Appraisal of Geomorphic Diversity with Special Reference to Basin-Area Extremity in Central Lesser Himalaya

Abstract

The standard for the selection of two fourth order watersheds for intensive geomorphic study was extremity in basin-area to assess diversity in between two watersheds in regard to their geomorphic environment. The diversity in geological traits reveals that the Phalal watershed was characterized by contact zone of two lithological formations (Augun gneiss 95% and Rautgara quartzites 5%) separated by north Almora thrust (NAT) while the entire Siya watershed was developed only in one formation, i.e. Rautgara (quartzites) Formation. The diversity in geomorphometric personality and geomorphic evolution speaks of a differential development of both watersheds in context of stage of erosion. The zone of critical-height above which the erosion is acute is 1700 to 1800 m in Phalal watershed, whereas 1500 to 1600 m in Siya watershed; the hypsometric integral determines Phalal watershed (49.96 %) under middle-mature stage while Siya watershed (57.07 %) achieved early-mature stage. Diversity in erosion status was observed along the varying altitudes of the watersheds under different land use/cover. Diversity in the spatial distribution of altitude, erosion intensity, average slope versus land use/cover status under both watersheds determines the impact of basin-area extremity. The hazardous geomorphic processes also indicate the impact of basin-area extremity as eleven types of geomorphic hazards were experienced by the Phalal watershed while only four types of hazards were experienced by Siya watershed. Phalal watershed was 18.42 % hazardous area while 21.04 % hazardous area was possessed by Siya watershed. The hazard of ‘surficial erosion’ covers maximum area, i.e. 13.78 % in Phalal watershed while 20.52 % area is possessed by Siya watershed. Likewise maximum study units attained degree 4 instability for Phalal watershed (80%) while degree 2 instability for Siya (50%) watershed. Thus, basin-area has direct posture on geological traits, geomorphic evolution, geomorphometric personality and hazardous geomorphic processes while land use/cover status has no bearing on basin-area extremity under the studied watersheds.