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REVIEW ARTICLE
Climate Change and Environmental Sustainability (April 2017) 5(1): 20-34
DOI: 10.5958/2320-642X.2017.00002.3
Assessment of River Ecosystems and Environmental Flows: Role
of Flow Regimes and Physical Habitat Variables
Venkatesh Dutta1* ••
••
• Urvashi Sharma2 ••
••
• Ravindra Kumar3
Abstract Globally, rivers are under tremendous
anthropogenic stress caused by flow fragmentation, land use
changes and regulation. Floodplains had been cut out from
rivers by embankments due to urban extension and most of
the riparian lands in the river basin are under intensive
agriculture. There was also widespread water quality
degradation due to the industries and municipal wastewater
causing a steep decline in the freshwater biodiversity across
the world. It was recognised in the literature that the integrity
of flowing water systems depended largely on their natural
dynamic character which in turn maintained the habitat.
Habitat characteristics and presence and absence of particular
species suggests that most fishes of flowing water streams
are habitat specialists and physical habitat variables including
flow regimes played critical roles in the maintenance of their
richness. This paper integrated broad environmental flow
concepts and defined a new framework for e-flow assessment
and implementation based on a review of supportive
understanding of variable flow regimes and their benefits to
river ecosystems. The main purpose of the framework was
to stimulate the emerging discussion on environmental flows
prospects in India and other parts of the world. The paper
provided an example of the framework applied to River
Ganga in India. We end by examining research needs and
gaps in our understanding of the role of variable flow regimes
and physical habitat variables and their ecological effects
on river ecosystems.
Keywords River systems, River basins, Flow regime, Eco-
hydrology, Environmental flows, Water quality, Habitat
suitability.
1. Introduction
Human activities such as abstraction of water, disposal
of excess waste-water, irrigation and clearing of vegetation
1Assistant Professor & Coordinator – DST Centre for Policy Research, 2Ph.D. Scholar, Department of Environmental Science (DES), Babasaheb
Bhimrao Ambedkar Central University, Lucknow, Uttar Pradesh, India
3Advisor, WWF-India, New Delhi, India
*Corresponding author E-mail id: dvenks@gmail.com
can change the natural flow regime. These activities can lead
to either an increase or a decrease in quantity of flow as
well as changing the timing, duration and seasonal pattern
of ecologically important flow events. Climate change is
also contributing to changed flow regimes in the rivers such
as the reduction in flow seen in various parts of the world
(south-west Western Australia, Ganga Alluvial Plain). Many
of the major rivers of the world no longer support
ecologically and socially valued diversity of native species
or sustain healthy ecosystems that provide important
ecological goods and services (Dutta et al., 2011, 2015;
Dudgeon, 2000; Naiman et al., 1995; Poff et al., 1997a,
1997b). While academicians and researchers have considered
rivers as part of living ecosystems whose ecological integrity
depends upon their physical, chemical and biological
characteristics and interactions within their catchments, river
engineers and planners have largely treated rivers as water-
delivery networks ignoring ecosystem interactions in
designing water allocation schemes and reservoirs.
Restoration and management of riparian and riverine
ecosystems are of significant importance in the face of
extensive and multiple development pressures (Grygoruk
and Acreman, 2015; Arthington, 2012). A thriving river
maintains functional integrity under changing social and
environmental conditions and performs many functions
through its several processes – geo-morphological,
ecological, hydrological and socio-cultural. The combined
functional integrity gives rivers resilience (Acreman et al.,
2015; Poff et al., 1997a, 1997b). Rivers support a multitude
of goods and services that benefit mankind and ecology, such
as supporting aquatic and riparian biodiversity (flora and
fauna), influencing micro-climate, recharging groundwater,
diluting pollutants and supporting self-cleaning systems,
sustaining livelihoods, transporting silt and enriching the
soil. A sustainable river ecosystem not only meets the needs
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Climate Change and Environmental Sustainability (April 2017) 5(1): 20-34
of society over the lifetime of the water infrastructure but
also maintains key ecological functions that support the
provision of ecosystem goods, services and values (Pittock
and Lankford, 2010).
A river is not simply water running over the land, but a
catchment area – that is, a system linked internally by a
hierarchical or cumulative network of river channels.
Deteriorating flow regimes and the discharges of pollutants
affect a river’s health adversely particularly in the light of
climate change, population growth and economic
development. The focus of water management professionals
in developing countries is still largely on maximising water
supply for drinking and irrigation, hydropower generation
and flood protection. The river ecologists appreciate the
ecosystem approach in environmental flow allocations while
river engineers are comfortable with integrated water
resources management (IWRM) concept with some amount
of interests in basin-wide approach. The water and irrigation
departments are mainly concerned about human livelihoods
and social well-being, while river ecologists and hydrologists
wish to define the flow requirements with respect to desirable
ecosystem conditions. Acreman et al. (2014a) note that
‘although hydrological sciences may be at its heart, an
environmental flow is truly a cross-disciplinary issue’.
Environmental flows are defined as the variable stream-flows
necessary to maintain and sustain habitats, including channel
morphology and substrate, support spawning and passage
of fauna species to previously unpopulated habitats, facilitate
the processes upon which succession and biodiversity depend
and maintain the desired nutrient structure within lakes,
streams, wetlands and riparian areas (MoWR, 2005). Some
radical river regulation measures are being taken up in India
and other parts of the world under river-restoration projects,
but they are largely civil related earth works and
channelisation schemes containing the river flow. In such
projects, geo-morphological wisdom is seldom considered
at design stage with widespread loss of river habitat and
floodplain integrity.
