Environmental flows A methodology of calculation for India (Part 1)

Balancing the environmental flows with the growing population and rapid urbanisation is most essential to tackle the problem of water scarcity

 

IWMI Abstract

In order to maintain the ecological goods and services of rivers and other hydrological regimes like wetlands, lakes, etc., environmental flow allocations (eflows) are a necessity. At the same time, water demands in India are increasing and will keep increasing and solutions like waste water treatment, pollution control, correction of leakages and wastage of water, efficient irrigation systems, efficient agricultural systems, etc., will take considerable time to evolve, even with our best efforts. So what should we do in the meantime? There are vulnerable ecological systems on the verge of collapse..How do we respond to these challenges?

One of the options is to adopt an approach which allocates eflows on priority. This involves working out a specific ‘Environmental Management Class’ (EMC) of a river based on ecological and physical criteria. River basins and hydrological systems which have high biodiversity and unique habitats, or which provide considerable ecological goods and services to its dependant population, or which are seriously threatened due to challenges like abstraction, pollution, impoundment, etc. will have a higher EMC and need to be prioritized for conservation and eflow allocation.

Currently, this approach only involves ecological criteria. But in India, social and cultural criteria can also play an important role in river conservation. As the field of environmental economics progresses, no doubt an economic criterion can be added to these!

In 2007, a team from IWMI, including Dr. Arunachalam worked on “Developing procedures for assessing Ecological Status of Indian River basin in context of Environmental Flow Requirements”. This is a summary of the report in two parts. The current post describes the methodology, and a succeeding post will describe the results of applying this methodology to some Indian rivers.

Dr. Arunachalam, head of the Sri Paramakalyani Centre for Environmental Sciences, from Manomaniam Sundarnar University, Alwarkurichi, Tamil Nadu is an aquatic ecologist who has been trying to link flows, regulation, pollution, with aquatic diversity. He has worked extensively on ecological assessments of rivers in India, especially in the Western and Eastern Ghats and has discovered several fish species. He can be contacted at: drarunacm@gmail.com.

Introduction:

Environmental water requirements, also referred to as ‘Environmental Flows’ are a compromise between water resources development and the maintenance of a river in some ecologically acceptable or agreed condition. The issue of environmental flows is relatively new in the world. Existing environmental flow assessment methods reflect the diversity of opinions on this subject and range from comprehensive expert panel approach to arbitrarily selected hydrological indices. In many developing countries, such as India, the issues of environmental water demand have not yet received the required attention. The first National Workshop on Environmental Flows, held in New Delhi, in March 2005, brought together over 60 participants from national agencies and research institutions. The workshop generated a significant interest to the concept of environmental flows in the country, and it also revealed the existing confusion in this field.

One of the major problems with developing environmental flow work in countries like India, is that despite existing significant knowledge on some aquatic ecosystem components (e.g., fish), it has never been interpreted in the context of environmental flow assessments.

The impacts of reducing/ increasing high or low flows on fish, invertebrates, riparian vegetation, or sediment regime (which is one determinant of aquatic habitat), for example, are not quantified. In some countries, the lack of such relationships and quantitative knowledge is addressed by expert panels and/or by certain scoring systems, which rank a condition of an ecosystem and/or its sensitivity to flow changes . Such scores are then fed into the determination of an environmental category or environmental management class (EMC). EMC, in turn, is used (together with measures of flow variability or analysis of hydrological time series) to determine the acceptable limits of flow reduction/increase in a river, i.e., actual environmental flows. It is assumed that the higher the EMC, the more water will need to be allocated for ecosystem maintenance or conservation and, more flow variability will need to be preserved. The existing scoring systems reflect the level of available expertise and ecological data.

