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🌤 Sky is clear and the sun is out, but the worst is yet to come for Colombo.

⭕️ Looking at the last two major floods, 2016 and 1989, Colombo’s peak water level usually arrives about 30 hours after the peak at Hanwella.

⭕️ In the current situation, Hanwella crossed its major flood level of 10.00m at 10 PM on the 28th, and Nagalagam St crossed its 7 ft major flood level at 6 AM on the 30th, showing a similar delay (32 hours).

⭕️ Since Hanwella reached its peak at 12 AM on the 30th, Colombo’s peak at Nagalagam St is expected around 8 AM tomorrow, 1 December, and water is likely to remain at that elevated level for at least two days.

#SriLanka 🇱🇰 #StaySafe 🙏

30 Nov 2025, 11:47

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  1. Original post on X — Numbers.lk (@numberslka)

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  1. But in 2016 , 200mm+ Heavy Rain over 24 hours during this gap contributed to the rise, In this instance only upstream water is running down - Therefore predictions might go wrong

    10 months agoLikes:11
    1. Anushka Maduranga Nope. The analysis is still relevant because the time gap (hydraulic lag) mainly depends on river hydraulics, not rainfall consistency. Continuous rainfall may affect how long the water stays and the level of the peak, but not much on the time delay. Due to the bottlenecks upstream, I believe the timing of the high tide will affect the flood level more than the rain continuity near Colombo. I'm not an expert, though.

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10 months agoLikes:2
  • Thanks and interesting discussion. Chathura are you working for a govt agency or a university in sri lanka.

    10 months ago
  • Aqeel Rifdy

    10 months ago
  • Good analysis Numbers.lk

    10 months ago
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