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Jaivime Evaristo

"Growth, prosperity and rising population will inevi-"Growth, prosperity and rising population will inevi-"Growth, prosperity and rising population will inevi-tably push up energy needs over the coming decades. tably push up energy needs over the coming decades. tably push up energy needs over the coming decades. But we cannot continue to rely on insecure and envi-But we cannot continue to rely on insecure and envi-But we cannot continue to rely on insecure and envi-ronmentally unsustainable uses of energy…the world ronmentally unsustainable uses of energy…the world ronmentally unsustainable uses of energy…the world is locking itself into an unsustainable energy future is locking itself into an unsustainable energy future is locking itself into an unsustainable energy future which would have farwhich would have farwhich would have far---reaching consequences.” reaching consequences.” reaching consequences.”

T his was the warning issued by International Energy Agency (IEA) Executive Director Ma-ria van der Hoeven during the World Energy

Outlook 2011 Conference in London last November 9 (IEA, 2011). However, according to the IEA (2011) report, although oil is expected to remain as the lead-ing fuel, the role of renewable energy technologies – led by hydropower – will account for about half of the new installed capacity that will meet the growth in primary energy demand through to 2035.

This optimism in the huge potential of renewable en-ergy resources, particularly in hydropower, may be appropriately considered as the technology’s renais-sance since the emergence of academic and socio-political treatises began to cast doubts on the effec-tiveness of hydropower (Rosenberg et al., 2000) as well as on the ecological, cultural, and even social jus-tice implications of the same (WCD, 2000). Hydroe-lectric dams are, indeed, among the most controver-sial of all types of development projects, most often resulting in highly polarized, politically charged de-bates across social strata (World Bank, 2003) and in-ternational mandates. Despite the relatively large number of literature against (Ligon et al., 1995; Colli-er et al., 1996; Pringle et al., 2000; Rosenberg et al., 2000; St. Louis et al., 2000; Dudgeon, 2000; Nilsson and Berggren, 2000; Richter et al., 2010) hydrological alteration technologies, however – be these for elec-tricity production; water supply for agriculture, indus-tries, and municipalities; flood mitigation; navigation; and, recreation – it is apparent that the construction of large dams will continue to emerge as one of the important policy alternatives to meet water (Bikwas and Tortajada, 2001) and electricity demands, espe-cially in the developing world. In developing coun-tries, rapid urbanization and continued population growth will ensure increased demand for electric pow-

er for decades to come, even with the most suc-cessful of demand management and energy effi-ciency measures (World Bank, 2003).

As of 2008, IEA (2010) reports that hydropower produced 3,288 terrawatt-hours (TWh) worldwide, just over 16% of global electricity production; its overall technical potential, however, is estimated to be more than 16,400 TWh yr-1. Like fossil fuel resources, which are concentrated in just a few countries worldwide, about two-thirds of present hydropower generation – despite its impressive storage capacity and fast-response characteristics in meeting variable electricity demand – is also concentrated in just ten countries globally (IEA, 2010). Unlike fossil fuel resources, however, the presently skewed distribution of hydropower pro-duction is not geologically intrinsic by design but structurally limiting by access, mainly because of limited financial resources as well as controversies about its environmental and social costs (Koch, 2002). It is conceivable, therefore, that such limi-tations could eventually distill the “dams debate” down to a level of scale, that is, “small dams versus large dams”. Unfortunately, the costs and benefits that may be derived out of hydroelectric dams are not linearly related to scale, as was shown in a number of studies from both sides of the debate (Goodland, 1997; Mason, 1995; WCD, 2000; World Bank, 2003; ICOLD, 2010). This means that all large and small hydroelectric dams are not alike, not only from an environmental standpoint but also from an electricity generation standpoint, which supposedly defines the primacy of their ex-istence.

*Author Jaivime Evaristo is a graduate student in Univer-

sity of Pennsylvania’s Master of Science in Applied Geosci-

ences program. His email is evaristo@sas.upenn.edu.

**IGEL is a Wharton-led, Penn-wide initiative to facilitate

research, events and curriculum on business and the envi-

ronment. IGEL Student Research Briefs are written by

students on relevant issues in business and the environ-

ment and do not represent the views of Penn, Wharton or

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Therefore, this paper examines not only the benefits but also the trade-offs between large dams and small dams; evaluates what factors should be considered when dams are removed or when new dams are built; and, comments on the viability of hydroelec-tric dams as an energy source, not only from a pure-ly scientific and technical perspective but also from environmental and socio-economic standpoints.

