This document discusses river ecosystems and the Brahmaputra River Basin. It describes the importance of natural flow regimes and habitat heterogeneity for river health. Various habitats in the Brahmaputra River Basin are described, including fast flowing sections, pools and riffles, river confluences and meanders, the open river, and floodplain lakes. Livelihoods of local communities depend on resources from these ecosystems. An integrated ecohydrological approach is needed to assess and manage freshwater sustainability that considers the interrelationships between water and biology.

1. Sanchita
• In a river system, water with their own properties
and natural behaviour maintains its own ‘health’,
also provides ecological security to their
dependent ecosystems and organism therein,
offering many economic benefits to the living
communities
• In maintaining river health, the water quality and
quantity is the master variable, which includes
natural flow regimes, physico-chemical properties,
sediment transport and drainage basin runoff
1

2. • Flow regime is of central importance in sustaining
the ecological integrity of flowing water systems
• The river channel presents a three dimensional
form defined by its slope, cross section and
pattern.
• The natural flow of a river varies on time scales of
hours, days, seasons, years and longer
• Five critical components of the flow regime
regulate ecological processes in river ecosystems:
magnitude, frequency, duration, timing and rate
of change of hydrologic conditions
2

3.  These components can be used to characterize
entire range of flows and specific hydrologic
phenomena, such as floods or low flows that are
critical to the integrity of river ecosystems.
 River ecosystems are adapted to the natural
hydrological regime and many components of these
systems rely on floods for the exchange, not just of
water, but also energy, nutrients, sediments and living
organisms.

4. HABITAT VARIABILITY OF THE
BRAHMAPUTRA RIVER BASIN

5. Fast flowing river

6. 1. Fast flowing river:
This section of the river has a shallow stony
bed that harbour small stream fish genera like
Nemacheilus, Garra, Barilius, and Danio which
hardly grow beyond 15 cm. 52 nos. of species
recorded.

7. Pools and riffles

8. 2. Upstream pools and riffles:
These are the sluggish and deeper parts of the
river. Species like Tor spp., Labeo pangusia, L.
dero, Neolissocheilus hexagonolepis, Raiamas
bola inhabit this type of habitat.

9. Confluence
/Meanders

10. 3. River meandering and confluence:
The eddy, counter-current system at the
junction of two rivers (tributary and main river)
is an ideal place for fish assemblages. The
confluences are also the passageways for
upstream fish migration. Similarly, the channel
meanderings offer suitable habitats for a large
number of fish species and river dolphins.

11. Open river

12. 4. Open river:
The main river harbour a wide variety of fish
species (167 fish species) and other aquatic fauna
including river dolphins (Platanista gangetica).

13. Flood plain lakes/wetlands (FPL)

14. 5. Floodplain Lakes (FPL):
FPL’s are weed infested shallow water bodies
temporarily (closed) or permanently connected
(open) with the main river. These act as feeding
and breeding grounds for many riverine species
but do have a ‘residential’ fish population of
which air-breathing forms like Channa, Clarius,
Anabus, etc. constitute about 40 % of the total
species.

15. Shallow marginal areas

16. Space between boulders
and cobbles

17. Livelihood options of BRB Floodplain community people
Timber yielding plant
Grazing land
Transportation
Boat and houses
Thatching materials
Gravel & sand mining
17

18. Driftwood collection
Fishing activities
Community fishing
18
Wetland fishing (wet period)
Wetland fishing (dry period)

19. Ecological Responses to Environmental Changes

20. Ecological
Socio-economical
Siltation of water bodies
Limited agricultural
development
Eutrophication
Limited scope for tourism
KEY ISSUES
Agricultural Pollution
Unemployment
Industrial Pollution
Loss of productivity
Destruction of Biodiversity

21. Ecological theory generally states three necessary
conditions for natural river functioning (Whittington
et al., 2004):
 Habitat heterogeneity — the biotic
community is structured by the availability of
habitat and at a broad level there is a relationship
between biodiversity and habitat heterogeneity.
 Connectivity — along the river, with the
floodplain and riparian vegetation, and with
groundwater;
 Metabolic functioning — the source and
amount of organic matter produced will have a
significant effect on the food web.

22. The Sustainable Rivers Audit defined river health as:
“the degree to which aquatic ecosystems support and
maintain processes and a community of organisms
and habitats relative to the species composition,
diversity and functional organization of natural
habitats within a region.” (Whittington et al., 2004).

23. • The evaluation of how and to what extent biotic
processes can modify the flow of water, nutrients,
sediments and pollutants into an aquatic ecosystem
has led to the integration of the two branches of
science- hydrology and ecology, into a new paradigm
ECOHYDROLOGY thereby providing a new insight
into the
interrelationship of water and biota
(Zalewski,1998).

24. • An ecohydrological approach to freshwater
management maybe summarized as,
– Monitoring and control of hydrological
processes towards enhancement of resistance
and resilience of aquatic ecosystems;
– Enhancement of resistance of aquatic
ecosystems to anthropogenic stress by
restoration of their homeostasis;
– River valley and catchment restoration.

25. This integrated approach, or ecohydrological approach, creates a
new background for the assessment and management of freshwater
resources (e.g. river restoration and governance) and accelerates the
implementation of new ideas to sustainable development, i.e.,
elimination of threats and amplification of chances
Chances
ZONE OF SUCCESS
Amplification of chances
Elimination of threats
Threats
Fig 34: Sustainable Management of Freshwater Resources- application of
Ecohydrology as a factor of maximizing chances (after Zalewski,1998).

26. Improved Water Governance
• Analyses of
– driving forces,
– pressures,
– state
– impact
– response of system components in
adherent “what-if?” scenarios.