Good and Bad Dams

Latin America and Caribbean Region sustainable learning Working root word 16 Good dam ups and murderedly Dams Environmental Criteria for Site Selection of hydroelectric attends November 2003 George Ledec Juan David Quintero The arna depose Latin America and Caribbean Region environmentally and sociablely sustainable suppuration De secernatement (LCSES) Latin America and the Caribbean Region Sustainable Development Working report card No. 16 Good Dams and ruinous Dams Environmental Criteria for Site Selection of hydroelectric Projects November 2003George Ledec Juan David Quintero The instauration Bank Latin America and the Caribbean Region environmentally and Socially Sustainable Development welkin Management Unit George Ledec has worked with the field Bank since 1982, and is presently Lead Ecologist for the Environmentally and Socially Sustainable Development Unit (LCSES) of the World Banks Latin America and Caribbean regional Office. He specializes in the environmenta l discernment of education projects, with particular focus on bio regeneration and link conservation oncerns. He has worked ex ten dollar billsively with the environmental aspects of obturates, roads, oil and gas, forest management, and protected argonas, and is one of the briny authors of the World Banks cancel Habitats Policy. Dr. Ledec earned a Ph. D. in Wildland Resource Science from the University of California-Berkeley, a Masters in Public personal matters from Princeton University, and a Bachelors in Biology and Environmental Studies from Dartm step to the foreh College.Juan David Quintero joined the World Bank in 1993 and is presently Lead Environmental Specialist for LCSES and Coordinator of the Banks Latin America and Caribbean Quality Assurance Team, which monitors compliance with environmental and neighborly safeguard policies. He specializes in environmental assessment of infrastructure projects, primarily roads, hydro bureau, oil and gas, urban transport, and we t supply and sanitation. He has received the Regional Award from the International Association for Impact Assessment (IAIA) for promoting improvements in environmental reach assessments without Latin America.He is a well-behaved engineer with graduate student degrees in Environmental and Sanitary Engineering. The findings, interpretations, and conclusions in this document argon those of the authors, and should non be attributed in any manner to the World Bank, its affiliated organizations, members of its posting of executive director Directors, or the countries they represent. This working piece of music series is produced by the Environmentally and Socially Sustainable Development Sector Management Unit of the Latin America and Caribbean Regional Office. Additional copies whitethorn be pay offed from the authors or from LCSES chopine Assistant Peter Brandriss (email&160protected rg, or tel. 1-202-473-9379). C everywhere photos (clockwise from focal ratio left) Loksop D am, southbound Africa Guavio Dam, Colombia Yacyreta Dam, Argentina/Paraguay All photos by George Ledec ii Contents Acknowledgments .. iv preface .. v Executive Summary ii Introduction 1 unfavourable Environmental Impacts of Hydro origin Development 3 Key Indicators of potential Environmental Impacts .. 9 Overview of Environmentally Good and Bad hydroelectric Dam Sites 13 Conclusions .. 5 Bibliography. 17 tabularises 1. Hydroelectric Projects indecent Impacts and temperance Options 4 2. Land playing ara Flooded and spate Displaced in Large Hydropower Projects iii 12 Acknowledgments Doug mason (consultant) compiled information on more than twenty complete Latin Ameri give the gate hydroelectric projects this information was real utilitarian in our analysis of environmental and genial impacts, mitigation measures, and send selection criteria.Several current and former World Bank Group staff members provided useful comments and oft encouragement, including Aless(pre nominal)andro Palmieri, John Briscoe, Teresa Serra, Tony Whitten, Robert Goodland, Tor Ziegler, warren Van Wicklin, William Partridge, Maria Clara Mejia, Kristine Ivarsdotter, Mateen Thobani, Salman Salman, and A. J. Glauber. This cover also reflects the helpful comments provided by Dominique Egre and Gaitan Guertin (Hydro-Quebec), Jose Goldemberg (World missionary work on Dams), and Paul Dulin. Peter Brandriss helped edit and prep ar the bill for publication. iv ForewordFew types of development projects arouse as practically controversy as hydroelectric dekameters. Their often serious environmental disparage has been amply documented deep down the past decade. Nonetheless, umteen countries, in Latin America and world huge, rely upon hydroelectric decameters for a major ascribe of their electric power. Electricity cadaver a key ingredient for improving the lives of poor people al al near everywhere. In developing countries, rapid urbanization and wrap upd population g rowth pass on look into increased demand for electric power for decades to come, still with the closely successful of demand management and energy efficiency measures.Energy planners in many developing countries atomic itemise 18 thus in all probability to continue seeing hydroelectric dekametres as a promising source of renewable electric power. This composition provides cardinal advice for substantially reducing the environmental damage from future hydroelectric dams (whether or non they receive World Bank Group financing) by spuriouss of inviolable project site selection. Although the reports conclusions atomic proceeds 18 draw primarily from a review of Latin Ameri tummy dams, its innovative methodology for dam site selectionbased on robust environmental and social criteria