Unplanned sewage tanks led to land subsidence in Nalagarh villages

Ambika Sharma

Solan, September 26

Unplanned sewerage put in place by owners of individual houses in Nalagarh villages reportedly triggered land subsidence as the soil got saturated following heavy rain recently.

The construction of sewage tanks led to soil compaction, altered the groundwater flow pattern and exacerbated landslides in various villages of Nalagarh subdivision.

Observations by Mining officer

• House owners in Nalagarh villages have constructed individual sewage tanks on their premises, which are also used for the disposal of waste water
• Prolonged torrential rain saturated the soil below these sewage tanks, reduced its cohesion and triggered slope failures
• Most of the damaged houses were found tilted towards the sewage tanks on the premises

These observations have been made by Assistant Geologist-cum Mining Officer Dinesh Kumar, who examined the land subsidence cases in several villages in the subdivision. “Prolonged torrential rain saturated the soil below sewage tanks, reduced its cohesion and this triggered slope failures at places like Rug Docchi village in Manlog Kalan panchayat of Nalagarh,” he said.

Seven of the 11 houses were badly damaged. The damage began from the edge of a vertical slope along the Gamrola khud. Heavy rain eroded the toe of the hill, thus posing a risk to nearby habitations.

“Most of the damaged houses were found tilted towards the individual sewage tanks, which are also used for the disposal of waste water. Prolonged torrential rain saturated the soil below, thus reducing its cohesion and triggering slope failures,” observed Dinesh Kumar.

To prevent such incidences, the sewage from the village should be scientifically treated to prevent groundwater related inundation, he said.

As a precaution, early warning systems on rainfall monitoring and groundwater level measurement should be put in place in landslide-prone areas. “The residents should be alerted whenever rainfall exceeds 200 mm. As against the usual rainfall of 200 mm this season, the average rainfall in Solan was about 600 mm,” he added.

To prevent further damage, suggestion to erect step crate walls from the hill toe along the Gamrola Khud bank towards the Rug Docchi village should be undertaken.

The landslides at this village have impacted 50-70 houses, forcing the residents to shift to safer locations along with their cattle. To check further erosion of the hill, the flow of the khud should be diverted from the toe of the hill. Motors should be installed in nearby borewells to drain out excessive groundwater.

The residents were awaiting initiation of restoration measures by the state government in various affected villages. A report has been sent to the Director (Industries). The situation would be further examined by the state government to recommend remedial measures.