26320 Water Resources and Environment Technical Note C.1 Environmental Flows: Concepts and Methods Series Editors Richard Davis Rafik Hirji WATER RESOURCES AND ENVIRONMENT TECHNICAL NOTE C.1 Environmental Flows: Concepts and Methods SERIES EDITORS RICHARD DAVIS, RAFIK HIRJI The World Bank Washington, D.C. Water Resources and Environment Technical Notes A. Environmental Issues and Lessons Note A.1 Environmental Aspects of Water Resources Management Note A.2 Water Resources Management Policy Implementation: Early Lessons B. Institutional and Regulatory Issues Note B.1 Strategic Environmental Assessment: A Watershed Approach Note B.2 Water Resources Management: Regulatory Dimensions Note B.3 Regulations for Private Sector Utilities C. Environmental Flow Assessment Note C.1 Environmental Flows: Concepts and Methods Note C.2 Environmental Flows: Case Studies Note C.3 Environmental Flows: Flood Flows Note C.4 Environmental Flows: Social Issues D. Water Quality Management Note D.1 Water Quality: Assessment and Protection Note D.2 Water Quality: Wastewater Treatment Note D.3 Water Quality: Nonpoint-Source Pollution E. Irrigation and Drainage Note E.1 Irrigation and Drainage: Development Note E.2 Irrigation and Drainage: Rehabilitation F. Water Conservation and Demand Management Note F.1 Water Conservation: Urban Utilities Note F.2 Water Conservation: Irrigation Note F.3 Wastewater Reuse G. Waterbody Management Note G.1 Groundwater Management Note G.2 Lake Management Note G.3 Wetlands Management Note G.4 Management of Aquatic Plants H. Selected topics Note H.1 Interbasin Transfers Note H.2 Desalination Note H.3 Climate Variability and Climate Change Copyright © 2003 The International Bank for Reconstruction and Development/THE WORLD BANK 1818 H Street, N.W., Washington, D.C. 20433, U.S.A. All rights reserved. Manufactured in the United States of America First printing March 2003 2 CONTENTS Foreword 5 Acknowledgments 7 Introduction 9 Environmental Flows and River Management 11 Environmental flows--the water left in a river ecosys- tem, or released into it to manage the condition of the ecosystem--are critical for maintaining ecosys- tems. The Significance of Different Flows 13 The flow regime of a river can be divided into base flows, small floods that occur every year, and occa- sional large floods that spread out onto floodplains. Identifying these flow components--and understand- ing the ecosystem consequences of their loss or modi- fication--is central to a flow assessment. Methods for Quantifying Environmental Flows 16 Authors Catherine Brown, Jacqueline King Many methods have been developed over the last 20 years to establish environmental flows. There is a Technical Adviser considerable body of experience for temperate and Stephen Lintner semi-arid rivers, but only limited experience in the ap- plication of these methods to tropical rivers. Editor Robert Livernash Environmental Flows in the Decisionmaking Process 24 Flow assessments are increasingly used as part of en- Production Staff vironmental assesments, as well as tools in water re- Cover Design: Cathe Fadel source management that display the wider costs as well as the benefits of development. Design and Production: The Word Express, Inc. Implementation 25 Environmental flows should be only one part of an in- Cover photo by tegrated set of environmentally sensitive water resource Curt Carnemark, World Bank developments. River, Chile This series also is available on Conclusion 27 the World Bank website (www.worldbank.org). Further Information 28 3 WATER RESOURCESANDENVIRONMENT · TECHNICAL NOTE C.1 Boxes 1. Terminology 11 2. Examples of valued features of rivers that could be protected through environmental flows 12 3. Effects of different components of a flow regime on rivers 13 4. Actions that impact flow and consequences for aquatic ecosystems 14 5. Instream flows that are not environmental flows 15 6. Features of prescriptive and interactive methodologies 16 7. Incorporation of social data into flow assessments 23 8. Desirable features for a successful environmental flows implementation 26 Figures 1. An annual hydrograph of daily flows in a river 13 2. Hypothetical schematic illustrating the general relationships between ecosystem use and condition 15 3. Wetted-perimeter method 19 4. The "building blocks" of the modified flow regime created using the BBM 20 5. Conceptualization of how PHABSIM calculates habitat values as a function of flow 22 6. Basic components of a DRIFT assessment 23 Tables 1. Relative data and time requirements of selected flow assessment methods 17 2. Tennant Method: percentage of average annual flow (AAF) required to achieve different objectives 17 3. Phases of IFIM and DRIFT 21 4 ENVIRONMENTAL FLOWS: CONCEPTSANDMETHODS FOREWORD The environmentally sustainable development and priority in Bank lending. Many lessons have been management of water resources is a critical and learned, and these have contributed to changing complex issue for both rich and poor countries. It attitudes and practices in World Bank operations. is technically challenging and often entails difficult trade-offs among social, economic, and political con- Water resources management is also a critical de- siderations. Typically, the environment is treated velopment issue because of its many links to pov- as a marginal issue when it is actually key to sus- erty reduction, including health, agricultural tainable water management. productivity, industrial and energy development, and sustainable growth in downstream communi- According to the World Bank's recently approved ties. But strategies to reduce poverty should not lead Water Resources Sector Strategy, "the environment to further degradation of water resources or eco- is a special `water-using sector' in that most envi- logical services. Finding a balance between these ronmental concerns are a central part of overall objectives is an important aspect of the Bank's in- water resources management, and not just a part terest in sustainable development. The 2001 Envi- of a distinct water-using sector" (World Bank 2003: ronment Strategy underscores the linkages among 28). Being integral to overall water resources man- water resources management, environmental agement, the environment is "voiceless" when other sustainability, and poverty, and shows how the 2003 water using sectors have distinct voices. As a con- Water Resources Sector Strategy's call for using sequence, representatives of these other water us- water as a vehicle for increasing growth and re- ing sectors need to be fully aware of the importance ducing poverty can be carried out in a socially and of environmental aspects of water resources man- environmentally responsible manner. agement for the development of their sectoral in- terests. Over the past few decades, many nations have been subjected to the ravages of either droughts or floods. For us in the World Bank, water resources man- Unsustainable land and water use practices have agement--including the development of surface and contributed to the degradation of the water resources groundwater resources for urban, rural, agriculture, base and are undermining the primary investments energy, mining, and industrial uses, as well as the in water supply, energy and irrigation infrastruc- protection of surface and groundwater sources, pol- ture, often also contributing to loss of biodiversity. lution control, watershed management, control of In response, new policy and institutional reforms water weeds, and restoration of degraded ecosys- are being developed to ensure responsible and sus- tems such as lakes and wetlands--is an important tainable practices are put in place, and new predic- element of our lending, supporting one of the es- tive and forecasting techniques are being developed sential building blocks for sustaining livelihoods and that can help to reduce the impacts and manage for social and economic development in general. the consequences of such events. The Environment Prior to 1993, environmental considerations of such and Water Resources Sector Strategies make it clear investments were addressed reactively and prima- that water must be treated as a resource that spans rily through the Bank's safeguard policies. The 1993 multiple uses in a river basin, particularly to main- Water Resources Management Policy Paper broad- tain sufficient flows of sufficient quality at the ap- ened the development focus to include the protec- propriate times to offset upstream abstraction and tion and management of water resources in an pollution and sustain the downstream social, eco- environmentally sustainable, socially acceptable, logical, and hydrological functions of watersheds and economically efficient manner as an emerging and wetlands. 