ENVIRONMENTAL FLOW REQUIREMENTS OF INDIAN RIVER

BASINS

VLADIMIR SMAKHTIN and MARKANDU ANPUTHAS

International Water Management Institute (IWMI), Colombo, Sri Lanka

Workshop on India’s Water Futures to 2025/2050. March 9, 2006, Anand, Gujarat, India

OBJECTIVES OF THIS STUDY COMPONENT

• review the current status of environmental flow estimation methods in the world and examine the applicability of those in the Indian context

• provide a pilot method for quick estimation of environmental flow requirements of rivers and apply it for major Indian river basins

• suggest the way forward in environmental flow assessment in India, which can be pursued to enhance environmental water research and policies in India

THE CONTEXT

• Major water transfers are planned between a number of river basins, but very little if any assessment of environmental aspects of the plans has been done

• Virtually no previous studies exist in India on Environmental Flow Requirements (EFR), but interest to these problems grows

• Access to hydrological time series data (which forms the basis of EF assessment) is extremely difficult and for many basins – impossible.

GENEARL PRINCIPLES OF EFR

• Flow is a major determinant of physical habitat in rivers, which in turn is the major determinant of biotic composition.

• Flow regime changes lead to habitat alterations, changes in species distribution and abundance, loss of biodiversity of native species.

• The invasion and success of exotic and introduced species in rivers is facilitated by the alteration of flow regimes. Inter-basin water transfers represent the major mechanism for the spread of exotic species.

• Maintenance of flow variability is the primary goal of environmental flow assessment and management

TYPES OF EFR METHODS

• Detailed assessment, using primarily holistic methodologies, or methods based on habitat modeling. Complex, data intensive and time consuming.

• Desktop assessment, using primarily ecologically relevant hydrological characteristics (indices) or analysis of hydrological time series. Low confidence but quick

• Both types require observed or simulated flow time series representing unmodified (natural) flow regimes

FLOW DATA

• Most of the observed flow data downloaded from the Internet, some -primarily for recent 10-15 years - provided by Dr Mohile to the project. Those are impacted and therefore could be used for placing the EFR estimates “into the context”, but not usable for EFR otherwise.

• Monthly time series, with missing data, different periods of record, etc

• Altogether we are estimating EFR for 13 sites located at the outlets of 13 major river basins.

THE APPROACH USED

• Large task +limited EFR work +limited flow data => Desktop EFR method and major rivers only.

• The approach still has to cater for all ecosystem components and therefore has to describe EF variability, not just to set some minimal flow

• Take the most advanced Desktop EFR method to date and simplify it to avoid excessive parameter estimation and to make it commensurate with the very limited flow data available

• Use management categories (levels of environmental protection) as a concept useful to set different EFR for different river conditions.

• Calibrate the newly developed method against the original Desktop for those limited cases where “reasonably” good flow data are available

• Develop a draft procedure for the assessment of the most suitable management category for a basin using local knowledge and expertise – Indian aquatic ecologists.

CATEGORIES OF ENVIRONMENTAL PROTECTION (ENVIRONMENTAL FLOW MANAGEMENT CLASSES - EMC)

EMC ECOLOGICAL DESCRIPTION MANAGEMENT PERSPECTIVE

A: Natural Pristine condition or minor modification of in-stream and riparian habitat

Protected rivers and basins. Reserves and national parks. No new water projects allowed.

B: Slightly modified

Largely intact biodiversity and habitats despite water resources development and/or basin modifications.

Water supply schemes or irrigation development present or allowed.

C: Moderately modified

The habitats and dynamics of the biota have been disturbed, but basic ecosystem functions are intact.

Multiple disturbances associated with the need for socio-economic development, e.g. dams, diversions, etc

D: Largely modified

Large changes in natural habitat, biota and basic ecosystem functions have occurred. A clearly lower than expected species richness.

Significant and clearly visible disturbances associated with basin and water resources development, including dams, diversions, transfers, habitat modification and water quality degradation

E: Seriously modified

Habitat diversity and availability have declined. A strikingly lower than expected species richness. Alien species have invaded the ecosystem.

High human population density and extensive water resources exploitation.

F: Critically modified

Modifications have reached a critical level and ecosystem has been completely modified with almost total loss of natural habitat and biota.

This status is not acceptable from the management perspective. Management interventions are necessary to restore flow pattern, river habitats etc (if still possible / feasible).

USE OF ENVIRONMENTAL INDICATORS TO SET

ENVIRONMENTAL MANAGEMENT CATEGORY

• What is the Ecological Sensitivity and Importance of the river basin? – The higher the ES and I of a aquatic ecosystems in a river basin,

the higher the environmental category should ideally be. Consequently, more water should be allocated to aquatic ecosystems and more flow variability should be preserved.

• What is the Current Condition of aquatic ecosystems in the river basin?– The more pristine the current condition of the basin is, the higher

the environmental category should be. Consequently, more water should be allocated to aquatic ecosystems and more flow variability should be preserved to maintain it in the existing condition. Also, the better the current condition, the more incentive should be to keep it at that.

