I’m retrofitting two detention basins this fall and need dependable level monitoring for drawdown verification and flood alerts during 2–3 in/24 hr events. Has anyone compared low-cost ultrasonic nodes (Senix or MaxBotix with LTE loggers) to vented pressure transducers (HOBO U20L or In-Situ Level TROLL) in wet, debris-heavy stormwater — accuracy, clogging, and battery life?
Ultrasonics (Senix/MaxBotix) were jumpy in 2–3 in/24 hr events from spray and webs; a vented Level TROLL in a 2 in slotted stilling well has been boringly reliable. > transducers (HOBO U20L or In-Situ Level TROLL) in wet, debris-heavy stormwater — accuracy, clogging, “Pressure wins — U20L isn’t vented; add a copper mesh cap and fouling disappears, and with LTE at 5‑min sample/15‑min send I get about 18 months, bumping to 1‑min during storms without killing the battery.”.
For debris-heavy basins, I’d go vented pressure in a small PVC stilling well and budget to change the vent desiccant every 3–6 months; my ultrasonic + LTE setups got spiky in “2–3 in/24 hr” pulses and hammered batteries — . If vent maintenance is a nonstarter, a low-power 80 GHz radar node has shrugged off mist for me, but it’s pricier upfront. What’s your sample/transmit schedule and how often can you service the site?
In splashy, trash‑prone basins, small 80 GHz radar has beaten ultrasonic for me; a VEGAPULS C‑11–type head with a tight beam shrugs off spray/webs and sips power when you only wake it for a few seconds per read (example: https://www.vega.com/en-us/products/product-catalog/level/radar/vegapuls/vegapuls-c-11)… @jackson30 is right on the stilling well; if you stay with pressure, use a short PVC stilling tube with a cleanout and a hydrophobic vent cap, and put desiccant swaps on your PM so you don’t chase “mystery tides.” One gotcha: HOBO U20L is non‑vented, so plan for baro comp or pick a vented model if you want straight‑to‑dashboard levels.
For “drawdown verification” I’d skip vented and run an absolute probe (HOBO U20L) with a cabinet baro, sampling 1–5 min and LTE‑bursting only during storms. Avoids vent upkeep in trashy basins, has been steadier than ultrasonics, and with a short slotted 3/4 in sleeve I haven’t had clogging; D‑cell + duty‑cycled LTE has lasted a season. @jackson30’s radar point is good if you’ve got clean sightlines — do you have a dry cabinet for the baro?