Dear Dr. Nagar D P,

I will try to answer your question. In Slovak Republic, we have these calculations for "Ecological Flow" - aka Minimum Balance Flow - MQ:

- for streams under reservoirs:

MQ = Q355d

- for other streams:

MQ = (Qmin m + Q100 min d)/2

where:

Qmin m - a value taken from probabilistic field of the average month flows for a high level of safeguard, usually 98 %;

Q100 min d - a value of minimal day-flow with an average occurence once in 100 years

It is necessary to re-evaluate these results for every catchment due to local specific conditions.

Best wishes,

Tomas

Minimal flow in Czech Republic:

-streams with flow Q355d < 0,05 m3.s-1: a long-term value of uninfluenced Q330d recommended

-streams with flow Q355d = 0,05–0,5 m3.s-1: a long-term value of uninfluenced (Q330d+Q355d) * 0,5

-streams with flow Q355d = Q355d = 0,51–5,0 m3.s-1: a long-term value of uninfluenced Q355d

-streams with flow Q355d > 5.0 m3.s-1: a long-term value of uninfluenced (Q355d+Q364d) * 0,5

Tomas

Thank you very much Dr. Tomas and Abhishek for your valuable reply.

Dear Mr. Nagar,

        Based on my experience in assessing e-flow in respect of hydro-electricity project clearance from MoEF, I attach the required write-up for your use. Best method of e-flow assessment at present is to follow MIKE 11 tool.

 Environmental Flows

Riverine ecosystems are among the most impacted ecosystems worldwide. Human activities, such as the construction of dikes, dams, barrages and weirs, the straightening and deepening of river channels, the conversion of floodplains to agricultural land, water abstraction, water transfer and pollution; etc., have heavily modified most large lowland rivers. As a result, a large number of fish species became threatened or endangered and the fish productivity of most riverine ecosystems has declined. This is all the more troubling since, large lowland rivers support a significant proportion of the world’s fish diversity and their fisheries provide a major source of food, employment and income to society. Until now, the flow regimes of most large lowland rivers have been heavily manipulated to serve the needs of society. To balance the interests of different stakeholder groups, many countries have implemented water resources management plans. Water policy decisions are typically made with little or no consideration of fish conservation and fisheries, despite a high public perception of fish. The reason is not only the relative lower socioeconomic importance of fisheries compared to ecosystem services such as flood protection and navigation. Whereas the optimal flow regime for navigation, agriculture and flood protection (in terms of magnitude, timing and duration of flow events) is comparably easy to determine, the consequences for fish diversity and fisheries are much more difficult to quantify.

Environmental flow refers to the water considered sufficient for protecting the structure and function of an ecosystem and its dependent species. Environmental flows are required to be maintained through a river reach for sustaining its ecosystem and dependent species. It means enough water is to be released in the downstream of the river system after utilizing the water for the development projects in order to ensure downstream environmental, social and economic benefits. Realizing its importance, several countries have made ensuring environmental flows mandatory. For example, The Mekong River Agreement, 1995; South Africa’s National Water Act, 1998 and the Swiss Water Protection Act, 108. These legislations attempt to ensure required minimum flow in the river system to sustain ecosystem services. A wide range of environmental flow methodologies (EFMs) have been developed to determine flow thresholds for various objectives such as the preservation of natural conditions, the maintenance or restoration of ecological integrity and cultural and recreational values. Most of these methods were developed primarily to protect endangered fish species and to maintain fisheries resources in human-modified rivers. Until now, these methodologies have been mostly applied to small upland rivers and headwater streams. Although a growing body of literature summarizes the status of available EFMs the question remains whether or not these EFMs are suitable to protect fish diversity and fisheries resources in regulated large lowland rivers.

 Methodologies for estimation of environmental flows worldwide

Most currently available EFMs can be grouped in four main categories:

