Terrain response to the extreme rainfall event of June 2013: Evidence from the Alaknanda and Mandakini River Valleys, Garhwal Himalaya India

Abstract

The present study is based on the field observations and geochemical analyses of flood sediments to ascertain the nature and causes of destruction in the Mandakini and Alaknanda river valleys during June 2013. The study suggests that the sediments were contributed from two major sources: the moraines and alluvial fans located in the Trans and Higher Himalaya; and the landslides in the Higher and Lesser Himalaya. Although the flood was the result of a high intensity rainfall event, the magnitude was increased due to the proliferation of settlements along the river and a series of partially constructed barrages on the river bed. Geochemical analyses of the flood sediments indicated that the contribution of power-project generated debris locally enhanced the flood magnitude. Further, the study argues that the terrain north of the Main Central Thrust (Higher Himalaya) should be kept free from major interventions, including hydropower projects, to reduce flood hazards. The study finally calls for a critical reevaluation of current development policy and the approach towards harnessing the enormous hydropower potential of the Himalayan rivers in general and in the Uttarakhand Himalaya in particular.