Brahmaputra Plain Research Articles

A novel approach to flood risk assessment: Synergizing with geospatial based MCDM-AHP model, multicollinearity, and sensitivity analysis in the Lower Brahmaputra Floodplain, Assam

Floods persist as a recurring and daunting peril in the Brahmaputra plain of Assam. Notwithstanding advancement, Bongaigaon is a highly flood-afflicted district in the lower part of this region, inflicting significant damage to both lives and property almost every consecutive year. Hence, the delineation of precise and reliable flood risk susceptibility zones within the district constitutes the foremost concern of the study. The present work considered a total of sixteen multi-collinearity free parameters integrating with the GIS- based Multi-Criteria Decision Making-Analytical Hierarchy Process (MCDM-AHP) model for identifying potential flood hazard zones (FHZ), flood vulnerability zones (FVZ), and flood risk zones (FRZ) for the region. The result revealed that over 28% of the district's total area falls under the high to very high flood risk zone. Srijangram circle covers the highest flood risk zone with 343.19 sq. km. The FHZ map of the district demonstrated reliability exceeding 90% in ROC-AUC and below 40% in MSE and RMSE. Additionally, sensitivity analyses depict the role indicators in the predictive model, placed as a virgin gap for study in the region. Moreover, a multivariate correlation statistic is used to examine the potential risk zones and temporal flood effects on different Revenue Circles (RC), showing R2 over 0.6 in each category. The robustness of this model manifests sensible findings, aiding in fortifying sustainable flood management strategies to mitigate risks at different levels. Strategies adopted here contain greater potential for current as well as future trends in similar domains of research. This study may provide invaluable insights for decision-makers, thinkers, administrators, and developers working in this region.

Deciphering the role of late Quaternary sea level fluctuations in controlling the sedimentation in the Brahmaputra Plains

Continent-continent collision between Eurasian and the Indian plate during the Cenozoic period lead to the formation of the Himalayan Mountain chain and the development of the Indus-Ganga-Brahmaputra foreland basin to the south. Complex climate-tectonic interactions in this orogenic belt are responsible for the rapid erosion and filling of the Indus-Ganga-Brahmaputra foreland basin with the eroded materials. This study based on geomorphic mapping, lithofacies analysis, and geochemical (Strontium-Neodymium i.e., SrNd analysis) provenance characterization, as well as optically stimulated luminescence (OSL) ages, provides a dated sedimentation framework for the western Assam lowland areas. The dated relict fan surface lies ~40 m above mean sea level (msl), is incised and forms a regional valley terrace T1 composed of meandering channel deposits. Modern braided rivers flow on the T0 surface. The findings suggest that the alluvial fan is composed of three distinct lithofacies associations and aggraded during 27 to 3 ka. The bottom-most gravelly-sandy facies indicates progradation of the fan during the last glacial maximum (LGM), owing to the increased gradient of the Himalaya bound rivers. The middle facies is a sheet flood deposit which formed during the Latest Pleostocene-early Holocene period with rising sea level and increasing precipitation. During the Mid-Late Holocene, the uppermost facies is deposited as rivers lost their gradient in response to high sea level stand, resulting in inland sedimentation within muddy meandering channels. Our analysis found that falling sea level during the late Holocene was associated with greater precipitation and allowed the river to incise, to form gullies over the fan surface and form the valley terrace T1. The SrNd isotope fingerprints have been used to identify varying fan sediment sources in the Himalaya's southern front (i.e., Lesser and Higher Himalaya) as a function of changing monsoon conditions.

Avulsion distribution on rivers in the Himalayan foreland region

ABSTRACT Despite recent advances, we still do not have a synoptic dataset on river avulsion across a mountain foreland belt. Here we report a novel account of chronological avulsion records (for the period 1990–2019) across the Himalayan foreland region (HFR), one of the largest and most avulsion-hit areas in the world. The chronological records discerned river avulsion frequency and distribution across HFR. We identified the eastern Brahmaputra plains as amongst the most avulsion-affected areas in HFR. As many as 19 tributaries across HFR have recorded ≥ 6 avulsion events. Most of these avulsion-affected rivers are smaller, with hilly catchments < 500 km2. These avulsions often occurred near the proximity of the Himalayan front. Transitional reaches (and adjacent braided/meandering sections) of the tributaries have experienced higher avulsions. Observation suggests that the 1950 Assam earthquake, non-incised channels, and rapid transition in tributaries’ morphologies are decisive in the region’s frequency and distribution of river avulsions.

