Thrust Related Mid-Channel Bar Formation in Gravelly Rivers: An Example from the Darjeeling Himalayan13; Fold-and-Thrust Belt, West Bengal, India

Mukul, Malay (1999) Thrust Related Mid-Channel Bar Formation in Gravelly Rivers: An Example from the Darjeeling Himalayan13; Fold-and-Thrust Belt, West Bengal, India. Technical Report. CMMACS/ National Aerospace Laboratories, Bangalore, India.

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    Abstract

    The Birrik and the Kalijhora thrust faults cut across the river Teesta in the foothills of the Darjeeling Himalayan fold-and-thrust belt and affect the morphology and the13; sedimentology of the turbulent and gravelly river. Tectonic activity along these thrust faults raises the hanging wall or the upstream side of river bed relative to the footwall or the downstream side and causes flow-separation bubbles to form both upstream and downstream of the thrust-related uplift of the river bed. The separation bubbles consist of a highly turbulent and sluggishly recirculating separated flow which results in deposition of the sediments being transported by the river. The initial deposition of these sediments occurs near the centre of the channel because the coarsest sediments are usually transported along the centre of the channel due to less friction and high flow velocity there. The deposited13; sediments act as nuclei for further deposition of sediments resulting in the formation of both upstream and downstream mid-channel bars which may grow and merge with continued activity along the fault. These thrust-related mid-channel bars are triangular in shape and13; taper downstream. They grow in size as long the associated thrust fault is active and are reduced in size through erosion once activity along the fault ceases. The river may also be ponded into a reservoir upstream of the fault zone when the uplifted river bed comes close to the water surface and the river flow is arrested. The reservoir is drained once the river erodes through the uplifted barrier after activity along the fault ceases. An analysis of these thrust related features along the river Teesta reveal that the Birrik thrust is active while the13; Kalijhora thrust is not indicating that the deforming wedge is probably building taper in the region by out-of-sequence thrusting along the Birrik thrust.

    Item Type: Proj.Doc/Technical Report (Technical Report)
    Uncontrolled Keywords: Thrust belt;Mid-channel bar;River;Himalayan fold
    Subjects: GEOSCIENCES > Geosciences (General)
    Division/Department: CSIR Centre for Mathematical Modelling and Computer Simulation
    Depositing User: Mr. Ravikumar R
    Date Deposited: 17 Jul 2006
    Last Modified: 24 May 2010 09:44
    URI: http://nal-ir.nal.res.in/id/eprint/1910

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