By yesterday evening, river levels were receding
Residents of Bjizam in Trongsa were evacuated to safety at 6.30am when rising water level of Mangdechhu triggered the automatic alarm at Jongthang, about 40km from Bjizam on the Thimphu -Trongsa highway yesterday.
Fifty adults and nine children reached the evacuation point near the school immediately after the siren.
By 3am, the automatic water level station (AWLS) at Jongthang showed that the river had reached 5.91 meters (m) and exceeded the 5.90m alert threshold.
Three hours later, the river size crossed the 7m depth, the threshold to sound the alarm, and touched 7.16m.
Jongthang is the first monitoring station of Mangdechhu. The next station is at Bjizam. However, water level at Bjizam station remained within the safety limits at 4.2m by 7am.
Following forecast of heavy rainfall, officials said that they expected most rivers to swell. However, Mangdechhu rose more than their expectations.
The residents returned to their homes by yesterday evening as the water level showed no sign of rising.
An engineer with the National Centre for Hydrology and Meteorology (NCHM), Sangay Tenzin said that at the alarm level, the river does not inundate the place.
“However, any slight increase from this point will lead to inundation and the people downstream will not have enough time to evacuate,” he said. “Should Glacial Lake Outburst Flood occur at such times, then the situation could be out of control.”
When the river level rises to alert level, all stakeholders including the hydropower plants that are downstream of the rivers and respective dzongkhag administrations along the river basins are warned.
At the alarm level, people are evacuated from areas of potential flooding as indicated in the standard operating procedures.
Meanwhile, both Phochhu and Mochhu rose and has entered the alert level. The AWLS at Dangsa upstream of Phochhu reported water level of 5.54m at 3.45am and Mochhu rose to nine meters at Tashithang AWLS at 12.30am almost touching the alarming level. Both rivers remained in alert stage throughout the day.
The two rivers merge at Punakha and flow down the basin as Punatsangchhu, which was also at the alert level.
The river inundated a brick factory and the Natural Resources Development Corporation Ltd’s sand dredging area near the Wangdue bridge.
The water level of Mangdechhu at Jongthang remained at 7.11m by 8pm yesterday. However, no damage was reported from Mangdechhu hydro power plant.
Officials from Department of Disaster Management and Department of HydroMet met yesterday afternoon to assess the situation. Prime Minister Tshering Tobgay and home secretary Sonam Topgay also attended the meeting.
Senior program officer at the disaster information unit, Jigme Chogyal said residents along both the Punatsangchhu and Mangdechhu basins have been prepared well to respond to a flood situation. “Residents in Bumthang had moved to evacuation points when the siren due to a technical fault went off last year.”
He said that the disaster management response teams helped the families of the brick factory in Wangdue to salvage their properties,” he said.
Trongsa disaster management officer, Jamyang Chojay said the residents moved to their evacuation point without any trouble and panic.
“They’re prepared through mock drills and had drawn evacuation plans, so everyone was ready,” he said.
Meanwhile, Mochhu subsided below the alert level to 9.55m, while Phochhu still remained in the alert level measuring 5.59m at 8pm yesterday.