and straightforward, quantitative indicatorsshould prove useful worldwide.The report also help to the full summarizes the environmental mitigation options for the improved operation of exis ting hydroelectric dams. As such, this report should be of considerable pastime to people interested in hydroelectric dams, whether at the World Bank, opposite multilateral and bilateral development institutions, government agencies, private energy companies, consulting firms, environmental and another(prenominal)(a) NGOs, and academia. This report is part of the LCR Sustainable Development Working Paper Series published by the Latin America and the Caribbean Regions Environmentally and Socially Sustainable Development Sector Management Unit (LCSES).This series seeks to disseminate the results of our analytic and operational work, present preliminary findings, and describe best practices with respect to major sustainable development issues facing the region. The findings, interpretations, and conclusions expressed in these papers atomic identification number 18 entirely those of the authors and should not be attributed to the World Bank, members of its Board of Executive Dir ectors, or the countries they represent. John Redwood Director Environmentally and Socially Sustainable Development Latin America and Caribbean Region The World Bank v Executive SummaryLarge dams vary considerably in their indecorous environmental and related social impacts. From an environmental standpoint, there atomic number 18 relatively safe dams and bad dams. art object or so extensive dams are relatively favorable, others admit ingestd major environmental damage. The severity of environmental impacts from a hydroelectric project is rangyly fixed by the dam site. succession dams at sound sites weed be very defensible from an environmental standpoint, those proposed at bad sites go a demeanor infixedly be elevatedly elusive, even if all feasible mitigation measures are in good order implemented.This paper provides a simple, yet robust, methodology for comparing proposed hydroelectric project sites in scathe of their expected negative environmental impacts, a nd relating these to power time benefits. The paper also summarizes the environmental mitigation options for full-size dams. If properly implemented, these mitigation measures domiciliate impressively prevent, besmirch, or compensate for many (though not all) of a hydroelectric projects negative impacts.Nonetheless, the most effective environmental mitigation measure is good site selection, to ensure that the proposed dam will draw relatively minuscular damage in the freshman place. The paper presents quantitative indicators (using data that are relatively easy to obtain) for paygrade and ranking proposed new hydroelectric projects in terms of their seeming untoward environmental impacts. Projects with a dinky informant surface realm (relative to power multiplication) tend to be most desirable from both an environmental and social standpoint, in part be stir they minimize pictorial habitat deprivationes as well as resettlement needs.In general, the most environment ally benign hydroelectric dam sites are on upper tributaries, small-arm the most problematic ones are on the macro briny stems of rivers. Power expansion prep should ensure that environmental criteria, of the type outlined in this paper, are brainiaced(p) discriminate weight in hydroelectric project site selection. many another(prenominal) of the more problematic dam sites are best left undeveloped, because the environmental or related social impacts are likely to be unacceptably high. In those cases, other power generation technologies are likely to be more environmentally desirable.Conversely, hydroelectric dams at good sites (with relatively piteous wayward impacts) and with effective implementation of proper mitigation measures are likely to be more attractive from an environmental standpoint than the most likely power generation selections. vii Introduction 1. Large hydroelectric dams are among the most controversial of all types of development projects. They founder been the focus of much criticism of the World Bank and other international financing agencies. The great dams debate is often highly polarized.Critics of macroscopical hydroelectric projects point to a wide range of negative environmental and related social impacts, from the close of unique biodiversity to the displacement of vulnerable valet de chambre populations. Defenders of ample dams note that they are often the economically least-cost source of electric power available, specially to large urban centers they are a renewable electrical energy source and most other power generation technologies also imply signifi open firet ominous environmental impacts. 2.Worldwide, many countries rely upon hydropower for a substantial serving of their electricity. In developing countries, rapid urbanization and continued population growth will ensure increased demand for electric power for decades to come, even with the most successful of demand management and energy efficiency measur es. Electricity remains a key ingredient for improving the lives of millions of poor people doneout the developing world. Energy planners in many countries are likely to continue seeing hydroelectric dams as a promising, renewable source of electricity.Major new-made international initiativesincluding the World Summit on Sustainable Development (Johannesburg, 2002), World Water Forum (Kyoto, 2003), World Commission on Dams (1997-2002), and the ongoing Dams and Development Project of the United Nations Environment Program nurse reaffirmed the commitment of many governments and international agencies (including the World Bank) to hydropower development, but in a manner which richly reflects modern environmental concerns. 