So, what are dams to begin with?

In a broader sense, dams may be considered as a hydrological alteration. Rosenberg et al. (2000) de-fines hydrological alteration as any anthropogenic disruption in the magnitude or timing of natural riv-er flows. They place special emphasis particularly on impoundments as a major cause of disruptions on a global scale, built to store water to compensate for fluctuations in river flow, thereby providing a meas-ure of human control over water resources; or to raise the level of water upstream to either increase hydraulic head or enable diversion of water into a canal. It is implicit in this broad definition the vari-ous types of dams that could serve a single or multi-ple purposes. This then begs the questions, what are the different types of dams and how are they classi-fied?

Perhaps, one of the main reasons why the “dams de-bate” can linger through time and can be very perva-sive across socio-political landscapes is the fact that there exists a fundamental disagreement as to how best to classify the different types of dams. Even if the disagreement has never been active and confron-tational, the fact that a classification exists in isola-tion of the others proves an essential conceptual dis-cord. It goes without saying that this fundamental disagreement, while practically useful up to certain utilitarian boundaries, can also be highly unique as to serve only a specific user’s purposes and intents. For example, the US Army Corps of Engineers’ Na-tional Inventory of Dams (USACE, 2000) focuses on dam safety and defines dams as large if they meet one of the three criteria (Poff and Hart, 2002): (1) a high hazard potential, i.e. likely loss of human life if the dam fails, regardless of the dam’s absolute size; (2) a low hazard potential but height exceeding 7.6 m and storage capacity greater than 18,500 m3; or, (3) a low hazard potential but height exceeding about 1.8 m and storage exceeding 61,700 m3.

On the other hand, the International Commission on Large Dams (ICOLD) classifies dams as large if ei-

ther their height exceeds 15 m, or their height is be-tween 5 and 15 m and a reservoir greater than 3 x 106 m3 is impounded (WCD, 2000). Moreover, the IEA (2010) classifies dams based on the amount of energy (in MW) generated, i.e. small, if it generates less than 10 MW; medium, if it generates between 10 and 300 MW; and, large, if it generates greater than 300 MW. Still others more simply classify dams as either low-head or high-head (EnergyIdeas, 2001), depending on whether their height is less than 30 m or greater than 30 m, respectively.

Since it is not within the scope of this paper to choose or endorse any of these existing dam classifi-cations, we are therefore at liberty to decide which classification system, or some modification thereof, will best meet the objectives of this deductive dis-course. Because we are interested in hydrological alterations, or dams, in the context of power or elec-tricity generation, we can therefore adopt, with slight modifications, the IEA (2010) classification system:

Table 1. Modified Classification of Hydroelectric Dams

Source: Modified from IEA (2010) Classification of Hydropower

Note the absence of a Medium category, which was originally defined by IEA as having a per unit output of between 10 and 300 MW and could either be run-of-river (for 10-100 MW schemes) or dam and reservoir (for 100-300 MW schemes).

Before we proceed, let us qualify and clearly deline-ate a straightforward feature in the classification of hydroelectric structures in Table 1. In this modified classification system, we assume that small hydroe-lectric projects not only have a per unit output of less than 10 MW per year but also that they do not have a reservoir, i.e. they only use run-of-river to generate electricity, which therefore somewhat dis-qualifies them from being a “dam” in the strictest definition of the term (although some run-of-river systems may have a small pond or partial dam at the

Cate-gory

Out-put/

unit

Storage Pow-er

use (load

)

Invest-ment

costs

(US$ m/MW)

Small < 10 MW

Run-of-river

Base load

2-4

Large > 300 MW

Run-of-

river / Dam and reservoir

Base

and peak

2-3 for 10-300MW

projects; <2 for

>300MW projects

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inlet). Having made that qualification, however, we still believe that this is a fair assumption considering the amount of evidence and types of arguments raised on both sides of the debate regarding the ben-efits and costs of small and large hydroelectric dams. In addition, one major practical advantage of an-choring our definitions of small and large dams on the per unit output parameter as well as on storage, or the lack of it, is the avoidance of bias that normal-ly arises from using physical parameters such as height or area under submergence, especially when neither of these physical variables has been shown to singly stand as an acceptable indicator of the neg-ative social and environmental impacts of dams (Shah and Kumar, 2008). With these underpinnings in our modified classification system, we are now ready to dissect the benefits and costs of small dams and large dams.

