Environmental Fluid Mechanics

1
Environmental Fluid Mechanics
2
Mass Transfer in Natural Systems
3
Mass Transfer in Natural Systems
4
Dispersion
5
Case Studies

• Contaminated Sediments
• Water Quality Modeling Dissolved Oxygen
• Fish Passage

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Contaminated Sediments

• Significant Problem in Harbors, Rivers, Lakes
• 4.3 Million Cubic Yards / Year in Port of NY

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Remediation Techniques

• Capping
• Not suitable for harbor facilities
• Bioremediation
• Appropriate / effective for some sites
• Dredging
• Most common technique

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Types of Dredges

• Mechanical Dredges
• Clam Shell (Grab)
• Excavators
• Bucketline dredges
• Hydraulic Dredges
• Hopper dredges
• Cutterhead Dredges

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Dredged Material Disposal
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Confined Disposal Facility
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Opportunities for Chemical Release During Dredging
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Opportunities for Chemical Release After Dredging
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Current Knowledge

• Sediment resuspension due to dredging
• Transport of fine-grained sediments
• Scaling effects on flocculation
• Turbulence in open channels
• Contaminant sorption to particles

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Sediment Resuspension
400
300
Lower Water Column
TSS (mg/L)
200
Middle Water Column
100
Upper Water Column
0
0
10
20
30
40
50
60
Distance from Dredge X/D
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Fine-Grained Sediment Transport

• Particle transport a function of settling
  velocity, hydrodynamics in water column
• Settling velocity related to particle size
• Fine-grained sediments form flocs
• Floc formation a function of turbulence

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Turbulence in Open Channels

• Nezu Nakagawa Relationship

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Equilibrium Partitioning

• Sorbed/Aqueous Concentration

POC
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Dissolved Oxygen Water Quality Modeling
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Historical Perspective

• Streeter-Phelps Equation (1925)
• C cross-sectional mean DO concentration
• Cs equilibrium (saturation) DO concentration
• U cross-sectional mean flow velocity
• L BOD
• K1 BOD decay rate coefficient
• K2 reaeration coefficient, KL/h

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Solution to Streeter-Phelps Equation

• Cs is known at a given temperature and pressure
• Lo is the BOD at x 0, which is known from
  outfall and river
• K1 is determined from BOD tests
• K2 is the (old) problem

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Why is K2 the problem?

• K2 is function of river flow parameters
• Difficult to scale down the river
• Expensive to perform site-specific field
  measurements
• Predictive equations for K2 have confidence
  interval of ?800

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C. vs. X for varying K2
Typical Stream Q 10 m3/s, depth 2 m, slope
10-4, velocity 0.3 m/s LO 5 mg/l, Measured
K1 7x10-6 sec-1, Predicted K2 Below
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Common Water Quality Models

• QUAL2E (EPA) 1-d model for streams
• DO, Temperature, BOD, N, P, algae
• WASP 4 (EPA) - 1, 2, 3-d model for streams
• Dissolved Oxygen (DO), BOD, nutrients
• HEC-6 (COE) - 1-d sediment transport in rivers
  reservoirs
• CORMIX (Cornell) - Pipeline (sewage) outfalls