Nawalapitiya Mahaweli Ganga water level

Probably staying below alert level for the next 24 hours.

Published as 2.06 m (alert 3.5 m, minor flood 5.0 m, major flood 6.0 m)

Elevated river-flow outlook this week.

• Alert (11.5 ft): unlikely, about 2 in 10
• Minor flood (16.4 ft): unlikely, about 1 in 10
• Major flood (19.7 ft): unlikely, about 1 in 10

Rain that fell

0.4 mm in the last 3 hours, 85 mm in the last 24 hours at this gauge (heavy rain)

Rain forecast

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

Satellite estimate of rain over the catchment: 8.5 mm in the last 6 hours, 32.5 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 1806 m3/s in its highest member within 7 days, above the 1-in-20 level (732 m3/s). This is a heads-up only; it does not change the levels above.
• · Part of the range is above the highest level this model has seen (9.4 ft); treat it as a rough guide.
• · At 3 h, 6 h, 12 h nothing we tested beat 'level stays the same' for this gauge, so that is the line, with a range taken from how much the gauge has really changed over that time.

• How this is worked out
• · Latest level at Nawalapitiya 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 5 grid cells above Nawalapitiya): 40 mm modelled for the last 24 hours, 12 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.
• · The 24 hour steps read the rain the satellite measured over Nawalapitiya's catchment (JAXA GSMaP, corrected for how it reads here), with rain beside the gauge and rain on the channels upstream timed separately (about 0 h from beside the gauge). Tested storm by storm it was closer than the version that reads the weather model's rain.
• · Heavy rain upstream is part of the 24 hour steps: rain that has fallen or is forecast over the catchment above Nawalapitiya raises the level, and the top of the range allows for the heavier forecast rain. Tested storm by storm (leaving each storm out, Ditwah included) it was closer than the river's own trend alone.