Small Dams vs. Large Dams

Our approach in this section is to first look at the respective advantages and disadvantages of small dams and large dams. And then, we compare and contrast the main features of the two in the end.

Small Dams

Small dams are in most cases run-of-river; in other words any dam or barrage is quite small, usually just a weir, and generally little or no water is stored (Parish, 2002). Although our working definition for small dams, as illustrated in Table 1, are those with a unit output of less than 10 MW yr-1, it may work to our appreciation that in China this could go to as high as 25 MW (The EU-China Small Hydro Indus-try Guide, 1999).

High-head small dams are generally the most cost-effective schemes, since the higher the head, the less water is required for a given amount of power (Parish, 2002); hence, less costly equipment is need-ed. This raises the viability of mountainous regions since even small streams, if used at high-heads, can have high power output yields at relatively lower costs. The obvious drawback to this, however, is that high-head sites tend to be in areas of low population density, where the demand for electricity is relative-ly small. Moreover, if electricity is transported downstream to high-density urban centers, the costs of transmission over long distances could easily off-set the low-cost benefits of high-head electricity gen-eration. Another drawback to this site-specific, high-

head advantage would be that high-head sites are relatively rare (Fulford et al., 2000). This means that the greatest potential in expanding the use of small dams is in low-head sites.

Apart from site-specific advantages of small dams, some systemic issues in the finance and economics of small dams also come into play (Khenas et al., 2000). For example, a new small dam appears to produce rather expensive electricity, not because of site-specific or hydraulic head advantage issues but because the high capital expenditures are usually written off over a short period of only 10 to 20 years. Given the lack of economies of scale advantages typ-ical of large dams, this facet in the economics of small dams proves to be a major barrier to their use, especially in areas where they might be mostly ap-propriate and needed.

Advantages

The main advantages of small-scale hydropower, or small dams by our definition in this paper, are the following (Parish, 2002):

Can potentially provide electricity to hilly or mountainous areas where the national or region-al grid will normally never reach

More concentrated energy resource than either wind or solar power

Energy available is readily predictable

Electricity is usually continuously available on demand

No fuel and/or limited maintenance require-ment

Minimal social impact in terms of displacement of local peoples

Relatively long-lasting, at least 50 years, and has very minimal environmental impact because of the lack of or limited storage, smaller structures required and therefore generally less fragmenta-tion and impact on habitat and biodiversity

Disadvantages

The main disadvantages of small dams, on the other hand, are the following (Parish, 2002):

Viability and effectiveness are highly dependent on the site. That is, sites that can demonstrate hydraulic head advantage, while being in a loca-tion where the power generated can be exploited the most, are not all that common

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There is always a maximum useful power output available from a given site, thereby limiting any desired expansion of activities

River flows often vary considerably with the sea-sons, especially where there are monsoon-type climates, which then can limit the firm power output to quite a small fraction of the possible peak output

Lack of familiarity with the technology and know-how inhibit the exploitation of small hydro in many areas, especially in developing countries

In essence, although small hydroelectric dams tend to have very minimal environmental and even social impacts, in terms of displacing local populations of people, the main trade-off is the relatively limited amount of electricity that small dams can provide. When placed in a context where large dams are also viable options, the opportunity costs in going for small dams can be tremendous.

Large Dams

Large dams generally attract more attention from policy-makers, scientists, civil society, and financial institutions than small dams do. And, for a good rea-son because the perceived and real impact – benefits and costs – of large dams are generally far more per-vasive than small dams, not only technically but also environmentally, socially, and politically. A land-mark illustration to the immense role that large dams play in modern societies worldwide was the 356-page report by the World Commission on Dams (WCD) in 2000, which identified equity, governance, justice, and power as the main issues “at the heart of the dams debate” (WCD, 2000). The relevance of this report was not trivial since the 26 guidelines that the report endorsed were supposed to serve as a framework for countries and international banking organizations on which future large dam develop-ments must be based. For all its intents and purpos-es, the WCD 2000 Report may be argued as to have served a collective mandate, which is to put a re-straint on largely unregulated, often controversial dam building in just about anywhere where a per-ceived need is identified, with little or no regard for their impact on local peoples and the environment. On the policy side, the general awareness that the WCD 2000 Report imparted to the world may be laudable to some extent. On the practical side, the same may be regarded as a blanket strategy that nor-mally does not account for special conditions and development needs of a place or a country.