Hydrogeochemical assessment of groundwater quality for drinking and irrigation in Biswanath and Sonitpur district of the Central Brahmaputra Plain, India

In recent times, the contamination of groundwater in the north-eastern states of India has become a reason for concern. The lack of appropriate irrigation water management hinders the practice of sustainable agriculture. Hence, it is vital to understand the groundwater quality for the proper planning and management of groundwater resources to ascertain its use for drinking and irrigation purposes. This study was conducted in the districts of Biswanath Chariali and Sonitpur, Assam, India, to evaluate the groundwater quality and its suitability for irrigation and drinking purpose. Fifty-six water samples were collected from various sources across the two districts and analyzed for general physicochemical parameters and heavy metals namely arsenic (As) and iron (Fe). Groundwater suitability was evaluated by comparing the results of the physicochemical analysis with Indian Standards, and the results revealed the mean concentrations of the cations were observed in the order Na+&amp;gt;Ca2+&amp;gt;Mg2+&amp;gt;K+ whereas the anions in the order of HCO3-&gt;Cl−&amp;gt;SO42-&gt;PO43-. Furthermore, several parameters were considered for assessing the groundwater suitability for irrigation namely sodium adsorption ratio (SAR), sodium percentage (Na%), magnesium adsorption ratio (MAR), permeability index (PI), and Kelly's index (KI). All parameters suggested the water to be suitable for irrigation except for MAR values which implied unsuitability. Moreover, high Fe and As were detected with 95 and 25% of the total, respectively, exceeding the WHO permissible limit for drinking water. The highest concentration of As (0.08 mgL−1) was observed in Tewaripal, Biswanath Chariali, and Fe (32.20 mgL−1) in Gereki, Biswanath Chariali. Gibbs plot discerned the aquifers' underlying hydrogeochemical processes such as silicate, carbonate, ion exchange, and reverse ion exchange processes predominated the region. A significant positive correlation was observed between As and PO43- which may indicate a common source of origin for both and maybe pinpoint the contribution of anthropogenic activities toward As enrichment. Overall, the study revealed that although the groundwater is apt for irrigation in regard to SAR, Na%, MAR, PI, and KI, however, As and Fe concentrations suggest otherwise. The outcome of the study may be helpful to the farmers, and policymakers in planning and management of the groundwater resources.

Hydrogeochemical analysis of groundwater quality for drinking and irrigation with elevated arsenic and potential impact on agro-ecosystem in the upper Brahmaputra plain, India.

The upper Brahmaputra floodplain is considerably enriched with geogenic contaminants, mainly Arsenic (As) exhibiting high spatial heterogeneity. With this concern, the present study was conducted in Lakhimpur district located in the upper Brahmaputra floodplain aiming to assess the groundwater (GW) suitability for drinking and irrigation. Chemical analysis of 78 GW samples revealed significantly high As (max 0.12 mgL-1, mean 0.02 mgL-1) followed by iron (max 62.2 mgL-1, mean 19.94 mgL-1) showing uneven distribution. Hydrogeochemical analysis of the GW samples revealed that majority of the water samples belong to mixed Ca2+- Na+- HCO3- type with weathering and forward ion exchange as the dominant processes in the aquifer system. Positive correlation among iron (Fe) and As, together with close grouping in hierarchical cluster analysis and principal components analysis, indicated the involvement of reductive hydrolysis process. Calculation of saturation indices indicated that, precipitation of Fe minerals may lead to de-coupling of Fe and As contributing to the enrichment of both the elements in the GW. Further, assessment of key parameters for irrigation water quality including water quality index indicated the GW to be suitable for irrigation purpose. Finally, toxicity implications of crops produced from As contaminated water indicated higher accumulation potential of As in the food grains implying significant impacts on the agro-ecosystem and associated health hazards.