Methodology:

Ideally, the definition of the environmental management class (EMC) should be based on existing empirical relationships between flow changes and ecological status/conditions, which are associated with clearly identifiable thresholds. Therefore, EMC is a management concept that has been developed and used in the world because of a need to make decisions regardless of the limited lucid hydro-ecological knowledge available. The following are points that would go into determining the EMC for a particular river:

  • What is the ecological sensitivity and importance of a river basin? The rationale for this is that the higher the ecological sensitivity and importance of aquatic ecosystems in a river basin is, the higher the EMC should be, ideally.
  • What is the current condition of aquatic ecosystems in a river basin? The more natural the current condition of the basin is, the greater the incentive for its maintenance as such.
  • What is the trajectory of change? This question aims to identify whether a river is still changing, and in what direction, how fast and due to what impacts. The rationale is that if the deterioration of aquatic environment continues, it will be more difficult to achieve a higher EMC, even if it is necessary, due to its high importance and sensitivity

As this is the first time that such an approach is introduced in India, the focus should be on highlighting the main aquatic features and problems of each basin. This means that aggregate environmental indicators, which reflect different features or conditions of a river basin, could be used for scoring. Among the recent relevant works on this,  

The first question above may be seen as an attempt to design a condensed measure of the ecological value of the basin, albeit in non-monetary terms. An arbitrarily selected set of semi-quantitative and quantitative indicators includes:

  • Presence of rare and endangered aquatic biota
  • Presence of unique (e.g., ‘endemic’) aquatic biota
  • Diversity of aquatic habitats
  • Presence of protected areas, areas of natural heritage and pristine areas, which are crossed by the main water course in the basin
  • Sensitivity of aquatic ecosystems to flow reduction

Indicators from this group are calculated using national ecological surveys and databases. Considering that most of the ‘ecological’ attention in countries like India has so far been given to fish, such indicators as rare and endangered biota and unique biota are calculated here using available fish data. Rare and endangered fish species are first identified using IUCN (1994) categories such as CR (critically endangered) and EN (endangered). Their cumulative number is then expressed as the proportion of the total number of fish species found in a river basin. The assessment of diversity of aquatic habitats and sensitivity of aquatic ecosystems to flow reduction requires expert judgment and knowledge of a particular river. Presence of protected or pristine areas can be assessed against existing guidelines for protected area management, i.e., IUCN (1980), which sets the aim of 10 percent of the basin to be protected.

The second question above relates to what the river system looks like at present, compared to a reference condition in the past (e.g., prior to construction of major dams), or compared to some similar and relatively undisturbed subbasins in the same physiographic settings. The indicators used in this study include:

  • percentage of the watershed remaining under natural vegetation cover types
  • percentage of the floodplain areas remaining under natural cover types
  • percentage of aquatic biota that are exotics
  • overall richness of aquatic species
  • the degree of flow regulation
  • the degree of river fragmentation
  • human population density in a river basin
  • (percentage of population density in the main floodplains)
  • overall water quality in the basin

The first two indicators are normally estimated from the GIS maps, remote sensing data, or already published literature sources. In some cases, a percentage of the floodplain areas actually remaining in a basin compared to some past reference condition may be used as an alternative to the second indicator. A proportion of exotic species (e.g., fish), can be calculated as a percentage of the number of total fish species recorded in the basin. Overall species richness may be assessed as a proportion of the total number of species in a country, or in a larger geographical region, whichever is more appropriate, or by an expert score on a scale from low to high. The most straightforward way of calculating the degree of flow regulation is as a ratio of total storage of all dams to the long-term mean annual natural flow volume of the basin. It is acknowledged though that this approach does not recognize timing or types of flow events that are altered—which may be more critical than change in volume per se. A degree of river fragmentation can be represented by a simple indicator of spatial changes to habitat—longitudinal and latitudinal (river-floodplain) connectivity of rivers. Human population density in a river basin as a percentage of population density in the main floodplains (which could be seen as an aggregate indicator of human pressure on aquatic ecosystems) may be calculated using Census data and GIS, where the floodplains are arbitrarily defined as areas within 2.5 kilometers (km) of either side of the main channel and the channels of the main tributaries. (It is acknowledged that such a definition does not fully recognize the difference between the typical riparian zone and floodplains). An approximation of the overall water quality in a river is indexed using Indian national water quality categorization, which has several classes, from A to E —depending on the level of pollution—expressed by ranges of several constituents.