2. The Importance of Variable Flow Regime
Flow is generally seen as the master variable influencing
the nature of rivers because of its ability to affect all other
aspects of the physical and chemical environment in a river
(Arthington, 2012). There is no single correct e-flows regime
for a river, as every river has a unique ecological system
that depends upon complex interactions between physical,
biological and other fluvial attributes. In assessing the e-
flow for a river, the answer has been largely on what people
want from a river. The available knowledge base is very
limited and for most of the rivers there is a reference
condition of ‘natural flow’ that existed prior to major river
regulation. Very little research has been carried out on
understanding implications of environmental-flow releases
in managed streams in different climatic regions of the world.
There is a lack of evidence, on how managed river
ecosystems evolve when flow-regimes are restored. The flow
regime of a river system is an important indicator of its health
and it represents the variable quantity, duration and seasonal
pattern of flows. Many aspects of flow can be analysed but
seven key parameters are recognised by river scientists as
essential ecological and social attributes of flow. Using these
key aspects, hydrological data can be summarised to describe
a river’s natural, present and possible future flow regimes.
Magnitude: quantity of water moving through a given
location per unit time
Frequency: number of flows of a given magnitude per unit
time (also described as the return period)
Predictability: certainty of flows of a specific magnitude
returning on an annual basis
Timing: dates when flows of a certain magnitude begin
Duration: length of time of flow of a certain magnitude
Rate of change: rate at which the magnitude of flow changes
(important for dam releases)
Variability: natural daily, seasonal and longer variability of
flows.
This variable regime is instrumental in maintaining the
distinct ecological richness in the river and influences the
flora and fauna compositions. It is observed that some species
require permanent inundation of water to a certain depth
range while some are naturally adapted to low flow periods.
The variable flow regime also influences the lifecycle
activities of fauna such as spawning and the survival of larvae
and juveniles. The high flow conditions are required to
deposit nutrients around the banks, distribute seeds as well
as for emigration of certain aquatic species. Any change to
a river’s flow regime for a longer duration disturbs the
composition and richness of the fauna community present,
including the fish and macro invertebrates. It can also disturb
the river ecosystem by permanently changing aquatic and
riparian vegetation, aquatic connectivity, changes in water
quality parameters as well as erosion and sedimentation
dynamics. Riparian communities are often subjected to
multiyear droughts and flood events which help in
maintaining the particular habitat (Figure 1).
It is a well-accepted fact that the health of a river and
its associated ecosystems deteriorates if the flow falls below
a minimum range of values. A poor understanding of river’s
ecosystem and flow-dependent habitat lies at the heart of
the widespread neglect of rivers (Sunding, 2011). As long
as the discharge is above a threshold value, the river is able
to function satisfactorily. However, researchers have agreed
that maintaining the e-flows is not the only thing, but all
elements of a flow regime, including high, medium and low
flows are important. The fact is, river supports a variety of
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ecosystem services and the bio-physical and social systems
supported by rivers are too intricate to be summarised by a
single assessment of minimum flow requirements. No matter
how advanced and accurate the environmental-flows
assessment is, the output remains on paper if no actual
releases are made. There is also a fundamental difference
between environmental flow requirements (EFR) and
environmental flow allocations/releases (EFA) – while EFR
show how different flows would achieve different ecological
status, EFR refer to the actual release of water to the
environment. Even though the science of eco-hydrology
dealing with the flow-ecology relationships is confronting
the challenge of uncertainties, the scientists need to show
the utility of research outcome rather than stressing upon
the challenges of system complexity (Acreman et al., 2014a).
Monthly peak flow, annual water yield and long-term
hydrological trends of River Ganga at the downstream of
Farakka are shown in Figures 2 and 3. The graph shows
how the monthly peak flow and corresponding water yield
varies on a long-term basis. There is a change in monthly
peak flow after 1985 with more variability than before. In
contrast annual water yield seems to show less variability
after 1985. During monsoon season flows, the gates are
generally left open. They are then gradually lowered as the
flood recedes. Although downstream movement of cetaceans
through barrages can occur while the gates are open, high-
velocity currents within the openings probably prevent, or
at least impede to a considerable degree, upstream
movement. This characteristic flow pattern has been
instrumental in development of a particular habitat type in
the river segments. The Padma River that supported dolphins
has been greatly affected by the Farakka Barrage which
divides the overall population of Gangetic dolphins at
approximately the geographical centre of their range. The
Kanpur Barrage further fragments dolphins in the Ganges
mainstem. A remarkable impact of barrages on migratory
fish is that after completion of the Farakka Barrage, landings
of hilsa (Hilsa ilisha), a commercially important anadromous
fish, declined upstream of the barrage by more than 99%
(Jhingran, 1982). Also below Farakka, saline encroachment
has most probably reduced the amount of habitat available
to dolphins thus reducing their population (Figures 2–4).
Reductions in water supplies downstream of barrages
have resulted in diminishing of dry season habitat. It is also
Figure 1. Representative hydrograph showing different components of the variable flow regime in a river (Green et al., 2010)
Figure 2. Monthly peak flow and long-term hydrological trends of River Ganga at the downstream of Farakka (flow in 104 m3/s)
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Climate Change and Environmental Sustainability (April 2017) 5(1): 20-34
noteworthy that magnitude of e-flows varies with local site
conditions as well as flow characteristics. Sometimes the
flow fluctuates so widely that there is little scope for
regulation. If the catchment area is large and flow magnitude
is high, the estimates of e-flows are also high and there is a
rapid onset of high flows. The computed values of e-flows
generally vary according to assessment methods and
location. In regulated rivers, e-flows are often defined
through vulnerability assessments involving scientists,
government agencies and water users to sustain desired
ecological processes or conditions downstream of dams (Poff
et al., 2010).
