NEW JOB, FIRST ASSIGNMENT or Uh 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 EPond DPond 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 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%