3. In this context, it is important to remember that all large hydroelectric dams are not alike.Large hydroelectric projects vary tremendously in the extent of their unfavourable environmental and related social impacts. (In this paper, we define large hydroelect ric dams as those with 10 megawatts or more of installed generating substance, to distinguish them from small or micro-dams which generate power on a small scale. ) For example, the dmegawatt Pehuenche Hydroelectric Project in Chile outpouringed only most 400 hectares of land (with minimal damage to forest or wildlife resources) and has had no peeing flavour problems.By contrast, the Brokopondo Dam in Suriname flood about 160,000 hectares of biologically valuable tropical rainforest and is known for serious piddle quality and aquatic stinkpot problems, while providing relatively little electric generating capacity (only 30 megawatts). 4. We conducted a review of more than twenty absolute hydroelectric dam projects in Latin America, along with several well-known projects from other regions. Our study found that close to large dams are relatively benign, while others have caused substantial environmental and related social damage.This paper provides a methodology for comf ortably comparing proposed hydroelectric project sites in terms of their expected adverse environmental impacts, relative to their power generation benefits. The expert criteria and quantitative indicators in this paper should be viewed as completing to 1 2 LCR Sustainable Development Working Paper No. 16 the broader and often more process-oriented advice of other recent reports on dams, including the 2000 Dams and Development report of the World Commission on Dams.This papers recommendations are fully compatible with the World Banks Water Resources Sector Strategy, although this paper provides more technical detail regarding specific environmental impacts, mitigation options, and site selection criteria. Adverse Environmental Impacts of Hydropower Development 5. The range of adverse environmental and related social impacts that tush result from hydroelectric dams is remarkably diverse. While about impacts amount only during eddy, the most important impacts unremarkably are over due(p) to the long-term existence and operation of the dam and source.Other significant impacts can result from complementary civil works such as door roads, power infection lines, and quarries and hook on pits. put off 1 summarizes the adverse environmental and social impacts associated with dams and rootages, along with the typical kinds of mitigation measures often proposed (and, less often, in effect implemented). 6. Our analysis indicates that with properly implemented mitigation measures, many of the negative environmental and related social impacts of hydroelectric projects can be reduced to very accep circumvent trains.As outlined in Table 1, mitigation measures can efficaciously prevent, minimize, or compensate for most adverse impacts, but only if they are properly implemented. In our review of Latin American hydroprojects, we found wide variation in the extent to which environmental mitigation measures were planned, budgeted, and actually implemented. 7. Mor eover, for some types of negative impacts, at some project sites, the available mitigation measureseven when properly implementedare inherently unsatisfactory.Examples of adverse environmental impacts which croak at some hydroelectric projects and cannot be fully mitigated involve (i) irreversible biodiversity disadvantage, if vital inborn habitats not occurring elsewhere are semiaquatic (or left dry) by the dam (ii) search passage facilities frequently cannot mend the pre-dam ecological balance of a river, in terms of species composition or tip migrations and (iii) some cultural property (including sacred sites) cannot be adequately salvaged prior to reservoir inundation. 8.Thus, because mitigation measures are often not fully implemented, and are sometimes inherently inadequate, the iodin most important environmental mitigation measure for a new hydroelectric project is good site selection, to ensure that the proposed dam is will be largely benign in the number 1 place. In the fol imprinting summary of typical adverse environmental impacts and corresponding mitigation options, it is important to keep in mind that all these types of impacts can be either avoided or minimise through good project site selection. 3 4Note All of these impacts can be avoided or minimized by good dam site selection, the single most important environmental measure. Environmental Impacts relief Options Impacts of the Dam and rootage Flooding of Natural Habitats Some reservoirs permanently flood extensive natural habitats, with topical anaesthetic and even global extinctions of animal and plant species. Very large hydroelectric reservoirs in the tropics are especially likely to cause species extinctions (although such losses are only infrequently documented due to the lack of scientific data).Particularly hard-hit are riverine forests and other riparian ecosystems, which naturally occur only along rivers and streams. From a biodiversity conservation standpoint, the terr estrial natural habitats garbled to flooding are ordinarily much more valuable than the aquatic habitats created by the reservoir. One occasional exception to this rule is that shallow reservoirs in dry zones can provide a permanent oasis, sometimes important for migrant piddlefowl and other terrestrial and aquatic fauna.To offset the loss of natural habitats to reservoir flooding or other project