Environmental Flow Practice in India

Multi-purpose demands for water exist throughout the year, and these are increasing with time. Storage and withdrawal of river water reduce natural flows downstream of the control structure on the river. Downstream of the control structure, there could be critical reaches in which altered flows are not able to sustain the riverbed ecology and riparian environment existing prior to the construction of the control structure on the river. Strengths and limitations, as well as the requirements of input data and the outcomes of available environmental flow assessment (EFA) methodologies, are reviewed. In the USA, the percentages of the mean flow are specified that provide different quality habitats for fish, e.g., 10% for poor quality (survival), 30% for moderate habitat (satisfactory), and 60% for excellent habitat. The indices have been adapted for other climatic regions in North America and have been widely used in planning at the river basin level. An Environmental Management Class (EMC)-based flow duration curve (FDC) Approach is an FDC-based approach that links environmental water requirement (EWR) with EMC. EMC refers to the prescribed or negotiated condition/status of an ecosystem. Several methodologies (particularly holistic ones) reviewed ( Table 14.1 ) require extensive data, which are usually not available for rivers in India. Unlike other countries, consideration of tropical monsoon hydrology, socio-economic, cultural, and religious roles of rivers in India is also necessary in prescribing environmental flows. Rivers are worshipped as mothers, and many of the customs and festivals are linked with them. The EFA practice in India is gaining importance. At present, environmental flows (EFs) are usually prescribed in terms of simple hydrological indices [by the Central Water Commission (CWC) and the Ministry of Environment, Forest & Climate Change (MoEF&CC)]. Table 14.1 Input, Output, Strengths, and Limitations of Various EFA Methodologies Method Input Output Strengths Limitations Lookup tables (hydrologic index method) Monthly/seasonal FDC; Average annual flow Exceedance probability flows (percentile flows) Relatively rapid, non-resource intensive; appropriate at the planning level or in low controversy situations; The Tennant method is most applicable for mountain streams with virgin flow Low resolution estimate of EF. High potential for under-allocation when uses and diversions are poorly known, with little provision for recommending spates and floods. Based on the assumed relationship between habitat suitability and proportions of mean annual flow. Allocations are more generous than required in regions with variable flows Desktop methods using hydrologic data Gauged or modeled daily/weekly/monthly flow data Percentage of mean annual runoff, FDCs in relation to EMC Useful when no ecological information available; relatively rapid, non-resource intensive; appropriate at planning level or in low controversy situation; Examine the whole range of river flow regimes rather than simple pre-derived statistics of lookup tables Low resolution estimate of EF; based on assumed relationship between habitat suitability and proportions of mean annual flow Desktop methods using hydrological and ecological data Hydrologic and ecological data Relationship between the score of the observed taxon and the river flow Utilize the existing ecological and hydrological data; flow and ecology are directly addressed Difficult to derive biotic indices that are sensitive only to flow; time series of ecological data may not be independent and thus may violate assumptions of statistical techniques Hydraulic rating method Hydrologic and hydraulic data and hydraulic relations to habitat Relation between discharge and % reduction in hydraulic habitat availability Hydraulics is used as a surrogate for the biota; provides simple indices of available habitat Inflection points in the relationship between flow and wetted perimeter may be absent or poorly defined. Poorly developed species-specific habitat requirements increase the potential for errors; the distance between transects and the total number of transects are critical in determining the reliability of estimated changes in habitat structure Habitat Simulation Methodologies discharge; hydraulic related biological response: biota Habitat-discharge curve; habitat-time curve Deal with micro-habitat; environmental flow recommendations are based on the integration of hydrological, hydraulic and biological response data Require hydrologic, hydraulic, and biological response data at multiple cross-sections and habitat simulation modeling Holistic approach Expert opinion, fluvial geo-morphology, hydraulic, ecology, hydrologic, social, and recreational aspects, and field visits EF regime on a month-by-month and element-by-element basis; alternate water use scenarios Incorporates more detailed assessment of flow variability than early BBM studies; includes the method for generating trade-off curves for examining alternative water use scenarios; applicable to regulated/unregulated rivers and for flow restoration; high potential for application to other aquatic ecosystems; recommends a monitoring program as a crucial component; allows for using a wide array of quantitative methods and tools Some risk of inadvertent omission of critical flow events; lack of structured set of procedures and clear identity for EFM hinders rigorous routine application; it is based on quantification of links between flow and outcomes for aquatic ecosystem which may not be correctly known Building