Tectonic geomorphology in parts of Koyna region, Maharashtra

Abstract

Geomorphic signatures in parts of Koyna region were analysed using satellite images and morphometric indices (stream length gradient index and valley width to height ratio) with limited field checks in key areas for understanding the role of tectonics in this seismically active zone. The Koyna River zone, particularly downstream of Koyna dam wall up to Kajali Nadi, is characterised by incised narrow valleys, steep escarpments and structurally controlled drainage. Presence of knick points at consistent elevations between 825 m to 675 m, steep gradients in an otherwise gradual longitudinal profile and valley width to height ratio less than 1.0 suggest readjustment of the streams along NW-SE and N-S directions. The escarpment slopes in general have en echelon arcuate ridge pattern ∼ N45°-N 225° in the western part, and then becomes ∼N 10°- N 190° near Donachiwadi, almost orthogonal to the E-W Koyna River. The Donachiwadi fault runs parallel to the escarpment slopes observed near Kodoli. The fluvial system in Koyna thus indicates rejuvenation controlled by basement propagated structures.