components (such as borrow pits), one or more compensatory protected stadiums can be established and managed under the project. If an existing area is protected on paper only, a useful project option is to strengthen its onthe-ground bulwark and management. The area protected under the project should ideally be of comparable or greater size and ecological quality to the natural area confounded to the project.Under the World Banks Natural Habitats Policy, hydroelectric and other projects should not be sited where they would cause the significant conversion or degradation of critical n atural habitats that do not occur elsewhere (and, hence, cannot be adequately compensated). Loss of Terrestrial Wildlife The loss of terrestrial wildlife to drowning during reservoir filling is an inherent consequence of the flooding of terrestrial natural habitats, although often treated as a separate impact. Although they whitethorn be useful for public traffic purposes, wildlife rescue efforts rarely succeed in restoring wild populations.Instead of drowning, the captured and relocated animals typically starve, are killed by competitors or predators, or fail to reproduce successfully, due to the limited carrying capacity of their new habitats. Wildlife rescue is most likely to be middlingified on conservation grounds if (a) the species rescued are globally threatened with extinction and (b) the relocation habitat is ecologically suitable and efficaciously protected. However, the money spent on rescue would usually do much more for wildlife conservation if it were invested in co mpensatory protected areas.The most effective way to minimize wildlife mortality in hydroelectric projects is to opt dam sites which minimize the wildlife habitat flooded. LCR Sustainable Development Working Paper No 16 Table 1. Hydroelectric Projects Adverse Environmental Impacts and Mitigation Options Environmental Impacts Mitigation Options Involuntary Displacement Involuntary displacement of people is often the main adverse social impact of hydroelectric projects. It can also have important environmental implications, such as with the conversion of natural habitats to carry resettled rural populations.For physical displacement, the main mitigation measure is the resettlement of displaced populations, including new housing, replacement lands, and other material assistance, as needed. Success usually requires consultation and participatory decisionmaking by both the resettled and host populations (mandatory for World Banksupported resettlement). Effective resettlement of vulnera ble ethnic minorities is peculiarly challenging because some of these people are highly vulnerable to adverse social changes.Accordingly, the World Banks Involuntary Resettlement and natal Peoples policies afford special consideration to these populations, specifying that, among other requirements, all viable alter inborn project designs should be explored sooner considering physical displacement for these groups. For people who are not physically displaced but suffer an economic loss of livelihoods (based on angleeries, rural or grazing lands, river-edge clay for brick and tile production, or other resources), mitigation measures should involve the provision of replacement resources, new job training, or other income restoration assistance, as needed.Deterioration of Water Quality The damming of rivers can cause serious weewee quality deterioration, due to the reduced oxygenation and dilution of pollutants by relatively stagnant reservoirs (compared to fast-flowing rivers), f looding of biomass (especially forests) and resulting underwater decay, and/or reservoir stratification (where deeper lake water lack oxygen).Water pollution stop measures (such as sewage treatment plants or enforcement of industrial formulas) may be needed to improve reservoir water quality. Where poor water quality would result from the decay of flooded biomass, discriminating forest clearing within the impoundment area should be completed forwards reservoir filling. Downriver Hydrological Changes These adverse impacts can be minimized through attentive management of water releases.Objectives to consider in optimizing water releases from the turbines and spillways intromit adequate downriver water supply for riparian ecosystems, reservoir and downriver slant survival, reservoir and downriver water quality, aquatic weed and disease vector control, irrigation and other human uses of water, downriver flood protection, cheer (such as whitewater boating), and, of course, powe r generation. From an ecological standpoint, the ideal water release conformation would usually closely mimic the natural flooding government activity (although this may not be feasible for densely settled floodplains where flood protection is a high priority).Dams that generate baseload electricity are typically more capable of replicating near-natural downriver flows than those that produce peaking power (where daily water releases may fluctuate sharply, often to the detriment of aquatic organisms that are adapted to less frequent flow changes). Environmental management plans for hydroelectric projects should specify environmental water releases, including for dams owned or operated by the private sector. Good Dams and Bad Dams 5Major downriver hydrological changes can destroy riparian ecosystems dependent on biannual natural flooding, exacerbate water pollution during lowflow periods, and increase saltwater encroachment near river mouths. Reduced depository and nutrient load s downriver of dams can increase river-edge and coastal erosion and damage the biological and economic productiveness of rivers and estuaries. Induced desiccation of rivers