• What is the Trend of Change?– If deterioration of aquatic environment still continues (negative

trend) it will be more difficult to achieve a higher ecological condition even if it is necessary due to high importance and sensitivity. The rate of change may also be assessed here and taken into account. This question may be interpreted as the one addressing the future vulnerability of the basin

USE OF ENVIRONMENTAL INDICATORS TO SET

ENVIRONMENTAL MANAGEMENT CATEGORY

• Each of the above questions is answered by using a set of quantitative and qualitative indicators. Each indicator has its scoring system. The total score leads to placement of a basin into some environmental category

• Example indicators: – Rare and endangered aquatic biota (primarily fish)– Overall richness of aquatic species (fish)– 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– Degree of flow regulation– % of the basin remaining under natural cover types, etc

• The following basins or parts thereof are currently assessed by local experts in aquatic ecology:– Krishna, Narmada, Cauvery, Peryar and parts of Ganga

LATERAL SHIFT OF THE FLOW DURATION CURVES FOR THE ESTIMATION OF “ENVIRONMENTAL” CURVES FOR DIFFERENT

MANAGEMENT CATEGORIES

100.0

1000.0

10000.0

0.01 0.1 1 5 10 20 30 40 50 60 70 80 90 95 99 99.9 99.99

% Time flow exceeded

Month

ly F

low

(M

CM

)

Original A class B class C class D class

Direction of shift

Reference (original) FDCA

BC

D

EFR DURATION CURVES FOR KRISHNA OUTLET

0.1

1.0

10.0

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0.01 0.1 1 5 10 20 30 40 50 60 70 80 90 95 99 99.9 99.99

% Time f low exceeded

Mon

thly

Flo

w (

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M)

Original A class B class C class D class Class E Class F

EFR DURATION CURVES FOR MAHI OUTLET

1.0

10.0

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0.01 0.1 1 5 10 20 30 40 50 60 70 80 90 95 99 99.9 99.99

% Time flow exceeded

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Original Class A Class B Class C Class D Class E Class F

Estimates of long-term EWR volumes (expressed as % of natural MAR) at river basin outlets for different environmental management classes

River Natural MAR, BCM*

EWR estimates (% natural MAR)

Class A Class B Class C Class D Class E Class F

Brahmaputra 585 78.2 60.2 45.7 34.7 26.5 20.7

Cauvery 21.4 61.5 35.7 19.6 10.6 5.8 3.2

Ganga 525 67.6 44.2 28.9 20.0 14.9 12.1

Godavary 110 58.8 32.2 16.1 7.4 3.6 2.0

Krishna 77.6 62.5 35.7 18.3 8.4 3.5 1.5

Mahanadi 66.9 61.3 34.8 18.5 9.7 5.6 3.6

Mahi 11.0 41.9 17.1 6.5 2.3 0.8 0.3

Narmada 45.6 55.5 28.8 14.0 7.1 3.9 2.5

Pennar 6.3 52.7 27.9 14.3 7.3 3.8 2.0

Tapi 14.9 53.2 29.9 16.6 9.0 4.9 2.6

Periyar 5.1 62.9 37.3 21.2 12.1 6.9 3.9

Sabarmati 3.8 49.6 24.2 12.1 6.6 3.7 2.1

Subarnarekha 12.4 55.0 29.9 15.4 7.4 3.4 1.5

HOW TO GENERATE AN EFR TIME SERIES FROM ITS FDC

EXTRACTS FROM ACTUAL AND SIMULATED TIME SERIES AT VIJAYAVADA (KRISHNA OUTLET)

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Months since January 1991

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Observed at present Simulated natural EFR Class B EFR Class D

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1 11 21 31 41 51 61

Months since January 1991

Mo

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Observed at present Simulated natural EFR Class B EFR Class D

OUTPUTS OF THIS STUDY

• A new EFR methodology which could be replicated in other basins and in the same basins – with addition data, at different reaches

• A summary of EFR for each basin outlet in the form of Flow Duration Curves for each environmental management category

• Corresponding EFR estimates as % of the natural MAR

• Corresponding EFR time series

• A draft methodology for the assessment of the most suitable environmental management category for a basin

• IWMI Research Report (submitted), CPWF report and journal article – later in the year

CONCLUSIONS

• A new EFR method is simple and quick to apply and is the first-ever EFR method actually developed for Indian conditions. At the same time, it is generic and can be used elsewhere

• The study was conducted in the conditions of extreme lack of flow data. The method needs to be tested more in different Indian rivers and at much smaller scales than used herein. Lack of access to data will impede all EFR initiatives in India in the future, if not resolved.

• A requirement for better ecological justification of the method represents an ideal opportunity to initiate several comprehensive EFA studies and feed the future ecological information into the method.

• A few studies on ecological sensitivity and value of rivers in India have been initiated. But they are largely illustrative at present – they show what can be done. This needs to be done in other basins and at finer scales.

• EFR are estimated to achieve specific ecological objective (e.g. provide ecologically important flow-related habitat). EFR are not motivated to solve water quality problems by dilution. Severely polluted Indian rivers are at risk if only the recommended EF remain in the river without non-point source pollution control and without effluent treatment at source.

• Actual environmental flow provisions are not the same as environmental water demand estimates. No matter how advanced and accurate the EFA is, its output remains on paper if no actual releases are made or if the prescribed limit of water resource exploitation is violated.

• Ideally, each planned water transfer of NRLP should go through at least quick EFR assessment – at donor and recipient sites.

THANK YOU !