aca-bottacin · Title aca-bottacin.pdf Author: Administrator Created Date: 10/29/2014 10:05:11 AM
NIMA SABOKROUHIYEH, ANDREA MARION 0.6 b*= 0...EFFECT OF BASIN SHAPE AND VEGETATION PATTERNS ON...
1
EFFECT OF BASIN SHAPE AND VEGETATION PATTERNS ON WETLAND PERFORMANCE ANDREA BOTTACIN - BUSOLIN School of Mechanical, Aerospace and Civil Engineering, University of Manchester, UK NIMA SABOKROUHIYEH , ANDREA MARION Department of Industrial Engineering, University of Padua, Italy EFFECT OF VEGETATION PATTERNS CHANNELIZED VEGETATION DISTRIBUTIONS For lower ratios n*=n 1 /n 2 the hydraulic RTD has an evident bimodality, indicating that mass transport is characterized by two distinct time scales [1,2] The development of a pronounced bimodality as n* decreases supports the decomposition of the overall RTD into two components associated with the transport in the main flow channel (MFC) and in the lateral vegetated zones (LVZs) CONCLUSIONS METHODS INTRODUCTION Wetlands can be highly effective in the removal of contaminants from industrial and municipal wastewaters. Understanding the processes that control the treatment performance of wetlands can help optimise their design and maintenance operations. OBJECTIVES OF THE STUDY To obtain a quantitative understanding of the relationship between wetland performance and: Basin shape Spatial vegetation distribution To develop optimal design criteria for waste- water treatment wetlands ● For channelized vegetation patterns, the partition of the flow between main channel and vegetated zones leads to a bimodal behaviour of the hydraulic RTD. ● For spatially correlated heterogeneous fields, the maximum concentration reduction is shown to not coincide with the condition of maximum mass removal. Mass removal is a combined effect of concentration reduction and flow rate, and the results clearly show that there is an optimum value of stem mean density producing maximum mass removal. ● The average stem density remains the dominant factor determining total mass removal. However, a significant effect is associated also to the vegetation distribu- tion represented by the stem density variance and correlation length. 0 0.5 1.0 1.5 2.0 2.5 3.0 0 0.5 1.0 1.5 2.0 2.5 3.0 R t*=t/T [–] n*=1.00 n*=0.26 n*=0.07 n*=0.67 φ(t*)T [–] R 0 0.2 0.4 0.6 0.8 1.0 0 0.2 0.4 0.6 0.8 MFC discharge, LVZs discharge, LVZs discharge, MFC discharge, n* Q i / Q b*= 0.1 b*= 0.2 b*= 0.1 b*= 0.2 1D model 1D model 2D model 2D model A simplified 1-D transport model The solute breakthrough curves are found to be well described by a simplified 1-D model assuming two transport domains: where: and where the weight coefficient w 1 is a func- tion of the normalized stem density n*: 1000 1400 1800 2200 2600 50 55 60 65 70 75 80 85 90 95 100 n (stems m ) –2 – η C (%) 1200 1600 2000 2400 2800 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 n (stems m ) –2 – discharge, (m s ) Q 3 –1 1000 1400 1800 38 40 42 44 46 48 50 n (stems m ) –2 – mass removal (g s ) –1 traditional design 2200 2600 3000 L L L L = 3 m = 5 m = 10 m = 15 m c c c c / n = 0.83 / = 8.30 / = 33.3 – n – n – inlet outlet L B b ሻ (, ሻ = 1 1 (, ሻ + (1 − 1 ሻ 2 (, (, ሻ = 0 ( − ሻ 4 τ 3 exp − − 2 4 − 1 = 1 =1− 1+ 1 ∗ ∗ 1− ∗ −1 Concentration reduction efficiency Wetland discharge Mass removal rate =1− Stem density (stems m –2 ) x (m) y (m) Residence time distribution (RTD) decreasing density ratio n* = n 1 /n 2 Streamwise velocity HETEROGENEOUS VEGETATION DISTRIBUTIONS Concentration reduction efficiency increases monotonically with mean stem density For a given hydraulic head loss between inlet and outlet, the discharge decreases monotonically with vegetation density The combined effect of the increasing concentration reduction and the decreasing discharge produces a non-monotonic behaviour of the mass removal, which has a peak for a certain value of the stem density Mass removal is lower for higher values of stem density variance, and the effect of variance is more pronounced for higher correlation lengths low high Simulation parameters h o = 0.5 m Δh = 0.05 m L = 400 m B = 300 