With regard to the third question above, no specific indicators are used and ‘trend assessment’ is left primarily to professional judgment. It may be seen as an attempt to foresee how the river will look like in the short-term (e.g., 5 years) and in the long-term (e.g., 20 years) in case of a ‘do-nothing-toprotect- aquatic-environment’ scenario.  Regardless of the original units and ways of estimation of every individual indicator, all indicator values in this study are then converted to a standard scoring system, which includes ratings: 1 (none), 2 (minor), 3 (moderate), 4 (high) and 5 (very high). Table 1 summarizes the indicators which have been used in this study, and explains why an indicator has been considered and how it is relevant in the context of the estimation of environmental water demand. The scores for individual indicators are then summed up and their sum is expressed as a percentage of the maximum achievable score. The actual percentage shows the degree of the deviation of a basin from its natural condition and, therefore, the most probable EMC. The latter, in turn, may be related to the amount of water that needs to be allocated for environmental purposes in this basin.

Table 1

A preliminary set of basin indicators, their scoring systems and justification.

Indicator Range  Score
Justification in the Context of Environmental Flow Assessment
Indicators Related to Ecological Value (Importance and Sensitivity)
Rare and endangered aquatic fauna

Very High

High

Moderate

Minor

None

5

4

3

2

1

The total number of rare and endangered species can be expressed as a percentage of the total number of species in a country, region or basin—depending on the scale of analysis. These percentages may be related to the range and to the score. The more rare and endangered aquatic biota is present in the basin, the more sensitive the rivers generally are to flow changes (e.g., to reduction). Consequently the more effort is needed to maintain the flow in a river at least at existing levels.
Unique aquatic biota

Very High

High

Moderate

Minor

None

5

4

3

2

1

The number of unique (endemic) species can be expressed as a percentage of the total number of species in a country, region or basin—depending on the scale of analysis. These percentages may be related to the range and to the score. The assumption is that the more unique aquatic biota is present in the basin, the more important it is to ensure that they do not get affected by flow modifications. Therefore, more flow and more flow variability needs to be preserved in a river.
Diversity of aquatic
Habitats

Very High

High

Moderate

Minor

None

5

4

3

2

1

Can be estimated either by professional judgment or a more quantitative approach, e.g., by identifying different habitat types in representative river reaches and then calculating the representative value for a basin. Example of habitats include runs (rapidly flowing water with a gradient over 4% with no surface turbulence), pools, glides (a shallow stream reach with a maximum depth of under 5% of the average, and without surface turbulence), pocket water (one or a series of small pools in a section of flowing water containing numerous obstructions), backwater (abandoned channel that remains connected to the active main river or secondary channel in which the inlet is blocked with deposition at low water velocities but the outlet remains connected with the active main channel), floodplains and marshes (including mangroves), etc. The assumption is that the more habitat types are present, the more incentives should exist to preserve them to ensure the aquatic biodiversity as well.
Presence of protected areas of natural heritage and pristine areas which are crossed by the main watercourse in the basin

>10

5-10%

3-5%

1-3%

<1%

5

4

3

2

1

Based on the IUCN aim of 10% of the basin area to be rotected. The more area that is protected, pristine or 'a must to be reserved,' the more flow is likely to be necessary to be left in rivers, or to be released into them for maintenance of aquatic life.