Coincidental to the WCD 2000 Report, however, was

an increasing concern on the impacts of climate change, particularly on the poor in terms of intense droughts and floods (Richter et al., 2010). This prompted policy-makers to rethink on the role of large dams in mitigating climate change impacts. As of 2010, there are 1,200 dams under construction, of which more than 370 dams are classified as either large or major (ICOLD, 2010). The majority of these dams are in the developing world and in fast-growing economies in Asia and South America where the demand for additional hydroelectricity are rising. Figure 1 shows that while global investment in dams dropped in the 1990s, a sharp rebound was observed until fairly recently. This renewed opti-mism in building large dams is both a direct result of increased demand for electricity as well as a source of funds to finance other development projects such as irrigation and drinking water supply (Richter et al., 2010).

Fig. 1. Global investment in dams showing the drop and rise before and after the turn of the new millennium. Source: World Bank Group, 2009 as cited by Richter et al. (2010)

To be able to understand in much clearer contexts the value, both positive and negative, of large dams, let us examine very briefly their general advantages and disadvantages.

Advantages

The main advantages of large-scale hydropower, or large dams, are the following (ICOLD, 2010):

Plays an important role in diversification of ener-gy portfolio since it can generate power that are comparable in magnitude to conventional sources like oil and natural gas

Viability and effectiveness are less dependent on sites in a river basin since impoundments can

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store enough water to achieve expected power output based on design

High life-cycle energy payback ratio. That is, the total energy produced over the lifetime of a plant divided by the energy needed to build, operate, fuel, and decommission it (Gagnon, 2005). Com-pared to coal, solar, wind, biomass, and nuclear energies, the energy payback ratio in a large hy-droelectric dam could reach to as high as 280 and as low as 206. Conversely, conventional coal, solar, biomass, nuclear, and wind can only have energy payback ratios of 5.1, 6, 5, 16, and 34, re-spectively (See Figure 2)

Economies of scale and therefore has a very high potential for transmission over long distances, as well as expansion and adoption in many areas where hydropower is a feasible option

Serves a central role in delivering other uses like flood control, irrigation, water supply, naviga-tion, recreation, and broader social security (Shah and Kumar, 2008)

Fig. 2. Energy payback ratio of electricity generation options based on life-cycle assessments (Source Gagnon, 2005)

Disadvantages

The main disadvantages of large dams are the fol-lowing:

Although cost per unit of power produced is low-er than smaller dams (Table 1), the sheer size of large dams means that huge capital costs are re-quired, which can be a major barrier especially in developing countries, where its drivers like rapid urbanization and high population growth (World Bank, 2003) may be more pronounced

In addition to financial capital, the design com-plexity of large dams often entails huge human and technological capital, which can either be limiting or inflationary to overall capital costs

Negative social and cultural impacts can include displacement of a large number of people (see Table 3 and discussion below) because of con-struction, inundation, and operations; other im-pacts include cultural dilution, or even cultural eradication, especially in areas where indigenous cultures are still relatively intact

Adverse environmental impacts (see Table 2)

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Environmental Impact Description

Flooding of natural habitats

Some reservoirs permanently flood extensive natural habitats, with local 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)

Loss of terrestrial wildlife

The loss of terrestrial wildlife to drowning during reservoir filling is an inherent conse-quence of the flooding of terrestrial natural habitats, although often treated as a separate impact

Involuntary displacement

Involuntary displacement of people is often the main adverse social impact of hydroelec-tric projects. It can also have important environmental implications, such as with the con-version of natural habitats to accommodate resettled rural populations

Deterioration of water quality

Damming can cause serious water quality deterioration, due to reduced oxygenation and dilution of pollutants by relatively stagnant reservoirs (compared to fast-flowing rivers), flooding of biomass (especially forests) and resulting underwater decay, and/or reservoir stratification (where deeper lake waters lack oxygen)

