nira salant department of geography university of british columbia
DESCRIPTION
Effects of Streambed Periphyton on Hydraulics and Sediment Deposition in Streams. Nira Salant Department of Geography University of British Columbia. What is periphyton?. What does periphyton do?. Food and habitat. Physical effects?. I. Hydraulics. II. Sediment deposition. - PowerPoint PPT PresentationTRANSCRIPT
Nira SalantDepartment of Geography
University of British Columbia
Effects of Streambed Periphyton on Hydraulics and Sediment
Deposition in Streams
What is periphyton?
What does periphyton do?
Food and habitat
Physical effects?
I. Hydraulics
II. Sediment deposition
Sediment deposition
Trapping,Adhesion,Clogging
Turbulence
Algae: High profile Diatoms: ‘Sticky’
Sediment content of surface samples
0.01
0.10
1.00
10.00
100.00
1000.00
10000.00
0.1 1 10 100AFDM (g/m2)
AM
(g/
m2)
Graham 1990 vanDijk1993Yamada2002 Collier2002Kiffney2003 Runck2007Jowett1997 Hope RiverFlume-Diatoms Flume-Algae
Deposition from water column: Diatoms
Diatoms: ‘Sticky’
0.00
0.50
1.00
1.50
2.00
2.50
0 1000 2000 3000 4000 5000
Time (Seconds)
C/C
0
0 g/m25 g/m210 g/m2
Deposition from water column: Diatoms
Highest deposition velocity when near-bed and upper flow
shear stresses are lowand biomass is moderate
(moderate adhesion, low clogging)
Biomass increases:
Near-bed shear stress increases (structural roughening)
Deposition velocity decreases(high upward stresses and infiltration decreases = ‘clogging’)
0
1
2
3
4
5
6
0.0 2.0 4.0 6.0 8.0 10.0 12.0AFDM(g/m2)
Dep
soiti
onal
vel
ocity
wd
(cm
/h)
0
1
2
3
4
5
6
7
TK
E s
hear
str
ess
(Pa)
Depositional velocity
Max shear stress
Near-bed shear stress
Deposition from water column: DiatomsEvidence for clogging?
-6
-5
-4
-3
-2
-1
0
0.01 0.10 1.00% <125um
Dep
th (
cm)
0 g/m2
0 g/m2
3 g/m2
5 g/m2
8 g/m2
10 g/m2
Deposition from water column: Algae
Algae: High profile
Deposition from water column: Algae
0.00
0.50
1.00
1.50
2.00
2.50
0 1000 2000 3000 4000 5000
Time(S)
C/C
0
0 g/m2
15 g/m2
24 g/m2
Unclear relation between biomass, shear stress, and
depositional velocity
0
1
2
3
4
5
6
0 5 10 15 20 25 30AFDM(g/m2)
Dep
osit
iona
l vel
ocit
y w
d (c
m/h
)
0
1
2
3
4
5
6
7
TK
E s
hear
str
ess
(Pa) Deposition
decrease with biomass? Clogging?
But…
Deposition from water column: Algae
Shear stress increases with
growth stage
Surface deposition decreases with
growth stage
Later growth stage Increase in shear stress
0
5
10
15
20
25
0 5 10 15 20 25Growth stage (Weeks)
AM
(g/m
2)
0
1
2
3
4
5
6
7
TK
E s
hear
str
ess
(Pa)
0
1
2
3
4
5
6
0 5 10 15 20 25Growth stage (Weeks)
Dep
osit
iona
l vel
ocit
y w
d (c
m/h
)
0
1
2
3
4
5
6
7
Less surface deposition
BUTHigher advection and infiltration
(subsurface deposition)
Total deposition = balance of surface and subsurface deposition
High biomass reduces infiltration
Depositional velocity
Max shear stress
Near-bed shear stress
Surface samples AM
Deposition from water column: Algae
Turbulence Less surface deposition, deeper infiltration (A8 A20)
Biomass Reduced infiltration despite high advection (A16)
-6
-5
-4
-3
-2
-1
0
0.01 0.10 1.00% <125um
Dep
th (
cm)
00A8A16A20
Implications
Streambed patchiness and complexity
Flow conditions, sediment accumulation, interstitial infiltration Habitat
condition
Organism behavior
…a function of periphyton structure
and distribution
Decrease in concentration over timeExponential model
kteCtC 0)(C0 = peak concentration at time t = 0
k = decay (or deposition) rate (T-1)
h
wk
s
ws = settling velocity (D/T) = depositional velocity wd when fit to
exponential model
h = flow depth (D)
I. Hydraulics
‘Closed’ ‘Open’
Filamentous periphyton ‘patches’
'Closed'
BEp
BEeff
ADV Probe
'Open'
BEpBE
eff
ADV Probe
BEp > BE
eff = Open BE
p = BE
eff = Closed
Height measured by ADV above BE
eff
(plus 5 cm)
WSE
Flow
a)
~10 cm
~2.5 cm
Flume wall
~2.5 cm
Velocity distribution
u0
Ux
umax
0.6
0.5
0.4
0.3
0.2
0.1
PeriphytonNone
0.0 10.0 20.0 30.0 40.0 50.0
u (cm/s)
0.0
0.5
0.4
0.3
0.2
0.1
0.0 10.0 20.0 30.0 40.0
z/H
50.0
0.6
u (cm/s)
Shear stress distributionTwo-layered flow
0.0 0.01-0.01 0.02 0.03
0.1
0.2
0.3
0.4
0.5
0.6
z/H
0.1
0.2
0.3
0.4
0.5
0.6
z/H
τRe/ρUx2
Closed
Open
Logarithmic layer
Peak shear = top of Roughness layerPeriphyton
No periphyton
Shift in height of roughness layer topSame thickness
0
0.05
0.1
0.15
0.2
0.25
0.3
0 0.005 0.01 0.015 0.02 0.025Re/ρUx
2 (
z/H
Near-bed turbulence reduction
PeriphytonNone
2) Hydrodynamic smoothing(Closed mats)
1) Shift in location of peak shear (Open mats)
Higher upper flow stress
Reduced turbulent transfer
Diatoms 24 WeeksDiatoms 4 Weeks
None