 

Sensitivity of aquatic
ecosystems to flow
reduction

Very High

High

Moderate

Minor

None

5

4

3

2

1

Can be evaluated using professional judgment and knowledge of a river. A limited decrease in flow in some rivers may result in particular habitat types (e.g., floodplains, riffles, brackish costal wetlands, estuaries) becoming unsuitable for biota, compared to other rivers, e.g., smaller rivers versus larger rivers, rivers in drier areas versus those in more humid ones, etc. The assumption is that highly sensitive ecosystems need more water to maintain them in the current or desired condition.
Indicators Related to Ecological Condition of Aquatic Ecosystems in the Basin   
Percentage of
watershed remaining
under natural vegetation
cover types

70--100%

50--70%

30--50%

10--30%

<10%

5

4

3

2

1

Can be estimated using RS images, from literature sources or based on field surveys. These are measures of the extent to which natural vegetation communities have persisted in a watershed or a floodplain. An area that retains a high proportion of natural cover types may be expected to also have many essential ecosystem services, such as flood control, still intact. Because it still Contains 'natural capital' in the form of natural communities, the ecological structures and functions of such a watershed or floodplain would also be expected to be more sustainable, and their resilience and ability to cope with anthropogenic and natural stress would be greater. The assumption is that the higher the values of both indicators, the more biodiversity is likely to be preserved and the more the basin is insured against the functional degradation. If the natural capital is important to maintain at existing conditions, the higher EMC will be necessary and more environmental flows will be required.
Percentage of floodplain
remaining under natural
vegetation cover types

70--100%

50--70%

30--50%

10--30%

<10%

5

4

3

2

1

Degree of flow regulation

>100%

50--100%

20- -50%

10- -20%

0-10%

1

2

3

4

5

The first indicator is the total dam storage in a basin as a percentage of the mean flow, the second—the catchment area upstream of dams as a percentage of the total catchment area. These are important determinants of the habitat condition and aquatic biodiversity. Many riverine species move large distances through channel networks as part of their life history requirements. Dams and weirs disrupt longitudinal connectivity and fragment populations leading to decline in aquatic biodiversity. Migratory species often form the basis of productive fisheries and are typically the most affected by such barriers. A high density of impoundments prevents biota from migrating to preferred habitats such as upstream spawning beds. As these ecological processes are degraded, the sustainability and coping capacity of the system is reduced. Environmental flows should be allocated to cater for longitudinal and lateral connectivity. The more the river system is fragmented, the lower is the ecological status, hence a lower environmental management class is achievable.
Percentage of the
watershed closed to
movement of aquatic
biota by anthropogenic
structures

70--100%

50--70%

30--50%

10--30%

<10%

1

2

3

4

5

A preliminary set of basin indicators, their scoring systems and justification (contd).

Indicator Range Score Justification in the Context of Environmental Flow Assessment
Indicators Related to Ecological Condition of Aquatic Ecosystems in the Basin
Degree of flow fragmentation 0

0.001-0.01

0.01-0.1

0.1-1

>1
5

4

3

2

1
This indicator is an alternative to the above one. The ranges are expressed in a number of structures per km of river length.
Naturally flowing river without structures.
  • With/out upstream storage reservoirs and with possibilities of movement upstream—like fish ladders—for aquatic fauna.
  • With/out upstream storage reservoirs and with possibilities of movement upstream—like fish ladders—for aquatic fauna.
  • With/out storage reservoirs with/out possibility for movement upstream for aquatic fauna only during monsoon.
  • With/out storage reservoirs with/out possibility for movement upstream for aquatic fauna only during monsoon.
Percentage aquatic
biota that are exotics

0%

<5%

<10%

<20%

>20%

5

4

3

2

1

Successful invasion by exotic species often incurs losses and disruptions in ecosystem structures and functions (e.g., loss of biodiversity due to competitive exclusion and predation, disruption and modification of food webs, loss of habitat for fish and wildlife). Thus, the percentage of exotic species in a reach or a basin provides information on its likely sustainability and coping capacity. The higher the proportion of exotic species the lower the achievable EMC is.
Fish species relative
richness, aquatic plant
species relative richness, etc.