infra dams (when the water is diverted to another portion of the river, or to a different river) kills fish and other fauna and botany dependent on the river it can also damage agriculture and human water supplies.Mitigation Options Water-Related Diseases Some infectious diseases can tail cover around hydroelectric reservoirs, particularly in warm climates and densely populated areas. Some diseases (such as malaria and schistosomiasis) are borne by water-dependent disease vectors (mosquitoes and aquatic snails) others (such as dysentery, cholera, and hepatitis A) are spread by contaminated water, which frequently becomes worse in stagnant reservoirs than it was in fast-flowing rivers.Corresponding public health measures should include preventive measures (such as awareness refugee campaigns and window scree ns), monitoring of vectors and disease outbreaks, vector control, and clinical treatment of disease cases, as needed. Control of floating aquatic widows weeds (see below) near populated areas can reduce mosquito-borne disease risks. Fish and Other Aquatic life-time Hydroelectric projects often have major effects on fish and other aquatic life. Reservoirs positively affect certain fish species (and fisheries) by ncreasing the area of available aquatic habitat. However, the net impacts are often negative because (a) the dam blocks upriver fish migrations, while downriver passage through turbines or over spillways is often unsuccessful (b) many riveradapted fish and other aquatic species cannot survive in artificial lakes (c) changes in downriver flow patterns adversely affect many species, and (d) water quality deterioration in or below reservoirs (usually low oxygen levels sometimes gas super-saturation) kills fish and regaining aquatic habitats.Freshwater molluscs, crustaceans, an d other benthic organisms are even more polished to these changes than most fish species, due to their limited mobility. Management of water releases may be needed for the survival of certain fish species, in and below the reservoir. Fish passage facilities (fish ladders, elevators, or trap-and-truck operations) are intended to help migrant fish move upriver past a dam they are usually of limited effectiveness for various reasons (including the difficulty of ensuring safe downriver passage for many adults and fry).Fish hatcheries can be useful for maintaining populations of native species which can survive but not successfully reproduce within the reservoir. They are also often used for stocking the reservoir with economically desired species, although introducing non-native fish is often devastating to native species and not ecologically desirable. Fishing regulation is often essential to maintain viable populations of commercially valuable species, especially in the waters immedi ately below a dam where migratory fish species concentrate in high numbers and are by artificial means easy to catch.Floating Aquatic Vegetation Floating aquatic vegetation can rapidly proliferate in eutrophic reservoirs, causing problems such as (a) flying habitat for most species of fish and other aquatic life, (b) improved gentility grounds for mosquitoes and other nuisance species and disease vectors, (c) impeded navigation and swimming, (d) congest of electro-mechanical equipment at dams, and (e) increased water loss from some reservoirs. Pollution control and pre-impoundment selective forest clearing will make reservoirs less contributory to aquatic weed growth.Physical removal or containment of floating aquatic weeds is effective but imposes a high and recurrent expense for large reservoirs. Where compatible with other objectives (power generation, fish survival, etc. ), occasional drawdown of reservoir water levels may be used to kill aquatic weeds. Chemical drunkennes s of weeds or related insect pests requires much environmental circumspection and is usually best avoided. LCR Sustainable Development Working Paper No 16 Environmental Impacts (table continues on following page) 6 Table 1.Hydroelectric Projects Adverse Environmental Impacts and Mitigation Options (continued) Environmental Impacts Mitigation Options Loss of Cultural space Cultural property, including archaeological, historical, paleontological, and unearthly sites and objects, can be fill by reservoirs or destroyed by associated quarries, borrow pits, roads, or other works. Structures and objects of cultural interest should undergo salvage wherever feasible through scientific inventory, careful physical relocation, and documentation and stock in museums or other appropriate facilities.However, it is often not possible to replace the loss of, or damage to, unique or sacred sites which may have great religious or ceremonial significance to indigenous or other local people. Reservo ir Sedimentation Over time, live storage and power generation are reduced by reservoir depositary, such that much of some projects hydroelectric energy might not be renewable over the long term. If effectively implemented, washstand management can minimize sedimentation and extend a reservoirs useful physical life, through the control of road construction, mining, agriculture, and other land use in the upper catchment area.Protected areas are sometimes established in upper catchments to reduce sediment flows into reservoirs, as with the Fortuna Dam in Panama and the proposed Rio Amoya (Colombia) and Nam Theun II (Laos) projects. Aside from watershed management, other sediment management techniques for hydroelectric reservoirs may at times be physically and economically feasible they include, among others, upstream check structures, protect dam outlets, reservoir flushing, mechanical removal, and increasing the