DOI: 10.1007/s00267-001-0058-3
PROFILE
River Systems as Providers of Goods and Services:
A Basis for Comparing Desired and Undesired
Effects of Large Dam Projects
ANNA BRISMAR*
Department of Water and Environmental Studies
Linköping University
581 83 Linköping, Sweden
ABSTRACT / In developing countries, large dam projects continue to be launched, primarily to secure a time-stable freshwater supply and to generate hydropower. Meanwhile, calls
for environmentally sustainable development put pressure on
the dam-building industry to integrate ecological concerns in
project planning and decision-making. Such integration requires environmental impact statements (EISs) that can communicate the societal implications of the ecological effects in
terms that are understandable and useful to planners and decision-makers.
The purpose of this study is to develop a basic framework for
assessing the societal implications of the river ecological effects expected of a proposed large dam project. The aim is to
In developing countries, large dam projects continue to be launched as central means to realize largescale irrigated agriculture, industrialization, and overall
socioeconomic development. In semiarid subtropical
regions, large dam projects are implemented primarily
to secure a time-stable freshwater supply for irrigation
and to generate hydroelectricity. In monsoonal regions, their primary purpose is often to protect against
flooding. Additionally, commercial fish hatcheries are
sometimes set up by the reservoir to increase the utility
of the dam.
In the last decade, a growing worldwide awareness of
the environmental risks associated with large dam
projects have led to increased calls for proper consideration of potential adverse ecological effects in planning and decision-making (WCD 2000). However, despite the introduction of national laws and regulations
and international conventions that serve to protect enKEY WORDS: Large dam project; Ecosystem goods and services; Environmental impact assessment; Flow regulation; River
ecology
*Author to whom correspondence should be addressed; email: annbr@
tema.liu.se
Environmental Management Vol. 29, No. 5, pp. 598 – 609
facilitate a comparison of desired and potential undesired effects on-site and downstream. The study involves two main
tasks: to identify key river goods and services that a river system may provide, and to analyze how the implementation of a
large dam project may alter the on-site capacity and downstream potentials to derive river goods and services from the
river system.
Three river goods and six river services are identified. River
goods are defined as extractable partly man-made products
and river services as naturally sustained processes. By four
main types of flow manipulations, a large dam project improves the on-site capacity to derive desired river goods, but
simultaneously threatens the provision of desirable river goods
and services downstream. However, by adjusting the site, design, and operational schedule of the proposed dam project,
undesirable effects on river goods and services can be minimized.
vironmental interests, large dam projects continue to
be planned and implemented without proper attention
to the ecological effects (Swales and Harris 1996).
Since its introduction in the United States in 1969,
environmental impact assessment (EIA) has become a
major tool for ensuring environmentally sound management practices (Ebisemiju 1993). EIA is a procedure
used to predict, assess, estimate, and communicate the
environmental consequences, both beneficial and adverse, of a proposed development project and to ensure
that these consequences are taken into account in
project design, implementation, and management
(OECD 1992, Glasson and others 1999). The EIA report or environmental impact statement (EIS) should
function as a crucial document to decide whether to
proceed, modify, or reject a proposed project (Glasson
and others 1999). It also should be used as a basis for
comparing desired and undesired effects of alternative
development projects and to clarify some of the conflicts of interests involved.
In developing countries, the progress of adopting
EIA as a practical tool has been extremely slow (Ebisemiju 1993). In those countries where EIA has been
formally embraced, its practical performance still re©
2002 Springer-Verlag New York Inc.
River Systems as Providers of Goods and Services
mains poor and the EIA is often seen only as a postscript to planning (Ebisemiju 1993). It is here argued
that an important reason for the poor performance of
EIA is that conventional EISs do not effectively communicate the societal implications of the ecological effects.
Predicted adverse ecological effects are often presented
in a fragmented and technical manner that makes a
comparison with the desired effects of the project more
difficult. As a result, the EIS cannot significantly influence the site, design, and operational schedule of a
proposed dam project, and the project is planned
mainly on political, economic, and technological
grounds.
In order to increase the usefulness of the EIS, adverse ecological effects need to be identified and translated into a terminology that is comprehensible and
relevant to the decision-makers (Firth 1998). This
would facilitate a comparison of desired functions and
undesired effects expected from the proposed dam
project and help to support compromise building
among conflicting interests.
