roughness of floodplain plants using plants to improve ... · v = water velocity. manning n has no...
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Roughness of Floodplain PlantsUsing Plants to Improve Flood Management
What is Roughness?
TextureFrictionBlockage
Resistance toflow
Plants have roughness
So do theThings we Put in channels
We measure roughness using Mannings n –a number used in a whole bunch of hydraulic
analyses
(1/ )R2/3S 1/2n=(1/v)R2/3Sf1/2
R= hydraulic radiusSf= friction slopeV = water velocity
Manning n has no units.
Manning's n Coefficients for Open Channel Flow
Material Manning n Material Manning nNatural Streams Excavated Earth ChannelsClean and Straight 0.030 Clean 0.022
The fluid mechanics calculations website
Major Rivers 0.035 Gravelly 0.025Sluggish with Deep Pools 0.040 Weedy 0.030
Stony, Cobbles 0.035Metals FloodplainsBrass 0.011 Pasture, Farmland 0.035Cast Iron 0.013 Light Brush 0.050Smooth Steel 0.012 Heavy Brush 0.075Corrugated Metal 0.022 Trees 0.15Non-MetalsGlass 0.010 Finished Concrete 0.012Clay Tile 0.014 Unfinished Concrete 0.014Brickwork 0.015 Gravel 0.029Asphalt 0.016 Earth 0.025Masonry 0.025 Planed Wood 0.012
Unplaned Wood 0.013
Type of Channel and Description Minimum Normal Maximum
Natural streams - minor streams (top width at floodstage < 100 ft)
1. Main Channels
a. clean, straight, full stage, no rifts or deep pools 0.025 0.030 0.033
b. same as above, but more stones and weeds 0.030 0.035 0.040
c. clean, winding, some pools and shoals 0.033 0.040 0.045
d. same as above, but some weeds and stones 0.035 0.045 0.050
e. same as above, lower stages, more ineffective slopes and sections
0.040 0.048 0.055
f. same as "d" with more stones 0.045 0.050 0.060
g. sluggish reaches, weedy, deep pools 0.050 0.070 0.080
h. very weedy reaches, deep pools, or floodways with heavy stand of timber and underbrush
0.075 0.100 0.150
2. Mountain streams, no vegetation in channel, banks usually steep, trees and brush along banks submerged at high stages
a. bottom: gravels, cobbles, and few boulders 0.030 0.040 0.050
b bottom: cobbles with large boulders 0.040 0.050 0.070
Mannings n – average of all textures, but used as a model fitting parameter.
Inaccuracy in other model parameters:Shape, channel form, grade, slope, sinuosity velocity water densitysinuosity, velocity, water density, …
get assigned to roughness
O’Connor Lakes, Star Bend
Lots of variation:
Pre‐project velocities
Lots of variation:∆ velocity = ∆ roughness
The need for improving safety and ecosystem management prompted us
to look at the role some common plants play in creating roughness.
Plants selected because they are adapted to flooding, are common in our floodways, and
provide good habitat value
Mulefat Wild Rose
Sandbar willow
California Blackberry
H
Depth Control Weir
x= 47'
x =60'
V
2’
Flume tail tank
x =0'
x=33'
Pumps
6’
AC
x=19'
B
Point gage locations and
velocity measurement sections
Pumps
Velocity measurement locations in a cross-section
Flume width 5 ft
6 ft
Flume width 5 ft
6 ft
4 ft bin Width
8 ft
2 ft
4 ft bin Width
8 ft
2 ft
Water depth higher than 2 ft
Water depth lower than 2 ft
Velocity and Water Surface Profiles
V Scale X 19.5 33.5 472 Z 2.65 2.54 2.56
2.17 4.39 4.69 4.861.67 4.18 4.56 4.641.17 4.11 4.42 4.440.67 4.00 4.20 4.030.25 3.62 3.47 3.36
V (ft/s)
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
0 10 20 30 40 50 60 70
X [ft]
