Dams in Distress

Dudhava Dam across Mahanadi developed foundation trouble in the very first year of its construction. The downstream became slushy and ‘boils’ were noticed. The condition was opined as potentially dangerous and the reservoir was not allowed to fill. It was found that the presence of a deep column of sand in the foundation and lack of positive cut-off were the main causes of the trouble. During construction, portions of the natural clay cover on the upstream had also been dug out exposing the sandy bed. All these led to interconnection between upstream and downstream. Remedial measures consisting of drilling deep relief wells near the downstream toe and providing an elaborate drainage system were carried out in consultation with the C.W. & P.O. The reservoir was filled during the rains of 1967 and is behaving very well.

In April 1961 the 21-3 m. (70 ft.) high Sampna Dam in Madhya Pradesh suffered a heavy slip. The Government appointed an Enquiry Committee which came to the conclusion that the casing soil used had high clay content and proved unequal to the slopes adopted. As the soil was not self-draining, water remained locked resulting in high pore pressure under drawdown conditions. The damaged portion was repaired with a flatter slope. Three years later a second slip occurred. A one man Enquiry Committee found the causes of failure the same as on the first occasion. Now the reconstruction of the whole dam with a flatter slope is being taken up.

Kedarnala Dam in Raigarh District burst in the first year of its filling during a heavy downpour. The same one man Enquiry Committee investigated into the causes of its failure. Its report is under consideration of Government.

The author has been intimately associated with the postconstruction behaviour and treatment of all these dams. In this paper he has presented the story of these dam accidents with a view to highlight the technical and constructional inadequacies of earthen dams and the manner in which those can be tackled.