dams height. babys room Gases Greenhouse gas releases from reservoirs can be reduced by a primitive salvage of commercial timber and fuelwood, although frequently this does not happen because of (a) high extraction and transportation costs, (b) marketing constraints, or (c) political and economic pressures not to delay reservoir filling. The surest way to minimize greenhouse gas releases from reservoirs is to choose dam sites that minimize the flooding of land in general, and forests in particular. table continues on following page) Good Dams and Bad Dams 7 Greenhouse gases (carbon dioxide and methane) are released into the atmosphere from reservoirs that flood forests and other biomass, either slowly (as flooded radical matter decomposes) or rapidly (if the forest is cut and burned before reservoir filling). Greenhouse gases are widely considered to be the main cause of human- generate global climate change. Many hydroelectric reservoirs flood relatively little forest or other biomass.Moreover, most hydroprojects generate sufficient electricity to more than offset the greenhouse gases which would otherwise have been produced by electrocution fossil fuels (natural gas, fuel oil, or coal) in power plants. However, some projects which flood extensive forest areas, such as the Balbina Dam in Amazonian Brazil, break through to emit greenhouse gases in greater amounts than would be produced by burn natural gas for many years of comparable electricity generation. Mitigation Options Impacts of Complementary Civil Works Access RoadsNew access roads to hydroelectric dams can induce major land use changes particularly deforestationwith resulting loss of biodiversity, accelerated erosion, and other environmental problems. In some projects (such as Arun II in Nepal), the environmental impacts of access roads can greatly exceed those of the reservoir. The siting of any new access roads should be in the environmentally and socially least damaging corridors. Forests and other environmentally mass medium areas along the chosen road corrid or should receive legal and on-the-ground protection.Road engineering should ensure proper drainage, to protect waterways and minimize erosion. Environmental rules for contractors (including penalties for noncompliance) should cover construction camp siting, gravel extraction, waste disposal, avoiding water pollution, worker behavior (such as no hunting), and other construction practices. See Ledec and Posas (2003) for details. Power Transmission Lines Power transmission line rights-of-way often reduce and fragment forests indirectly, they occasionally facilitate shape up deforestation by improving physical access.Large birds are sometimes killed in collisions with power lines, or by electrocution. Power lines can also be aesthetically objectionable. Power lines should be sited to minimize these concerns and built using good environmental practices (as with roads). In areas with concentrations of vulnerable bird species, the top (grounding) wire should be made more visible with pla stic devices. Electrocution (mainly of large birds of prey) should be avoided through bird-friendly tower design and proper spacing of conducting wires.Quarries and Borrow Pits Quarries and borrow pits are used to provide material for construction of the dam and complementary works. They can considerably increase the area of natural habitats or agricultural lands that are lost to a hydroelectric project. To the greatest extent feasible, quarries and borrow pits should be sited within the future inundation zone. Where this is not feasible, the pits should be rehabilitated after(prenominal) use, ideally for conservation purposes such as wetland habitats. Impacts of Induced DevelopmentAssociated Development Projects Hydroelectric dams often make possible new development projects with major environmental impacts, including irrigation, urban expansion, and industrial facilities (due to new water supplies). New development projects should be planned to minimize adverse environmental and social impacts. Environmental impact assessment studies should be carried out in the early stages of project grooming the resulting environmental mitigation plans should be fully implemented. Additional DamsThe construction of the first dam on a river can make the subsequent construction of redundant dams more economical, because flow regulation by the upriver dam can enhance power generation at the downriver dam(s). The environmental impact assessment study for the first dam on any river should include a cumulative environmental assessment of the likely impacts of proposed additional dams on the same river system. Implementation of mitigation measures for cumulative (rather than dam-specific) impacts should be completed or well underway prior to construction of the second dam on the river. LCR Sustainable Development Working Paper No 16Environmental Impacts 8 Table 1. Hydroelectric Projects Adverse Environmental Impacts and Mitigation Options (continued) Key Indicators of Likely Environmental Impacts 9. Before a dam site is chosen (with a project-specific environmental impact assessment), sector-level environmental analysis can rank potential sites according to their degree of environmental desirability. A sectoral environmental assessment (SEA) should be carried out prior to making major power sector planning decisions, especially in the comparison of hydroelectric and other power generation (and demand management) alternatives.However, even without a detailed SEA, it is possible to carry out a simple environmental and ranking of different hydropower sites using basic, often readily available technical data. There exist various quantitative, easily metrical indicators that can be used to estimate the extent of adverse environmental impacts for any proposed hydroelectric project. 