Managing river ecosystems sustainably under uncertain
climatic and hydrological scenarios poses new and
significant challenges (Acreman et al., 2014b).
Implementation of e-flow estimates become unpractical in
an over-allocated river basin where controversial regional
political situations exist, particularly when the river passes
through more than two states. In such cases, e-flows are just
used as preliminary estimates for initial planning purposes.
There would be increasing stress on river basins due to
widespread hydrological alterations and climate extremes
(Table 4) (Lehner et al., 2011; Vörösmarty et al., 2010).
The adaptive management deals with balancing between the
acceptable levels of risk that stakeholders are willing to
accept and the stakeholder-defined engineering and
ecological goals. As river basins across the world become
increasingly over-allocated, there is an urgent need for a
Figure 3. Annual water yield with long-term hydrological trends of River Ganga at the downstream of Farakka (flow in 104 m3/s)
Figure 4. Aquatic biodiversity and natural flow regimes as defined by four principles
Source: Arthington (2012)
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24 Climate Change and Environmental Sustainability (April 2017) 5(1): 20-34
broader conception of sustainable river management that
implements credible e-flows as a necessary ingredient for
water ecosystem integrity and the social well-being it
supports (Griggs et al., 2013; WRI, 2005).
3. Environmental-Flow Management in a Stressed River
Basin
The e-flow management in a stressed river basin works
better in a continuously dynamic framework which integrates
future changes in societal cost functions and shifts in
ecological conditions under evolving climate and socio-
economic conditions (Poff et al., 2015). A critical review of
literature published from 2000 to 2015, reveals that new
nationwide directives are emerging to develop and manage
river ecosystems in more holistic and environmentally
sustainable ways that retain social and ecological benefits.
E-flows assessment procedures are both generic and
site-specific. While rivers follow the same general pattern
irrespective of climatic zone, every river is different – there
are no specific type A or B. The best methods employ
evidence based principles rooted in geomorphic (landscape)
perspectives, catchment specific insights and consideration
of restoration strategies using checks and balances. Some
of the earlier methods relied upon wetted perimeter (1998)
approach, hydrological method (flow-health), holistic
approaches. They were mostly used to justify low-flow
allocations and assessments were often done in isolation with
emphasis on ‘getting a number’ syndrome. There is also
evidence that e-flows will not maintain a pristine river
condition.
It is widely observed that water management designs
(such as channelisation, river-front development,
downstream discharge releases from dams etc.) are often
not compatible with socially valued ecological functions
(Stratford et al., 2015). Researchers have emphasised that
range and value of ecosystem services provided by rivers
increase with the degree to which they are allowed to function
naturally (Cluer and Thorne, 2014; Palmer et al., 2005). The
concept of e-flows was extended and made functional from
minimum flow in the early 1980s to strengthen the idea that
health and integrity of the entire river ecosystems are
fundamental to sustaining human well-being. According to
Table 1. Evolution of environmental-flows assessment in India
Year Agency/Project E-flow Criteria Shortcomings
1999 National Commission for Integrated 2% of total natural water requirements for Not based on scientific
Water Resources Development Plan environment and ecology reasoning
(NCIWRDP, 1999)
1999 Supreme Court directed the Govt. to Minimum flow of 10 cubic metre per second (m3/s) Arbitrary keeping in view the
ensure minimum flow of 10 cubic committed utilisations from
metre per second (m3/s) in Yamuna the river
in Delhi
2003 Water Quality Assessment Authority EFA used in other parts of the world are unlikely
(WQAA): a separate Working Group to be applicable in India, advised Tennant method
made in 2003 to estimate ‘minimum
flows in rivers to conserve the
ecosystems’
2004 Amarasinghe et al. 2005, 476 km3 or 25% of total renewable water resources EWR not EF
and Smakhtin et al., 2004 of the country
2005 NIH-Roorkie, EFA in the Brahmani- Hydrology-based Range of Variability Approach
Baitarani River Systems of Richter et al., 1997 with 7-day minimum and 1-
day maximum flows
2005 Ministry of Water Resources For Himalayan Rivers, minimum flow to be not less Recommendations of the
(MoWR) Report of Working Group than 2.5% of 75% of the Dependable Annual Flow committee are based on what
to advise Water Quality Assessment (DAF) expressed in m3/s, one flushing flow during is practical considering
Authority (WQAA – WG) on the monsoon with a peak of not less than 250% of various constraints into the
minimum flow requirements in Indian the 75% DAF. For other rivers, minimum flow in account. It may not lead to
Rivers: Tennant Method any 10-day period to be not less than the observed desirable outcome for
10-day flow with 99% exceedance (where 10-day ecological needs
flow data is unavailable, this may be taken as 0.5%
of 75% of the DAF). One flushing flow during the
monsoon with a peak of not less than 600% of 75%
of the DAF, expressed in m3/s
Source: Authors’ own elaboration
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Climate Change and Environmental Sustainability (April 2017) 5(1): 20-34
Krchnak et al. (2009), the term e-flows essentially refers to
a ‘variable flow regime’ that has a definite volume and
specific timings that has been designed and implemented –
such as through intentional releases of water from a dam
into a downstream reach of a river – in an effort to support
desired ecological conditions and ecosystem services. Flow
in the river is viewed as the master variable because it exerts
immense impact on aquatic habitat, river morphology,
biodiversity, river connectivity and water quality (Jain,
2012). The early studies carried by Poff et al. (1997b) and
King and Tharme (1994) led to the understanding that all
elements of a flow regime, including high, medium and low
flows, are important from the ecosystem point of view (see
Table 1). In an earlier study, six environmental management
classes (EMC) were defined from A (natural) to F (critically
modified) based on expert judgement (DWAF, 1997). The
flow duration curve (FDC) for the particular site for natural
conditions is drawn and depending upon the desired EMC,
the FDC is shifted to the left to obtain the desired e-flow
regime. The growing piece of literature has confirmed the
idea that e-flows will have to closely follow the natural flow
regime, even though in today’s context, it is very difficult to
maintain the full functional integrity and resilience of river
ecosystems by e-flows alone (Arthington, 1998; King et al.,
2003; Acreman and Ferguson, 2010). It should be pointed-
out here that this contrasts with modern thinking about flow
variability, as the FDC loses all temporal sequencing of the
flow regime.
