A Provisional Physiographic Zonation of Bhutan

The concept of physiography integrates all of the maincomponents of the natural environment, such as bedrock,surface drift deposits, landform, soils, climate, water, andplants and animals. This paper summarizes the provisionalphysiographic zonation of Bhutan, based on soil surveyfieldwork by the National Soil Services Centre, with somematerial incorporated from other environmental disciplines.The main influence in shaping the landscape of Bhutan hasbeen the uplift of the Himalayas following the collision of theIndian and Asian continental plates. This has given rise tothe basic topographic structure of the country with the HighHimalaya in the north from which long ranges formed ofmetamorphic rocks run southwards and then descend steeplyto the duars. The main valleys follow more or less northsouthcourse, but show considerable variation in theirlongitudinal profiles. They all have narrow gorge-like sectionsin the South but vary in the sections upstream. In westernand central Bhutan the riverbeds have stepped profiles andthe flatter sections form Inner Valleys with relatively gentleside slopes and wide floors at altitudes ranging from 1100 mat Wangdi to 2600 m at Jakar. The rivers in the east are cutdeeper, and their valleys are narrow and steep throughout.