
1.81.410.60.20
-0.2-0.6-1-1.4-1.8
VerticalVelocity (m/s)
x/h from dune crest
z/h
-20 -15 -10 -5 0 5 10 15 200
2
4
6
8
54.543.532.521.510.50
Turbulent KineticEnergy (m²/s²)
Parsons et al 2004
Other modelling approaches
- complex systems
Werner 1995
Momiji et al 2000
Baas 2002
Other modelling approaches
- analytical solutions (Hersen, Sauermann, Herrmann, Andreotti)
Schwammle & Herrmann 2003
Hersen 2004
Hersen et al 2004
Out
put s
and
flux
Dune width
Dunes in dis-equilibrium….?
Parker Gay Jr 1999
Hersen 2004
Conclusions
1. dune research is in a healthy state!
2. measurements of airflow structure improving BUT requires improved understanding of turbulence / sediment transport relationships
3. calibration of computational models allowing greater understanding of form/flow interactions
4. results of analytical models suggest a requirement for more fieldwork focusing on:
dynamics of sediment transfers at the dune and inter-dune scale
longer time-series measurements of dune evolution