5 WATER RESOURCES ANDENVIRONMENT · TECHNICAL NOTE C.1 With the support of the Government of the Nether- The Notes are in eight categories: environmental lands, the Environment Department has prepared issues and lessons; institutional and regulatory is- an initial series of Water Resources and Environ- sues; environmental flow assessment; water qual- ment Technical Notes to improve the knowledge ity management; irrigation and drainage; water base about applying environmental management conservation (demand management); waterbody principles to water resources management. The management; and selected topics. The series may Technical Note series supports the implementation be expanded in the future to include other relevant of the World Bank 1993 Water Resources Manage- categories or topics. Not all topics will be of inter- ment Policy, 2001 Environment Strategy, and 2003 est to all specialists. Some will find the review of Water Resources Sector Strategy, as well as the past environmental practices in the water sector implementation of the Bank's safeguard policies. useful for learning and improving their perfor- The Notes are also consistent with the Millennium mance; others may find their suggestions for fur- Development Goal objectives related to environmen- ther, more detailed information to be valuable; while tal sustainability of water resources. still others will find them useful as a reference on emerging topics such as environmental flow assess- The Notes are intended for use by those without ment, environmental regulations for private water specific training in water resources management utilities, inter-basin water transfers, and climate such as technical specialists, policymakers and variability and climate change. The latter topics are managers working on water sector related invest- likely to be of increasing importance as the World ments within the Bank; practitioners from bilateral, Bank implements its environment and water re- multilateral, and nongovernmental organizations; sources sector strategies and supports the next gen- and public and private sector specialists interested eration of water resources and environmental policy in environmentally sustainable water resources and institutional reforms. management. These people may have been trained as environmental, municipal, water resources, ir- rigation, power, or mining engineers; or as econo- mists, lawyers, sociologists, natural resources Kristalina Georgieva specialists, urban planners, environmental planners, Director or ecologists. Environment Department 6 ENVIRONMENTAL FLOWS: CONCEPTSANDMETHODS ACKNOWLEDGMENTS The Bank is deeply grateful to the Government of ter Cullen of the Cooperative Research Centre for the Netherlands for financing the production of this Freshwater Ecology in Australia. Technical Note. This Technical Note was reviewed by the following Technical Note C.1 was drafted by Catherine Brown Bank staff: Hans-Olav Ibrekk, Alessandro Palmieri, and Jacqueline King of the Southern Waters Eco- Tor Ziegler, and Jean-Roger Mercier. We are grate- logical Research and Consulting Pty (Ltd) in Cape ful for their suggestions. Town, South Africa. The authors wish to thank Pe- 7 ENVIRONMENTAL FLOWS: CONCEPTS AND METHODS INTRODUCTION The flows of the world's rivers are increasingly be- eries will be considered in decisions concerning ing modified through impoundments such as dams the operation of reservoirs and the allocation of wa- and weirs, abstractions for agriculture and urban ter." The World Bank's environmental assessment supply, maintenance of flows for navigation, drain- policy (Operational Policy 4.01) is triggered if modi- age return flows, and structures for flood control. fications to river flows lead to adverse environmental These interventions have had significant impacts, risks and impacts. If changes in flow have the po- reducing the total flow of many rivers and affecting tential to cause significant loss or degradation of both the seasonality of flows and the size and fre- natural habitats, borrowers must also comply with quency of floods. In many cases, these modifica- the Bank's natural habitats policy (Operational tions have adversely affected the ecological and Policy 4.04) in order for a loan to be approved. hydrological services provided by water ecosystems, which in turn has increased the vulnerability of Technical Notes C.1 to C.4 deal with environmen- people--especially the poor--who depend on such tal flows. Although changes in flow will affect wa- services. There is now an increasing recognition ter quality--for example, by increasing or decreasing that modifications to river flows need to be balanced turbidity--the focus in these notes is primarily on with maintenance of essential water-dependent eco- the direct effects of flow on the ecological function- logical services. The flows needed to maintain these ing of rivers and the management of water quan- services are termed "environmental flows," and the tity. Note C.1 introduces concepts and methods for process for determining these flows is termed "en- determining environmental flow requirements for vironmental flow assessment," or EFA. rivers, including a description of how different sorts of river flows contribute to the maintenance of riv- The recognition that modifications to river flows are ers, the practicalities of undertaking a flow assess- an important source of riverine, floodplain, and in ment, the need for balancing environmental and some cases estuarine degradation is relatively re- offstream demands for water, and the challenges cent. The methodology linking downstream re- faced in implementing environmental flows. Note source degradation and C.2 reviews some impor- their social consequences tant case histories. Note is also in its early stages C.3 describes the rein- of development. The statement of flood re- World Bank acknowl- Bank leases from reservoirs for edged the issue in its 1993 orld W, floodplain inundation. Water Resources Manage- Note C.4 addresses the ment Policy, which in- downstream social issues Carnemark cluded as an objective that arising from changes in Curt "the water supply needs of by flows. rivers, wetlands, and fish- Photo River crossing agricultural fields, Nepal 9 ENVIRONMENTAL FLOWS: CONCEPTS AND METHODS ENVIRONMENTAL FLOWS AND RIVER MANAGEMENT Environmental flows are the water that is left in a flows and ecosystem functioning, so that environ- river ecosystem, or released into it, for the specific mental flows can be specified that will halt or re- purpose of managing the condition of that ecosys- verse this decline, and to help minimize the loss of tem (Box 1). valued ecosystem features (Box 2). This understand- ing can be used to describe flows for a river that The failure to maintain such flows has led to a de- will: cline in the health of many of the world's water- I minimize or mitigate the impacts of new water- dependent ecosystems, largely as a result of resource developments increasing pressure from water and catchment de- I rehabilitate systems impacted by past develop- velopments. These ecosystems include not just in- ments river fauna and flora, but also the floodplains and I allow calculation of the costs of compensating wetlands watered by floods, groundwater-depen- people for such impacts. dent ecosystems replenished through river seepage, and estuaries. These flow descriptions can be as simple as the specification of a water depth to provide wetted Not only does the decline in water-dependent eco- habitat for a fish species, or as complex as a de- systems threaten environmental values such as scription of a completely modified flow regime to maintenance of biodiversity and protection of threat- maintain a whole river and floodplain ecosystem. ened species, but it directly affects many economic Armed with this knowledge, decisionmakers are sectors that rely on such ecosystems. In many parts better equipped to achieve a satisfactory balance be- of the world, people depend on properly function- tween consumptive uses and ecosystem uses of the ing rivers and estuaries for fish and navigation; water resource. Of course, environmental flows floodplain vegetation for grazing, fiber, and food; alone are seldom a sufficient prescription for healthy and wetlands for sediment trapping and pollution rivers. Environmental flow allocations should be removal. Biophysical changes impact livelihoods. considered in combination with other complemen- tary mitigation measures--such as water quality im- The understanding that flows are critical for main- provements--in order to achieve a cost-effective taining ecosystems has triggered an international combination of management interventions (see move to understand and describe the links between Skagit River Case Study in Note C.2). BOX 1. TERMINOLOGY Several terms are used to describe flows for ecological I Drought IFR: a drastically reduced flow regime for maintenance of rivers. "Environmental flows" is a recognized drought years that is sufficient to main- comprehensive term that encompasses all components tain species in a system without necessarily support- of the river, is dynamic over time, takes cognizance of ing reproduction. the need for natural flow variability, and addresses social and economic issues as well as biophysical ones. Other I Minimum flow: a general term used to describe a terms include: flow required to maintain some feature of a river ecosystem. The concept of minimum flow originated I Instream flow requirements (IFRs): an earlier, less-com- in the United States as a streamflow standard to limit prehensive term for environmental flows, usually fo- the abstraction of water during the dry season, cused on flows for fish. and may not be relevant in arid and semi-arid I Maintenance IFR: a flow regime required to maintain regions. all river ecosystem functions, and to provide sufficient access to water to allow plants and animals to repro- All of the above terms describe the maintenance of duce in most years. healthy conditions in a river. 