Nature Conservancy shows multi-evidence tailwater monitoring; some meters produce implausible readings

The Nature Conservancy presented an experiment using multiple, independent lines of evidence to estimate flows pumped off Delta islands, focusing on tailwater pump stations where a few measurement points can provide insight into larger diversion volumes.

Kirk Klausmeier (The Nature Conservancy) outlined five evidence streams: pump tests (instantaneous capacities), PG&E energy use (kilowatt-hours), pressure transducers in pipes, insertion mag meters, and pond-level level sensors. He stressed that stacking those lines provides timing and magnitude insight but also exposes measurement problems when instruments disagree. "Good start, but I don't believe the results quite yet," Klausmeier said after showing plots where one pump's flow meter readings were far lower than expected and another pump's readings were an order of magnitude too large.

Why it matters: tailwater pumps can be a tractable place to measure return flows and portions of diverted water because power records and a small number of monitored pumps can be used to back-calculate diverted volumes. TNC's tests showed cases where pressure transducers and insertion meters aligned well on timing and magnitude, and other cases where calibration, clogs or device settings appear to be producing unreliable values.

Practical details and next steps: TNC will continue running experiments through winter and perform meter maintenance, recalibration checks, and settings reviews (pulse factors, meter configuration). Participants recommended plotting float trigger heights and comparing energy and pressure traces to better interpret on/off timing and seepage influence.

Klausmeier and others asked for continued collaboration and shared diagnostics as the group pursues methods to infer return flows and net usage.