new job, first assignment or uh oh, i don’t remember any calculus by dick bogaert wetlands...
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NEW JOB, FIRST ASSIGNMENT
orUh Oh, I Don’t Remember Any
Calculus
By
Dick Bogaert
Wetlands Biologist/Analyst
Mt. View Sanitary District
Moorhen Marsh
• Constructed marsh receiving highly treated wastewater.
• One of the first marshes to receive wastewater for marsh enhancement.
• Raised concerns about the quality of habitat produced.
Pond E Pond D Pond C
Pond A-2
Pond A-1
Pond B
Flow Scheme in Moorhen Marsh
• Treated effluent flows first to pond D, then splits to pond C and E. These two recombine to flow to Fat Slough then split again to enter ponds A or B.
Peyton Slough
Treatment Fat Slough
How Does the Water Really Travel—the Flow Regimen?
• Regulatory agencies were concerned that there might be pockets of low dissolved oxygen or that the water would rush through without interaction with the marsh.
• Mosquito abatement was concerned that stagnant areas would produce mosquito breeding pockets.
• A flow regimen would reveal stagnation, short circuiting or high flow flushing.
Characterize the Water Flow Regimen Through the Marshes
• The flow regimen reveals obstacles and short circuits that alter the actual time a liquid remains in a volume.
• Residence time in a container or pond can be calculated directly knowing the volume of the container and the rate of liquid flow.
• In a marsh, contours, vegetation, and relation of entry and exit points affect how long a portion of water remains in the marsh.
Use Flow, Concentration and Time to Show the Flow Regimen in
Moorhen Marsh
• Use a tracer to imitate and detect flow through the marsh.
• Use a conservative tracer—bromine, a substance that is not absorbed, adsorbed or otherwise taken from the marsh system
• Measure water flow out of the subject marsh through a V-notch weir.
• Collect samples at known times and flow.
Tracer Flow Through a Typical Marsh
• The tracer imitates water flow.
• Water plus bromine tracer flows through the marsh as clouds of concentration.
• Samplers at the exit will sample patches of high or low concentration.
Theoretical Curves for Bromine Concentration
• In the Conc vs Time graph, the higher curve indicates shorter retention time.
• In the “% Br Emitted” graph, the shape of the curve provides clues as to how the water flows through a marsh.
Conc.
% Emit’d
Time
Time
Conc. Vs. T
% Br Emitted
Combine Concentration, Flow and Time Data
• After nine days, bromine concentration fell back to background level.
• But does the water short circuit or stagnate?
Br
Background Br
mg/L Br
Flow
CFS
Days
Integration
• Integrate mass and flow over time…DUH!...
• Cut out each section representing a time and mass.
• With an analytical balance, weigh the sections.
• Each section is proportional to the real mass.
Cutout &
Weigh
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