The natural flow regime is crucial for sustaining native
aquatic biodiversity and maintenance of ecological processes
in fluvial ecosystems (Bunn and Arthington, 2002; Jardine
et al., 2015) and fragmented riverine ecosystems have altered
flow regimes resulting in loss of fluvial habitat. In
implementing e-flows in managed rivers, serious questions
arise concerning the nature of the pre-disturbance condition
to which a given river should be restored. First of all, the
likely sequence and habitat impacts of channel adjustments
associated with restoration of e-flows are not clear. Second,
it may be better to adjust the flow regimes to the prevailing
hydrological and sediment regimes to develop a more
resilient ecosystem in the long run in the face of climate
change (Cluer and Thorne, 2014). The tendency to
implement ‘static e-flows’ rules by water resource
practitioners ignore natural system complexity and such
mindset will ultimately contribute to further degradation of
river ecosystems (Arthington et al., 2006). Similarly,
quantification of arbitrary minimum flow is inadequate as it
fails to relate patterns of temporal and spatial variation in
river flows to the structure and function of a riverine
ecosystem (Lytle and Poff, 2004). There is also a difference
between river conservation and river restoration, while the
conservation approach puts emphasis on maintaining the
flow regime as near to natural as possible, identifying
unacceptable thresholds of ecological change, the restoration
approach stresses on restoring flow regime towards natural
pattern (Figure 5).
There are significant engineering and ecological trade-
offs, at the same time, unprecedented opportunities for
ecosystem restoration (Stratford et al., 2015; Jain, 2012).
With initial water allocation from the rivers, economic
benefits initially increase sharply and ecological loss is low.
However, with further increase in water allocation, the
incremental benefits are lesser and ecological costs will be
more.
Several EFA methodologies have evolved since early
1980s and they are used globally (Table 2). The first-
generation EFA methods are essentially desktop methods
which may or may not be ecologically relevant. They ignore
Figure 5. River conservation versus river restoration – designs from ‘drawing table’ to more proactive approach
Source: Arthington (2016)
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Table 2. Evolution of EFA methodologies and their shortcomings
Timeframe Approach Specific Methodology Shortcomings
Types
First generation Desktop, rapid assessment, using Hydrologic methods, Hydraulic -Used to justify low-flow allocations
(1980–1995) primarily ecologically relevant Rating Methods -Prescriptive and assessments often
hydrological indices or analysis of done in isolation
hydrological time series data, static -‘Get a number’ syndrome for a
single flow regime
-E-flow will not maintain a pristine
river condition
Second Comprehensive habitat assessment, Habitat rating methods, in-stream -May not be ecologically relevant to
generation using primarily methods or habitat flow incremental methodology advise on suitable flow restoration
(1995–2010) modelling (IFIM), Expert Panel Assessment, -Importance of changes in river’s
DRIFT physical attributes for the aquatic
biota not fully explored
Third generation Integration of habitat and ecosystem Ecological Limits of Hydrologic -Full tolerance of the flow-
(2010–2015) benefits with human well-being, Alteration (ELOHA, Poff et al., ecosystem relationships is still not
structured and dynamic with 2010); Stream Evolution Model possible
ecological values in a changing (Cluer and Thorne, 2014) -Adaptive management of flow
climate scenario, synthesis of regimes with respect to changing
several EFA techniques climate/social preferences being
worked out
Source: Authors’ own elaboration.
parameters of the flow regime to the response of aquatic
species and communities. Hydraulic rating methods (HRM)
were based on channel-discharge relationships and
considered wetted perimeter to calculate e-flows.
Breakpoints were identified in the habitat–discharge
response curve where habitat quality degrades with reduction
in discharge. They also failed to link channel morphology
to habitat supporting aquatic biota. The Building Block
Methodology provides an excellent approach to link river
objectives to flow requirements (King and Louw, 1998). This
method had been applied to Ganga by WWF-India by one
of the co-authors. The second generation EFA methods were
mostly based on habitat-rating approaches – the most
common method of which is the in stream flow incremental
methodology (IFIM). IFIM was developed in the USA; it is
rarely used in full, but the Physical Habitat Simulation
(PHABSIM) model is used. It considers relative
contributions to habitat quality and diversity made by
different channel forms (King and Tharme, 1994), which
was also later advanced by Williams (2010). Stream
Evolution Model developed by (Cluer and Thorne, 2014)
recognises that river streams may naturally be multi-threaded
prior to disturbance and represents stream evolution as a
cyclical, rather than linear phenomenon, recognising an
evolutionary cycle within which streams advance through
the common sequence. The streams skip some evolutionary
stages entirely, recover to a previous stage or even repeat
parts of the evolutionary cycle.