Very High

High

Moderate

Minor

None

5

4

3

2

1

These are measures of biodiversity remaining in a system and therefore—of its ecological capital and ability to self-organize and sustain itself and cope with stressors. It is important to address relative richness, rather than just species counts because the baseline biodiversity of an area is conditional on habitat types, geographical locations, etc. Thus, the number of species that inhabit a watershed should be expressed as a percentage of the number that would be expected to occur there in the absence of human interventions. Xenopoulos et al. (2005) have shown that fish species numbers are reducing with reducing discharge. The reference condition is, however, very often difficult to establish and consequently the quantification of ranges is also difficult. As a surrogate for the percentage of some 'natural' reference condition, the species richness may be quantified as a percentage of overall species in the country or geographical zone, or established by professional judgment.
Human population density  in the entire river basin as a percentage of the
population density in the main floodplains

10%

10-20%

20-40%

40-60%

>60%

1

2

3

4

5

Can be estimated using Census data. Districts located primarily in floodplain areas can be used to estimate population density in floodplains, other districts - to estimate population density in the rest of the basin. It is assumed that this measure may be seen as an aggregate indicator of human pressure on aquatic ecosystems and as an indicator of disruption of lateral connectivity in river basins.

 

Overall water quality in
the basin

Class A

Class B

Class C

Class D

Class E

5

4

3

2

1

National Indian categorization of water quality is used, where each class is characterized by certain ranges of constituents. Water in Class A can be used for drinking after disinfection; water in class B is only for swimming and bathing; water in Class C requires conventional treatment and disinfection before drinking; water in Class D is suitable for propagation of wildlife and fisheries; and water in class E is only suitable for such uses as irrigation and industry cooling.

<!--[if gte mso 10]>

5

4

3

2

1

Indiacators for the Periyar Basin

Indiacator Value Score Justification and Comments Data Sources
Rare and endagered aquatic biota Very high 5 Periyar basin has 5 critically endangered fishes and 14 threatened species. Fourteen species have become extinct. Some fish speies disappered over the past few years. Including some cyprinids, goby, catfishes and eeis. Arun (1998)
Kurup et al (2001)
Unique aquatic biota Very high 5 Fifty-Sic percent of the endemic fishes of Kerala are reported from Periyar (32 species), which makes it a unique ichthyfaunal basin of southern india    Kurup et al (2001) Arun (1998)
Diversity of aquatic habitats Very high 5 Many threatened fish species inhabit pools, streams, runs, cascades-a diverse aquatic habitat types system. Arunachalam (2000a)
Presence of protected and pristine areas Very high 5 The river flows through the famous peniyar Wildlife Sanctuary Latest sateillite imagery shows that around 30% of the basin is covered by dense pristine forests  
Sensitivity of aquatic reduction High 4 Multiple dams reduced flow which leads to decline in fish diversity extinction of fish, prawans and shrimps prticularly in lower reaches Large-scale fish mortality between Edamalayar and Eloor industrial sites are reported as well as algal bloom of Osicillatoria sp. Given the number of impacts and that Periyar is a relatively small river, the sensitivity to further flow reduction is high. Joseph (2004)
Percentage of the watershed under natural vegetation 30-50% 3

National Remote Sensing data shows 30% of the watershed is covered by dense natural forests.

 

Joseph (2004)
Degree of flow regulation 20-50% 3 Calculated as the ration of total storage capacity (3.27BCM) to long-term mean annual flow volume at the outlet (12.3 BCM). Which equals 25% KSEB (2004)
Percentage of the basin closed to movement of aquatic biota by structures 70-100% 1

The construction of 15 dams and wiers have almost closed the river system to movement of the biota through the basin.

 

 
Percentage of aquatic biota that are exotic <10% 3 Some species have been introuduced in reservoirs (carp) which can be found in streams as well at present Sugunan (1995)
Fish species relative richness Very high 5 The basin is verry rich in fish species havingg 208 species out of the toal of 287 species in the Western Ghats (70%) or out of estimated total 577 in India (36%) Joseph (2004)
Overall water quality Class B 4

Water quality of the upstream and middle reaches is as a rule in class B. The water quality was rated as class C in the most downstream parts.

 

Singh and Anandh (1996) Joy and Balasrishnan (1990)

In the next post, we will look at the above results for the Periyar basin and some other Indian river basins more closely.

Download the complete paper from the NRLP-IWMI website here.

Regions

Subscribe to <none>