Kanaka river dam slowly receding

KalimNews, Mangan, 17 August 2016: Less rain has facilitated draining of the artificial dam/lake due to a landslide occurred at 'So-Bhir' cliff near Dzongu and blocked Kanaka river, a small tributary of the Teesta. 

The lake like dam was formed on 13th August in the Kanka river, a tributary of river Teesta. Due to rain water level in the dam seem to be fluctuating, it had dropped 6 ft but increased by 4 ft later after the rain. 

Water is slowly being drained out and it is hoped that it will ease the further danger to the adjoining areas of flooding. Two relief camps for villagers and affected families of Mentyam has been set up at Lingthem and Tingvong. 

So far no casualties is reported except a few injuries by falling boulders and shattering of windowpanes and submerging of a few houses. GSI estimates the landslide, which is said to be a rock avalanche to be 1km long and width 572m. 

As per reports from the site, the slide is still active with large rocks still sliding down occasionally. It was found that the base width of the natural dam formed is around 100 metres and the depth could be 200mts and hence the probability of a dam burst is low at the present juncture but it cannot be ruled out and high vigil has to be maintained. 

The landslide dam has been breached and the outflow from the dam and water levels in the lake is being monitored continuously. 

The channel appears to be eroding laterally rather than vertically and that there also appears to be large boulders in the channel that may be inhibiting basal erosion. Though the danger is not over at this site, the dam could still enter a failure mode through piping, through erosion of the downward face or through basal erosion. The dam has yet to be tested in a high flow event (and this is the monsoon season). The site needs detailed assessment and monitoring, and all should be on their guard till the blocked portion opens completely. 

It is reminded that on 13th August at around 1.30 pm, a massive landslip occurred at the 4th mile area in Upper Dzongu under Passingdong Subdivision. The entire hillside opposite Mentyam village spanning around 100 metres slide off and the debris from the slide collected over the Kanaka river creating a huge natural dam stopping the river flow. The height of the natural dam created over this river has been high enough to submerge the 200 ft high suspension bridge which connects the villages of Tingvong ,Sakyong Pentong and Lingdem in Upper Dzongu from Mangan. 

Five houses situated in the landslide vicinity in Mantyam village has been submerged and all houses in Mantyam village have been evacuated. 

Today Indian Airforce helicopters landed in Mangan Helipad with relief material consisting of food materials and other necessary items to the villagers who are in the relief camps and are in their villages but cutoff due to the landslide. Relief materials are also being collected and sent by different agencies and NGOs. * Sources: Voice of Sikkim, save the hills,