Thalgahagoda Nilwala Ganga water level

Above alert level now and expected to stay there for the next 24 hours.

Published as 1.46 m (alert 1.4 m, minor flood 1.7 m, major flood 2.8 m)

Elevated river-flow outlook this week.

• Minor flood (5.6 ft): unlikely, about 1 in 10
• Major flood (9.2 ft): unlikely, about 1 in 10

Rain that fell

0.0 mm in the last 3 hours, 24 mm in the last 24 hours at this gauge (moderate rain)

Rain forecast

24 mm in the next 24 hours over the catchment (moderate rain). Forecast model estimate.

Satellite estimate of rain over the catchment: 52.5 mm in the last 6 hours, 134.1 mm in the last 24 hours (to 1:30 am). It can differ from the gauges. GSMaP data by Japan Aerospace Exploration Agency (JAXA)

• · Outlook: the GloFAS global flood model has river flow at 263 m3/s in its highest member within 7 days, above the 1-in-20 level (89 m3/s). This is a heads-up only; it does not change the levels above.
• · Some rain is forecast over the catchment: about 24 mm in the next 24 hours (ensemble range 11 to 41 mm).

• How this is worked out
• · Latest level at Thalgahagoda and recent change. No gauge sits upstream of it (or none reports in step with it), so the catchment rain is its upstream signal.
• · Forecast model estimate of catchment rain (Open-Meteo, area average over 14 grid cells above Thalgahagoda): 45 mm modelled for the last 24 hours, 24 mm forecast for the next 24 hours, with ECMWF ensemble spread.
• · The 1, 3, 6, 12, 24 hour steps use this gauge's own recent changes and the other gauges on the river (fitted to about 11 months of hourly readings, including the November 2025 Ditwah floods); where this was tested against 'level stays the same' it missed by less.