Channel evolution of the Himalayan tributaries in northern Brahmaputra plain in recent centuries

Channel evolution of the Himalayan tributaries in northern Brahmaputra plain in recent centuries

Geospatial differences among natural regions in the utilization of maternal health care services in India

BackgroundThe chances of a woman dying or becoming disabled during childbirth are closely connected to her socioeconomic status, cultural norms and values, and her home's geographical remoteness. Most of the studies were undertaken to address the issue of accessibility of the hospital's location and its impact on utilization of maternal healthcare utilization. Some studies also attempted to understand the pattern of utilization of healthcare utilization according to administrative and political regions. ObjectivesThis study aims to identify the Geographical differences in the utilization of maternal health services in India according to geographical regions, caste, religion, wealth status, and place of residence. Data and methodsData for analysis was taken from the National Family Health Survey-4 (2015–16). Data management and analysis were performed using statistical software Stata 13.0. To identify the regional differences in the use of maternal healthcare services, study used the 75 th round of NSS's classification of India into 88 natural regions. Regional variations in the usage of maternal health care were plotted using ArcGIS 10.5, and the bivariate method. ResultsResults shows that the utilization of partial ANC ranges from 33.8% to 91.9%. Utilization is lowest in the Northern Kerala region (33.8%) and, in ascending order, higher in Lakshadweep (34.4%), Goa (36.2%), Puducherry (43.1%), Southern Kerala (43.4%), Inland Tamil Nadu (44.5%), and Andaman and Nicobar Island (46.2%), the mountainous region of Jammu and Kashmir (46.7%), Coastal northern Tamil Nadu (49.9%) and Eastern Maharashtra (51.6%). Institutional delivery was the highest in Northern Kerala (100%) and lowest in the Nagaland (35.7%). Near-universal institutional delivery was also found in Southern Kerala (99.9%), Puducherry (99.9%), Coastal Northern Tamil Nadu (99.6%) and Lakshadweep (99.2%). ConclusionsDifferences in the utilization of MCHS by women can be seen among India's natural regions. Utilization is lagging in the Himalayan Mountain ranges, areas with dense forest cover, the Ganga and Brahmaputra plains, and the Desert region of Rajasthan.

Assessment of the tectonically induced Quaternary landforms and active deformation in the area between Main Boundary Thrust and Himalayan Frontal Thrust, south of the Siang Antiform, Arunachal Himalaya, India

The present study area represents one of the active segments of the frontal part of the Arunachal Himalaya. The major structural boundaries traversing the area are the Main Boundary Thrust (MBT) and the Himalayan Frontal Thrust (HFT) and other local faults are tectonically active, as evident from the landforms that evolved in the fault zones. Strath terraces and uplift fluvial terraces are observed in the hanging‐wall block of the HFT and MBT, and along the HFT straight to curvilinear mountain fronts are observed. Normal faults both transverse and parallel to the strike of HFT are observed in the hanging‐wall block of the HFT. West of Pasighat the sub‐Himalaya terrain resembles a duplex, where there is gradual rise in elevation from the Brahmaputra Plain to the low‐lying hills of the sub‐Himalayan and sudden rise in elevation across the MBT. Drainage aligning to the bedrock structures and stream migrations are observed in the fault zones. Along the MBT, the sub‐Himalayan rocks are thrusted over either by quartzite or black carbonaceous shales, in some sections the MBT is behaving as a back‐thrust that dips towards the south. The MBT has also been displaced by almost N–S‐trending transverse faults where highly sheared bedrocks are also observed. Tilting of Quaternary fluvial deposits are observed in the hanging‐wall blocks of intraformational thrusts at two locations. Signatures of paleoseismic activities in the form of various soft‐sediment deformational structures are observed in Quaternary deposits in the HFT zone and also in the hanging‐wall block of the MBT. To determine the deformation and strain rate accumulation, we have re‐analysed the available GNSS results of the area, which indicate a deformation rate of up to 16 mm/year in the vicinity of the Pasighat region. The GPS‐derived deformation rates are well corroborated with the existing results of peak ground acceleration (PGA) anomalies. The component–wise motion indicates higher fault perpendicular motion in this part, which reveals an accumulation of more strain along the major Himalayan faults.