11 WATER RESOURCES ANDENVIRONMENT · TECHNICAL NOTE C.1 BOX 2. EXAMPLES OF VALUED FEATURES OF RIVERS THAT COULD BE PROTECTED THROUGH ENVIRONMENTAL FLOWS Feature Explanation of value Examples of environmental flows required Aquatic animals Freshwater fish are a valuable source of I flows to maintain the physical habitat; protein for rural people. Other valued fauna I flows to maintain suitable water quality; include: angling fish, rare water birds, or the I flows to allow passage for migratory fish; small aquatic life that forms the base of the I small floods to trigger life-cycle cues such food chain. as spawning or egg-laying. Riparian vegetation Stabilizes river banks, provides food and firewood I flows that maintain soil-moisture levels in for rural people and habitat for animals, and the banks; buffers the river against nutrient and sediment I high flows to deposit nutrients on the losses from human activities in the catchment. banks and distribute seeds. River sand Used for building. I flows to transport sand and to separate it from finer particles. Estuaries Provide nursery areas for marine fish. I flows that maintain the required salt/ freshwater balance and ocean connection to estuary. Aquifers and Maintain the perennial nature of rivers acting I flows to recharge the aquifers. groundwater as sources of water during the dry season. Floodplains Support fisheries and flood-recession agriculture I floods that inundate the floodplain at the for rural people. appropriate time of the year. Aesthetics The sound of water running over rocks, the smells I sufficient flow to maximize natural and sights of a river with trees, birds, and fish. aesthetic features, including many of the flows mentioned above. Recreational and Clean water and rapids for river rafting or clean I flows that flush sediments and algae, and cultural features pools for baptism ceremonies or bathing. that maintain water quality ­ see also Also features valued by anglers, birdwatchers, aquatic animals. and photographers. Ecosystem services Maintain the capacity of aquatic ecosystems I flows that maintain biodiversity and to regulate essential ecological processes, for ecosystem functioning. instance to purify water, attenuate floods, or control pests. Overall environmental A wish to minimize human impacts and conserve I some or all of the above types of flows. protection natural systems for future generations. 12 ENVIRONMENTAL FLOWS: CONCEPTS AND METHODS THE SIGNIFICANCE OF DIFFERENT FLOWS In general, the closer decisionmakers want the aquatic The temporal characteristics of the flow regime also system to be to natural, the greater the volume of the have an important influence on the overall charac- original flow regime that will be required as an en- ter of a river ecosystem. Fluctuations between low vironmental flow. However, the pattern of flow over flows and small and large floods change conditions time is as important as the overall quantity. through each day and season, creating mosaics of areas inundated and exposed for different lengths The flow regime of a river can be divided into base of time. The more diverse the physical conditions, flows (low flows), small floods that occur every year, the higher the biodiversity and the greater the re- and occasional large floods that spread out onto flood- silience of the ecosystem to disturbance. plains (Figure 1). Different components maintain different parts of aquatic ecosystems (Box 3). The BOX 3. loss or degradation of one component of a flow re- EFFECTS OF DIFFERENT COMPONENTS OF A FLOW REGIME gime will affect a system differently than the loss of ON RIVERS some other component. Identifying these flow com- ponents--and understanding the ecosystem conse- Flows Importance to river ecosystem quences of their loss or modification--is central to a Low flows: Low flows occur when the river is not in flow assessment. The timing of these flow compo- their range flood. They are larger and more varied nents within a year is also important, since tempera- in dry and in the wet season than in the dry, and ture and other temporal cues play an important part wet define whether the river flows all year, in ecosystem functioning. However, these cues can seasons only during the wet season, or just after rains. They create different conditions in often depend on real-time conditions that are not different seasons, dictating which (and exactly fixed by calendar day or month. Consequently, how many) biotic species occur at any some environmental flow prescriptions allow river time of the year. operators to exercise discretion, within specified Small Small floods stimulate spawning in fish, rules, to ensure that the flows are effective. floods: size, flush out poor-quality water, cleanse the number riverbed, and sort the river stones by per year, size, thereby creating different kinds of FIGURE 1. and timing habitat. They trigger and synchronize AN ANNUAL HYDROGRAPH OF DAILY FLOWS IN A RIVER , activities as varied as upstream migra- BEGINNING IN OCTOBER OF ONE YEAR AND CONCLUDING tions of fish and germination of seed- IN EPTEMBER OF THE FOLLOWING YEAR S . THISIS CALLED lings on riverbanks. A FLOW REGIME . Large Large floods trigger the same in-river floods: size responses as small ones, but also 80 and timing provide scouring flows that shape the 70 channel. They move and cleanse large (infrequent) floods cobbles and boulders on the riverbed, 60 and deposit silt, nutrients, eggs, and /s) 3 seeds on floodplains. They re-charge (m 50 soil moisture levels in the banks, ge enabling seedlings of riparian trees to 40 grow, and maintain links with the sea by small (relatively frequent) floods scouring estuaries. These floods inun- 30 Dischar date backwaters, secondary channels, 20 and floodplains. They trigger bursts of growth in many floodplain species, lowflows 10 including waterbirds such as ibis. Note C.3 describes the release of water for 0 large floods. October September 13 WATER RESOURCES ANDENVIRONMENT · TECHNICAL NOTE C.1 Different developments will affect different compo- ments, the components of the flow regime most com- nents of the flow regime and, in turn, elicit various monly affected, and examples of the consequences responses from the aquatic ecosystem. However, not for aquatic ecosystems. These consequences have a all changes to the flow regime arise from direct ma- direct impact on human populations dependent on nipulations of flows. For instance, deforestation of an these ecosystems. Thus, the reduction in small-to- upland catchment can significantly increase the en- medium-sized floods following the building of a ergy of floods, resulting in changes to the form of the large dam can remove cues needed for fish breed- riverbed as well as deposition of excessive sediment ing, and so affect the livelihoods of downstream on floodplains. Box 4 summarizes typical develop- water-dependent communities. BOX 4. ACTIONS THAT IMPACT FLOW AND CONSEQUENCES FOR AQUATIC ECOSYSTEMS Management Example of the Examples of ecosystem actions impact on flow consequences Irrigation flows Dry-season lowflows I Can result in higher flows in the dry than in the wet season. Hydrau- (using the river increased, and lic and thermal conditions, in particular, can become mismatched as a conduit) seasonal variability with life-cycle requirements, causing species to decrease in reduced. numbers and abundance. Pests are often able to take advantage of such environmental conditions and increase in abundance. Run-of-river Wet and dry season I Reduces habitat availability and restricts movement of aquatic diversion lowflows reduced. animals, thus increasing competition for space and vulnerability to predation. I Increases diurnal temperature fluctuations, concentrates effluents, and can lead to toxic algal blooms. Large dams Frequency and I Flood cues that trigger fish spawning or seed germination may duration of floods occur at the wrong time of the year or not at all, resulting in a failure reduced. to