Elev
atio
n [f
t]
Water Surface Flume Top Elevation Bottom Elevation
Velocity at P#2 Velocity at P#3 Velocity at P#4
V= 2 ft/s
Flow Regime S15
STREAMBED BARE SOIL SAMPLE PREPARATION
Sandbar Willow1st replicate
Sandbar Willow3rd replicate
3
4
5V|x=16ftV|x=34ftV|x=47ft
3
4
5V|x=16ftV|x=34ftV|x=47ft
V=1.5 ft/s H=1.5 ft V=3.0 ft/s H=1.5 ft
Velocity Profile Sandbar Willow
0
1
2
0 2 4 6Velocity (ft/s)
Z(ft)
0
1
2
0 2 4 6Velocity (ft/s)
Z(ft)
3
4
5V|x=16ftV|x=34ftV|x=47ft
3
4
5V|x=16ftV|x=34ftV|x=47ft
V=1.5 ft/s H=5 ft V=3.0 ft/s H=5 ftVelocity Profile Sandbar Willow
0
1
2
0 2 4 6Velocity (ft/s)
Z(ft)
0
1
2
0 2 4 6Velocity (ft/s)
Z(ft)
3
4
5V|x=16ftV|x=34ftV|x=47ft
3
4
5V|x=16ftV|x=34ftV|x=47ft
V=4.5 ft/s H=3 ft V=6.0 ft/s H=3 ft
Velocity Profile Sandbar Willow
0
1
2
0 2 4 6Velocity (ft/s)
Z(ft)
0
1
2
0 2 4 6Velocity (ft/s)
Z(ft)
0.050.060.070.080.09
ng's
n
Bare Soil
Willow1
Willow2
Willow3
Roughness Coefficient vs Reynolds Number
Sandbar Willow
0.000.010.020.030.04
0 200,000 400,000 600,000Re
Man
ni Linear (Bare Soil)
Linear (Willow1)
Linear (Willow2)
Linear (Willow3)
3
4
5
h (ft
)
V|x=16ftV|x=34ftV|x=47ft
Velocity Profile Mulefat
3
4
5
h (ft
)
V|x=16ftV|x=34ftV|x=47ft
V=4.5 ft/s H=3ft V=6 ft/s H=3 ft
0
1
2
0 2 4 6
Velocity (ft/s)
Dep
th
0
1
2
0 5 10
Velocity (ft/s)
Dep
th
0.06
0.08
0.10
0.12
ning
's n
Bare SoilWillow (March)Willow (April)Willow (May)Mule Fat (Nov-Dec)Mule Fat (Oct-Nov) Linear (Bare Soil)Linear (Willow (March))Linear (Willow (April))Linear (Willow (May))Linear (Mule Fat (Nov-Dec))Linear (Mule Fat (Oct-Nov) )
Comparative Roughness: Mulefat & Sandbar Willow
0.00
0.02
0.04
0 100,000 200,000 300,000 400,000 500,000 600,000 700,000
Re
Man
3
4
5
6
ht (f
t)
V|x=16ftV|x=34ftV|x=47ft
V=6 ft/s Ht=3.4ft
4
5
6
t (ft
)
V|x=16ftV|x=34ftV|x=47ft
V=3 ft/s Ht=5ft
Velocity Profile California Blackberry
0
1
2
3
0.0 2.0 4.0 6.0
Velocity (ft/s)
Hei
gh
0
1
2
3
0.0 2.0 4.0 6.0
Velocity (ft/s)
Hei
ght
0 08
0.10
0.12
0.14
0.16
ng's
n
Blackberry(Mar)Blackberry(Apr)Blackberry(May)Willow (March)Willow (April)Willow (May)Mule Fat (Oct-Nov) Mule Fat (Nov-Dec)Mule Fat (January)Mule Fat (February)Bare SoilLinear (Blackberry(Mar))Linear (Blackberry(Apr))Linear (Blackberry(May))
Roughness coefficients vs Reynolds NumberCalifornia Blackberry
0.00
0.02
0.04
0.06
0.08
0 100,000 200,000 300,000 400,000 500,000 600,000 700,000Re
Man
nin Linear (Blackberry(May))
Velocity profile Wildrose
3
4
5
6
dept
h (f
t)
V|x=16ftV|x=34ftV|x=47ft
3
4
5
6
r de
pth
(ft)
V|x=16ftV|x=34ftV|x=47ft
V=4.5ft/s H=3ft V=6ft/s H=3.4ft
0
1
2
0 2 4 6 8
Velocity (ft/s)
Wat
er
0
1
2
0 2 4 6 8
Velocity (ft/s)
Wat
er
0.10
0.12
0.14
0.16s
nBlackberry(Mar)Blackberry(Apr)Blackberry(May)Willow (March)Willow (April)Willow (May)Mule Fat (Oct-Nov) Mule Fat (Nov-Dec)Mule Fat (January)Mule Fat (February)Bare SoilWildrose#1(Jun)Wildrose#2(Jun)Wildrose#3(Jul)Linear (Blackberry(Mar))Linear (Blackberry(Apr))Linear (Blackberry(May))Linear (Wildrose#1(Jun))Li (Wild #2(J ))
Mannings Coefficient vs Reynolds NumberRose and Blackberry
0.00
0.02
0.04
0.06
0.08
0 100,000 200,000 300,000 400,000 500,000 600,000 700,000Re
Man
ning
's Linear (Wildrose#2(Jun))Linear (Wildrose#3(Jul))
Erosion Summary
2
3Erosion (in)
mulefat
Bare soil
3 51
1
Velocity (ft/sec)
willow
rose
Swim Response to Sandbar Willow
○ = TBF Swim Chamber● = MO2■ = TBF Flume
(1 5 ft/s)
(3.0 ft/s)
(0.5 ft/s)
(1.5 ft/s)
As built – velocity A Mosaic of Plants