block methodology Expert opinion, fluvial geo-morphology, hydraulic, ecology, hydrologic, social, and recreational aspects, and field visits Rapid advice on EF, physical, ecological, social, and economic consequences of a water resource project, scenario-based assessments of alternative flow regimes Rigorous and extensively documented (manual and case studies available); prescriptive bottom-up approach; includes social component (dependent livelihoods); incorporates a monitoring program; high potential for application to other aquatic ecosystems; links to public participation processes; less time, cost and resource intensive than DRIFT; applicable to regulated or unregulated rivers and in flow restoration context; now incorporates a method facilitating top-down Limited potential for examination of alternative scenarios relative to DRIFT; risk of omission of critical flow events (common to all holistic methodologies) Expert panel assessment method Expert opinion, visual assessment of trial releases, available data Professional judgment, EFR using fish communities as indicators Good for initial assessment; site-specific focus; rapid and inexpensive; low resource intensity; makes use of field-based ecological interpretation of multiple trial flow releases from dams, at one or a few sites, to determine EFR (expressed as flow percentiles) Limited resolution of EF output; aims to address river ecosystem health, rather than to assess multiple ecosystem components; strongly reliant on professional judgment; no explicit guidelines for application; poor congruence in opinion of different panel members (due to subjective scoring approach, individual bias) Scientific panel assessment method Same as above + collection and interpretation of field data, prior empirical studies, theoretical literature Recommendations on many aspects of flow regime, flow-related ecological requirements, flow strategies More refined and transparent version of EPAM; key features of the ecosystem and hydrological regime and their interactions at multiple sites are used as a basis for EFA; includes stakeholder-panel member workshop; well-defined EFA objectives; potential for inclusion of other ecosystem components; moderately rapid, flexible and resource intensive Limited use of field data; poor definition of output format for EFR; less quantitative supporting evidence Habitat analysis method Hydrologic and hydraulic data, panel expertise, infrastructure development. In catchment, water quality, morphology, fish population, important habitat Critical flow requirements of habitats and sensitivity levels Relatively rapid, inexpensive, basin-wide reconnaissance method for determining preliminary EFRs at multiple points in catchment; Technical Advisory Panel Workshop-based method, superior to simple hydrological EFMs; field data limited or absent; represents a simplified version of the holistic approach Inadequate for comprehensive EFAs; little consideration of specific flow needs of individual ecological components; requires standardization of process and refinement of flow bands linked to habitats Instream flow incremental methodology Hydrologic, hydraulic data at multiple transects, target taxa Discharge-related changes in usable area (measure of habitat) for target taxa Considers both policy and technical issues; integrates micro and macro habitats; useful in negotiations; institutionalized and being applied in an inflexible fashion Wide range of issues included providing avenues for criticism; more emphasis on modeling at the expense of other critical steps; Downstream response to imposed flow transformation Hydrologic, hydraulic, geomorphologic, and water quality data, aquatic and health profiles of water users, animals, socio-economic data Scenarios of future flow regimes and consequences for the condition of the river, impacts on subsistence users of river resources Rigorous and well-documented top-down, scenario-based process; appropriate for comprehensive EFAs (1–3 years) based on several sites within representative and critical river reaches; ability to address socio-economic links to ecosystem; scope for comparative evaluation of alternative modified flow regimes; potential for application to other aquatic ecosystems; output is suitable for negotiation of tradeoffs; links to external public participation process and macro-economic assessment; applicable to regulated or unregulated rivers and for flow restoration; recommends a monitoring program Resource intensive; limited inclusion of flow indices describing system variability; requires documentation of the generic procedure for wider application India faces several water-related challenges. Balancing the water requirements of the environment and other uses is becoming critical in many of the river basins in India due to the increase in population and associated water demands. The CWC has specified EFs for the Himalayan and Ganga, Krishna, and Godavari river basins. Government policy on environmental flow in Indian rivers is stated in a policy brief for public information. In a study of the Nathpa Jhakri Hydroelectric Project (NJHEP), a methodology comprising hydrological and ecological studies has been developed and applied to assess environmental flows. The main affected phenomenon is riverbed ecology. Hydrological (river mapping), hydraulic (cross section, water depth, and velocity), and ecological features (river bed and bank flora and fauna) in the study reach have been determined. Available practices for the assessment of EF have been applied, and hydraulic habitat analysis has been carried out.