Thanks again for such a prompt and thorough reply, yet again.
We have continuous data starting in last July. The variation in depth over four months was consistently in the neighborhood of +265-275mm. There was a period of very cold temps around Christmas and the edge of the stream froze but I don’t think that the probes were encased in ice. However, after that freeze event, the variation in depth (b/t digital sensor and visual measurement on staff gauge) became much more variable, without any logical pattern.
I will do a thorough check of the cable, record readings when probes are out of the water, and see if I can clean the pressure disk. The turbidity measurements seem more accurate and responsive to weekly cleaning – both before and after the freeze event – so the issue is isolated to the depth sensor or the cable. Will post update later in the week when I get a chance to do more investigations and a more thorough cleaning.