4. Role of Physical Habitat Variables in Maintaining River
Ecosystems
Physical habitat variables play major role in the
distribution of fish and other aquatic species. The physical
habitat of a river includes sediment size and heterogeneity,
channel and floodplain morphology and other geomorphic
features (Poff et al., 1997a). Habitat alteration and
fragmentation has brought about significant endangerment
of freshwater fish fauna in most of the rivers in India. Among
various habitat attributes, water depth, dissolved oxygen,
flow rate and pH are the most important variables in shaping
fish distributions. Fish assemblages are also shaped by the
flow rates, faster current has negative impact on the total
number of fish species. Higher dissolved oxygen stretches
have higher species richness. Similarly, depth less than 1 m
has negative impact on fish diversity. Presence of more deep
pools with low-to-moderate water velocity supports higher
fish diversity. Open river, shallow water and deep pools are
the primary habitats contributing to the maximum diversity,
therefore, protection of these particular habitats is
recommended for conservation and management of the fish
biodiversity (Lakra et al., 2010). The literature also suggests
that species occurrence and richness are driven more by
relationship with abiotic factors (physical habitat variables)
than species interaction. Optimum ranges of physical habitat
variables are provided in Tables 3 and 4.
Regarding the microhabitat, hydro-morphological
parameters (depth and velocity) followed by temperature,
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Climate Change and Environmental Sustainability (April 2017) 5(1): 20-34
turbidity and total dissolve solids are of significance for the
structure of the fish community. Conductivity is another
important factor that explained the major proportion of the
variability affecting fish in their habitat choice. The other
local habitat variables like overhanging vegetation and land
use were of secondary but significantly important for the
assemblage of the fishes. During the flooding season, greater
accessibility of aquatic habitat and food resources enhances
feeding opportunities and early life-stage survival and
storage of fat helps sustain fish during the dry season when
resources become limited and most fish populations
experience greater competition and predation mortality
(Röpke et al., 2017; Lowe-McConnell, 1987) (Figure 6 and
Table 5).
4.1 Between Upstream and Downstream Stretches
In flowing water systems, the habitat characteristics are
largely shaped by physical processes especially the
movement of water and the sediment within the channel and
between the channel and floodplains (Poff et al., 1997a).
Fish communities in riverine system typically follow a
pattern of increasing species richness, diversity and
abundance from upstream to downstream. Fish species
richness decreases with increasing elevation. However, in
some tributaries of Yamuna such as Betwa River, opposite
trend has been observed. Species diversity and species
richness were both less in the downstream areas compared
with the upstream areas (Lakra et al., 2010). It was earlier
observed that increasing community and habitat diversity
followed stream – order gradients (Gorman and Karr, 1978).
4.2 Land use Pattern of the Catchment Areas
Natural streams support fish communities of high
species diversity which are otherwise seasonally more stable
than the lower – diversity communities of modified streams
(Gorman and Karr, 1978). Land use is a primary factor that
cause the declining of aquatic biodiversity in stream
ecosystems (Schlosser, 1991; Karr et al., 1985; Salo and
Table 3. Physico-chemical, biological, physiographic and topographic parameters for defining fluvial habitats
Physico-chemical Biological Variable Physiographic Variable Topographic Variable
Variable
Turbidity (NTU) Phytoplankton (cells/L) River discharge (m3/s) Basin area (km2)
Water temperature (°C) Phytobenthos (cell/cm2) Water velocity (m/s) Slope (m/km)
Total Dissolved Solids (mg/L) Macro-invertebrates (individuals/m2) Slope (m/km) Drainage density (km/km2)
Electrical conductivity (µS/cm) – – –
pH – – –
Dissolved oxygen (mg/L) – – –
Table 4. Fish diversity and habitat relationships – role of physical habitat variables
Physical Habitat Lower Higher Optimum Remarks
Variables Range Range Range
pH 6.1 8.2 7.1–7.5 Both acidic and basic media are not liked by the fresh water species
Temperature (°C) 10.5 25 22–23 A sudden increase or decrease in water temperature may cause fish mortality
Turbidity (NTU) 10.4 46.5 26.5–30.5 While some turbidity may afford greater protection for juvenile fish from
predators; excessive high water turbidity showed negative effect on fish egg
survival, hatching success, feeding efficiency (mainly on filter feeders) and
growth rate and population size
Conductivity (µS/cm) 205 540 300–350 High conductivity areas witness low species richness
TDS (ppm) 135 400 250–300 Higher dissolved solids have adverse effect on abundance of fish diversity
Depth (m) 2.5 9.4 4–5.5 Depth less than 1 m has negative impact on fish diversity in most of the
alluvial rivers
Flow (m/s) 0.14 1.5 0.50–0.75 Water discharge is the best predictor of fish species richness patterns in the
Himalayan rivers. Faster current has negative impact on total number of fish
species. Slow and swift flows are associated with higher fish abundance
Dissolved oxygen 3.63 8.5 4.6–5.8 One of the most important factors for fish abundance and distribution, DO
(mg/L) generally effect the survival of fishes especially juvenile
Source: Authors’ own elaboration.