produce new generations of individuals. I Reduced wetting of banks stresses riparian vegetation and reduces establishment of seedlings. Bank stability is weakened and soil erosion increases. I Reduced flows into estuaries reduces access for marine fish using estuaries as nursery areas. I Reduced flooding of riparian wetlands and floodplains causes loss of fisheries and other attributes. See Lesotho Highlands Water Project in Note C.2. Hydropower Timing and distribution of I Mismatched flows and abnormal flow fluctuations impact life-cycle stations flows altered. stages of many animals and plants. See Skagit River case study in Rate of change between Note C.2. high and low flows decreased. Afforestation Wet and dry season I Reduces flood cues that trigger fish spawning or seed germination, of catchment lowflows reduced and and decreases wetted habitat through the year. small floods attenuated. Deforestation Energy of medium- I Increases bank and bed erosion, which alters the available habitat of catchment large floods increased; for aquatic species. dry season flows I Reduces habitat availability in the dry season. increased. I Increases the risk of animals being washed away. 14 ENVIRONMENTAL FLOWS: CONCEPTS AND METHODS BOX 5. INSTREAM FLOWS THAT ARE NOT ENVIRONMENTAL FLOWS Hydropower releases Water released to generate hydroelectricity creates wide fluctuations in downstream river flow, flooding, and drying out habitat for aquatic species such as fish (see Note C.2). To some extent, such flow surges can be controlled to mitigate their impact on the downstream river. Irrigation releases Irrigation water releases can cause seasonal reversal of the flow regime, with flows that are higher in the dry season than in the wet. Life-cycle cues for aquatic species, provided by the flow, become mismatched with temperature and other required conditions, causing loss of species and other ecosystem imbalances. Navigation Unnaturally high flows for navigation can cause bank and bed erosion, and can also dampen or remove flow variability (Box 3). Dilution of pollution Diluting pollutants as a way to improve water quality is poor management. If pollutants are controlled at the source and not through high dilution flows, more water is available for other uses. Release of wastewater Same as for navigation, but with added pollution impact. Interbasin transfers Water moved from one catchment to another can have many of the above effects. It can also impact on biodiversity through the introduction to a catchment of competitive or alien species. Water released down a river for nonenvironmental managers. In the past, some development costs, par- purposes (Box 5) may damage the aquatic environ- ticularly those affecting the environment and borne ment. Any flow assessment that is part of a devel- by economically weak communities, have been ig- opment proposal should include the ecosystem nored. As a general rule, the overall benefits from impacts of nonenvironmental flows. exploitation of water resources increase to a point beyond which use is no longer sustainable, as the Balancing the multiple and competing demands for systems degrade with exploitation and the costs water is one of the greatest challenges facing water eventually outweigh the benefits (Figure 2). FIGURE 2. HYPOTHETICAL SCHEMATIC ILLUSTRATING THE GENERAL RELATIONSHIPS BETWEEN ECOSYSTEM USE AND CONDITION Increased degradation of the river system High-risk use Sustainable use Non-Sustainable use enefitsB Overall benefits of use for modern humans Increased exploitation of the river system 15 WATER RESOURCES ANDENVIRONMENT · TECHNICAL NOTE C.1 METHODS FOR QUANTIFYING ENVIRONMENTAL FLOWS Many methods have been developed over the last The methods presented in this Note are chosen to 20 years--primarily in Europe, the United States, illustrate different degrees of data and time require- South Africa, and Australia--to establish environ- ments, as well as the reliability of the results and mental flows. Some techniques were developed for the level of experience required to apply the method protection of specific (often threatened) species, (Table 1). while others were developed for broader ecosys- tem protection. These techniques have now been applied in over 25 countries, resulting in a consid- PRESCRIPTIVE APPROACHES erable body of experience for temperate and semi- arid rivers, but only limited experience in the These can be divided into four broad categories: application of these methods to tropical rivers. I Hydrological index methods are mainly desk- top approaches relying primarily on historical Environmental flow assessment methods fall into flow records to make flow recommendations for two categories, prescriptive and interactive (Box 6). the future. Little, if any, attention is given to the Methods based on the prescriptive approach usu- specific nature of the considered river or its ally address a narrow and specific objective and biota. result in a recommendation for a single flow value I Hydraulic rating methods use the relationship or single component of the flow regime. Their out- between the flow of the river (discharge) and comes tend not to lend themselves to negotiation, simple hydraulic characteristics such as water because effort is mostly directed to justifying the depth, velocity, or wetted perimeter to calcu- single value, and insufficient information is sup- late an acceptable flow. These methods are an plied on the implications of not meeting the rec- improvement on hydrological index methods, ommended value to allow an informed compromise. since they require measurements of the river Interactive approaches, on the other hand, focus on channel, and so are more sensitive than the the relationships between changes in river flow and desktop approaches to differences between riv- one or more aspects of the river. Once these rela- ers. However, judgment of an acceptable flow tionships are established, the outcome is no longer is still based more on the physical features of restricted to a single interpretation of what the re- the river rather than on known flow-related sulting river condition would be. Methods based on needs of the biota. the interactive approach are thus better suited for I Expert panels use a team of experts to make use in negotiations. They do tend to be more com- judgments on the flow needs of different aquatic plex, however, and have more onerous data and time biota. requirements, than do prescriptive approaches. Sev- I Prescriptive holistic approaches require collec- eral methods have been developed in each category. tion of considerable river-specific data and make BOX 6. FEATURES OF PRESCRIPTIVE AND INTERACTIVE METHODOLOGIES Prescriptive Interactive Often provide a single flow regime to maintain a single Provide a range of flow regimes, each linked to a objective (river condition). different river condition. Motivate for the inclusion of specific parts of the flow regime. Explain the consequences of flow manipulations. Not conducive to exploring options. Conducive to exploring options. Suited for application where objectives are clear and the Suited for application where the eventual environmental chance of conflict is small. flow is an outcome of negotiations with other users. 16 ENVIRONMENTAL FLOWS: CONCEPTS AND METHODS TABLE 1. RELATIVE DATA AND TIME REQUIREMENTS OF SELECTED FLOW ASSESSMENT METHODS Approximate Relative Data and time duration of confidence in Level of Output Method requirements assessment output Experience Prescriptive Tennant Method Moderate to low Two weeks Low USA/extensive Wetted- Moderate 2-4 months Low USA/extensive Perimeter Method Expert Panels Moderate to low 1-2 months Medium South Africa, Australia/ extensive Holistic Moderate to high 6-18 months Medium Australia/ Method very limited Interactive IFIM Very high 2-5 years High USA, UK/extensive DRIFT High to very high 1-3 years High Lesotho, South Africa/very limited structured links between flow characteristics of input from experts. The results compare relatively the river and the flow needs of the main biotic well with those from data-intensive techniques. The groups (fish, vegetation, invertebrates). Two approach is based on trends derived from field ob- examples are included here. servations in the United States of the relationship among river condition, the amount of flow in the Hydrological index methods. The Tennant (or Mon- river, and the resultant fish habitat. These are used tana) Method is a desk-top approach that is rela- to recommend environmental flows for the main- tively inexpensive, quick, and easy to apply. Its tenance of fish, wildlife, recreation, and related re- development required considerable research and sources (Table 2). For example, if the average annual TABLE 2. TENNANT METHOD: PERCENTAGE OF AVERAGE ANNUAL FLOW (AAF) REQUIRED TO ACHIEVE DIFFERENT OBJECTIVES (AAF EXPRESSED AS INSTANTANEOUS FLOW ) Recommended percentage of