What river flood alert levels mean
Lankawa shows Irrigation Department ArcGIS gauges on the disaster page, and uses lk-flood-api for alert summaries. When lk-flood-api station levels go stale, district lists fall back to the same Irrigation readings. Each station has its own threshold lines.
What you see on Lankawa
A station card compares current water level (metres) against alert, warning, and danger thresholds set for that river reach.
Peradeniya (Mahaweli)
Mahaweli Ganga · illustrative
- Current level
- 2.14 m
- Alert threshold
- 2.00 m
- Warning threshold
- 2.50 m
- Danger threshold
- 3.00 m
Alert line
Warning line
Danger line
NORMAL
Below alert threshold — routine monitoring.
ALERT
First threshold crossed — watch forecasts and upstream rain.
WARNING
Significant rise — prepare according to local guidance.
DANGER
Highest station threshold — follow DMC and local authority instructions.
What this means
Water level is measured in metres above a station datum — essentially how high the river is at that gauge point, not how deep floodwater is in your street.
NORMAL means the level is below the station's alert threshold. ALERT means the level crossed the first threshold — increased monitoring, not necessarily public danger.
WARNING and DANGER are progressively higher thresholds for that specific station. A WARNING at one river does not mean the same risk at another — each gauge has different geography.
Remarks and timestamps come from the upstream feed. If history is unavailable, sparklines degrade gracefully — we show what we have and mark freshness honestly.
What we will not claim
River gauges are one input for preparedness. They do not replace DMC bulletins, local authority warnings, or on-the-ground judgment during heavy rain.