Colombo drains through canals that end at the Kelani river or the sea. Both rise and fall with the tide, so heavy rain near high tide drains slowly.
Colombo canals are tidal near their outlets. High tide around 3:06 am today and 3:03 pm today. They drain slowest around high tide, and when the Kelani is high.
It is around high tide now. Canals drain slowest for the next hour or so. Next high tide around 3:03 pm.
Sea level at the Kelani mouth is rising (reading 1:15 am). Canal levels: CUrW / SLLDC (pub.curwsl.org)
Tide times are predicted from the daily rise and fall at the Nagalagam Street gauge, fitted to its own readings. Predicted tide; times can be off by up to an hour.
Tap an area, a canal or a gauge to see where its water goes. Moving dots show the way the main canals drain.
Water here drains into the Kolonnawa canal and out to the Kelani through the North Lock pumps and gates at Nagalagam Street and the Gothatuwa gates. When the sea is high or the Kelani is high the canal cannot empty, so heavy rain plus high tide or a high river slows draining.
3.3 ft above sea level
Reading 1:15 am
4.7 ft above sea level
Reading 1:15 am
7.8 ft above sea level
Reading 1:15 am
WellampitiyaKolonnawaKotikawattaMulleriyawaAngodaMeethotamullaGothatuwaOrugodawattaSedawatta
Water here drains into Parliament Lake (the Diyawanna Oya). From the lake it goes north through the Kolonnawa canal to the Kelani, and south through the Kotte canals to the sea at Wellawatta and Dehiwala. Heavy rain plus high tide or a high Kelani slows draining.
3.3 ft above sea level
Reading 1:15 am
2.7 ft above sea level
Reading 1:15 am
7.0 ft above sea level
Reading 1:15 am
3.9 ft above sea level
Reading 1:15 am
RajagiriyaBattaramullaKottePita KotteEthul KotteNawalaKoswattaThalangama
Water here drains through the Dematagoda and St Sebastian canals and Beira Lake towards the Mutwal tunnel and the Kelani mouth, which rise and fall with the tide. Heavy rain at high tide, or a high Kelani, slows draining.
3.5 ft above sea level
Reading 1:15 am
2.6 ft above sea level
Reading 1:15 am
2.8 ft above sea level
Reading 1:15 am
2.3 ft above sea level
Reading 1:15 am
DematagodaGrandpassMaradanaBorellaBloemendhalKotahenaMattakkuliyaModaraColombo
Water here drains south through the Kirulapone and Wellawatta canals and the Dehiwala canal straight to the sea. These canals rise and fall with the tide, so heavy rain at high tide drains slowly. The Kelani gauge does not decide flooding here.
Reading 1:00 am
2.7 ft above sea level
Reading 1:15 am
2.4 ft above sea level
Reading 1:15 am
2.5 ft above sea level
Reading 1:15 am
2.1 ft above sea level
Reading 1:15 am
Canal levels: CUrW / SLLDC (pub.curwsl.org) · Their live charts
"Usual" means this gauge's own recent range. Tidal canals rise and fall with the sea twice a day; they are judged by their low-tide level.
In past heavy rain, water reached low spots in Wellampitiya, Kolonnawa, Kotikawatta, Mulleriyawa, Orugodawatta, Dematagoda, Angoda, Meethotamulla and Gothatuwa first. Only a small share of streets in each place are low enough; most stay dry.
It happened mostly after about 60 mm or more of rain in a day, and more easily when the tide was high or the Kelani was high. Rain and tide are context only: they do not make a whole town flooded. The flood estimate for each town still follows the river gauge and official warnings.
Canal levels are shown with credit to CUrW / SLLDC. We have written to them and will change this if they ask.