AAF Objective Autumn-Winter Spring-Summer Flushing or maximum flows 200 200 Optimum range of AAF 60-100 60-100 Percentage AAF required to maintain a required river condition Outstanding 40 60 Excellent 30 50 Good 20 40 Fair or degrading 10 30 Poor or minimum 10 10 Severe degradation 10-zero flow 10-zero flow 17 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE C.1 flow (AAF) in a river is 100 x 106 cubic meters per catchment scale or greater. Because it is widely used annum (m3a-1), then for an "outstanding" river con- in the United States, there is a great deal of exper- dition, the flow in the river in Autumn-Winter would tise and experience to draw upon. need to be 40 percent of the average instantaneous flow, or 1.3 cubic meters per second (m3s-1). The The method is based on the assumption that fish-rear- method is claimed to be applicable to a wide range ing is related to food production, which in turn is re- of river types and sizes, and the general approach, lated to how much of the river bed is wet. It uses at least, may be applicable in many parts of the relationships between wetted perimeter and discharge, world. Once the initial relationship between river depth, and velocity to set minimum discharges for fish condition and flow has been established for a re- food production and rearing (including spawning). gion, the data requirements of the method are mod- The relationships are constructed from measuring the erate, requiring measured or easily simulated length of the wetted perimeter at different discharges monthly hydrological data. in the river of interest. The resulting recommended discharges are based on inflection points on the wet- As with all rapid assessment methods, the Tennant ted-perimeter/discharge curve, which are assumed Method is most suited to the region--in this case, to represent the maximum habitat for minimum flow the western United States--where it was developed, before the next inflection point (Figure 3). where the hydrological and ecological characteris- tic of the rivers are well-studied and well-under- The disadvantage of the method is that the observed stood. It was designed principally for managing trout relationships between wetted-perimeter and dis- habitat, which may limit its applicability to other charge used to recommend suitable habitat for fish biota in other parts of the world. are based on general principles, and are not proven to be relevant to the fish of a particular river. To In new regions where time is a major constraint, a remedy this, detailed studies have to be undertaken specially tailored Tennant approach, based on field on the relationship between wetted perimeter and observations of the habitat responses of the biota the survival and reproduction of particular fish spe- of interest in that region, would provide a good me- cies. Although these studies increase the reliability dium-resolution technique for determining envi- of the results, they also add considerably to the time ronmental flows. The outcome of such a "Tailored required and the costs of the method. Tennant" approach would be a table similar to that in Table 2, but based on empirical observations that Expert panel. The family of expert-based methods are relevant to the country where they were taken. described here have the common feature that they use a team of experts to make judgments on the Other examples of hydrological index methods in- flow needs of different aquatic biota. The composi- clude the Flow Duration Curve Analysis, Range of tion of the panel will depend on the specific envi- Variability Approach, and the Desktop Method. ronmental and social features of the river in question, but typically includes a hydrologist, geo- Hydraulic rating methods. Like hydrological index morphologist, aquatic botanist, and fish biologist. methods, hydraulic rating methods also use the hy- In many cases, one or more community represen- drological record. However, they link this to simple tatives will join the panel. The collective experience cross-section data collected in the river of interest. of the panel members is used in the absence of re- The Wetted-Perimeter Method is a low-resolution, liable, predictive flow-ecology models. By putting river-specific method that is used for determining these experts on a panel, rather than employing seasonal flows required to maintain fish popula- them independently, it is expected that an integrated tions. It is relatively quick and cost-effective. The assessment of flow needs will emerge. number of measurements taken and field visits made will depend on the level of confidence required Although the procedure varies from panel to panel, for the study. It is useful as a planning method at it is usual for the panel to undertake field inspec- 18 ENVIRONMENTAL FLOWS: CONCEPTS ANDMETHODS FIGURE 3. WETTED-PERIMETER METHOD : (A) HYPOTHETICAL CHANNEL CROSS SECTION AND B GRAPH OF WETTED PERIMETER VERSUS - ( ) DISCHARGE . BREAKPOINTS IN SLOPE INDICATE THE MAXIMUM AVAILABLE FISH HABITAT FOR THE LEAST AMOUNT OF WATER UNTIL , THE NEXT BREAKPOINT . a) b) Banktop Banktop perimeter etted W Break points in slope Water levels corresponding to break points Discharge tions at different points in the river. If the river has Holistic approaches. Holistic approaches are essen- upstream impoundments, it is also common for tially ways of organizing and using flow-related data different-sized flows to be released during these field and knowledge. They often incorporate some of the visits so that the experts can see the extent of inun- methods described above, particularly the expert dation and, in some cases, the response of ecologi- panel methods. They are better described as meth- cal compartments to these different flows. The panel odologies, which implies the linking of several dis- meets with stakeholders during the course of the tinct procedures or methods to produce an output field visits to understand the water use requirements that none could have produced alone. They were of different communities along the river. The panel developed in the southern hemisphere, mainly be- also has access to the hydrological records for the cause northern hemisphere methods, which tend river as well as ecological data and reports. Based to target individual (often commercially valuable) on this array of information, the panel produces a species, were too limited when the aim was to man- draft report describing the likely ecological re- age the health of the whole river ecosystem. sponses of the river biota to different flow regimes, including low, medium, and high flows. The report The Holistic Method in Australia and the Building is discussed at one or more workshops attended by Block Methodology (BBM) in South Africa were de- stakeholders and managers before being finalized. veloped in collaboration and share the same basic tenets and assumptions. Both require early identi- The method has been widely applied in the eastern fication of the future desired condition of the river. states of Australia with considerable success. Its An environmental flow regime is then constructed-- advantages are its rapidity, ability to effectively cap- on a month-by-month basis, through separate con- ture and integrate the knowledge of different ex- sideration of different components of the flow re- perts, and its flexibility. It does not rely on the gime (Figure 4)--to achieve and maintain this existence of models (although models can be em- condition. Each flow component is intended to ployed if available). However, the results are site- achieve a particular ecological, geomorphological, specific and non-reproducible, and therefore more or water-quality objective. Given the similarities be- open to challenge than traditional data-intensive/ tween the two methodologies, only the BBM is dis- modeling approaches. cussed further here. 19 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE C.1 FIGURE 4. veying of cross-sections at representative sites along THE "BUILDING BLOCKS OF THE MODIFIED FLOW REGIME " the river, and development of the relationship be- CREATED USING THE BBM. tween flow and water depth, velocity, and area of inundation. The biological specialists also conduct field studies, from which they develop an under- CHANNEL AND HABITAT MAINTENANCE FLOODS (second building blocks) standing of the links between aquatic species and the flow in the river at different times. After data ge collection, a desired future condition for the river SPAWNING/ MIGRATION is described in a specialist workshop. FRESHES Dischar (third building blocks) The specialists then reach consensus on a modi- fied flow regime that would help achieve the de- LOW FLOWS (first building blocks) sired condition. JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC The strength of the BBM lies in its ability to incor- Months porate any relevant knowledge, and to be used in both data-rich and data-poor situations. It