SEQUENCE OF VALLEY DEVELOPMENT OF ALAKNANDA AND ITS TRIBUTATIES & QUATERNARY SEDIMENTATION, GARHWAL HIMALAYA, PARTS OF CHAMOLI TEHRI UTTAKASHI & PAURI UTTAR PRADESH (UTTRARKHAND STATE) INDIA

The sedimentological study in Alaknanda and its tributaries in upper Ganga basin has been attempted in parts of de Uttarkashi,Chamoli, Pauri and Tehri districts in parts of QA sheet 53Jand 53 N on 1:50000 scale of Garhwal Himalaya U.P presently known as Uttrakhand State of Union of India. The area of Upper Ganga basin consisting of Alaknanda,Bhagirathi,Bhilangna, Nandakini, Mandakini, Pindar, Dhauli- Ganga Bal- Ganga , Madhmeshwar Ganga and Berhi Ganga The Alaknanda is characterized by six terraces AT1_AT6 followed by Bhagirathi with five terraces BT1_BT5, Bhilangna BHT1_BHT4 Nandakini four terraces NT1_NT5, Mandakini MT1_MT6 /Pindar PT1_PT3 /Dhauli-Ganga DGT1_ DGT3 /Balganga three terraces BGT1, to BGT3, Madhmshwar Ganga MDT1, to MDT2Ganga two terraces and Berhi Ganga one terrace BRT1, amidst these Alaknanda is trunk stream and others are tributaries. The sequence of valley development and Quaternary sedimentation in Alalknanda and its tributaries is established in stratigraphic sequence has been attempted for the first time. The area genetically comprised of terraces of three domains, viz. Glacial, Fluvio-glacia and Fluvial which represent distinct environment of sedimentation of Pleistocene, late Pleistocene and Holocene time during Quaternary period. The Glacial terraces are identified at an average elevation of 1150 m above MSL, the fluvio-glacial terraces at an average elevation of 975m above MSL and fluvial terraces at an average elevation between 650 to 900 m above m.s.l, type area is attempted in to understand the nature of Quaternary sedimentation in these valleys in increasing antiquity. The statistical parameters of sediment of fluvial terraces of Alaknanda revealed tha the average mean size for AT1 is 1.550 Ø (medium sand) and it varies from -0.3240 Ø to 2.250Ø (coarse sand to fine sand), for AT2 average mean size is -0.5350Ø (coarse sand) and it ranges from -1.742Ø to 1.565Ø (very coarse to medium sand),AT3 the average value is 1.760Ø whereas it ranges between -0248 to 2,650 Ø The average and range values of means size of Alaknanda terraces (ATo to AT3) predominantly consist of both coarser and finer sediments, whereas younger terraces (ATo to AT1) primarily consist of very fine sand. The mean size of sediment in sequence of terraces except in AT2 has strong tendency to decrease in decreasing antiquity i.e. from AT3 to AT1 towards the younger terraces. The progressive increase of finer sediments towards younger terrace revealed the constant and steady decrease in load carrying capacity of Alaknanda from early to late history of river sedimentation. The anomalous values of mean size in the terrace AT3 indicate sudden reactivation in energy condition of the channel system during sedimentation perhaps due to tectonic dislocation in watershed region of Alaknanda which is also manifested in disposition of sediment in vertical column of AT3 terrace in the valley. The average value of standard deviation for terrace AT0 is 0.3740 Ø (well sorted), whereas it varies from 0.2530 to 0.4665Ø (well sorted). The average value for AT1 is. 0.3.320Ø it ranges from 0.255 Ø to 0.440 Ø, average value for AT2 – AT6 is 0.3.35 Ø and it varies from 0.348 to 0.555 Ø . The average value for terrace AT3 is 0.6120Ø (moderately sorted) and it varies from 0.540 Ø to 0.710Ø (moderately sorted). The average and range value of (S) indicate that sediments are poorly sosource.