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Table 5. Habitat stressors and habitat responses and their associated hydrologic and geomorphic responses
Habitat Associated Hydrologic Geomorphic Habitat References
Stressors Changes Responses Responses
Impoundment Discharge seasonality Channel fragmentation, Alternating periods of Fausch et al. (1990),
by dams and influences the biota and downstream channel erosion, resource scarcity during the Rosenberg et al. (1997),
hydroelectric land–water interactions, reduced sediment loads, dry season and resource Sultana and Thompson
development results in significant altered frequency of surplus during the wet (1997), Galat (1998) and
departure from the usual floodplain inundation season, emergence of Ou and Winemiller
hydrological regimen, community dominated by (2016)
reduced discharge few species many of which
downstream of dams, are tolerant forms, habitat
capture sediment moving better suited to many non-
downstream, reduced native biota, during floods
magnitude and frequency some species enter irrigation
of high flows, more canals or channels
stabilised flow regimes, downstream of dams where
change in magnitude of the they die when water levels
annual flood pulses fall during the dry season
Excessive Reduced magnitude and Reduced baseflows, channel Delayed fish breeding Ferguson et al. (2013),
water extraction frequency of high flows down-cutting, fragmentation migrations, may not begin Dudgeon (2000),
for irrigation of hydrological connectivity until flows have passed a Dudgeon (2010)
between rivers and wetlands critical threshold; increase
in discharge may fail to
initiate any population
response, juveniles are
confined within channels,
curtailment of fish migrations
Drainage-basin Retraction of water over the Bank erosion Habitat degradation by Berkman and Rabeni
alteration floodplain is hampered, siltation, altering in stream (1987), Dudgeon
especially increased run-off peaks, habitats, food webs and (1999), Dudgeon
deforestation may concentrate pollutants, flow conditions during (2010), Poff and
alter precipitation and reproductive periods, Zimmerman (2010)
evapo-transpiration in the declines in secondary
basin, increased productivity, declines in
sedimentation and increased reproduction, recruitment
magnitude and frequency of and population abundance
high flows and flash floods
Over harvesting Species loss, lower genetic Pinsky and Palumbi
of fishes diversity (2014)
Water quality Deoxygenation and acidity, Altered nutrient cycling Habitat degradation, inland Lakra et al. (2010) and
deterioration by reduced dilution of fisheries decline and species Sarkar and Dubey
pollution pollutants loss, native fish and (2016)
invertebrate populations
often are limited by adverse
water
Source: Authors’ own elaboration
Cundy, 1987). The variations in the habitat attributes like
pH, turbidity, total dissolved solids and conductivity across
different sites are basically attributed to differences in land
use pattern, which in turn is responsible for variation of
species diversity and distribution (De Silva et al., 2007) and
a consequent decline in fish spawn availability in river. To
capture the ecological and economic significance in relation
to the e-flow requirements for the different reaches of River
Ganga a longitudinal river zonation is required, taking into
account the main physical, environmental and socio-cultural
features and gradients found from the headwaters to the river
mouth (Table 6).
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Climate Change and Environmental Sustainability (April 2017) 5(1): 20-34
Figure 6. An example of natural and environmental flows for maintaining the salmon habitat for spawning and emigration
Source: Naiman et al. (2008)
Figure 7. Habitat wise fish species richness (FSR) in River Betwa
– tributary of Yamuna. Bars with different superscript letters are
significantly different (P < 0.05)
Source: Lakra et al. (2010)
4.3 Impact of Damming
Damming leads to loss of native species as well as
invasion by exotic species (Liermann et al., 2012), because
exotic species can establish in modified or degraded
freshwaters (Poff et al., 2007). Populations isolated in
upstream areas by dams are subject to extirpation when
reproductive failure or high mortality rate cannot be counter-
balanced by re-colonisation from downstream sources
(Winston et al., 1991). Open river habitats are the most
preferred habitat for fishes inhabited in the tropical rivers
(Sarkar et al., 2010; Lobb and Orth, 1991; Aadland, 1993;
Arunachalam, 2000), however, in certain stretch due to
damming, there is a minimum depth of water that is
maintained throughout the season. There is a positive
influence of reservoirs connected with the river as well as
due to existence of more ‘open river, slow water and pool
habitats’ along with macrophytes which might have
importance in fish assemblage and aggregation (Figure 7).
Changes in hydrology especially more reservoir types of
situation due to barriers across river seems be responsible
for the flourishing of exotoic species Cyprinus carpio in
Ganga basin. In the middle stretch of the river Ganges
(Allahabad), Hilsa (Tenualosa ilisha), which used to form a
good share in catches below Allahabad, has almost
disappeared after inception of Farakka barrage despite fish
ladders were installed.
4.4 Altered Habitats as Red Zones
Altered habitat support less biological communities
while less disturbed sites are characterised by a diverse fish
fauna in a variety of habitats (Shahnawaz et al., 2010).
Variables that have negative impact on fish abundance: (red-
zones) – are mainly due to low fish richness due to
degradation of their breeding grounds. For River Ganga, such
altered habitat zones could be:
(a) Stretch having effluent discharge from industries,
thermal power plants and sewerage systems – high BOD
areas are in Hardwar, Kanpur, Allahabad, Varanasi and
Diamond Harbour near Kolkata
(b) High water velocity stretch/due to sudden discharge
(c) High sedimentation rate stretch – Many floodplains have
already lost their connection with main channel due to
heavy siltation. Floodplains serve as breeding and
nursery grounds for several species.