Downriver hydrological changes

Major downriver hydrological changes can destroy riparian ecosystems dependent on peri-odic natural flooding, exacerbate water pollution during low-flow periods, and increase saltwater intrusion near river mouths. Reduced sediment and nutrient loads downriver of dams can increase river-edge and coastal erosion and damage the biological and economic productivity of rivers and estuaries

Water-related diseases

Some infectious diseases (such as malaria, schistosomiasis, dysentery, cholera, etc.) can spread around hydroelectric reservoirs, particularly in warm climates and densely popu-lated areas

Fish and other aquatic life

Blocks upriver fish migrations; some fish species are not adapted to artificial lakes; change in downriver flow patters adversely affect many species; hypoxia in or below reservoirs kills freshwater species, especially benthic organisms, and damages aquatic habitats

Floating aquatic vegetation

Floating aquatic vegetation can rapidly proliferate in eutrophic reservoirs, causing (a) de-graded habitat for most species of fish and other aquatic life, (b) improved breeding grounds for mosquitoes and other nuisance species and disease vectors, (c) impeded navi-gation and swimming, (d) clogging of electro-mechanical equipment at dams, and (e) in-creased water loss from some reservoirs

Loss of cultural property

Cultural property, including archaeological, historical, paleontological, and religious sites and objects, can be inundated by reservoirs or destroyed by associated quarries, borrow pits, roads, or other works

Reservoir sedimentation

Over time, live storage and power generation are reduced by reservoir sedimentation, such that much of some projects’ hydroelectric energy might not be renewable over the long term

Greenhouse gases

CO2 and CH4 are released into the atmosphere from reservoirs that flood forests and other biomass, either slowly (as flooded organic matter decomposes) or rapidly (if the forest is cut and burned before reservoir filling)

Table 2. Adverse Environmental Impacts of Large Hydroelectric Dams (World Bank, 2003)

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In a recent study by Richter et al. (2010) (Table 3),

they estimated that globally, 472 million people have

been affected by approximately 7,000 largest dams

ever built. The potentially affected populations are

heavily concentrated in Southeast Asia and India,

which when combined account for more than half of

all large dams that have been built.

Table 3. Number of ‘potentially affected’ rural people (in millions) living downstream of large reservoirs close to (<10 km) rivers, tabulated by degree of regulation and by river

size

Source: Richter et al. (2010)

a Including western Russia and Middle East. b Including Central America and the Carribean. c If urban areas are included, this number becomes 1101.4 million. d Including Malaysia, the Phil-ippines, Indonesia, Burma, Cambodia, Thailand, Vietnam, Laos

In essence, although large hydroelectric dams tend to provide an enormous amount of electricity and higher energy payback ratio (Fig. 2); as well as can serve as a “spring board” of a myriad other uses like irrigation, flood control, etc. when compared to small dams, the main trade-off is that they also tend to pose adverse environmental and social impacts, which can reduce their attractiveness particularly in societies where social participation and buy-in play a key role.

Synthesis: small dams vs. large dams

It is almost impossible to form an educated opinion on the small vs. large dams debate without looking at specific case studies. If the relationship between

the size of a dam and its trade-offs were only linearly related, this task would have been easier and more straightforward. Unfortunately, the fact presses for itself that the relationship is not only that it is not linear but also that it can be a confluence of several other parameters, engaged in an interplay with vary-ing degrees of predictability. For example, Shah and Kumar (2008) analyzed data from 145 countries and 9,884 dams worldwide. They demonstrated that while there is a direct relationship between improv-ing a country’s water situation (expressed in terms of the sustainable water index) and its economic growth, not a single physical parameter in dam de-velopment can stand as an acceptable indicator of its negative social and environmental impacts. The au-thors suggested that a combination of physical crite-ria such as dam height, storage volume, and the area under submergence should be considered in classify-ing dams and in assessing their potential negative impacts.