Regional variation of drought parameters and long-term trends over India using standardized precipitation evapotranspiration index

Analysing historical drought pattern is vital for implementation of efficient drought adaptation and mitigation policies. In this study, we examined the meteorological drought characteristics of India during 1901–2015, using Climate Research Unit (CRU) based Standardized Precipitation Evapotranspiration Index (SPEI) at multiple timescales i.e., 1 month (SPEI01), 3 month (SPEI03), 6 month (SPEI06), 12 month (SPEI12). Here, we applied K-means clustering algorithm on SPEI12 (December) to find out different clusters with distinct drought characteristics. The six different homogeneous regions, i.e., cluster1 (C1), cluster2 (C2), cluster3 (C3), cluster4 (C4), cluster5 (C5), and cluster6 (C6) identified by K mean clustering largely resemble with the clusters mentioned in previous researches. Different drought parameters (duration, frequency, intensity) have been also analysed for each cluster on a monthly, seasonal and interannual basis. The study indicates that northern part of India (C6, C3) experienced frequent droughts at shorter timescales whereas the western (C2) and north eastern (C4) part of the country encountered frequent drought occurrences at longer timescale. It is worthy to mention that the C2 region comprising the semi-arid and arid western part of the country including the great Indian desert, is vulnerable to frequent, prolonged and severe droughts at longer timescale (SPEI12). The study revealed a significant regional variation in drought trends identified by Modified Mann-Kendall (MMK) trend test. The annual trend analysis shows statistically significant (p < 0.05) increasing drought trend over C3 and C4 regions comprising the fertile Gangetic and Brahmaputra plains. The seasonal MMK trend analysis reveals significant increase (p < 0.05) in droughts over C3 (−0.006) and C4 (−0.005) during monsoon. The increasing drought trend over the Gangetic plain (C3) is prominent especially in the months of July (p < 0.05, slope = −0.005) and August (p < 0.001, slope = −0.006). The study provides a region-specific understanding of drought characteristics and long-term trends crucial for preparing adaptive strategies to minimize the cumulative impacts of droughts.

Quantifying spatial variability of available zinc in alluvial soils of Brahmaputra plains, India

Occurrence of zinc (Zn) deficiency in soils and plants has been accounted for worldwide including northeastern India. The present study was conducted to determine the spatial distribution and degree of risk of Zn deficiency in Brahmaputra plains of northeastern India using statistics and geostatistics. With the help of handheld global positioning system (GPS), 5494 soil samples were collected using 1 km x 1 km grid at 0–25 cm depth from three districts of Assam state of India namely, Tinsukia, Morigaon and Nalbari representing upper Brahmaputra valley zone (UBVZ), central Brahmaputra valley zone (CBVZ) and lower Brahmaputra valley zone (LBVZ) covering 6249 km2 area and analyzed for pH, organic carbon (OC) and Zn. Dataset was normally distributed. Geo statistical analyses were carried out, including experimental variogram and model fitting. Analysis of the isotropic variograms indicates that the range values of 3900, 4400 and 5800 m for UBVZ, CBVZ and LBVZ, respectively. It implies that the length of the spatial autocorrelation was much longer than the sampling interval of 1 km. The nugget/sill ratio was 0.506, 0.859 and 0.589 for UBVZ, CBVZ and LBVZ, respectively and it indicates moderate spatial dependence. Further, with the ordinary kriging, spatial distribution map showed that the Zn is deficient for plants in the all the three zones of Brahmaputra plains. The probability map produced based on indicator kriging showed that Zn deficiency was noticed in 34% of crops grown area of the Tinsukia, 70% crops grown area in Morigaon and 85% of crops grown area in Nalbari districts. The correlation analysis showed that Zn was significantly and positively correlated with OC and significantly and negatively with pH in Brahmaputra plains. Thus, the present study is of immense help to minimize both yield loss and environmental threats of Zn toxicity due to under or overdose of Zn fertilizer application in Brahmaputra plains of northeastern India.

Long-term Rainfall Data Analysis of the Major Stations of Brahmaputra Plain in Northeast Region of India

Objectives: This study explores the rainfall variability and long-term trend in the Brahmaputra plain of northeast region of India. The data analysis is mainly focused on estimating the amount, frequency, and trend of rainfall, using daily recorded data between the year 1950 and 2013. Methods: Linear Regression analysis was utilized to check the correlation relation between elevation and rainfall. The Mann Kendall test was used to detect a significant trend in rainfall series. Sen’s slope method was used to measure the magnitude of trends in rainfall series. The correlation between time and rainfall was estimated by utilizing Kendall’s tau. Findings: Data analysis reveals a heaviest-rainfall pockets zone at North Lakhimpur region, wherein annual average rainfall occurs about 3249.57 mm. Another rain shadow zone has detected at Guwahati, wherein annual average rainfall occurs is about 1706.27 mm. A high-low-high gradient in the spatial distribution of seasonal and yearly rainfall has observed from west to east. A similar spatial trend has also observed from south to north along latitudes. The Linear regression analysis reveals a positive relationship between elevation and annual average rainfall. The Mann Kendall test detected a significant rainfall trend on a monthly and seasonal scale whereas, on an annual scale, no significant trend was detected. Rainfall intensity over each station was observed uniform for most of the years. The frequency of light, heavy and very heavy rainfall over the entire Brahmaputra plain region shows a non-significant decreasing trend. Whereas, Dibrugarh and North Lakhimpur experience decreasing trends in the frequency of rainy day and light rainfall and heavy rainfall respectively with a 5% significance level. Application: The result that comes out from this study shall be useful for the study of soil erosion, water resources management, and agricultural activity and may be useful for adopting flood disaster management policies. Keywords: Brahmaputra Plain Region, Rainy Day, Mann Kendall Test, Sen’s Slope Method.