1. Hydrological methods

2. Hydraulic rating

3. Habitat simulation methods

4. Holistic methodologies.

In European countries, hydrological and habitat simulation are the prevailing methods, while some developing countries and countries with newer environmental legislation have focused on holistic methods. Hydrological methods rely primarily on flow measures and indices, which are drawn from historical time series data on annual or daily mean flow. Still widely used is the Tennant method (also known as Montana method), which relates the ratio between river discharge and fish habitat availability to certain percentages of annual flows to meet predefined requirements (Tennant, 1976). The Tennant method assumes similarity of aquatic habitats when carrying the same proportion of average flow but rarely considered the effective habitat quality at varying flows. The method lists eight categories of in-stream flow that range from maximum to severe degradation. Below the threshold of 10% mean flow, the environmental conditions for fish are judged to be degraded, whereas 50% provides for excellent conditions in terms of stream width, water depth and velocity. While the Tennant method does not explicitly consider duration or the timing of flow events, some extensions integrate flow duration and frequencies. Other hydrological methods include duration percentiles or single flow indices that are usually generated from historical stream flow databases. One example is the widely used 7Q10, which is defined as the ‘seven-day, consecutive low flow with a ten-year return frequency; the lowest stream flow for seven consecutive days that would be expected to occur once in ten years’ (United States Environmental Protection Agency) or similar discharge indices. 

 Hydraulic rating considers the channel morphology of a given river and calculates acceptable flows by relating river discharge with a variety of hydraulic characteristics such as water depth, velocity or wetted perimeter. These methods rely on transects measured across a river section comprising habitat factors that are assumed to be limiting factors for target biota. The wetted perimeter method considers the variation in wetted perimeter or river width with water discharge. Plotting the wetted perimeter against discharge shows a breakpoint where a comparable small decrease in discharge results in a comparably larger decrease in wetted perimeter. This breakpoint is used as a minimum in-stream flow recommendation. The widely used habitat simulation methods are sophisticated extensions of hydraulic rating methods within a framework addressing many ecological components of riverine ecosystems (IFIM, In-stream Flow Incremental Methodology, Bovee, 1982). Within the context of IFIM, a broad range of modelling tools such as PHABSIM aim to predict how physical habitat conditions (i.e. water depth, velocity, cover, substrata) change with discharge. Typically, detailed hydrological and hydraulic data for a grid of cells in a river stretch are compared with the habitat suitability of a target species. The habitat suitability is expressed as a habitat suitability curve (e.g. suitability index curve, probability of use or preference curve), often seasonally defined, which specifies the assumed seasonal requirements of different species, life stages or habitat guilds. The curves depict the relationship of target organism’s response to a gradual changing habitat variable scaling from unsuitable to suitable, which are usually obtained from existing data or field measurements. By comparing the curves with the predicted habitat area at various flows, the minimum flow thresholds can be defined in a way so that the discharge provides optimal habitat conditions, retains a percentage of habitats at average flow or provides a minimum amount of habitat area. Most commonly, the flow threshold is set at the breakpoint in the habitat/flow curve where proportionally more habitat is lost with decreasing flow than is gained with increasing flow. The commonly used output of, for example PHABSIM quantifies the suitability of a location for a target species in terms of a weighted usable area (WUA; expressed as, e.g. m2 1000m stream length1). More advanced software tools such as 2D and 3D models achieve greater hydraulic representation. Other models allow for inclusion of water quality, temperature and other biological factors such as prey densities, energy allocation and behavioral components. The complexity of current models is growing and there are many approaches to establish statistical techniques that improve the predictability of species abundance on the basis of biotic and abiotic variables. The growing recognition that rivers are closely connected to their watersheds has led to the realization that protecting and rehabilitating riverine ecosystems requires sensitivity, not only to the key hydrological, biological and ecological, but also to the economic and social aspects of a riverine ecosystem. Assuming that a natural flow system will maintain the ecological function of a riverine ecosystem, so-called holistic methodologies will define the critical environmental flows of an entire riverine ecosystem rather than focusing on the needs of a single species.

Holistic methods rely less on modelling and more on multidisciplinary panels covering biophysical disciplines such as hydrology, geomorphology, sedimentology, water chemistry, botany and zoology. Advanced methodologies such as DRIFT (Downstream Response to Intended Flow Transformations Methodology, King et al., 2003) consist of different modules that integrate biophysical, and economic and social factors and aim at participating stakeholder groups. Within the biophysical module, various EFMs such as habitat-modelling tools can also be implemented. The growing recognition that rivers are closely connected to their watersheds has led to the realization that protecting and rehabilitating riverine ecosystems requires sensitivity not only to the key hydrological, biological and ecological, but also to the economic and social aspects of a riverine ecosystem. Assuming that a natural flow system will maintain the ecological function of a riverine ecosystem so-called holistic methodologies will define the critical environmental flows of an entire riverine ecosystem rather than focusing on the needs of a single species. Holistic methods rely less on modelling and more on multidisciplinary panels covering biophysical disciplines such as hydrology, geomorphology, sedimentology, water chemistry, botany and zoology. Advanced methodologies such as DRIFT consist of different modules that integrate biophysical, and economic and social factors and aim at participating stakeholder groups. Within the biophysical module, various EFMs such as habitat-modelling tools can also be implemented.

