Data
5 min read
Why our sensors stay for ten years
Kenji Arai
A defence is only finished when someone keeps measuring it. What ten years of readings give a city that a handover report cannot.
A handover report describes one day
Most coastal and river works end with a handover report: drawings as built, a few photographs, a signature. It describes the defence on the day it was finished. It says nothing about the third winter, the first real flood, or the settlement nobody expected.
What ten years give you
Our sensors stay for ten years after handover. Across our eight sites, 214 sensors take a reading every ten minutes, and since 2021 they have logged 9,184,227 readings. That is enough to follow a dune through several winters, a flood field through a real flood, and a soil that changes season by season.
Ten years also covers the events that count. The February 2025 flood at Vire-sur-Lône came three years after flood field E-2 was built. Without gauge V-07 still in place, we could not show that peak flow fell from 412 to 301 m³/s.
Who keeps the readings
The city keeps the readings. Every month we publish them against the indicator written into the contract, and once a year an outside reviewer checks the register: Kerrow & Lisle Hydrology for water levels and flows, Northfield Soil Laboratory for soil cores, Atlantic Survey Review for waves and beach profiles.
When a gauge needs cleaning or re-levelling, the correction is logged like any other reading. A register that hides its maintenance is not one a council should trust.