Every spring, our on-call rotation gets the same alert: a turbidity sensor somewhere in the Cedar Fork watershed jumps from a baseline of 3–5 NTU to 40+ within an hour. The instinct is to assume upstream erosion, and sometimes that's right — but we've learned to check three other things first.
First, correlate against the flow-rate channel on the same station. A turbidity spike with no corresponding flow increase is a strong signal of a sensor fouling event, not a real water-quality change — biofilm buildup on the optical window scatters light the same way suspended sediment does.
Second, check whether the spike is isolated to one station or shows up across the whole sub-basin. A single-station spike during otherwise normal flow is very often a maintenance issue, not a watershed event.
Third — and this is the one people skip — check the timestamp against our maintenance log. A surprising number of "mystery spikes" turn out to be a technician's boat wake fifteen minutes before a scheduled calibration visit.
Only once those three are ruled out do we treat it as a real erosion or discharge event and start pulling grab samples.