 Analysis of Environmental flows

Mostly, to maintain specific river classes, the E-flows are estimated world-wide at monthly time-scale using the Flow-Duration curve analysis. For this, generally, a minimum of 25 years river discharge time series data is used. It is the management and planning authority, who decides the quantity of E-flow to be released to maintain a particular environmental management class (EMC) of the river. A river may be classified into six environmental management classes of A, B, C, D, E, and F depending on the following flow.

modification category (Kleynhans, 1996). The more pristine is the desired management class, the higher is the E-flow requirement.

 Class A (Natural): Pristine river condition or minor modification of in-stream and riparian habitat.

 Class B (Slightly modified): Largely intact biodiversity and habitats in the river despite water resources development and/or basin modifications

 Class C (Moderately modified): The river habitats and dynamics of the biota have been disturbed, but the basic ecosystem functions are still intact. Some sensitive species are lost/or reduced in extent; however, the alien species are present.

 Class D (Largely modified): There is large changes in the river natural habitats, biota and basic ecosystem functions with a clearly lower than expected species richness. A clearly lower than expected species richness.

 Class E (Seriously modified): Habitat diversity and availability have declined. A strikingly lower than expected species richness. Alien species invaded the ecosystem.

 Class 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 river status is not acceptable at all.

Hence, the E-flow should be released from the dam so that it can maintain the EMC-B condition, which should not be less than the EMC-C condition in worst case.

Flow-Duration Curve (FDC) Method

The flow-duration curve is the plot between the percentages of time that flow in a stream is likely to equal or exceed some specified value of interest. The basic time unit used in preparing a flow-duration curve will greatly affect the nature of the curve. For most studies, mean daily discharges are used. These will give a steep curve. When the mean flow over a long period is used (such as mean monthly flow), the resulting curve will be flatter due to normalization of short-term peaks by averaging with intervening smaller flows during a month. The extreme discharge values are averaged out more and more, as the time period gets larger (e.g., for a flow duration-curve based on annual flows at a long-record station). The shape of a flow-duration curve in its upper and lower regions is particularly significant in evaluating the river and basin characteristics. The shape of the curve in the high-flow region indicates the type of flood regime the river basin is likely to have; whereas, the shape of the low-flow region characterizes the ability of the river basin to sustain low flows during dry seasons. A very steep curve (high flows for short periods) would be expected due to rainfall in small watersheds, as the watershed behave non-linearly to the rainfall-runoff transformation process. The floods due to snowmelt, which last for several days, or regulation of floods with reservoir storage, will generally result in a much flatter curve near the upper limit. In the low-flow region, an intermittent stream would exhibit periods of no flow; whereas, a very flat curve indicates that moderate flows are sustained throughout the year due to natural or artificial stream flow regulation, or due to a large groundwater capacity which sustains the base flow to the stream.

In this study, the available 10-daily averaged observed discharge time series in a particular month for different years are ranked using the Weibull plotting position method. The flow-duration curve for that specific month is represented by a table of flow values (percentiles) covering the entire range of probabilities of occurrence corresponding to 17 fixed percentage points: 0.01, 0.1, 1, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 99, 99.9, and 99.99%. These percentage points ensure that the entire range of flows is adequately accounted for. The flow-duration curve developed using the historical data is termed as the reference class. For estimating the Environmental Flow (E-flow) requirement for different categories of EMC, the flow duration curve is shifted by one step, two steps, three steps, and four steps for EMC-A, EMC-B, EMC-C, and EMC-D, respectively. The E-flow is computed based on the 90% dependable flow of this FDC for different EMCs. The E-flow thus computed for different months is routed along the river reached downstream by using the MIKE 11 Hydrodynamic Model (DHI-Water & Environment, 2012) to simulate the spatial distribution of discharge, flow depth, and flow velocity at different sections of the river downstream under no lateral flow condition.

