1 1. Buoy update - progress 2. Plume dilution - basics OMSAP 6/29/09 Mike Mickelson, MWRA.
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Transcript of 1 1. Buoy update - progress 2. Plume dilution - basics OMSAP 6/29/09 Mike Mickelson, MWRA.
11/20
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Salinity 44013
Salinity 44029
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Temperature 44013
Temperature 44029
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DO mg/L 44013
Chlorophyll 44013
Chlorophyll 44029
Data from NOAA NWS NDBC buoy 44013 (The Boston BF buoy)
and the GoMOOS A buoy operated by U Maine and also designated as NOAA 44029
13/20
2. Plume dilution - basics:Effluent plume dynamics in relation tooutfall monitoring sampling design
• Don't sample too close or too far
• Within the "initial mixing zone" the plume is too patchy to sample.– Initial mixing occurs within about 10 minutes,
and about 60 meters distance from the diffuser.
– At that time the plume has diluted to about 100:1
• The plume then becomes more uniform, and dilutes slowly over a few hours.
• The plume disperses and breaks up, and is undetectable after a few days, or about 20 km away from the outfall.
14/20
ocean currents
Dilution in the near field due to self-induced turbulence.
Dilution in the far field due to horizontal buoyant spreading and ambient turbulence.
Mixing zones:
• Regulatory
• Hydrodynamic
• Zone of initial dilution
Terminology: Mixing Zones
Near field Far field
Transition:Buoyant spreading
Internal jump
Diffuser
Effluent plume plume rise height
from Phil Roberts
15/20
stronger ocean currents. perpendicular to diffuser axis
Near field dilution increases with several factors
Lower effluent flow per unit length of diffuser
higher rise of the plume
16/20
0 90 m
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20 m
Laser imagery of dye in a scale model plume
(distance legend is scaled and approximate)
"0.010 C/Co" means plume concentration C is 1% of effluent concentration Co, i.e. 100:1 dilution
from Phil Roberts
17/20
Processes and Scales for Ocean Outfalls
Near field Far fieldTransition Long-term flushing
Spatial scale (m)
Time scale (min)
10 102 103 104 105
1 10 102 103 104 105
1 km
1 day 1 week 1 month
10 km 100 km
1 hour
Advection by ocean currents
Ambient diffusion
Buoyant spreading
Large-scale flushing; upwelling; sedimentation
Jet and plume turbulence;
internal jumps
from Phil Roberts
18/20
ADCP, 5 mbs, January 2000
71oW 54' 48' 42' 36' 30'
15'
20'
42oN 25.00'
30'
35'
Five Km
ADCP, 5 mbs, July 2000
71oW 54' 48' 42' 36' 30'
15'
20'
42oN 25.00'
30'
35'
Five Km
ADCP, 20 mbs, January 2000
71oW 54' 48' 42' 36' 30'
15'
20'
42oN 25.00'
30'
35'
Five Km
24 Hour Particle Excursion
ADCP, 20 mbs, July 2000
71oW 54' 48' 42' 36' 30'
15'
20'
42oN 25.00'
30'
35'
Five Km
ADCP, 5 mbs, January 2000
71oW 54' 48' 42' 36' 30'
15'
20'
42oN 25.00'
30'
35'
Five Km
ADCP, 5 mbs, July 2000
71oW 54' 48' 42' 36' 30'
15'
20'
42oN 25.00'
30'
35'
Five Km
ADCP, 20 mbs, January 2000
71oW 54' 48' 42' 36' 30'
15'
20'
42oN 25.00'
30'
35'
Five Km
24 Hour Particle Excursion
ADCP, 20 mbs, July 2000
71oW 54' 48' 42' 36' 30'
15'
20'
42oN 25.00'
30'
35'
Five Km
24-Hour trajectories
from Brad Butman and Rocky Geyer
19/20
Plume Tracking Survey Dye results
• Plume moved to the southeast over 2 day survey
• Effluent Dilution of ~1000 in far field
Day 1
Day 2
20/20
Conclusions
• Based on MWRA data, EPA was able to certified that the outfall diffuser effectively dilutes effluent just as it was designed to do.
• Measurements closer than about 100m from the diffuser yield noisy data.
• Outfall effects are unlikely beyond 20 km from the diffuser.
• The plume can travel in any direction due to low-frequency currents driven by wind and river runoff
• Residual currents on the scale of weeks also affects circulation
• The plume is gone before algal abundance can increase measurably
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Days
Am
mo
niu
m o
r A
lga
e (u
M a
s n
itro
gen
)
0.5 uM ambient NH4
2 uM ambient algae
Initial dilution:Effluent (1200 uM NH4),diluted 1:100 withseawater (2 uM NH4),gives diluted effluent (12.5 uM NH4)
A parcel of water drifts toward the outfall,and then encounters the outfall at t minus 5 minutes.
The parcel of water continues to drift.Dilution continues slowly due to oceanic dispersion
Algae, assuming no growth
NH4 concentration decreases due to oceanic dispersionC
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Days
Am
mo
niu
m o
r A
lga
e (u
M a
s n
itro
gen
)
Ammonium, assuming no algal growth
Ammonium, with dinoflagellate growth
Ammonium, with diatom growth
Algae, assuming no algal growth
Algae, with dinoflagellate growth
Algae, with diatom growth
3.6 days, 2.2 uM dinoflagellates
2.4 days, 2.6 uM diatoms