AUGMENTATION OF WATER RESOURCES AT WELLINGTON, TAMIL NADU-INTEGRATED GEOPHYSICAL INVESTIGATIONS FOR ITS PROPOSED DAM: Fid-Bau Portal

AUGMENTATION OF WATER RESOURCES AT WELLINGTON, TAMIL NADU-INTEGRATED GEOPHYSICAL INVESTIGATIONS FOR ITS PROPOSED DAM

Ramteke, R. S. / Venugopal, K. / Ghosh, N. / Krishnaiah, C. / Panvalkar, G. A.

A 12 m high and 112 m long earthen dam was proposed to be constructed for augmenting surface water resources at Wellington, Coonoor district, Tamilnadu. For designine the foundation, the quality of sub surface formation was to be assessed and the geologically weak structures were to be delineated. As the topography of the area is not plane and also as thick lateritic formations are capping the deep-seated charnockite (bed rock), use of two different geophysical methods viz 1. Seismic Refraction and 2. Electrical Resistivity, was necessitated. The results of these two geophysical surveys have been integrated while characterizing the foundation. Two continuous seismic profiles along the proposed dam axis and four vertical electrical soundings in its reservoir bed were taken. The results revealed a four-layered stratum. The compressional wave velocities vary from 330 m/sec to 3345 m/sec and the resistivities from 22 ohm-m to 907 ohm-m. The low velocity and resistivity values (330 m/sec and 22 ohm-m respectively) are attributed to a loose and soft formation and their higher values (3345 m/sec and 907 ohm-m respectively) are attributed to a compact and hard formation. The depths of different geological layers obtained from these results were also co-related well with the borehole litho-logs. No geologically weak structures have been identified in the area by these investigations. The presence of compact formation and the absence of geologically weak structures at the site are favourable for founding the proposed structure.