m b = 10 m EFFECT OF BASIN SHAPE • increases with aspect ratio (Length/Width) • is higher for wetlands with diverging inlet and converging outlet Figure 3. Simulated velocity fields for different basin shapes for a 1 ha wetland with centrally aligned inlet-outlet of 10 m width and uniform vegetation density. Figure 4. Volumetric efficiency and dispersion efficiency versus vegetation density for different wetland shapes and aspect ratios. Figure 7. Discharge in the MFC and the LVZs predicted by the 2D and 1D model. Figure 6. Simulated residence time distributions in a channelized wetland. Figure 5. Magnitude of the streamwise velocity in a wetland with uniform (top) and channelized (bottom) vegetation distribution. Figure 1. Illustration of a channelized wetland. Figure 2. Example of a random vegetation density field. Figure 8. Concentration reduction efficiency, discharge and mass removal rate predicted by the 2D depth-averaged model as a function of mean stem density, for different variances and correlation lengths of the vegetation distribution. References [1] Musner, T., Bottacin Busolin, A., Zaramella, M., & Marion, A. (2014). A contaminant transport model for wetlands accounting for distinct residence time bimodality. Journal of Hydrology, 515, 237-246. [2] Savickis, J., Bottacin Busolin, A., Zaramella, M., Sabokrouhiyeh, N., & Marion, A. (2016). Effect of a meandering channel on wetland performance. Journal of Hydrology, 535, 204-2010. Hydraulic efficiency The transport of a contaminant in a conceptual wetland with flat topography is simulated by a 2-D depth-averaged hydrodynamic and solute transport model. Two types of vegetation distributions are considered: Channelized distribution (main channel with vegetation density n 1 and lateral zones with vegetation density n 2 ) Heterogeneous distribution (spatially correlated random field with prescribed mean, ത , variance, σ, and correlation length, L c ) Velocity (m/s) Velocity (m/s) Velocity (m/s) Velocity (m/s) Velocity (m/s) Velocity (m/s)
Transcript of NIMA SABOKROUHIYEH, ANDREA MARION 0.6 b*= 0...EFFECT OF BASIN SHAPE AND VEGETATION PATTERNS ON...
EFFECT OF BASIN SHAPE AND VEGETATION PATTERNS ON WETLAND PERFORMANCE
ANDREA BOTTACIN-BUSOLINSchool of Mechanical, Aerospace and Civil Engineering, University of Manchester, UK
NIMA SABOKROUHIYEH, ANDREA MARIONDepartment of Industrial Engineering, University of Padua, Italy
EFFECT OF VEGETATION PATTERNS
CHANNELIZED VEGETATION DISTRIBUTIONS
For lower ratios n*=n1/n2 the hydraulic RTD has an evident bimodality, indicatingthat mass transport is characterized by two distinct time scales [1,2]
The development of a pronounced bimodality as n* decreases supports thedecomposition of the overall RTD into two components associated with thetransport in the main flow channel (MFC) and in the lateral vegetated zones(LVZs)
CONCLUSIONS
METHODS
INTRODUCTION
Wetlands can be highly effective in the removalof contaminants from industrial and municipalwastewaters. Understanding the processes thatcontrol the treatment performance of wetlandscan help optimise their design and maintenanceoperations.
OBJECTIVES OF THE STUDY
To obtain a quantitative understanding of the relationship between wetland performance and:
Basin shape
Spatial vegetation distribution
To develop optimal design criteria for waste-water treatment wetlands
● For channelized vegetation patterns, the partition of the flow between mainchannel and vegetated zones leads to a bimodal behaviour of the hydraulic RTD.
● For spatially correlated heterogeneous fields, the maximum concentrationreduction is shown to not coincide with the condition of maximum mass removal.Mass removal is a combined effect of concentration reduction and flow rate, andthe results clearly show that there is an optimum value of stem mean densityproducing maximum mass removal.
● The average stem density remains the dominant factor determining total massremoval. However, a significant effect is associated also to the vegetation distribu-tion represented by the stem density variance and correlation length.
