Meteorological Cooperative › Warning systems › REP-LEW
REP-LEW, the landslide system
REP-LEW watches the slopes of the Republic and warns where ground is likely to move. It works on two limbs: continuous instrumental probing of slopes already known to be unstable, and a rainfall and saturation threshold applied to every slope unit in the territory. It entered service in September 2024, the most recent of the three warning systems after REP-FEW was specified.
Where the ground moves
Landslide in the Republic is uncommon and mostly small. Three settings account for almost all of it.
The western upland is the first. The Vandorum plateau bears thin acid soils over old rock, and roughly a fifth of the original forest stand was felled between 1929 and 1935 to pay for imports during the Depression. Slopes stripped in those years lost the root network holding the soil, and they have produced shallow translational slides in wet winters ever since. The replanting begun in 1983 runs on a hundred-year schedule, and the slide frequency on replanted ground has already fallen by about half.
The Belvacius hills are the second. They are steep, thinly settled and exposed, and their failures take the form of rockfall and of debris flow in gullies. The hills also lie on the seismic margin, so shaking is a trigger there and nowhere else in the Republic.
The third setting is engineered ground: road cuttings, rail embankments, quarry faces at Vandorum, and the coastal cliff at Cortius, where undercutting by the sea removes support at the base. Peat slides on the Kelvaqui moor form a small fourth category and threaten no settlement.
The probing limb
Two hundred and fourteen slopes are instrumented, chosen for a recorded history of movement, for proximity to a settlement or a route, or for both. Each installation reports continuously into the same archive as the seismic and meteorological stations.
| Instrument | Reports | Measures | Value in a warning |
|---|---|---|---|
| Borehole inclinometer | Hourly | Displacement with depth, locating the shear surface | Establishes whether a slope is creeping and at what depth |
| Piezometer | Every 15 min | Pore water pressure at two or three depths | The proximate cause of most failures; the strongest single predictor |
| Wire extensometer | Every 5 min | Opening of a tension crack at the crown | Acceleration ahead of failure, ordinarily over hours |
| Tilt sensor | Every 5 min | Rotation of a block or a retaining structure | Detects rotational movement early |
| Soil moisture probe | Every 15 min | Water content at 0.3, 0.6 and 1.2 m | Feeds the antecedent condition in the threshold |
| Satellite interferometry | Every 6 days | Millimetric surface displacement over the whole territory | Finds slopes creeping where nothing is installed |
Interferometry is obtained through exchange with the regional centres. It reveals slow creep across the whole territory and detects nothing on the timescale of a failure.
The threshold limb
The territory is divided into 1,860 slope units, each of uniform gradient, geology and land cover. For every unit the model holds a threshold made of two figures: how much rain falls over a short window, and how much has already fallen over the preceding weeks. The second figure describes how wet the ground was before the storm arrived. A slope fails when both are exceeded together, which is why the same hour of rain produces a slide in February and nothing in August.
The short window is filled from the 1 km rainfall nowcast and the short-range forecast, so the threshold is tested against rain that has fallen and against rain expected within the next twelve hours. Antecedent wetness comes from the soil moisture probes and from the water balance model of the same catchment used by REP-FEW.
| Step | Condition | Ordinary lead time | Statement and action |
|---|---|---|---|
| Watch | Threshold reached within 24 h on the forecast | 24 to 72 h | Published to the commune and to route operators; no public broadcast |
| Warning | Threshold exceeded, or monitored slope accelerating | 6 to 24 h | Broadcast to the affected slope units. Avoid the slope, the ground below it and the routes crossing it |
| Imminent | Extensometer acceleration above the failure curve | 10 min to 6 h | Broadcast with the action stated. Routes closed by the operator; dwellings below the slope evacuated by the commune |
| Movement | Failure detected or reported | None | Broadcast stating extent, the route affected and the closure in force |
Seismic coupling
Shaking at REP 7 and above ordinarily produces landslide on steep ground. REP-LEW receives the intensity field from REP-KJS as it is computed, tests it against the slope units within the affected area, and issues a landslide warning for units where the combination of shaking and current saturation exceeds the seismic threshold.
Lead time in that case is short or absent, since the shaking and the failure occur within the same minute. The value of the coupling lies in the hours afterwards, when slopes loosened by the shaking fail under ordinary rainfall. Every unit warned on a seismic trigger stays under a lowered rainfall threshold for fourteen days.
Performance record
| Measure | Count | Note |
|---|---|---|
| Movements of recorded volume | 26 | Over the period; 21 on unmonitored slopes |
| Preceded by a warning | 17 | Warning step or above, before movement |
| Occurring with no warning | 9 | Seven were shallow debris slides below the volume threshold of the model |
| Warnings with no movement following | 63 | The intended behaviour of a probabilistic threshold |
| Imminent steps issued | 4 | Three followed by failure; one slope stabilised without moving |
| Roads closed on a warning | 38 | Closure is decided by the route operator and not by the cooperative |
Limits
A threshold is a statement about probability. Sixty-three warnings over the period were followed by no movement, and that ratio is a design choice: a threshold tight enough to eliminate them would miss failures. The cooperative publishes both counts so the ratio is visible.
Shallow debris slides of a few hundred cubic metres fall below the volume the model resolves. They are the commonest failure in the Republic and the one most likely to arrive without warning. A slide of that size still kills a person standing under it.
The warning names a slope unit of 2 to 40 km² and never a point. Which slope within the unit will fail, and when within the stated window, are outside what the method can state.
Undercutting failures at the Cortius cliff and failures triggered by construction work develop without a rainfall signature, so the threshold limb sees nothing. Only instrumentation detects them, and only where instrumentation is installed.
See also
- REP-FEW, the flood system, which shares the catchment model
- REP-KJS, which supplies the intensity field on a seismic trigger
- Certified devices and RQUAK
- Observing network, including the monitored slopes