addresses a wide range of ecosystem components, and the fi- The BBM was designed to address the southern- nal environmental flow is arrived at through con- African realities of limited data, money, and time. sensus by the full BBM team of river specialists. It It depends on available knowledge, expert opinion, is well documented and is widely used in South Af- and limited new data, which are used in a struc- rica. Holistic approaches are new, however, and tured set of activities to describe an environmental judging their effectiveness will take time. flow. The major components of a river ecosystem, both physical (hydrology, physical habitat, and chemical water quality) and biological (vegetation, INTERACTIVE APPROACHES fish and macro-invertebrates), are considered, as is subsistence use of the river by riparian people. Flow-assessment methods that use an interactive For each of these disciplines, all available data are approach tend to be more complex than prescrip- synthesized and new data collected where neces- tive methods and are predominantly limited to two sary. Field measurements always include the sur- broad types: the habitat simulation and holistic methodologies. They are illustrated here by one of the oldest--the Instream Flow Incre- mental Methodology (IFIM)--and one of the newest--Downstream Response to Imposed Flow Transformations (DRIFT). Both are essentially problem-solving tools with similar approaches (Table 3). The output is a set of options--alternatives in IFIM terminology, or scenarios in DRIFT Bank terminology. Each option quantitatively de- World, scribes: I a modified flow regime Dewees I the resulting condition of the river, or eterP by species, whichever is being addressed I the effect on yield for offstream users Photo Kihansi Gorge, Tanzania I thedirecteconomiccostsandbenefits. 20 ENVIRONMENTAL FLOWS: CONCEPTS AND METHODS DRIFT also addresses the social costs and benefits provide objective, scientifically based input on the of changing river conditions, particularly for down- consequences for rivers of a range of flow manipu- stream riparian users (the population at risk) of river lations. These allow water managers to make more resources. Neither methodology provides a recom- informed decisions on the equitable use of water. mended environmental flow. Rather, each seeks to TABLE 3. PHASES OF IFIM ANDDRIFT PHASES IFIM DRIFT Problem I Identification of interested and I Identification of the main components of the project identification affected parties, their concerns, and the interested and affected parties. or issues information needs and relative I Identification of the population at risk. assessment influence or power. I Identification of the broad study area, and the extent of I Identification of the broad study probable impacts. area, and the extent of probable impacts. I Identification of social concerns (local, national, and international) to be addressed in the biophysical studies. Study Both approaches require: planning I Assessment of existing biophysical, social, and economic data, and evaluation of the need for further data. I Selection of representative river reaches. I Design of data collection procedures. I Identification of key data collection sites. Interdisciplinary integration of site selection and data collection avoids overlaps and gaps, and maximizes the usefulness of the data. Addition of social considerations in selection of study area and sites. In particular, compatibility ensured between biophysical data (collected at river sites) and social data (collected in rural villages). Study I Collection of hydraulic and I Collection of hydraulic, chemical, geomorphological, implementation biotic data. thermal and biotic data, and analyses to develop I Calibration of habitat model. predictive capacity on how flow changes will affect each. I Multidisciplinary workshop to compile a database of biophysical consequences of a range of flow manipulations. Options Both approaches require: analysis I Development of environmental flow alternatives or scenarios, each describing a possible future flow regime and the resulting river condition. I Yield analysis of water available for development with each scenario. I Determination of the direct I Determination of the direct costs and benefits of each costs and benefits of the scenario. alternatives I Additionally, for each scenario, determination of the social impacts and costs to the population at risk of changing river condition. Problem Both approaches require: resolution I Assessment of the bigger picture (for example, data on other costs/benefits of the water- resource development). I Negotiation with offstream water users. I Public participation I Transparent decisionmaking processes. 21 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE C.1 Habitat simulation methodologies: the Instream Flow concern, or because they are deemed to represent Incremental Methodology (IFIM). IFIM is the most the species and the general river condition desired. commonly used flow assessment method worldwide and the best-documented method currently avail- Microhabitat is the small physical area in any place able. It was developed by the U.S. Fish and Wildlife in a river that is directly relevant to the species be- Service's Instream Flow Group in the late 1970s. ing studied. The availability of suitable microhabi- It is founded on a basic understanding and descrip- tat over a range of flows is modeled using PHABSIM tion of the water supply and habitats within river II (Physical Habitat Simulation Model). This model reaches of concern. predicts how the water depth, water velocity, and riverbed features change with changing flow, and IFIM is used to evaluate the effects of incremental thus their changing suitability for the chosen spe- changes in discharge on channel structure, water cies (Figure 5). The model was designed for, and is quality, temperature, and availability of suitable usually applied to, fish habitat. The model requires microhabitat for selected target aquatic species. Both extensive field data and considerable understand- macrohabitat and microhabitat, as described below, ing to apply. It also requires a fairly detailed under- are assessed for key species. These species are cho- standing of the habitat preferences of the chosen sen either because they are the major species of species during their different life stages. For ex- FIGURE 5. CONCEPTUALIZATION OF HOW PHABSIM CALCULATES HABITAT VALUES AS A FUNCTION OF FLOW . (A) FIRST, DEPTH VELOCITY , , COVER CONDITIONS AND AREA ARE MEASURED OR SIMULATED FOR A GRID OF CELLS OVER A RANGE OF FLOWS , . (B) SUITABILITY INDEX (SI)CRITERIA ARE USED TO WEIGHT THE SUITABILITY OF EACH CELL AS HABITAT FOR EACH SELECTED SPECIES OVER THE SAME RANGE OF FLOWS . THE HABITAT VALUES FOR ALL CELLS IN THE STUDY REACH ARE SUMMED TO OBTAIN A SINGLE HABITAT VALUE FOR EACH FLOW (C). THE OPTIMUM MICROHABITAT FOR JUVENILES OF SPECIES A IS NOTED WITH AN ARROW . B: Habitat suitability criteria 1.0 A: Site specific microhabitat data 0.8 0.6 SI0.4 Cross section B 0.2 0 Flow 0 1 2 3 4 0 1 2 3 4 Cross section A Velocity (ft/sec) Depth (ft) 1.0 0.8 0.6 SI 0.4 0.2 0 0 0.2 0.4 0.6 0.8 1.0 Cover fractions C: Relationship between 100,000 discharge and microhabitat for juveniles of Species A ea ar PHABSIM usable ed ett W 0 0 Discharge 100 22 ENVIRONMENTAL FLOWS: CONCEPTS AND METHODS ample, some fish species require attached vegeta- FIGURE 6. tion for egg laying, others need clean pebble beds; BASIC COMPONENTS OF A DRIFT ASSESSMENT some require reeds or grasses for refuge, others need PAR large woody debris. In spite of these data and knowl- BIOPHYSICAL Flow-related areas of concern CURENT CURENT edge demands, some of the PHABSIM programs can CONDITION CONDITION be used with limited field data for reconnaissance Flo w or area-wide planning studies. -relat ECONOMICS CURENT CONDITION FLOW SCENARIOS: -river condition to develop prendictivecapacity Data collectio ed issues The suitability of microhabitat is qualified, in the macrohabitat component, by the suitability of wa- ter quality and temperature. Thus, even if the physi- andanalysis cal microhabitat requirements are met, some fish species will not breed if the correct water tempera- -economics ture and flow cues are absent. The results are a time -social series of suitable habitat for a particular species over -yield a period of changing flows (Figure 5). DECISION IFIM has been subjected to extensive scientific cri- tique, but this is more a product of its widespread use in flow assessments than an indication of its merits relative to other methods. Its main drawbacks DRIFT is essentially a system for managing data lie in its complexity, difficulty of use, its extensive and knowledge in a structured way, following five field data demands, requirements for good under- main steps. standing of target species needs, and questionable I Identification and isolation of