Identification of hydrologically sensitive areas in Valanchery watershed

Abstract

Soil erosion poses a significant threat to agricultural productivity and environmental sustainability, particularly in vulnerable watersheds. This study aims to identify Hydrologically Sensitive Areas (HSAs) within the Valanchery watershed in Kerala, India, to propose targeted soil and water conservation interventions. A total of 19 soil samples were collected across various land use types and analyzed for key physical properties, including bulk density, specific gravity, organic matter content, soil texture, and hydraulic conductivity. Spatial distribution maps of the soil properties were generated using Inverse Distance Weighting (IDW) in ArcGIS. The study employed digital elevation models (DEMs) to calculate the Topographic Wetness Index (TWI) and Soil Topographic Index (STI), critical for delineating HSAs. Results revealed that areas with STI values above 9 were prone to high runoff and erosion, typically concentrated along drainage lines and valley bottoms. Overlay analysis of Land Use/Land Cover (LULC) and STI maps indicated that paddy fields, barren lands, and mixed vegetation in these zones are most vulnerable. Accordingly, conservation measures such as contour bunds, percolation pits, agroforestry, and check dams are recommended based on IMSD guidelines. This study provides a replicable geospatial framework for erosion risk assessment and soil conservation planning in similar agroecological settings.