10. This paper presents 13 quantitative, easily calculated indicators that we consider especially useful for hydroproject site selection from an environmental standpoint. These i ndicators have high predictive value for likely adverse environmental (and related social) impacts.The first nine indicators (AI) use information that is normally easy to obtain from basic dam planning data, even without a separate environmental study. The other four indicators (JM) are also very important in the environmental comparison of alternative dam sites, but involve data that may require further environmental (or resettlement) study to obtain. Indicator A (hectares of land inundated) is perhaps the single most useful one in predicting the degree of environmental damage, because this indicator is positively correlated with many of the others.From a social standpoint, the number of people requiring resettlement (Indicator J) is an especially important. A. Reservoir scrape up Area 11. The area flooded by the reservoir is a sloshed proxy variable for many environmental and social impacts (Goodland, 1997). A large reservoir area implies the loss of much natural habitat and wil dlife and/or the displacement of many people. Very large reservoirs are typically in the low-lyings (often with tropical disease and aquatic weed problems) and usually impound larger rivers (with more fish and other aquatic species at risk).A very useful measure of environmental costs relative to economic benefits is the ratio of inundated hectares per megawatt (ha/MW) of electricity it varies by four orders of magnitude for large power projects (see Table 2). The global average for all large hydroelectric dams constructed to date (not just those in Table 2) is about 60 ha/MW (J. Goldemberg, pers. comm. ) it would be environmentally highly desirable for this average to be much reduced in future hydroprojects. B. Water Retention Time in Reservoir 12.Mean water retention time during normal operation (the shorter, the better) is very useful in estimating the extent to which reservoirs will have long-term water quality problems. This foretell (number of days) is calculated as a funct ion of reservoir intensity (cubic meters) and mean river flow (cubic liters per second). 9 10 LCR Sustainable Development Working Paper No. 16 C. Biomass Flooded 13. Biomass flooded is calculated in dozens per hectare based on the percent cover of different vegetation types in the reservoir area.For good reservoir water quality, dams should minimize flooding of forests (which have high biomass content). Flooding native forests also threatens biodiversity and releases greenhouse gases. D. Length of River Impounded 14. To observe aquatic and riparian biodiversity (including riverine forests), dam sites should minimize the length (kilometers) of river (main stem overconfident tributaries) impounded by the reservoir (measured during high flow periods). E. Length of River Left alter 15. This measures the kilometers of river left dry (with less than 50 percent of dry gentle mean flow) below the dam, due to water diversion.The length of dried-up river bed (before the next important d ownstream bird feeder) should be minimized, due to the loss of fish and other aquatic life, damage to riparian ecosystems, and disruption of human water supplies, agriculture, and/or fishing. F. Number of Downriver Tributaries 16. The more (major, undammed) tributaries downriver of the dam site, the better, in terms of maintaining accessible habitat for migratory fish, the natural flooding regime for riverine ecosystems, and nutrient or sediment inputs needed for the high biological productivity of estuaries. G. Likelihood of Reservoir Stratification 7. Stratification in a reservoir occurs when the lakes upper zone (epilimnion) is thermally divided from the deeper zone (hypolimnion) the last mentioned becomes stagnant and lacking in dissolved oxygen (anaerobic), thereby undesirable for most aquatic life. A rapid estimate of stratification tendencies in a reservoir can be obtained with the Densimetric Froude Number (F). F can be calculated as F = 320(L/D)(Q/V), where L = length of the reservoir (meters), D = mean reservoir depth (meters) (for which dam height can be a proxy), Q = mean water inflow (cubic meters per second), and V = eservoir volume (cubic meters). If F is less than 1, some stratification is expected, the severity of which increases with a smaller F. When F is greater than 1, stratification is not likely. H. Useful Reservoir Life 18. Useful reservoir life is the expected number of years before a reservoirs dead storage is completely filled, so that further sedimentation reduces the live storage and curtails power generation. Dead storage comprises all reservoir water beneath the level of the intakes for the dams turbines all of the water at or above this intake level is part of the live storage.Useful reservoir life is a function of dead storage and river-borne sediment loads. Useful reservoir life is a good indicator of the relative sustainability of electric power generation it varies from less than ten years before dead storage is filled (su ch as the Paute Dam in Ecuador) to potentially thousands of years. In general, reservoirs with the longest useful life are relatively deep and situated on rivers with low sediment loads. Maintaining low sediment loads over time typically requires good watershed management. Good Dams and Bad Dams 11 I. Access Roads through Forests 19.Where the risks of induced deforestation are high, project siting should minimize the kilometers of