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Sediment storage and release from Himalayan piggyback basins and implications for downstream river morphology and evolution.

Densmore, A.L. and Sinha, R. and Sinha, S. and Tandon, S.K. and Jain, V. (2016) 'Sediment storage and release from Himalayan piggyback basins and implications for downstream river morphology and evolution.', Basin research., 28 (4). pp. 446-461.

Abstract

Piggyback basins developed at the mountain fronts of collisional orogens can act as important, and transient, sediment stores along major river systems. It is not clear, however, how the storage and release of sediment in piggyback basins affects the sediment flux and evolution of downstream river reaches. Here we investigate the timing and volumes of sediment storage and release in the Dehra Dun, a piggyback basin developed along the Himalayan mountain front in northwestern India. Based on OSL dating, we show evidence for three major phases of aggradation in the dun, bracketed at ~41-33 ka, 34-21 ka, and 23-10 ka, each accompanied by progradation of sediment fans into the dun. Each of these phases was followed by backfilling and (apparently) rapid fan-head incision, leading to abandonment of the depositional unit and a basinward shift of the active depocentre. Excavation of dun sediment after the second and third phases of aggradation produced time-averaged sediment discharges that were ~1-2% of the modern suspended-sediment discharges of the Ganga and Yamuna rivers that traverse the margins of the dun; this sediment is derived from catchment areas that together comprise 1.5% of the drainage area of these rivers. Comparison of the timing of dun storage and release with upstream and downstream records of incision and aggradation in the Ganga show that sediment storage in the dun generally coincides with periods of widespread hinterland aggradation but that late stages of dun aggradation, and especially times of dun sediment excavation, coincide with major periods of sediment export to the Ganga Basin. The dun thus acts to amplify temporal variations in hinterland sediment supply or transport capacity. This conceptual model appears to explain morphological features of other major river systems along the Himalayan front, including the Gandak and Kosi Rivers, and may be important for understanding sediment flux variations in other collisional mountain belts.

Item Type:Article
Keywords:Himalayas, Ganga River basin, Sediment transport, Sediment storage, Erosion, Intermontane valley.
Full text:(AM) Accepted Manuscript
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Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1111/bre.12116
Publisher statement:This is the accepted version of the following article: Densmore, A. L., Sinha, R., Sinha, S., Tandon, S. K. and Jain, V. (2016), Sediment storage and release from Himalayan piggyback basins and implications for downstream river morphology and evolution. Basin Research, 28(4): 446-461, which has been published in final form at http://dx.doi.org/10.1111/bre.12116. This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.
Date accepted:16 January 2015
Date deposited:28 January 2015
Date of first online publication:06 March 2015
Date first made open access:06 March 2016

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