Rapid exhumation since at least 13 Ma in the Himalaya recorded by detrital apatite fission-track dating of Bengal fan (IODP Expedition 354) and modern Himalayan river sediments

Apatite fission-track analysis of middle Bengal fan sediments (IODP expedition 354) and modern Himalayan river sediments shows that most of the detrital apatites are very young compared to their depositional ages, independent of their uranium content. Bengal fan apatites display an average central age lag time as short as 2.26±1.6 Myr since at least ∼13 Ma. Such lag times reflect a mean exhumation rate on the order of at least 1-3 km/Myr. The occurrence of detrital apatites with relatively short AFT lag times since at least 13 Ma indicates that there have always been areas of rapid erosional exhumation, supplying detrital apatites to the fluvial system and delivering them to the paleo-Ganges and/or –Brahmaputra plains and finally to the Bengal fan. It also supports that temporary storage of detrital apatites in the floodplains or delta has always been negligible since at least 13 Ma. Comparison of the AFT data of the Bengal fan with those of the Central and Eastern proximal Neogene Himalayan foreland basin shows that both paleo-Ganga and –Brahmaputra catchments provided apatites with similar short lag time to the distal Bengal Fan basin.In the modern drainage system of the Bengal fan, the apatites with young fission-track cooling ages are principally derived from areas where the topography has a sharp relief controlled by threshold hillslope processes and stream power resulting in landslide erosion as a coupled response to tectonic and fluvial forcing. By analogy with the modern erosion processes in the Himalayan range, we suggest that over the past 13 Ma, apatites were mainly derived from areas of sharp relief, where river stream power was high and hill slopes close to the threshold angle. As the exhumation signal is rather consistent since the late Miocene the detrital apatite fission-track data are either not sensitive enough to detect rapid climatically controlled changes in exhumation rates, or overall long-term erosion rates on the orogen scale are not strongly affected by climatic variations such as the variability of the Indian Summer Monsoon. Given the already rapid exhumation rates controlled by tectonics, the impact of climate variability on surface erosion rates cannot be detected with our data, especially in the case of erosion processes dominated by threshold hillslope model.

Assessment of the reptilian fauna in the Brahmaputra Plains of two districts in Assam, India

Assessment of the reptilian fauna in the Brahmaputra Plains of two districts in Assam, India

High Arsenic Concentration in Blood Samples of People of Village Gyaspur Mahaji, Patna, Bihar Drinking Arsenic-Contaminated Water

Arsenic contamination in ground water is a serious and widespread global public health problem. It is estimated that more than 300 millions of population worldwide while about 180 million people in the Ganga–Meghna–Brahmaputra plains are exposed to arsenic poisoning. Out of 38 districts of Bihar, 18 are highly affected with ground water arsenic poisoning. A flood plain village of river Ganga Gyaspur Mahaji in Patna district was undertaken in the present study. The study deals with the survey of the entire village households with ground water arsenic quantification with special attention to know the health status of the arsenic-exposed population. The study revealed high arsenic concentration in the ground water of the village. The general health status of the village population was very poor as the subjects were exhibiting typical arsenicosis symptoms. Apart from this, they also had gastrointestinal problems, constipation, anaemia, loss of appetite, breathlessness, mental disability, etc. There were also reports of two cancer incidences from the village: one subject with squamous cell carcinoma of skin and the other with medullary breast cancer along with arsenicosis symptoms. The village population are getting infected and hence are at very high risk and may be impacted if they continue to drink arsenic-contaminated water in the future. Therefore, a proper strategy is urgently required for arsenic mitigation in this arsenic-exposed village through supply of safe drinking water.