In addition, the World Bank (2003) cautioned against drawing conclusions on the potential nega-tive effects of large dams, simply based on their elec-tricity generation size. For example, the 500–MW Pehuenche Hydroelectric Project in Chile flooded only about 400 hectares of land (therefore, with minimal damage to forest or wildlife resources) and has had no water quality problems. This is in con-trast to the Brokopondo Dam in Suriname, which inundated about 160,000 hectares of biologically valuable tropical rainforest and is known for serious water quality and aquatic weed problems, while providing relatively little electric generating capacity at only 30 MW. Meanwhile, on the case concerning small dams, the World Wildlife Fund (WWF, 2003) warned that while small hydropower can play an im-portant role, especially in developing countries, the cumulative impact of all the small hydropower plants in a river basin should be considered as this can often be worse than one large hydropower dam. It added that in countries where the potential for large dams has been exploited, further small schemes could cause considerable damage on the remaining rivers. This brief review of case studies and facts, surrounding small dams and large dams, points to the complexity of the issue at hand. In fact, the WWF warns that given these complexities, it is not possible to make generic statements about the desirability of small versus large dams. Each scheme needs to be judged on its own merits in relation to site-specific characteristics as well as in relation to its river basin-wide impacts.

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Having been able to emphasize the overarching, gov-erning principle in the debate between small and large dams, however, it may still be useful for our purposes in this paper to mention some general guidelines in the development of dams, particularly large dams, as they are the ones that tend to cause major environ-mental damage. The World Bank (2003) reports that, in general, the most environmentally benign hydroe-lectric dam sites are on upper tributaries, while the most problematic ones are on the large stems of riv-ers. Therefore, these should be considered in the de-velopment of hydroelectric dams. It adds that many of the more problematic dam sites are best left undevel-oped while the less problematic ones are pursued, but only with effective implementation of proper mitiga-tion measures.

Rather than picking a side on this debate, let us in-stead look at the typical features of environmentally “good” and “bad” hydroelectric sites. The rationale for this is simple. Everyone can agree on the benefits that can be derived from both small and large hydroelec-tric dams, but not everyone can, in fact not everyone will, agree on the trade-offs, which are by and large economic (in the case of small dams) and environ-mental (in the case of large dams) in nature.

A typical “bad” hydroelectric dam site from an envi-ronmental standpoint involves (World Bank, 2003):

A large reservoir surface area

Much flooding of natural habitats and consequent loss of wildlife

A large river with much aquatic biodiversity dam-aged

A relatively shallow reservoir

Few or no downriver tributaries

Water quality problems due to the decay of sub-merged forests

Location in the lowland tropics or subtropics, con-ducive to the spread of vector-borne diseases

Serious problems with floating aquatic weeds

A typical “good” hydroelectric dam site, on the other hand, from an environmental standpoint involves (World Bank, 2003):

A relatively small reservoir surface area

Little loss of natural habitats and wildlife

A relatively small (often highland) river with little aquatic biodiversity at risk

A deep reservoir which silts up very slowly

Many downriver tributaries

Little or no flooding of forests

No tropical diseases (often due to high elevations or temperate latitudes)

No aquatic weed problems

One might observe that the points just enumerated above are typically related more to large dams than to small dams. So, with this amount of criteria that should be considered in large dam development, does this imply that humanity is better off going for small dams than for large dams? The temptation to pick a side in this debate is ceaseless. However, in the con-text of a wider development agenda, especially in the developing world, looking at this debate through the lens of a trade-off, i.e. a technically balanced and par-ticipatory way of benefits-costs analysis is a more ap-propriate way than a simple one-size-fits-all ap-proach. Reiterating the recommendations by WWF (2003), each scheme needs to be judged on its own merits in relation to site-specific characteristics (technical, social, environmental) as well as in relation to its river basin-wide impacts.

Factors to consider in removing dams

Much of the arguments made thus far in this paper revolved around the concept of building dams – its benefits and costs, its advantages and disadvantages; and, as such, which is a better option, small dams or large dams? The evidence and arguments presented up until this point should be sufficient in illustrating what factors should be considered in building dams, regardless of size. Hereon forward, we will briefly look at the factors that should be considered when remov-ing dams.