Habitat Simulation Method

The main issue with the FDC method is a limited justification of the permissible FDC shifts per EMC. The currently accepted step of a shift (one FDC table point per class) is based on limited calibration of the proposed method. It is very difficult to evaluate the results when there are no ecological data available to confirm or deny the suitability of the estimated EF. It is, in principle, possible to collect some limited hydraulic information for rivers and examine the characteristics of the available habitat (water depth, wetted area and velocity, for example) under different flow conditions (natural and FDC shifting method recommendations). This is not, however, a real substitute for scientific information on the relationships between ecological characteristics and flow.

Keeping this in view, a further assessment is to be carried out using habitat simulation and hydraulic modelling. Habitat requirements have to be established in different seasons for baseline data collected .

From baseline data, habitat requirement are to be established to protect fishes in the river limbs. Dependency of the local population on rivers for other needs e.g. domestic requirement, irrigation, navigation, commercial fisheries. is not there.

Flow modeling has to be carried out for different release scenarios in different seasons using Mike11. Flow simulations generally to be carried out for 10%, 15%, 20%, 25%, 30%, 40%, 50% and 100% releases of the average discharge in 90% dependable year of the flow series. Annual series may be further divided into Monsoon, Lean and pre & post monsoon period. Flow release recommendations are to be made using this approach to ensure habitat requirements are met with throughout the year.

MIKE 11 Hydrodynamic Model

The MIKE11 hydrodynamic model (DHI-Water & Environment, 2012) is widely used world-wide to model the 1-D flood wave movement in rivers under steady and unsteady flow conditions. This model solves the de Saint-Venant equations of continuity and momentum using six-point Abbot numerical scheme. The Saint-Venant equations of continuity and momentum are to be followed.

 The MIKE11 model uses the E-flow as the upstream boundary condition, which is then routed along the river downstream to estimate the discharge, flow depth and velocity at different sections of the river reach at different time levels. MIKE11 is accepted by US Federal Emergency Management Agency for use in the National Flood Insurance Program.

  Comments

The Report on Estimation of Environment Flows Requirement for tropical rivers like India typically may include the following;

 Baseline Data, broadly given below, may be elaborated.

 Secondary sources based on literature covering fish fauna of rivers rivers

 Primary sources – Based on sampling and analysis covering physico-chemical and biological characteristics

 ·         Physico–chemical Characteristics (water and sediment)                                                     

·         Periphyton, Phytoplankton and zooplankton                                                                     ·         Macro-Invertebrates (benthic) Fish Fauna

 ·         Fish species sampled during different seasons

·         Catch Per Unit Effort

·         Size/s of fish caught during sampling in different season

·         Habitat Characteristics of sites where sampling was conducted like substrate, river depth, flow velocity, etc.

 The data from the seasonal sampling on water quality and biological features (phytoplankton, zooplankton, macro-benthos, fishes, etc) are to be included in the report along with discussion on seasonal trend in parameters and correlation, if any, between water quality and biological parameters of key species.

 Establishing habitat requirement based on Ecological and Social needs in different seasons – Lean (Winter), Monsoon, pre and post monsoon, i.e., Flow Depth, Width, Velocity, Turbidity, Flood Peaks, Intermittent Wetting of Riparian vegetation during high flows, etc. needs to be elaborated in a report.

 Meeting of habitat requirement through environment flow may also be elaborated in a report.

 ·        

·                                                                                

·         Spills from dam during monsoon to be assessed

·         

Hydrology

MIKE 11 has been used for hydro-dynamic modelling and several runs for different discharges must  be made with number of inputs .

 Maximum number of river cross-sections on river limbs need to be used for modelling (at least 9-10 sections on each limb). The use of data for several sections would facilitate assessment of critical stretch.

 . The entire river reach needs to be represented in the model set up using all the cross sections provided.

             The model output should include flow depth, velocity of flow and top flow width at each cross section of the study reach for 10%, 15%, 20%, 25%, 30%, 40%, 50% & 100% flow of the average of leanest 4 months, 4 monsoon months & other 4 months in 90% dependable year.

 The flow simulation results, viz., depth of flow, velocity and top flow width of all the three seasons need to be correlated with the respective riverine fauna to estimate the environmental flow requirements.

You can use the IWMI Environmental Flow Calculator, see more details in 'Smakhtin and Anputhas, 2006' and Indicators of Hydrologic Alteration (IHA) see details in 'Richter et al., 1997'.

Hi to all. Does anyone know how we can estimate the minimum ecological flow of springs?