Toxic Trace Metals in the Surface Water Sources of Jia–Bharali river basin, North Brahmaputra Plain, India—A Hydrochemical Elucidation

Surface water samples from thirty five sources in the Jia Bharali river basin in north Brahmaputra plain, North East India were analyzed for ten toxic trace elements namely As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn. This first ever systematic analysis reveals seasonal variation of these elements with invariably higher concentration during dry season (February–March) in compared to the wet season (July–August) concentration for a period of 2008–2010. All the trace metals were estimated by using atomic absorption spectrometer (Varian AA 220). The whole study area shows As and Zn content below the WHO permissible limit [39] while surface water of some areas are found to be contaminated with Cr, Pb and Fe. Cr is higher in as much as 92% samples in dry season and 69% samples in wet season. Higher Fe concentration is found in 86% dry season samples and in 46% wet season samples. Pb concentration is above permissible limit for most of the study area during dry season (0.11 mg/L). Cd, Ni and Mn are also found to be of higher concentration in isolated areas. The quantity of trace metals in watersources should be checked time to time as their accumulation will cause numerous problems to living being.

Assessment of water quality in and around Jia-Bharali river basin, North Brahmaputra Plain, India, using multivariate statistical technique

The present study envisages the application of multivariate analysis, water utility class and conventional graphical representation to reveal the hidden factor responsible for deterioration of water quality and determine the hydrochemical facies of water sources in Jia-Bharali river basin, North Brahmaputra Plain, India. Fifty groundwater and 35 surface water samples were collected and analyzed for 15 parameters viz pH, TDS, hardness, COD, Ca2+, Mg2+, Na+, K+, Fe, HCO3−, Cl−, SO42−, NO3−, PO43− and F− for a period of 3 hydrological years (2009–2011) in six different seasons (three wet and three dry). The results were evaluated and compared with WHO and BIS water quality standards. Except Fe (> 0.3 mg/L), all parameters were found well within the desirable limit of WHO and BIS for drinking water. Ca2+ and HCO3− were dominant ions among cations and anions. The piper trilinear diagram classified majority of water samples for both seasons fall in the fields of Ca2+–Mg2+–HCO3− water type indicating temporary hardness. Varimax factors extracted by principal component analysis indicates anthropogenic (domestic and agricultural runoff) and geogenic influences on the trace elements. Hierarchical cluster analysis grouped water sources into three statistically significant clusters based on the similarity of water quality characteristics. This study illustrates the usefulness of multivariate statistical techniques for analysis and interpretation of complex datasets, and in water quality assessment, identification of pollution sources/factors and understanding temporal/spatial variations in water quality for effective water quality management.

Hydrochemical and Multivariate Statistical Evaluation of Heavy Metals in Shallow Alluvial Aquifers of North Brahmaputra Plain, India

The aim of this study was to display distribution and relationships of heavy elements in the unconfined, shallow alluvial aquifers of the lower Jia Bharali catchment and adjoining areas in central part of North Brahmaputra Plain (NBP), India using hydrochemical as well as multivariate statistical techniques such as principal component analysis (PCA) and cluster analysis. The original matrix was made up of 10 trace elements (As, Cd, Cu, Co, Cr, Fe, Mn, Pb, Ni and Zn) estimated from 50 shallow alluvial dug wells in both the wet and the dry season for a duration of 3 hydrological years (2008–2011). Except As, Cu and Zn all the other toxic metals in the shallow aquifers were found exceeding the WHO maximum permissible limits for drinking water. PCA extracted five varimax factors as geogenic, agricultural and anthropogenic explaining about 71.2% of the total variance in the wet season and 69.3% total variance in the dry season. Hierarchical cluster analysis classified the dug wells into two groups in the wet season and three groups in the dry season with respect to the heavy elements. The results emphasized the need for routine monitoring and management in order to avoid contamination of groundwater sources in the NBP with respect to the dissolved trace elements.