The adverse impacts of dams on the environment – alteration of natural river flow, transforming the bio-logical and physical characteristics of river channels and floodplains, and fragmenting the continuity of rivers (Petts, 1984; Chisolm, 1994; Yeager, 1994; Li-gon et al., 1995; Ward and Stanford, 1995; Stanford et al., 1996; Poff et al., 1997) – have led to a search for solutions from mitigation to complete removal (Bednarek, 2001). In cases where mitigation is deemed ineffective or too costly, dam removal is con-

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sidered (American Rivers and NPS, 1996). As of 2001, over 100 small dams have been removed in the United States (Born et al., 1998; American Rivers et al., 1999) while many others have since been considered for re-moval (Wood, 1999), thereby, resulting in a growing attention to dam removal as a potential river and eco-logical restoration tool (Bednarek, 2001). In addition to environmental concerns, other reasons for dam re-moval include socioeconomic factors such as econom-ically inefficient power production or a risk of struc-tural failure of old, unsafe, or abandoned dams (American Rivers et al., 1999). Regardless of the moti-vations, however, it is crucial to understand and con-sider the ecological and downstream impacts of dam removals (Bednarek, 2001).

Some of the potential adverse effects of dam removal include the following:

Ecological impacts from and habitat modification due to large movements of sediments (especially when contaminants are present). For example, in the Baraboo River system (WI), the removal of several dams improved fish habitat quality within the former impoundments but decreased fish hab-itat downstream, (Catalano et al., 2001)

Reductions in wetland habitat

Reductions in groundwater recharge

Shifts in species abundance and distribution. For example, despite the recommended usage of dam removal to eliminate barriers to fish movement, there are some situations where removal could potentially increase the chances that exotic species presently blocked by dams could invade upstream habitats (Dodd, 1999)

Impairment of water quality through the downstream transport of sedi-ment-bound con-taminants (e.g. or-ganic substances and heavy metals) and the alteration of bio-geochemical cycles (Hart et al., 2002). For example, a large volume of fine sedi-ment contaminated with PCBs was pre-sent in the impound-ment upstream of Ft. Edward Dam on the

Hudson River, and these contaminants were trans-ported downstream when the dam was breached (Shuman, 1995)

Shifts in patterns of sediment movement, which con-trol the process of channel evolution (e.g., the rate of headward erosion in the former impoundment, the aggradation of downstream reaches, channel narrow-ing, creation of new floodplains), which in turn all have important consequences for the biogeochemical cycling and habitat availability (Hart et al., 2002).

Figure 3 illustrates the potential ecological responses to dam removal (Hart et al, 2002). Prior to removal, upstream and downstream free-flowing areas are sep-arated by an impoundment. Dam removal initiates a series of abiotic and biotic changes that vary from one place to another and occur at different rates. For ex-ample, the rate of sediment transport and channel ad-justment is a function of the distribution of sediment particle sizes and flow magnitudes, and the response rate of aquatic and riparian biota to these changes de-pends on their dispersal and growth rates. Bednarek (2001), however, believes that based on several rec-orded dam removals, the increased sediment load caused by removal should be a short-term effect and so as its associated ecological consequences.

Some of the undesirable effects of dam removal due to sedimentation, however, can be potentially reduced by developing improved restoration practices, particu-larly with respect to sediment management (ASCE, 1997). For example, an assessment of contaminant risks should include a review of the historical usage of

Fig. 3. A simple spatial and temporal context for examining po-

tential ecological responses to dam removal (Image from Hart et

al., 2002)

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a watershed. For example, an assessment of contami-nant risks should include a review of the historical usage of a watershed as well as an analysis of the type and grain size of sediments in the impoundment (Bushaw-Newton et al., 2001).

Other interventions that may arise out of such a com-prehensive assessment of potential sediment loads due to dam removal could include planting riparian vegetation to stabilize sediments (Shafroth et al., 2002) or collecting and relocating some species of fish and mussels that may be particularly vulnerable to dam removal (Hart et al., 2002).

Since geomorphic effects of dam removal are central to other effects on the ecology and biology of a river or a watershed, it is therefore important to mitigate the potential adverse effects of dam removal around a comprehensive knowledge of an area’s geomorpholo-gy before and after breaching a dam. Moreover, the removal process can also be scheduled and manipu-lated to minimize the undesirable effects (Pizzuto, 2002). For example, Pizzuto (2002) adds that a varie-ty of methods are already available to control erosion of the sediment fill and, therefore, to minimize the effects of increased sediment supply downstream.