required new or upgraded access roads passing through or near natural forests. J. Persons Requiring Resettlement 20. The number of people physically displaced by hydroelectric projects ranges from home in (e. g. Pehuenche, Chile) to over 50,000 in Latin America (e. g. Yacyreta, Argentina-Paraguay) and well over 1 million in Asia (Three Gorges, China). Dam siting should generally seek to minimize the number of individuals or households requiring resettlement from lands affected by the reservoir and complementary civil works.A useful measure for relating re settlement costs to hydropower benefits is the ratio of people displaced per megawatt (Table 2). Because of their usually greater vulnerability to social disruption, it is especially important to minimize the number of indigenous people with traditional land-based models of production who would require resettlement. K. Critical Natural Habitats Affected 21. It is important to know the number of sites and hectares of critical natural habitats that would be lost to inundation, borrow pits, or other project components.Critical natural habitats include existing and officially proposed protected areas, as well as insecure areas of known high importance for biodiversity conservation. To comply with the World Banks Natural Habitats Policy, hydroelectric projects should not cause any significant loss or degradation of critical natural habitats. On the other hand, some hydroelectric projects imply very important conservation opportunities by providing a strong justification (sediment reduct ion) and financial resources needed for protecting natural habitats in upper catchment areas.L. Fish Species Diversity and Endemism 22. Fish species diversity is the number of species known from the project area, including the dam and reservoir site, as well as the downstream zone of project influence. Fish species endemism is the number of native species known only from the project area, or the river system where the project is located, and nowhere else on Earth. Dams are environmentally less objectionable if they affect rivers with a naturally low diversity and endemism of native fish species.In general, large, sea-level rivers in warm (tropical or subtropical) climates have a high diversity of native fish and other aquatic organisms, while small rivers in cold (tropical mountainous or temperate) climates have relatively low diversity. Large, lowland rivers are also more likely to have significant seasonal worker fish migrations, which are effectively blocked by most dams. Howev er, highland rivers and streams often have relatively high endemism in their fish fauna, especially if they are isolated from other rivers by waterfalls or other natural barriers.River segments with threatened fish species found nowhere else should be sort out as critical natural habitats and, ideally, would receive permanent protection from dams or other potentially damaging civil works. However, dams and reservoirs in upper tributary rivers and streams need not threaten the survival of any endemic fish (or mollusks, or other aquatic life) if they affect only an insignificant portion of the river area used by these species (see Indicators D and E) they should also be sited so as not to block important fish migrations. M. Cultural attribute Affected 23.An indication of the cultural significance of the area to be inundated (or otherwise affected by the project) is the number (by type) of cultural (archaeological, historical, paleontological, or religious) objects or sites. It is imp ortant to note whether each type of cultural property at the project site is salvageable (totally, partially, or not at all). 12 LCR Sustainable Development Working Paper No. 16 Table 2. Land Area Flooded and People Displaced in Large Hydropower Projects Project (country) Arun II (Nepal) Pehuenche (Chile) Pangue (Chile) Guavio (Colombia) Tehri (India) Ghazi Barotha (Pakistan)Nam Theun-Hinboun (Laos) Ertan (China) Fortuna (Panama) Chixoy (Guatemala) Grand Coulee (United States) Three Gorges (China) Tarbela (Pakistan) Salvajina (Colombia) Zimapan (Mexico) Itaipu (Brazil/Paraguay) Victoria (Sri Lanka) Kararao/Belo Monte (Brazil) Aguamilpa (Mexico) Betania (Colombia) Urra I (Colombia) Mangla (Pakistan) Bakun (Malaysia) Ataturk (Turkey) El Cajon (Honduras) Ilha Solteira (Brazil) Guri Complex (Venezuela) Salto Grande (Argentina/Uruguay) Nam Theun II (Laos) Arenal (Costa Rica) Yacyreta (Argentina/Paraguay) Tucurui (Brazil) Narmada Sagar (India) Porto Primavera (Brazil)Churchill Falls (Cana da) Khao Laem (Thailand) Kedung Ombo (Indonesia) Kainji (Nigeria) Pak Mun (Thailand) Cabora Bassa (Mozambique) Aswan High (Egypt) Nam Ngum (Laos) Sobradinho (Brazil) Kariba (Zambia/Zimbabwe) Balbina (Brazil) Akosombo (Ghana) Bayano (Panama) Kompienga (Burkina Faso) Brokopondo (Suriname) Installed capacity (MW) 402 500 450 1,000 2,400 1,450 210 3, three hundred 300 300 6,494 18,200 3,478 270 280 12,600 210 8,381 960 510 340 1,000 2,400 2,400 300 3,200 10,300 1,890 1,086 157 3,100 3,980 1,000 1,815 5,225 300 29 760 34 2,075 2,100 150 1,050 1,260 250 833 30 14 30 Reservoir rea (hectares) 43 400 500 1,530 4,200 2,640 630 10,100 1,050 1,400 33,306 110,000 24,280 2,030 2,300 135,000 2,270 116,000 13,000 7,370 7,400 25,300 70,000 81,700 11,200 125,700 426,000 78,300 45,000 7,000 165,000 243,000 90,820 225,000 665,000 38,800 4,600 126,000 6,000 380,000 400,000 37,000 415,000 510,000 236,000 848,200 35,000 20,000 160,000 People displaced 775 0 50 4,959 100,000 899 0 30,000 446 3,445 10,000 & gt1,300,000 96,000 3,272 2,800 59,000 45,000 n. a. 1,000 544 6,200 90,000 9,000 55,000 4,000 6,150 1,500 n. a. 5,700 2,500 50,000 30,000 80,500 15,000 0 10,800 29,000 50,000 4,945