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

Interpretation

• Plot mass against time.• Chart now shows how

much bromine was emitted against time in days.

• The slight bulge in the curve indicates some bromine was retained.

• Retention of flow could produce stagnant areas.

100%

80%

60%

25%

40%