Twelve major reservoirs and nine medium-sized reservoirs are still spilling after the recent spell of bad weather, the Irrigation Department said, Hiru News reported on Saturday evening.
Spill gates have been opened at five major reservoirs, among them Yoda Wewa, Tissa Wewa, Wemedilla, Thabbowa and Alikota Ara. Gates are also open at two medium-sized reservoirs.
Spilling and discharging are not the same thing
The department’s statement distinguishes two counts that are easily conflated. A reservoir spills when water passes over the spillway on its own; gates are opened as a deliberate release to manage the level. Twenty-one reservoirs are in the first category; seven are in the second.
On that reading the managed releases have eased slightly. This desk recorded eight reservoirs discharging on 26 October, at the height of the rain that followed cyclonic storm Arnab, when Kala Wewa was over capacity at 103 per cent. Seven are discharging now.
The figure that complicates the picture
The same statement puts combined storage across the 74 reservoirs under Irrigation Department control at 45.2 per cent of capacity.
That is the number worth holding onto. Two dozen tanks spilling is a local flood risk wherever they sit, but it is not evidence of a full system — the department’s reservoirs are together less than half full with the north-east monsoon still to do most of its work. The rain has fallen hard on particular catchments rather than evenly across the network.
Thabbowa appears in both this account and the 26 October one, having been releasing into the Mee Oya for the better part of a week.
Not reported
The filing does not name the remaining spilling reservoirs, give discharge rates in cusecs or cubic metres per second for any of the gates now open, or identify which districts are downstream of them. It does not say whether any flood warnings are current, nor whether the 45.2 per cent figure is above or below the seasonal norm for the end of October.
Single source at the time of writing. Ada Derana has carried Irrigation Department reservoir notices through this period but its site has returned an HTTP 403 block to this desk for some 49 consecutive days and could not be cited.
