Delineation of Paleochannels in Periyar River Basin of Kerala Using Remote Sensing and Electrical Resistivity Methods

Abstract

In the present study, the paleo-river channels in the midland and coastal plain region of the Periyar and Chalakudy river basins, central Kerala, west coast of India were delineated applying remote sensing techniques and electrical resistivity methods. The river basin areas are flanked by Western Ghats in the eastern side and Lakshadweep Sea in the western side. Geologically, the area is overlain by charnockites and biotite gneiss in the midland and foothill region and fluvial and paleo-beach deposits in the western parts adjoining the sea. Laterite deposits are seen at several locations in the midland region of the basin. The main course of the river cuts across all the lithological units; the northern branch directly joins with sea and southern branch cut across older alluvial plain and reaches the Vembanad backwater system. Geomorphological mapping of the study area using IRS P6 LISS III data revealed the presence of two sets of paleochannels in the northern side of current channel of the river. The migratory trace of the river is indicated in the satellite images by the presence of meandering scars, crescent-shaped oxbow lakes in the older floodplain areas. Distinct vegetation alignment along the paleochannels is noted indicated by abrupt changes in tone and texture. Vertical electrical sounding (VES) survey was carried out at eight locations along the paleochannels demarcated. Good resistivity contrast obtained in five locations between the first and second layers. Apparent resistivity values obtained for the first layer (ρ ₁) varied from 22 to 422 Ωm with thickness ~1–2 m and the second layer (ρ ₂) varied from 5 to 80 Ωm with thickness ~2–7 m.