Morphological Dynamics of the Rivers of Brahmaputra

This study documents the sequential morphological dynamics of rivers of Brahmaputra. Landsat images for the year of 1976 and 1987–2016 (thirty consecutive years) are used in GIS environment to document the activities that have been shaping and reshaping the morphology of the rivers. The use of thirty year consecutive images facilitates an explicit assessment of morphological changes. Apparently, distributary activities, meandering activities, breaches and avulsions, and confluence migrations are the dominant geomorphic agents of morphological changes. A range of distributaries activities are readily noticed in Brahmaputra plain. The plain is densely dissected with numerous rivers and rivulets, and distributaries activities often lead to reorganization in channel network. Considering the frequency of incidence and preserved imprints of abandoned channels, majority of the rivers of Brahmaputra can be categorized as free meanders. Difference in fluvio-geomophic setups of rivers of both the banks is reflected palpably in meandering activities. The upper stretch of Brahmaputra encompassing the rivers Simen, Gai and Jiadhal is found to be the most active in terms of avulsions. High seasonal flow, large sedimentation and absence of distinct river bed in some stretches are presumably leading to these frequent avulsions. The river Simen, further, exhibited repeated confluence migration through avulsion near its confluence with Brahmaputra. The explicit picture of the morphological dynamics of rivers of Brahmaputra at basin scale presented in this work is a key aid in formulating riverine management programs which is conceivably among the most water-troubled region of the country.

Shallow alluvial aquifers for drinking and agricultural purposes: a case study from Jia Bharali River Basin, North Brahmaputra Plain, India

A preliminary assessment of groundwater quality for drinking and irrigational purposes in the lower Jia Bharali river catchment and adjoining areas of North Brahmaputra Plain, India, was carried out with respect to major cations, anions, and trace elements. Water samples from 50 shallow alluvial dug wells were collected in wet and dry seasons for a period of 3 hydrological years (2008–2011). Seasonal analysis showed major cation and anion contents in a definite trend across the basin as Ca: 4.2–68.9 mg/L > Na 1.9–62.5 mg/L > Mg:1.0–29.2 mg/L > K (1.3–26.1 mg/L) and HCO3 (16–118 mg/L) > Cl (2.8–138.3 mg/L) > SO4 (1.2–99.5 mg/L) > PO4 (BDL—1.50 mg/L) > NO3 (BDL—1.20 mg/L) within WHO acceptable limit for drinking water in all the seasons. Low SAR ( 60% and Kelly’s Index > 1. However, majority of the wells were found not suitable for drinking as well as irrigational purposes due to the presence of trace elements Cd (BDL—0.070 mg/L), Cr (BDL—0.24 mg/L), Fe (0.10–11.76 mg/L), Mn (BDL—1.37 mg/L), Ni (BDL—0.18 mg/L), and Pb (BDL—0.22 mg/L) beyond their respective standard limits. Piper trilinear diagram identified the major hydrochemical facies of the groundwater as alkaline earths (Ca, Mg) and weak acids (HCO3) over alkalis (Na, K) and strong acids (SO4, Cl).

Chemical characterization and source apportionment of aerosol over mid Brahmaputra Valley, India.

Aerosol samples (as PM10, n=250) were collected from three rural/remote receptor locations in the mid Brahmaputra plain region and were chemically characterized for metals (Al, Fe, Co, Cu, Cr, Cd, Mn, Ni, Pb), ions (Ca2+, Mg2+, Na+, K+, NH4+, F-, Cl-, NO3-, SO42-), and carbon. Vital ratios like NO3-/SO42-, EC/OC, K+/EC, K+/OC, enrichment factors and inter-species correlations were exploited to appreciate possible sources of aerosol. These empirical analyses pointed towards anthropogenic contributions of aerosol, particularly from biomass burning, vehicular emission, and road dust. The chemically characterized concentration data were subsequently fed into two receptor models viz. Principal Component Analysis-Multiple Linear Regression (PCA-MLR) and Chemical Mass Balance (CMB) for apportionment of sources of aerosol. The PCA-MLR estimates identified that the combustion sources together accounted for ∼42% of aerosol and the contribution of secondary formation to be 24%. Road and crustal dusts have been well apportioned by PCA-MLR, which together accounts for ∼26% of the aerosol. The CMB model estimates explained that the combustion sources taken together contributed ∼47% to the aerosol, which includes biomass burning (27%), vehicular emission (13%), coal (1%), kerosene (4%), and petroleum refining (2%). Other major sources that were apportioned were road dust (15%), crustal dust (26%), and construction dust (6%). There are inherent limitations in the source strength estimations because of uncertainty present in the source emission profiles that have been applied to the remote location of India. However, both the models (PCA-MLR and CMB) estimated the contribution of combustion sources to 42 and 47% respectively, which is comparable.