(d) Degraded shoreline habitats
(e) Riverfront development sites which disturb the wetted
shorelines/banks
(f) Fishing sites (exploitary zones)
(g) Stretch having exotic species habitats
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30 Climate Change and Environmental Sustainability (April 2017) 5(1): 20-34
Table 6. Main criteria for e-flow zoning for River Ganga
Sr. Main Crieteria for Elements to Map
No. E-flow Zoning
1. Aquatic ecosystems River – main channel
Streams – tributaries
Wetlands
Lakes
Reservoirs
2. Distribution of iconic Range of Snow Trout
species (Schizothorax richardsonii)
Range of Golden Mahseer (Tor
putitora)
Range of Indo-Gangetic Dolphin
(Platanista gangetica)
Range of Ghariyal (Gavialis
gangeticus)
Range of Indian Narrow-headed
Softshell Turtle (Chitra indica)
Range of Northern River Terrapin
(Batagur baska)
3. Distribution of National Parks
protected areas Wildlife Sanctuaries
Conservation Reserves
4. Riverine habitats Open River (Wide Valleys)
Confined River (Narrow Valleys)
Fast Water (Rapids)
Slow Water (Runs)
Deep Water (Pools)
Shallow Water (Flats)
Riffles
Confluences
Swamps (Marshes)
Riparian Forests
5. Hydrogeomorphological Channel Width
features Sand Banks
Sand Bars
Islands
Floodplains
Terraces
Braiding
Meanders
Oxbow Lakes
Anastomosing
6. Hydrological features Groundwater
Groundwater – Surface water
connections
7. Anthropogenic Dams/Barrages/Weirs
interventions Significant Abstractions
Punctual Pollution Sites
Diffuse Pollution Belts
Predominant Landuse of
Catchment
Cultural Sites
As a result of flow regulation along the River Ganges,
major carp fishery virtually disappeared after seasonal
inundation of the floodplain was prevented by flood control
structures (Natarajan, 1989). The total annual fishing
production in River Ganga has declined from 85.21 t during
1959 to 62.48 t during 2004, thus indicating that the fish
abundance has decreased during the last 5 decades. The
reported catch by the fisher folks have also reduced
temporally. Along with Mahseer (Tor putitora, T. tor) the
other migratory species like dwarf goonch (Bagarius
bagarius), yellowtail catfish (Pangasius pangasius), pangas
catfish (Silonia silondia), hilsa (T. ilisha) and long-whiskered
catfish (Sperata aor) from the middle and upper stretch is
under severe threat due to consequences of damming and
water diversions projects. Fish production has shown a
distinct change in the last two decades in the middle stretch
of River Ganga where the contribution of Indian major carps
has decreased from 41.4% to 8.3% and that of miscellaneous
and catfish species increased (Vass et al., 2008). A total of
143 freshwater fish species have been reported in the all
stretches of River Ganga which is about 20% of freshwater
fish of the total fishes reported in India. A total of 53 species
belonging to 11 families were reported in upper stretch of
Ganga up to foothills of Garhwal Himalayas. Out of 143
species, 29 species are listed under threatened category, 133
species were native to River Ganges and its tributaries and
remaining 10 species were exotics. High species richness
found in orders of Cypriniformes, Siluriformes and
Perciformes, accounting for 50.34, 23.07 and 13.99% of the
population, respectively. The family Cyprinidae (53.47%),
Bagridae (8.46%) and Channidae (1.47%) were found to be
the most dominant in the Ganges. Similarly, in Gomti River
– a tributary of Ganges, 56 fish species belonging to 20
families and 42 genera were earlier reported from various
sampling sites. Of the 56 species, five belong to the
‘endangered’ (EN) category and 11 belong to the vulnerable
(VU) category. Six major categories of habitat were
identified and pattern of fish assemblage and dominant
genera in each habitat studied. Apart from Indian Major
Carps (Labeo rohita, Catla catla, Cirrhinus mrigala), Chitala
chitala, Notopterus notopterus, Ompok pabda, Octopus
bimaculatus, Labeo bata, Labeo calbasu, Cirrhinus reba,
Channa marulius, B. bagarius and Clupisoma garua were
the important species.
5. Development of a Framework for Guiding Research
Questions: Opportunities and Initiatives
The proposed framework as outlined in Figure 8 can be
only a small adjustment to the existing water framework. It
assesses ecosystem vulnerabilities early in the planning
process. It also aids to inform social and economic choice
for preferred flow situation. Water allocation trade-offs are
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Climate Change and Environmental Sustainability (April 2017) 5(1): 20-34
identified and addressed accurately during e-flows
adjustments. The following questions may be specially
investigated during the research studies:
(a) What kind of sensitive ecosystems exist in the river’s
catchment and adjacent floodplains? Which functions
do these ecosystems perform in the maintenance of
sustainable water resources and in the provision of other
natural resources?
(b) What are the different downstream responses to flow
scenarios? How river ecosystems change with flow
changes (flow-ecosystem-relationships)? What are the
main threats to the maintenance of flow-regimes that
maintain integrity of freshwater ecosystems?
(c) What are critical ecological and hydrological thresholds
that maintain river functions and guide adaptive
management to achieve sustainable outcomes?
(d) How to define threshold values of ecological and
hydrological functions as a critical criterion for
identification and mitigation of stressors
(e) How can the protection of freshwater ecosystems be
integrated into joint riparian management strategies with
balancing river ecology and water resource
development?
The methodological framework designed for the study
comprises of four main components which are further
subdivided, as shown in Figure 2. The proposed framework
and the stepwise plan are summarised below:
5.1 Background Hydrology
Starting point in the assessment is the understanding of
river basin, its condition, present flow regime of the river
and how and when that has changed in the past. In the first
instance, ecological status of managed rivers compared with
their historical, unmanaged counterparts should be
characterised. Based on the long-term flow curves,
dependable flow and use and non-use allocation should be
quantified. The idea is to develop regional e-flow standards
vis-à-vis prevailing hydro-climatic and watershed controls.
(a) Characterise ecological status of managed rivers
compared with their historical, unmanaged counterparts
(b) Classify aquatic ecosystem of various disciplines like
rivers, streams, lakes, wetlands and reservoirs
(c) Develop links between stream evolution and ecosystem
services
(d) Develop indices based on time series of river flow data,
allocation based on percentage of MAR or values read
from flow duration curves (FDC). It should however,
be pointed-out here that this contrasts with modern
thinking about flow variability, as the FDC loses all
temporal sequencing of the flow regime.
(e) Define broader objectives to indicate the type of river
desired by stakeholders – achieve specific pre-defined
ecological, economic, or social objectives.
5.2 Assessment of Human Welfare (HW) and River-
Ecosystem Functions (REF)
Attempts should be made to develop plausible links
between stream evolution and ecosystem services. Flow-
dependent species should be identified in each of the river
basin/segments with attempts to define the reference state.
