1. Buoy update - progress 2. Plume dilution - basics

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1. Buoy update - progress2. Plume dilution - basics

OMSAP 6/29/09

Mike Mickelson, MWRA

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Salinity 44013

Salinity 44029

spacer1

spacer2

spacer3

Temperature 44013

Temperature 44029

spacer4

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

12/20

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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

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0 90 m

0

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'

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20'

42oN 25.00'

30'

35'

Five Km


71oW 54' 48' 42' 36' 30'

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20'

42oN 25.00'

30'

35'

Five Km

24 Hour Particle Excursion


71oW 54' 48' 42' 36' 30'

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20'

42oN 25.00'

30'

35'

Five Km


71oW 54' 48' 42' 36' 30'

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20'

42oN 25.00'

30'

35'

Five Km


71oW 54' 48' 42' 36' 30'

15'

20'

42oN 25.00'

30'

35'

Five Km


71oW 54' 48' 42' 36' 30'

15'

20'

42oN 25.00'

30'

35'

Five Km

24 Hour Particle Excursion


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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-1.0 -0.5 0.0 0.5 1.0

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niu

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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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-1 0 1 2 3 4 5 6 7 8 9 10

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

Documents

1. Buoy update - progress 2. Plume dilution - basics