wet-season and applicability outside its area of development. Its dry-season low flows, and small and large floods authors suggest that its strong scientific basis make from the long-term hydrological record. it appropriate for the most controversial project as- I Description of the consequences for the river of sessments and that other less onerous methods are partial or complete removal of each of these flow better employed for other projects. components (Box 3). I Creation of a biophysical database detailing the Downstream Response to Imposed Flow Transfor- consequences of flow alterations. mations (DRIFT). DRIFT was developed for the assessment of environmental flows for the Lesotho BOX 7. Highlands Water Project (see Note C.2). DRIFT cul- INCORPORATION OF SOCIAL DATA INTO FLOW ASSESSMENTS minates in one or more multidisciplinary workshops that are designed to produce an agreed number of In regions such as Africa, South America, and Asia, where large numbers of poor people rely directly on biophysical and socioeconomic scenarios. rivers for subsistence, flow assessments should include consideration of the social and economic implica- Specialists use methods that are specific to differ- tions of changes in river flow. In some cases these will ent components of the flow regime to collect data be obvious, such as loss of a food fish or plant, deterioration in the quality of potable water, or filling in and then, within the DRIFT structure, to predict of a pool used for ceremonies. In others, the impacts the consequences of flow changes. For instance, will be less obvious. Vitamins and minerals supplied by PHABSIM II could be used by the fish biologists to riparian plants may contribute to the overall health of a community, or certain levels of flow may dilute or model changes in fish habitat arising from medium- aid decomposition of wastes entering the river, so that level floods that affect in-stream fish habitat. DRIFT the water can be drunk without incurring health risks. also uses data on cultural and subsistence use of So often externalized in water-resource planning, these the river to predict the socioeconomic implications indirect costs of deteriorating river condition are usually borne by the poorest members of society. of river change (Figure 6, Table 3, and Box 7). 23 WATER RESOURCESAND ENVIRONMENT · TECHNICAL NOTE C.1 I Use of the database to describe how river con- planning studies, where a single number might dition will change with any future combination suffice. of high and low flows. I Description of the socioeconomic implications Within either category, the flow assessment method of the changes in river condition. This, together eventually chosen will depend on technical consid- with the previous step, constitutes the creation erations such as the quality and availability of data of environmental flow scenarios. on the study rivers, the location and extent of the study area, the prevailing time and financial con- CHOOSING THE RIGHT TECHNIQUE straints, and the level of confidence required in the final output. Eco-hydrology is a relatively new sci- The purpose of a flow assessment and the intended entific field, so there is only limited understanding use of the results should guide the selection of and very few models of species responses to varying the assessment method. Project-specific flow as- hydrologic conditions. Most of the data and under- sessments for large or controversial projects, which standing required for interactive approaches have are likely to call for considerable negotiation to be acquired on a site-by-site basis, considerably and tradeoffs between environment and develop- adding to the time, funding, and expertise required ment issues, require a more comprehensive ap- for a flow assessment. Probably because of this, most proach than do flow assessments for coarse-scale applications have used a prescriptive approach. ENVIRONMENTAL FLOWS IN THE DECISIONMAKING PROCESS ENVIRONMENTAL ASSESSMENT AND costs as well as the benefits of development, allow- ENVIRONMENTAL FLOW ASSESSMENT ing more informed tradeoffs to be made. Water policy and legislation can provide a vital sup- Environmental Assessment (EA) is the integrative port and guide to decisionmakers. Where policy and process of identifying and evaluating the likely bio- legislation define the need and objectives for envi- physical, social, and other relevant effects of devel- ronmental flows within the realm of sustainable uti- opment proposals prior to major decisions being lization, flow assessments need only determine the made. Mitigation measures are sometimes included volume and temporal distribution of an environ- in EA and sometimes described in separate Envi- mental flow. Without such a framework, they have ronmental Management Plans (EMPs). the burden of not only defining environmental flows but also of giving legitimacy to them. In the case of water development projects, a flow assessment should be an essential component of an With such legal support, a structured, transparent, EA. Impacts arising from alteration of a river's flow and widely accepted decisionmaking process can regime will always have the potential to be severe. address the results of engineering, economic, and These impacts can often be mitigated through the environmental studies, including flow assessments. design of environmental flows or compensated From this, an agreed decision can emerge on through resource substitution or community devel- whether, and in what way, to proceed with a water opment programs, and this can be shown in an EMP. resource development. In the event such a devel- opment is pursued, agreement on the desired fu- ALLOCATING WATER ture river condition and the flow allocations required to maintain that condition will provide the legiti- Increasingly, flow assessments are seen as tools in macy for environmental flow allocations. water-resource management that display the wider 24 ENVIRONMENTAL FLOWS: CONCEPTSANDMETHODS Flow-related effects that are not easily expressed parian people--will be undervalued and lead to dis- in monetary terms need to be included in this deci- proportionate costs being borne by those groups in sion process. If not, effects of development arising society who are not fully integrated into a market from changes in flow regime--such as the loss of economy, or fully represented in the decisionmaking a fish species, or the declining quality of life of ri- process. IMPLEMENTATION Environmental flows should be only one part of that a project manager may want to consider when an integrated set of environmentally sensitive embarking on the implementation of an environ- features. Complementary mitigation (biophysical) mental flows assessment. features that could be considered include fish ladders; multiple-level releases in reservoirs; Conversely, some of the common reasons for the water-chemistry and temperature sensors at the failure to implement assessments are: different off-take structures; outlet pipes able to I the perception among engineers and water take the volume from all the off-takes simulta- managers that "too much" water was requested neously if necessary; structures that minimize an- I lack of flow-related biological data that can be ticipated water-quality conditions such as anoxic used to justify the environmental flows, result- or super-saturated water; and a facility for passing ing in a heavy reliance on expert opinion sediments through reservoirs and past the dam walls I unwillingness or inability to incorporate inno- or weirs. vative, and possibly more expensive, release mechanisms into dams for environmental re- Compensation and mitigation programs should be leases developed on the basis of specific consideration of I lack of political or legislative pressure to im- downstream issues, which are often different than plement the environmental flows (usually be- upstream issues. Downstream impacts relate not cause other demands were seen as more only to the reduction in water flows, but also the important) associated transformation from an aquatic environ- I "lastminute"orpost-hocflowassessmentsthat ment to a terrestrial environment. Downstream is- are commissioned after most (if not all) the sues that may form part of the compensation and major decisions about the design and cost of mitigation programs for riverine resource losses the development, and the allocation of water, may include reduction in fish, vegetables, plants, have already been made animal forage, firewood, timber for other uses and I reluctance to move away from established prac- water supply for people, livestock and other uses tices. from direct and indirect changes in the amount, quality, and timing of flows. The methodologies for A monitoring program is particularly important addressing downstream social issues has not been given the generally poor understanding of the well established and the practice is still