The Irrigation Department has issued an amber flood warning for low-lying areas of the Attanagalu Oya basin in the Gampaha district, valid from 12.30 p.m. on Monday until 12.30 p.m. on Tuesday, after heavy rain in the upper catchment and the opening of spill gates at the Basnagoda reservoir pushed river levels up.
The department said water levels in the Attanagalu Oya are rising because of significant rainfall over the upper and middle parts of the basin, combined with the start of discharges through the Basnagoda reservoir’s spill gates, Hiru News reported.
Where the risk lies
The warning is based on the department’s analysis of readings from the river gauges it maintains within the Attanagalu Oya basin. On that basis it identified a risk of flooding in the coming period in low-lying parts of the Attanagalu Oya and Uruwal Oya valleys falling within nine divisional secretariat divisions:
Divulapitiya, Mirigama, Attanagalla, Mahara, Gampaha, Minuwangoda, Ja-Ela, Katana and Wattala.
An amber warning is the middle tier of the department’s colour-coded scale, indicating a flood situation is possible and that residents should stay alert, rather than one that is already under way.
An escalation from Sunday
The warning marks a clear change in the basin’s condition over 24 hours. In the Irrigation Department’s islandwide report issued at 6.30 a.m. on Sunday, the Attanagalu Oya at Dunamale stood at 3.75 metres and was falling, listed at alert level while a minor flood warning applied to the Nilwala Ganga in the south. The basin has since moved from a falling alert-level reading to a forward-looking warning with reservoir discharges added to the inflow.
The wider outlook
Separately, the Department of Meteorology said another atmospheric disturbance is developing over the south-east of the Bay of Bengal, the Daily Mirror reported, citing duty forecaster Udeni Weerasinghe. The department expects it to convert into a low-pressure system by 15 November, and asked the fishing and naval communities to stay alert for further notices.
Showers or thundershowers were forecast in parts of the country, with mist during the early hours in the Western, Sabaragamuwa, Central and Uva provinces. Winds over surrounding sea areas were expected at 20–30 kmph, strengthening temporarily to 60–70 kmph during thundershowers.
The Daily Mirror’s filing also reports the highest rainfall as 110.8 mm at Avissawella and 100 mm at Deraniyagala, with 55 mm at Kukuleganga, 36.4 mm at Rantambe and 31.6 mm at Randenigala in the hydro catchments. It said spill gates at around 15 reservoirs were at spill level, according to the Irrigation Department.
Two different dates for the low-pressure system
Readers should note a discrepancy between filings rather than a correction of one by the other. This desk reported on Sunday that the Meteorology Department expected a Bay of Bengal system to form by 11 November and deepen into a low-pressure condition by around 13 November, per Hiru’s account of the same department’s warning. The Daily Mirror’s Monday filing gives 15 November for the low-pressure stage and describes the system as “another” disturbance.
The two accounts cannot be reconciled from the filings available: it is not clear whether the Daily Mirror is describing a revised outlook for the same system or a second, later one.
Not reported
Neither filing gives the current water level at any Attanagalu Oya gauge, the discharge rate from Basnagoda, or the number of households in the nine divisions at risk. No evacuation instruction, relief arrangement or Disaster Management Centre advisory had been reported at the time of writing. The Daily Mirror attributes the Meteorology Department’s disturbance statement to “yesterday”, placing that briefing on 8 November rather than Monday.
Rainfall across the Western province follows the flash flooding that submerged much of Colombo on 6 November, after which a joint operation to clear 60 blocked drainage points began in the capital.
