Brahamaputra Basin

Brahamaputra Basin
6. Water quality
6.1 Surface water quality observations
Surface water has played an important role in the development of human civilization. Good water
quality resources depends on a large number of physio-chemical parameters and the magnitude and
source of any pollution load; and to assess that, monitoring of these parameters is essential.
Brahmaputra and its tributaries are one of the main and important sources of water for a large
population in basin for drinking and irrigation and its quality directly affects their lives. Central Water
Commission operates 72 stations which carry out observations for testing the surface water quality
of 68 water quality parameters which are considered to be the “Standard Hydrology Project Water
Quality Parameters” in the Brahmaputra basin.
Other organisation like Brahmaputra Board and the State Pollution Control Boards of Assam,
Nagaland and Sikkim at 68 locations are also doing the water quality monitoring of the River
Brahmaputra and it’s several tributaries in the basin (Source: STATUS OF WATER QUALITY IN INDIA
2009, CPCB).
All physical, chemical and biological water quality parameters are categorized further under sub
categories like field determinations, nutrients, organic matter, alkalinity, hardness, other inorganics,
major ions, coliforms and others. When compared to the other major rivers in India, the
Brahmaputra is less polluted but it has it is also facing problem of water pollution due to petroleum
refining units draining most of the industrial pollution load into the river along with other medium
and small industries. The problem is severe in Dibrugarh. Increasing trend in BOD level of
Brahmaputra river has been noticed when compared against 9.2 mg/l in 2011 and 6.3 mg/l in 2010
(Sourcs: CPCB website, Central Pollution Control Board Programme Projects Water Quality Pollution
NWMP).
The major ion chemistry of the Brahmaputra is characterized by high bi-carbonate content and
source rock influence. While higher values of TSM than TDS during monsoon indicate predominance
of physical weathering over chemical weathering, chemical weathering is relatively more
pronounced during the dry season. On average, 60 % of the bi-carbonates in the Brahmaputra water
come from silicate weathering and the rest from the carbonates.
Surface suspended sediments range from fine sand to clay,the size fraction greater than 12µm
constitute a large number. Surface suspended sediments are moderately to poorly sorted with
greater amounts of finer material in the distribution, particulalryduring the rainy season. The detrital
contribution in the from of Quartz, Feldspar and Mica make up more than 80% of the mineralogy.
Chlorite, Illite, and Kaolinite constitue about 95 % of the clay minerals. Suspended sediments play a
significant role on the overall solute and sediment bio-geochemistry of the river.
It has been also observed that river water of the basin is generally alkaline with comparatively high
bicarbonate, sulphate and dissolved silica concentration. Dissolved Oxygen (DO), Biochemical
Oxygen Demand (BOD), Fecal Coliform and turbidity are observed to be the common violating
parameters for most of the rivers of the basin. The higher values of TSM than TDS during monsoon
season also indicate predominance of physical weathering over chemical weathering in the
Brahmaputra River. The un-treated sewage waste and effluents of major towns situated along the
river also getting inside the main stream of river and degrading its quality for use in irrigation and
drinking purposes.
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