Flow Attributes and Biodiversity Conservation in
the Ganges-Brahmaputra-Meghna River System
Focus on flow attributes which encompass the range
of physical and ecological impacts of hydrologic
interventions – includes sediment and woody debris
Inclusive of a broad spatial perspective from high order
tributaries (species diversity increases as one proceeds
downstream) to estuarine channels of the Sundarbans
mangrove forest (or beyond?).
Recognizes the hydrologic
and geomorphic connectivity
of floodplain rivers, and
temporal dynamics of the
flood pulse.
(Ganges discharge = 12,000 cms;
range = 1,200–65,000 cms)
Upstream and downstream
Groundwater
and surface flow
On and off the floodplain
Guided by the principle that the sustainability of
biodiversity is critical to the well being of local people.
Ganges-Brahmaputra-River System
Third largest river system in the world.
High order tributaries and mainstem
flow through Nepal, India and Bangladesh.
Home to ~10% of the world’s human
population.
Socio-economic status of local people
is generally low.
River plays a strong role in the spiritual
life of local people.
Resources used intensively by local
people.
System highly modified by hydrological
interventions and intensive land use.
High level of species diversity.
Identifying flow attributes for conserving biodiversity
Well, I am just the dolphin guy,
so my perspective is from the
crows nest of how these large
predators have adapted to
freshwater environments.
From the perspective of dolphins and their prey,
studies in the far upstream and downstream extents
of their range have been especially informative.
In their far upstream range, below the
foothills of the Himalayas, Ganges River
dolphins occur in cool, clear waters of the
Karnali River, Nepal. Hydraulic constraints
limit their distribution to counter-currents.
Counter-currents are biological “hotspots”
within river systems and they are crucial for
preserving native biodiversity.
The attractive force of eddy currents traps primary nutrients
and woody debris and gives protection to riverine organisms.
Counter-currents retain nutrients in a circumscribed area,
creating a patchy distribution of biotic productivity and diversity.
Woody debris, trapped by counter-currents and deposited
on adjacent point bars, provides substrate and an array
of cover and hydraulic gradients, which support multispecies fish and invertebrate communities.
At the far downstream end
of their distribution Ganges
River dolphins share
mangrove channel habitat
with Irrawaddy dolphins
Sighting and environmental
sampling surveys in most
navigable channels during
high and low water seasons.
Border between Ganges River
and Irrawaddy dolphins about
4-9 ppt in the low-water season.
Border between Ganges
River and Irrawaddy
dolphins ~ 3 ppt
in high water
season.
In the offshore portion of Irrawaddy dolphin distribution
similar habitat partitioning exists with finless porpoises.
General Additive Models indicated that:
Ganges river dolphin distribution
was conditionally dependent on
low salinity, high turbidity and
moderate depth.
Irrawaddy dolphin distribution
was conditionally dependent on
high depth, increasing numbers
of large-small confluences,
low salinity, and high-low
extremes of turbidity.
In 2003-2005 the captains of three
nature tourism vessel operating in
the Sundarbans logged ~4,000
sightings of Ganges River dolphins
and ~600 sightings Irrawaddy
dolphins.
Chi-squared analyses of channel
segments grouped according
to channel width, sinuosity,
and presence of large and
small confluences indicated
that the distribution of both
species was dependent
on confluences and to a
lesser degree sinuosity.
Implications of the Sundarbans study:
Counter-currents also important in far downstream reaches
(similar observations in the middle Ganges and Brahmaputra).
Freshwater flow regimes critical for the physical forcing of
salinity gradients – which affects dolphins (and associated
biodiversity?).
Increasing sedimentation will reduce freshwater flows to an
even greater extent than by simply subtracting the amount of
water planned to be withdrawn from its projected availability.
Knowledge of habitat selection and the potential effects of
declining freshwater supplies should be incorporated into the
design of protected area networks for aquatic biodiversity.
Summary of flow attributes necessary for
conserving biodiversity
Lateral and longitudinal
connectivity, including
seasonal flood pulse.
Geomorphic complexity for
hydraulic refuge and microhabitat diversity.
Sufficient freshwater supply so
that large aquatic predators
can move between deep pools
And excessive sedimentation does
not reduce the availability of
these features, and for preventing
salinity encroachment.
Biodiversity Target “Strawmen”
Preservation of native species assemblages in core biodiversity
habitat - identified by “megafauna” occurrence and monitored
using indices of fish and invertebrate abundance and diversity,
and geomorphic equilibrium (e.g. pattern changes in the
morphology of channel cross sections, size and distribution of
floodplain sediments, etc.).
Choose representative focal river segments incorporating dolphin
“hotspots” in five tributaries of the GBM system e.g. Karnali-Gaghara and Koshi (Ganges), Chambal (Yammuna),
Kulsi (Brahmaputra) and Kalni-Kushiyara (Meghna);
five segments in the main rivers –
e.g. between the Bijnor and Narora barrages (upper Ganges),
Vikramshila Gangetic Dolphin Sanctuary (middle Ganges), river
segment of the Brahmaputra between Guwahati and Goalpara,
confluence of the Ganges and Brahmaputra, and confluence of
the Ganges and Meghna;
and five mangrove channel segments in the Sundarbans.
Threats - Biodiversity in the GBM System has been
greatly affected by dams, embankments, and tube wells.
The situation will worsen if India proceeds with planned
inter-basin water transfer projects, which will involve
additional regulation structures and freshwater abstraction.
At least 50 dams affect the ecology and fragment
biological diversity in the GBM system.
The India inter-basin linking project aims to store “excess”
monsoon flows behind at least nine high dams on major
tributaries of the Ganges and Brahmaputra and then link:
(1) tributaries of the Ganges
with the western rivers of
peninsular India and the
Yammuna River, and
(2) the Brahmaputra mainstem
and its tributaries with the
Ganges and then further
downstream to the to the
Peninsula Rivers Component.
Feasibility studies are underway.
Estimated cost 120-200 Billion.
Challenges for addressing
hydrological processes
and biodiversity
Three countries involved with long history of water disputes.
Abject poverty of local people in many areas – no margin for
economic sacrifices.
Lack of hydrological data and access to existing data is
restricted by governments – particularly India which
encompasses the majority of the river basin and where
most interventions are planned.
Lack of ecological data and few local scientists to address
biodiversity issues.
River system large, complex and already highly modified.
Conservation planning process so far
Well, I am still just the dolphin guy ……………………………….. ,
including whales on
occasion too!
Convened the Workshop on the Effects of Water
Development on River Cetaceans, 1997, Bangladesh.
Published and promoted:
Guidelines for Considering the
Needs of River Cetaceans during
the Planning and Management of
Water Development Projects.
Compiled Register of Water Development Projects
Affecting River Cetaceans in Asia.
Ecosystem Integrity - Maintaining the natural
attributes of a river is critical for conserving river
dolphins and other native species.
Four basic principles of riverine ecology must be
kept in mind:
• There is no "surplus" water; any large-scale
withdrawal will have ecological consequences.
• The floodplain is an integral part of the river.
• An alluvial river must be allowed to migrate.
• Rivers need to maintain their natural temporal
and spatial variability.
Essential flow attributes
Identified through the
Applied for the
habits and habitat of megafauna
benefit of biodiversity and local people.