The Kalu Ganga at Millakanda and the Deduru Oya at Moragaswewa are both at flood risk level and 25 reservoirs are spilling, the Irrigation Department said on Friday, as a second week of heavy rain continued across much of Sri Lanka.

L. S. Sooriyabandara, Director of the department’s Hydrology Unit, asked residents of low-lying areas to remain highly vigilant, NewsFirst reported.

The Kalu Ganga is the new name on that list. The Deduru Oya has been under warning since its spill gates were opened on 21 October, when it was discharging 16,500 cusecs; the Kalu Ganga, which drains the Ratnapura–Kalutara basin in the south-west, had not previously been reported at risk in this spell.

Two systems, not one

The weather accounts need separating, because two different low-pressure areas are in play and a reader could easily take them for the same one.

The system that produced this week’s rain is leaving. The Department of Meteorology says the low-pressure area that had been near Sri Lanka is moving westward, away from the island, Hiru News reported — though its effects were expected to persist through Friday.

A second low-pressure area is expected to form over the south-east and adjoining east-central Bay of Bengal, to move west-north-westwards and intensify further into a depression, according to the departmental statement carried by the Daily Mirror. Met Department climatologist Malith Fernando told the paper the depression could continue for a few more days and that rain could continue until around 27 October, with conditions expected to improve after October.

For Friday itself, showers or thundershowers were forecast in the Western, Sabaragamuwa, Central, Northern and North Western provinces and in the Anuradhapura and Galle districts, with fairly heavy falls of around 75 mm in places. The Met Department asked the public to guard against temporary localised strong winds and lightning.

What the rain has already done

Rainfall exceeded 100 mm in several places, with 150 mm recorded at Marawila, 136 mm at Araganwila and 116 mm at Wariyapola. Flood warnings were issued for the Deduru Oya, Mahawa, Nikaweratiya, Chilaw, Bingiriya and Pallama areas. Flood gates were opened at Polgolla, Rajangane, Ambewela, Kala Oya and Canyon, and the Irrigation Department reported Angamuwa, Omarankada in Anuradhapura and Uyanwewa in Galle at spill level. Heavy traffic built up on Colombo city roads through the morning.

Landslide warnings, with a discrepancy

Landslide warnings issued under Phases 1 and 2 for several divisional secretariat divisions remain in effect. The two filings do not name the same districts: NewsFirst lists Kalutara, Kandy, Kegalle, Nuwara Eliya and Ratnapura; the Daily Mirror lists Kandy, Ratnapura, Nuwara Eliya, Kegalle and Badulla. Four districts are common to both; the lists differ on Kalutara and Badulla.

The Daily Mirror’s account describes the position as at the Met Department’s statement the previous day, while NewsFirst’s is Friday morning, so the difference may be a change over time rather than a contradiction. Neither filing says so, and residents of either district should treat both as live.

Not reported

No filing gives the current discharge from the Deduru Oya, so the trend since Wednesday’s 16,500 cusecs cannot be stated. None names the 25 spilling reservoirs, gives overall storage levels, or reports evacuations, displacement, damage or casualties. The flood-risk thresholds for the Kalu Ganga and Deduru Oya gauges are not stated, so the margin by which they are exceeded is unknown.

A Daily Mirror filing on spill gate openings at major and medium reservoirs was published the same morning but could not be retrieved on any available route, and nothing from it is used here.

Sources