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Nature and Properties of Water and Sediments of the Ganges and the Brahmaputra Rivers in Bangladesh

M. S. Rahman
Bangladesh Rice Research Institute, Joydebpur, Gazipur

M. S. Hussain
Department of Soil, Water & Environment, University of Dhaka, Dhaka-1000, Bangladesh

S. M. A. Faiz
Department of Soil, Water & Environment, University of Dhaka, Dhaka-1000, Bangladesh

M. J. Uddin
Department of Soil, Water & Environment, University of Dhaka, Dhaka-1000, Bangladesh

Abstract/ Executive Summary:

The composition of the sediments and water of the two major rivers of Bangladesh - the Ganges and the Brahmaputra have been studied. The pH of the Ganges river water was alkaline and the water of the Brahmaputra river was slightly acidic. Electrical conductivity of the Ganges river is slightly higher than the Brahmaputra river water. Calcium, magnesium and sodium content in the Ganges water is higher than the Brahmaputra river and the other elements remain similar in both cases. The sediment content of water of both the river is higher in wet season compared to dry season. The cation exchange capacity is found higher in the sediments of Ganges river than the Brahmaputra. The pH value along with free lime percentage of the Ganges sediment have found higher than the Brahmaputra sediments. The particle size analysis of the sediments indicates that sand is the dominant size fraction followed by silt and clay. The X-ray analysis showed that Ganges sediments were dominated by smectite followed by mica and kaolinite minerals. In the Brahmaputra sediment, the dominant minerals are mica, kaolinite and vermiculite. Chlorite is present in trace amount.

Keywords: Sediments, Carrier of sediments, Ganges and Brahmaputra rivers

Location: Bangladesh Rice Research Institute, Joydebpur, Gazipur

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Land development productivity

Objectives:

Objective of the study was to evaluate the nature and properties of water and the suspended sediments of the Ganges and the Brahmaputra rivers of Bangladesh.

Methodology:

Sediments: Sediments were collected during wet season when water flow was strong. Suspended sediments in the water of the Ganges river were collected at Paksey- Bheramera point near Hardinge bridge and that of Brahmaputra river were collected at Bahadurabad-Fulcharighat point during the rainy season. Water: Water sample from the respective rivers were collected for analysis into two seasons of the year. One in wet season in the months of July and another in the dry season. During the time of collection water was filtered, bottled and acidified with IN HCI. The pH of the water was determined with glass electrode pH meter. Water EC of these river water was determined with the help of an electrical conductivity meter. Ammonium nitrogen was determined by distillation. For chloride determination Mohr's titration method was used. In this method AgN0₃ solution in the presence of K₂Cr₂0₇ as indicator titrated against water was used. Carbonate of water was determined by titrating against standard sulphuric acid using phenolphthalein as indicator. Sulphate content of water was determined by the extend of turbidity created by precipitated colloidal barium sulphate suspension. For determination of phophorus content in water, ammonium molybdate and potassium antimony tartarate react in acid medium with orthophosphate to form phosphomolybdic acid which to reduced to intensify coloured molybdenum blue by ascorbic acid. The blue colour development was measured in spectrophotometer at 660 nm wavelengths. Boron was determined colorimetrially by using curcumin. Water sample was acidified and evaporated in the presence of curcumin which gives a red coloured product and dissolved in solvent (ethyl alcohol) and the colour measured in spectrophotometer. Potassium and sodium of water were determined by flame photometry, calcium and magnesium of water were determined using atomic absorption spectrometer. During the monsoon season the area remains flooded for a period of at least 4 - 5 months. Both external and internal drainage is poor. The soils under the present investigation belong to the two physiographic units; Ganges river floodplain and Brahmaputra river floodplain. Ganges river floodplain comprises a meander floodplain landscapes of ridges, basins and old channels. The Ganges river is consistently shifting its course, eroding its banks and depositing large volumes of new alluvium on its beds banks, char lands and floodplains. Hydrology: The surface drainage of the areas under the present investigation is mainly provided by the Ganges and the Brahmaputra rivers and a few distributaries and other small rivers. Seasonal flooding is one of the most important features of hydrology in relation to agricultural development. Flooding is mostly caused by rainwater. In the Brahmaputra floodplains, flooding is mainly due to stagnation of local run-off in the monsoon season. Flood levels are controlled by the rainy season water levels of the Brahmaputra river and its tributaries and distributaries. Geology and landform: The studied area in the Ganges floodplain were developed from the recent and subrecent unconsolidated Ganges alluvial sediments. The deposits are generally calcareous. The Ganges river floodplain is divided into young and old depending on their relative age of deposits. Ganges sediments contain a considerable amount of calcite and dolomite. Agroecological regions: The area under the present study belongs to two agroecological regions of low Ganges river floodplain and Young Brahrnaputra-Jamuna floodplain. The low Ganges river floodplain occupies the north-eastern, eastern and south-eastern parts of Ganges meander floodplain. They have a landscape of broad, smooth ridges and basins with irregular areas near the former river channels. The ridges are mainly shallowly flooded, but basins become moderately deeply or deeply flooded in the rainy seasons.

Source of Information: J. Asiat. Soc. Bangladesh, Sci., 35(2): 113-122, December 2009

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

In conclusion, it can be said that the characteristics of sediments and water of the rivers- The Ganges and The Brahmaputra varies with the nature of the parent materials from which they have originated. The variation in the particle size, cation exchange capacity, exchangeable cations, and other chemical properties was statistically significant.

Knowledge Management: Journal