A Low-Cost Bridge-Scour Witness Instrument: A Tilt-Node Chain Design and Its Computed Detection Budget

SIMULATED, NOT MEASURED. A design and computation study of a low-cost bridge-scour witness instrument: a chain of 16 tilt nodes spaced 0.20 m apart at a pier. Computed budget: 3.2 m depth range with 0.20 m uncertainty, 15-minute detection latency, detection probability 0.892 within one hour, model false-alarm rate 0.0110 per chain per year, minimum certifiable sustained scour rate 0.20 m per day, computed battery life 9.32 years (service capped at 5.0 years), and parts cost $191.40 (under-$250 class). No hardware was built, deployed, or tested. Civilian safety instrument for bridge inspection support only.