evolving. links between flow and ecological response. The implementation of an agreed flow regime Experience in a number of countries has shown that should allow for adaptive management based on recommendations arising from environmental flow the monitoring. The monitoring program should assessments are not always implemented. The fea- be designed to provide essential feedback on tures that are likely to lead to successful implemen- whether: tation are summarized in Box 8. These features are I the agreed-upon flow is being released extensive; few projects would be able to satisfy all I the overall objective (desired river condition) of them. Nevertheless, the box provides a checklist is being achieved 25 WATER RESOURCES ANDENVIRONMENT · TECHNICAL NOTE C.1 I the objectives for different components of the biota to be separated from the effects of other inter- flow regime are being met ventions--for example, improved water quality from I the environmental flow allocation needs to sewage treatment plants--and from climatically in- be modified in the light of the observed responses. duced variations in river flows. In practice, this is ex- tremely difficult to do, and the interpretation of any The monitoring program should be designed to al- monitoring program will always rely on the experi- low the effects of environmental flows on different ence of the hydrologists and ecologists involved. BOX 8. DESIRABLE FEATURES FOR A SUCCESSFUL ENVIRONMENTAL FLOWS IMPLEMENTATION . Political will, I Recognition of tangible and intangible national costs of degraded rivers. legislation, and I Acceptance of flow assessments as a tool for use in integrated river-basin management. management I Supporting legislation to empower water managers to manage river flows according to strategies recommendations. I The necessary tools to implement and enforce legislation. I A structured and transparent decisionmaking process, whereby the results of engineering and economic studies, environmental flow assessments, and stakeholder input are jointly used to decide on future flow allocations and river condition. I Ethical, moral, and other intangible considerations form important inputs to the final decisionmaking process. I Commitment of politicians, developers, and water resource managers to adhere to agreed-upon environmental flow objectives. Data and tools I Long-term accurate hydrological data. I Hydrological models with daily time-steps. I Linked surface and groundwater models for intermittent rivers. I Long-term water chemistry records for rivers (and groundwater, where necessary), preferably linked to hydrographs. I Appropriate flow assessment methodologies. I Comprehensive data on the distribution, life histories, and flow-related habitat requirements of riverine species in the rivers of concern. Similar data for the abiotic aspects of rivers and, where relevant, for estuaries and coastal marine environments. Data on the tolerance ranges of riverine biota to physical and chemical variables. I A well-structured link between river and estuary flow assessments where appropriate. Specialist I Senior specialists, with first-hand knowledge of the rivers of concern, in the flow-related expertise aspects of the following disciplines: hydrology, geohydrology, hydraulics, geomorphology, sedimentology, water chemistry, biotic integrity, physical habitat, riparian and instream vegetation, fish, invertebrates, and possibly herpetofauna and terrestrial wildlife. I If socioeconomic aspects are to be included in the assessment, specialists in the following disciplines may be required: sociology, human geography, anthropology, public health, domestic-stock health, resource and project economics, and public participation proce- dures. Also required are specialists with knowledge of the flow-related aspects of waterborne diseases, and those of parasites and/or their hosts. Funds I Recognition that ecological and socioeconomic aspects of water resource development are as important as engineering and direct economic aspects. I Sufficient planning to provide adequate funds for flow assessments. Time I Suitable planning horizons for flow-related investigations management 26 ENVIRONMENTAL FLOWS: CONCEPTSAND METHODS CONCLUSION Provision for environmental flows is central to features that will enhance the chance of successful integrated water resources management. EFA implementation of environmental flows. methods are still evolving and World Bank ex- perience in addressing downstream biophysical Although the theory has developed rapidly in the and social impacts is limited, but developing. A last three decades, the practical application of en- recent review of the impact of dams on ecosystem vironmental flows has been retarded by a lack of function for the World Commission on Dams data and understanding of hydrology-ecology link- concluded that there were four principle ap- ages; a lack of specialists in developing countries; proaches to limiting the impacts of dams on natu- a lack of legislative support; and a reluctance on ral resources: avoidance; mitigation; compensation; the part of water resource developers, designers, and restoration. builders, and operators to move away from past practices. Provision of water for the environment Successful mitigation, compensation, and restora- will bring with it legal challenges from other po- tion of downstream effects are more likely if a thor- tential users of the water, yet the scientific knowl- ough flow assessment has been undertaken. edge base needed to defend environmental flows against such challenges remains poor. Much of this This Technical Note has outlined the principles is changing, however, and flow assessments are behind environmental flow assessments, provided becoming integrated with other tools such as EA a description of the methods that have been used to and water allocation planning for guiding decisions assist with such assessments, and highlighted the on water resource developments. 27 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE C.1 FURTHER INFORMATION The following reports provide contextual informa- Tharme, R.E. 19 96. "Review of the international meth- tion on environmental flows : odologies for the quantification of the instream flow requirements of riv ers." Water law review final report for policy de velopment for the D e- Bergkamp, G., M. McC artney P. Dugan, J. McNeely and M. partment of W ater Affairs and Forestry, P retoria. Acreman. 2 000. "Dams, ecosy stem functions and Cape Town: Freshwater Research Unit, Univ er- environmentalrestoration. "Contributingpaperto sity of Cape Town, Cape Town, South A frica. World Commission on D ams Thematic Re view. EnvironmentalIssuesI I.NewYork:UNEP.Down- loadable from www.dams.org or on C D from Information on specific techniques described in this Earthscan,L ondon, www.earthscan.co.uk Technical Note can be obtained from: Bizer, J.R. (2 000). "International mechanisms for a void- ing,mitigatingandcompensatingtheimpactsof Collings, M.R., R.W . Smith, and G.T . Higgins. 19 72. "The large dams on aquatic and related ecosy stems hydrology of four streams in w estern Washing- andspecies."SubmissionE NV249toWorldCom- ton as related to se veral Pacific salmon species. " mission on D ams. Ne w York: UNEP. Down- US Geological Service W ater Paper 1968. (Wet- loadable from www.dams.org or on C D from ted-perimetermethod) Earthscan,L ondon, www.earthscan.co.uk King,J.M.andD.L ouw.1998."Instreamflo wassessments Harper, D.M., and A.J.D. F erguson, eds. 19 95. The Eco- for regulated riv ers in South A frica using the logical Basis for River Management . Chichester, BuildingBlockMethodology ." AquaticEcosystems UK: John W iley and Sons. Health and Mangement 1:109-124. Stalnaker, C., B.L. L amb, J. Henriksen, K. Bo vee, and J. The following three documents provide compara- Bartholo w.1995."TheInstreamF lowIncremen- tive descriptions of environmental flow techniques: tal Methodology: A primer for I FIM." Biological Report 2 9, March 19 95. Reston, V A: US Depart- mentoftheInterior,NationalBiologicalService. Arthington,A.H.,andJ.M.Z alucki,eds.19 98."Compara- Swales, S . and J. H. Harris. 19 95. "The Expert P anel tive Evaluation of En vironmental F low Assess- Assessment Method (E PAM): A new tool for ment Techniques: Re view of Methods. " DeterminingEn vironmentalF lowsinRegulated Occasional P aper No 27/98. Canberra, Australia: Rivers." In Harper, D.M. and A.J.D. F erguson, LandandWaterResourcesResearchandD evel- eds. The Ecolog ical Basis for River Management . opmentC orporation. Chichester, U K: John W iley and Sons, pp 12 5- Dunbar,M.J.,A.Gustard,M.C.A creman,andC.R.N.Elliott. 134. 1998. Overseas Approac hes to Setting River Flo w Tennant, D.L. 19 76. "Instream flo w regimens for fish, Objectives . R&D Technical Report W6B(9 6)4. wildlife, recreation and related en vironmental Wallingford: Institute of H ydrology. resources." Fisheries 1(4): 6-10. 28