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P. Kotoky ¹, Baby Baruah ¹, R. Borgohain ²

Affiliations
1 Regional Research Laboratory, Jorhat-785 006, Assam, IN
2 Department of Applied Geology, Dibrugarh University, Dibrugarh-786 004, Assam, IN

Abstract

X-ray diffraction (XRD) and infrared (IR) spectral analyses of the Lakadong Limestone, Meghalaya indicate calcite as its dominant mineral phase. Association of dolomite at the base and presence of silica at the top of the sequence is evidenced from the spectra. A significant relationship between CaO content and the peak intensity of IR-spectra is found and needs standardisation before it can be utilised for rapid estimation of quality of limestone and can be an alternative for different time consuming analytical procedures. Stable isotope of δ¹³C {0.63 to 1.12‰( av.0.87±0.01‰)} points to enrichment of heavier C isotope and δ¹⁸O values {-7.34 to-10.55‰ (av.-9.06±0.01‰) ) to lighter O isotope enrichment. Isotopic grid analysis confirms the marine origin for the limestone. Biochemical fractionation along with diagenetic reorganisation might have played critical roles in controlling the isotopic ratios of this limestone.

Keywords

Geochemistry, Palaeocene, Limestone, Stable Isotope, Lakadong, Meghalaya.

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D. Bezbaruah ¹, P. Kotoky ¹, J. Baruah ¹, J. N. Sarma ²

Affiliations
1 Regional Research Laboratory, Jorhat - 785 006, IN
2 Dibrugarh University, Dibrugarh - 786 004, IN

Abstract

Wetlands are conspicuous features of the Rood plains along the Brahmaputra River, Assam. The sequential change in numbers and areas of wetlands (Bils) for a stretch of 260km have been studied using available topographic maps of the Survey of India (1914,1975) and Indian Remote Sensing satellite imagery (1998). The total number of swamps as evident from the study was 529 in 19 14,783 in 1975 and 781 in 1998. Moreover, total areas covered by the wetlands as observed was 93.73 km² in 1914, 161.23 km km² in 1975 and 182.73 km km² in 1998. The low lying nature of the basin, shifting of river channels in a relatively short span of time, associated tectonics of the region and allogenic processes in relation to flood control measures adopted have played a major role in extensive changes to the wetlands over this period. The data presented here aid in formulating an effective flood control strategy to be adopted for this perennial flood prone area, stabilisation of landforms and different wetland management approaches.

Keywords

Gepmorphology, Swamp, Floodplain, Brahmaputra River, Assam.

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P. Kotoky ¹, M. K. Dutta ², R. Goswami ², G. C. Borah ³

Affiliations
1 North East Institute of Science and Technology(NEIST- CSIR), Jorhat –785 006, IN
2 Jorhat Engineering College(JEC), Jorhat -785007, IN
3 North East Institute of Science and Technology(NEIST-CSIR), Jorhat –785 006, IN

Abstract

The bank sediments along the extremely meandered Dhansiri River channel, a south bank tributary of the mighty Brahmaputra River, with erosion potentiality have been investigated to evaluate its certain geotechnical characteristics. The study has shown that the bank sediments are basically composed of CL and ML types of soil. These types of sediments are very much prone to liquefaction which in turn related to erosion susceptibility. The bank stability analysis has differentiated the studied stretch into unstable, at risk and stable zones. Most of the erosion affected zones along the channel reach under study are located within the unstable or at risk zones. The field study around Butalikhowa, Barguriagaon, Golaghat and Duchmuagaon areas along the channel with active erosion activity has supported our contention and practical utility of the present study. It is expected that such type of study will help in providing certain inevitable baseline information for various channel management practices for this extremely flood prone areas of Northeast India.

Keywords

Bank Sediments, Geotechnical Properties, Dhansiri River, Erosion, Assam.

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P. Kotoky ¹, M. K. Dutta ², G. C. Borah ¹

Affiliations
1 North East Institute of Science and Technology (CSIR), Jorhat - 785 006, IN
2 Jorhat Engineering College, Jorhat - 785 007, IN

Abstract

Information on landuse/landcover change is a critical input for natural resource management policy decisions. Remote sensing data under GIS domain were utilized to evaluate the changes in land-use/land-cover (LU/LC) spanning a period of thirty three years during 1975 to 2008 along the Dhansiri River channel, Assam, India. Seven different types of LU/LC were categorized and out of them cropland was evident as the most important landuse/landcover practices followed by dense mixed jungle in 1975 and the settlement in 2008. Significant reduction (13.02%) in cropland area to settlement was observed. Moreover, teagarden also occupies 0.77% of the total area from cropland and open mixed jungle. The changes in the areas of swampy land as evident from the present study in turn will impact the environmental quality around it and will help to increase the surface run off leading to enhancement of erosion processes. It is believed that the present study will help to contribute towards sustainable land-use planning and management towards protection of extremely rich biodiversity of the North East India with mighty Brahmaputra River system.

Keywords

Landuse, Landcover, Remote Sensing, GIS, Dhanasiri River Channel, Assam.

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