Lastly, in addition to the technical side of dam remov-al just stated and illustrated, we must understand that other factors have to be equally considered in the exe-cution of this type of activity. Babbitt (2002) explains that cost can be a major obstacle to dam removal. Al-most ten years on, this is probably a far greater issue today, particularly within the context of the recent fi-nancial crisis and fiscal rationalization in the United States. Moreover, social and emotional considerations may also come into play, to certain extents, in the de-cision to remove a dam. Johnson and Graber (2002) highlight how some local communities can linger to their strong attachments to their dam and its im-poundment. The interplay between technical, envi-ronmental, social, and economic factors in removing a dam needs to be thoroughly considered if we are to desire an effective process that transcends the tech-nical and scientific considerations. Just as multi-sectoral, interdisciplinary considerations were central to the thematic tone in the earlier sections of this pa-per when building a dam, the same should drive the narrative in and when removing a dam.

In summary, where dam removal is identified as the best option available to restore river and watershed function and ecology – i.e. in more superior or practi-

cal terms than a status quo, structural repair, or other changes to dam operations (ASCE, 1997) – it can be expected that the disturbance may result in some un-desirable, adverse ecological effects. Although there is some consensus that these adverse effects may be short-term, any potential risks may still be mitigated, if not eliminated, by well-conceived and comprehen-sive watershed-level restoration strategies as well as one that includes buy-in and participation by affected communities.

Conclusion

In the author’s opinion, it is difficult to approach an environmental issue without having to touch on the demand side of the debate, i.e. the factors and varia-bles that drive a development agenda. In most cases, this boils down to high population growth and rapid urbanization. The issue on hydroelectric dams is no exception; in fact, it is a classic, colossal example of anthropogenic disruption aimed at meeting the elec-tricity demands of an exploding population. It goes without saying, therefore, that unless the high popula-tion growth rates, especially in developing countries, are halted; or, that unless other viable, environmen-tally acceptable alternatives to hydroelectric exist in providing reliable source of power; the political onus to build more dams – large and small – will persist. With dam building essentially becoming a normative developmental and social security issue, our best hopes to minimize its adverse environmental and so-cio-cultural impacts rely in assessing trade-offs and in managing risks. As regards the debate between small and large dams, although large dams tend to pose far greater environmental and social risks than small dams, it is still more prudent to approach the issue by assessing trade-offs and deciding based on equitable outcomes.

Having said that, it will not hurt if we follow some general guidelines to achieving a more sustainable end. For example, the intuitive finding by the World Bank (2003) that hydroelectric dam sites tend to be more environmentally benign on upper tributaries than on large stems of rivers can serve as a useful guide in future dam building. Looking at the entire dams debate through the lens of a trade-off, or what others formally call as a benefits-costs analysis (BCA) approach, rather than a one-size-fits-all position, may be the more pragmatic way of meeting future electrici-ty demands through dams while allowing enough and proper mitigation measures to address adverse envi-ronmental and social effects. Studies presented in this paper have shown that not one physical parameter is a good indicator of a dam’s environmental and social

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impacts. Moreover, some case studies have proved that the sheer size of a dam is neither definitive of its adverse environmental impacts nor is it indicative of the desired benefits in terms of electricity generation. As such, building on the WWF (2003) findings, it is therefore recommended that each scheme – small dam or large dam – needs to be judged on its own merits in relation to site-specific characteristics (technical, social, environmental) as well as in relation to its river basin-wide impacts. Moreover, where dam removal is identified as the best option available to restore river and watershed function and ecology, or to altogether ‘cut losses’ from economically underper-forming dams, the same should be pursued in a com-prehensive, well-conceived manner so as to minimize the adverse environmental effects, albeit short-term, and maximize the expected ecological and economic benefits.

Lastly, the author would like to emphasize one final point. While the developed world is relatively occu-pied in identifying which dams to remove and how, the developing world continues to gather momentum in building even larger, growing number of dams. As a matter of perspective, since the goal of development projects like dam building is by and large human de-velopment, the author is of the opinion that not a sin-gle lens should be used in assigning value or ‘de-value’ to either side. Both developed and developing worlds certainly have different socio-economic, per capita profiles; even their respective environmental settings may have varying levels of ecological resistance and resilience. As such, each side may have different views on development and, therefore, different political and socio-economic priorities from each other that must be respected and taken into their proper contexts and merits. In the end, it is our basic human right to im-prove our socio-economic situations; and, it is also our basic human responsibility to do so in an environ-mentally responsible and sustainable manner. How each side wields its way to getting there is probably more of a sovereign issue than an ideological one.

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