0 0.5 1.0 1.5 2.0 2.5 3.00
0.5
1.0
1.5
2.0
2.5
3.0
Rt*=t/T [–]
n*=1.00
n*=0.26n*=0.07
n*=0.67
φ(t
*)T
[–]
R
0 0.2 0.4 0.6 0.8 1.00
0.2
0.4
0.6
0.8
MFC discharge,LVZs discharge,
LVZs discharge,MFC discharge,
n*
Qi/ Q
b*= 0.1
b*= 0.2
b*= 0.1
b*= 0.2
1D model1D model
2D model2D model
A simplified 1-D transport model
The solute breakthrough curves are found tobe well described by a simplified 1-D modelassuming two transport domains:
where:
and where the weight coefficient w1 is a func-tion of the normalized stem density n*:
1000 1400 1800 2200 260050
55
60
65
70
75
80
85
90
95
100
n (stems m )–2–
ηC
(%
)
1200 1600 2000 2400 28000.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
n (stems m )–2–
dis
charg
e,
(m
s )
Q3
–1
1000 1400 180038
40
42
44
46
48
50
n (stems m )–2–
mass r
em
oval (g
s )
–1traditional
design
2200 2600 3000
LLLL
= 3 m = 5 m = 10 m = 15 m
c
c
c
c
/ n = 0.83/ = 8.30/ = 33.3
–
n–
n–
inlet outlet
L
B b
ሻ𝐶(𝑡, 𝑥ሻ = 𝑤1𝐶1(𝑡, 𝑥ሻ + (1 − 𝑤1ሻ𝐶2(𝑡, 𝑥
𝐶𝑖(𝑡, 𝑥ሻ =
0
𝑡𝐶𝑖𝑛(𝑡 − 𝜏ሻ𝑥
4𝜋𝐾𝑖τ3exp −
𝑥 − 𝑈𝑖𝜏2
4𝐾𝑖𝜏− 𝜆𝑖𝜏 𝑑𝜏
𝑤1 =𝑄1𝑄
= 1 − 1 +1
𝑛∗
𝑏∗
1 − 𝑏∗
−1
Concentration reductionefficiency
Wetland discharge Mass removal rate
𝜂𝐶 = 1 −𝐶𝑜𝑢𝑡𝐶𝑖𝑛
Stem density (stems m–2)
x (m)
y (
m)
Residence time distribution (RTD)
decreasing
density ratio
n* = n1/n2
Streamwise velocity
HETEROGENEOUS VEGETATION DISTRIBUTIONS
Concentration reduction efficiency increases monotonically with mean stem density
For a given hydraulic head loss between inlet and outlet, the discharge decreasesmonotonically with vegetation density
The combined effect of the increasing concentration reduction and the decreasingdischarge produces a non-monotonic behaviour of the mass removal, which has apeak for a certain value of the stem density
Mass removal is lower for higher values of stem density variance, and the effectof variance is more pronounced for higher correlation lengths
low high
Simulation parametersho = 0.5 mΔh = 0.05 m L = 400 mB = 300 mb = 10 m
EFFECT OF BASIN SHAPE
• increases with aspect ratio (Length/Width)
• is higher for wetlands with diverging inlet and converging outlet
Figure 3. Simulated velocity fields for different basin shapes for a 1 ha wetland with centrally aligned inlet-outlet of 10 m width and uniform vegetation density.
Figure 4. Volumetric efficiency and dispersion efficiency versus vegetation density for different wetland shapes and aspect ratios.
Figure 7. Discharge in the MFC and the LVZs predicted by the 2D and 1D model.
Figure 6. Simulated residence time distributions in a channelized wetland.
Figure 5. Magnitude of the streamwise velocity in a wetland with uniform (top) and channelized (bottom) vegetation distribution.
Figure 1. Illustration of a channelized wetland.
Figure 2. Example of a random vegetation density field.
Figure 8. Concentration reduction efficiency, discharge and mass removal ratepredicted by the 2D depth-averaged model as a function of mean stem density, fordifferent variances and correlation lengths of the vegetation distribution.
References[1] Musner, T., Bottacin Busolin, A., Zaramella, M., & Marion, A. (2014). A contaminant transport model for
wetlands accounting for distinct residence time bimodality. Journal of Hydrology, 515, 237-246.[2] Savickis, J., Bottacin Busolin, A., Zaramella, M., Sabokrouhiyeh, N., & Marion, A. (2016). Effect of a
meandering channel on wetland performance. Journal of Hydrology, 535, 204-2010.
Hydraulic efficiency
The transport of a contaminant in a conceptual wetland with flat topography issimulated by a 2-D depth-averaged hydrodynamic and solute transport model. Twotypes of vegetation distributions are considered:
Channelized distribution (main channel with vegetation density n1 and lateral zoneswith vegetation density n2)
Heterogeneous distribution (spatially correlated random field with prescribed mean,ത𝑛, variance, σ, and correlation length, Lc)
Velo
city (
m/s
)Velo
city (
m/s
)Velo
city (
m/s
)
Velo
city (
m/s
)Velo
city (
m/s
)Velo
city (
m/s
)