There are available literature and preliminary studies of
populations and communities of fish, macro-invertebrates,
macrophytes and phytobenthos and phytoplanktons.
Simulation of component species is required that would be
found in an ‘undisturbed’ state. Objective-based flow setting
as explained in Acreman and Dunbar (2004) would define
the broader objectives to indicate the type of river desired
by stakeholders – to achieve specific pre-defined ecological,
economic, or social objectives. Additionally, critical fish
habitats may be identified in the river basin to declare them
as fragile areas and conservation reserves. Many fishes might
use these protected areas for breeding and spawning grounds.
The framework should be able to assess effects of local
habitat variables on the structure of fish assemblage.
Additionally, there is also a need for integrating religious,
cultural and social connection between people and the river.
(a) Characterise and quantify river-ecosystem functions as
well as human welfare goods such as water for drinking,
hydropower, irrigation, ûoodplain agriculture, fishery
yield, desirable geomorphic form and native riverine
biodiversity
(b) Estimate dependable flow and quantify use and non-
use allocation
(c) Develop regional e-flow standards vis-à-vis prevailing
hydro-climatic and watershed controls
(d) Identify major ‘fluvial habitat types’ based on physical
and biological parameters. Within the major habitat
types, identify micro-habitats, which could have distinct
Figure 8. The methodological framework designed for the
comparative e-flow adjustments and trade-off assessment
Source: Authors’ own elaboration
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32 Climate Change and Environmental Sustainability (April 2017) 5(1): 20-34
attributes. Some iconic species should be identified
along with their distribution range
5.3 Scenario Development and Calibration
Possible drivers of human well-being, environmental
pressures such as climate change and land use change should
be assessed and quantified. The dynamics of how river-
ecosystem functions interact to affect ecosystem resilience
can be simplified through modelling techniques building
upon the approach recommended in Arthington et al. (2006)
and Poff et al. (2010). Decision consequences on multiple
human welfare (HW) and river-ecosystem functions (REF)
can be assessed in a formal analytical framework, including
non-market valuation of environmental amenity and social
preferences (Martin et al., 2015) in selected stretches.
Economically and environmentally acceptable strategies for
various river types (based upon evidence gathered from
different river basins) can be used to guide development of
flow standards for individual rivers and river segments.
(a) Understand how drivers of human well-being,
environmental pressures such as climate change and land
use change and river-ecosystem functions interact to
affect ecosystem resilience – application of simulation
models (ecosystem integrity of rivers in its full width
of spectrum)
(b) Explore decision consequences on multiple HW and
REF indicators in a formal analytical framework, non-
market valuation of environmental amenity
(c) Design management decisions that need to balance
ecosystem sustainability with desired economic
objectives, buffer aquatic and riparian ecosystems
against climate change in regulated rivers
5.4 Adaptive Management and Adjustments
The adaptive management toolkit will provide a clear
understanding of likely tradeoffs with e-flow implementation
that will alter the river-ecosystem function (REF) and their
watersheds, including the prevailing legal environmental
regulations. Water resources in India are under great pressure.
There is no possibility of returning River Ganga flows to
anything near natural. Therefore, possible reconciliation of
environmental flows and other water uses in Ganga could
be arrived at by reducing the water allocation to inefficient
irrigation system or by more adaptive management. This
could be done by:
(a) Quantify the interacting effects of multiple hydrological
and ecological drivers, environmental pressures and
intrinsic mechanisms, such as density dependence, on
the resilience of flow-dependent species (channel-
ecology, flow regimes and riverine ecosystems)
(b) Develop guidance on restoration principles, adaptive
management and conflict management principles and
test it regionally in a river basin
6. Conclusion
In this paper, some important aspects of the nature of
river ecosystems including environmental-flows have been
outlined. To attain the goal of freshwater sustainability, the
current river management philosophy must make a transition
beyond the narrowly defined ‘economic criteria’ to include
socially valued ‘ecosystem functions and services’.
Satisfying ecological objectives during e-flows management
may improve economic performance of water infrastructure
systems, thus improving human well-being as well as
ecosystem functions. This necessitates identification of
critical ecological thresholds that maintain river functions
and guide adaptive management to achieve sustainable
outcomes. Therefore, the need for scientifically credible flow
management guidelines that include stakeholder-defined
engineering and ecological goals is very much desired.
Therefore, there is a need to design a decision support
framework, that explicitly and quantitatively explores trade-
offs in implementation of e-flows across a range of possible
management actions under unknown future hydrological and
climate states, using evidence from river basins across the
different parts of the world. Such framework should be able
to identify critical ecological thresholds that maintain river
functions and guide adaptive management to achieve
sustainable outcomes – considering how biological diversity
is important in delivering ecosystem services of rivers. The
framework should also include metrics of natural capital
(such as abundance, diversity or interactions in food web
structure) that could help define critical ecological thresholds
for e-flows; above which rivers deliver ecosystem services
and are resilient, below which services stop and the system
degrades. Several approaches can be combined together
using grounded theory and bottom-up embedded approaches
in operationalising ecologically contextualised sustainable
river ecosystem functions. The integrated approach to study
variable flow regime in understanding the river ecosystems
can help in understanding
(a) River system integrity: Are the proposed environmental
flows adequate for maintaining the ecological integrity of
the River?
(b) Strategic interventions philosophy: What changes in the
Legal and Policy framework are necessary to implement an
environmental flow? And
(c) Evidence-based eco-hydrology: What tools can be
developed to enhance our understanding of the river systems’
integrity and science of eco-hydrological system? Lastly,
no matter how advanced and accurate the e-flows
assessments are, the ecological integrity of a river basin
remains vulnerable if flow regimes are drastically managed
and no actual releases are made to restore the flows.
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