In the field of ecological economics, the concept
ecosystem goods and services has been developed to
facilitate a dialogue between economists and ecologists.
An ecosystem good or service is defined as any natural
phenomenon that has a perceived societal function or
value (e.g., Daily 1997). Ecosystem goods and services
are fundamentally generated by ecosystems (e.g., rivers,
forests, lakes, or wetlands), but their provision can be
enhanced or weakened by human intervention. Many
ecosystem goods and services provide the basis for human existence (Daily 1997, Dasgupta and others 1994),
while some contribute to enhance human welfare and
societal development (Costanza and Folke 1996). Attempts have been made to identify the various goods
and services that river systems may provide (Meyer
1997, Postel and Carpenter 1997, Strange and others
1999). However, no study has been found that addresses how the capacity of a river system to provide
such goods and services is influenced by the implementation of a large dam project.
The purpose of this study is to develop a basic framework for assessing the societal implications of key river
ecological effects that large dam projects may induce,
in order to facilitate comparison of desired and undesired effects of dam project proposals. The study involves two main tasks: to identify key river goods and
services that a river system may provide, and to analyze
how the implementation of a large dam project may
alter the on-site capacity and downstream potentials to
derive river goods and services from the river system.
The paper focuses on developing countries, where
large dam projects for irrigation and hydroelectric
599
power generation will continue to be motivated by the
overall need for socioeconomic development and by
high seasonal and annual variations in precipitation
and runoff. By definition, a large dam has a height of
15 m or more from the foundation, or a height of 5 m
or more but a reservoir volume of more than 3 million
m3 (WCD 2000).
Viewing the River System as a Provider of
Goods and Services
The river system can be viewed as a potential provider of so-called river goods and services, which are of
importance for human life and the functioning of society. The provision of river goods and services fundamentally depends on the natural characteristics of the
river ecosystem. It also is affected by the presence of
man-made river structures and by natural and human
forces acting upon the river system. A large river system
is naturally composed of channels, banks, floodplains,
inland and coastal deltas, estuaries, and associated
groundwater aquifers. As a result of societal development, most river systems also contain such man-made
structures as dams, hydroelectric power plants, and
irrigation canals.
Defining River Goods
River goods are defined as products that are of
societal use when extracted or diverted from the river
system. Although the generation of river goods fundamentally is determined by the natural river system, in
part, it also depends on human interventions and technologies. Worldwide, the most desired river goods are
fresh water, hydroelectric power, and fish.
Fresh water. River systems constitute important
sources of fresh water for traditional and modern societies all around the world. River water is used for all
types of freshwater-dependent activities, including domestic, municipal, industrial, and irrigation uses. In
semiarid subtropical regions, where rainfall is low, erratic, and seasonally highly varied (Falkenmark and
Chapman 1989), rivers function as indispensable
sources of fresh water for irrigated agriculture.
Water is diverted from the river channel with or
without obstruction of the river flow. Without flow
obstruction, fresh water is diverted by canals, shunts,
furrows, and natural stone cracks, or by means of
pumping. Often, the river flow is stored behind dams,
weirs, or barrages before diversion.
Hydroelectric power. A large river system also provides
the potential for the generation of hydroelectric power.
Hydroelectric power is also a highly demanded natural
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A. Brismar
resource and is often preferred as an alternative to the
energy produced by coal-fueled, oil-fueled, or nuclear
power plants. High flow rates and large elevation differences increase the potential to generate hydroelectric power. The main stream, therefore, often provides
the most favorable locations for hydroelectric power
plants.
There are three main types of hydroelectric power
plants: storage, run-of-river, and pumped storage plants
(Novak and others 1996, Gulliver and Arndt 1991). A
storage plant presupposes a storage dam to effectively
regulate the flow in response to the electricity demand.
In contrast, a run-of-river plant does not involve a storage dam and thus cannot regulate the flow. Instead, it
relies upon the natural flow of the river. In most parts
of the world, a weir or barrage is used to concentrate
the flow and to raise the upstream river level sufficiently
to generate power. Only a day or week’s water volume
can generally be stored above the weir or barrage; thus
the electric output varies with the seasonal fluctuations
in flow and is unevenly generated over the year. In
some cases, water is diverted from the river into a canal
or a long penstock installed with a weir and power
station. A pumped storage plant is the least common
type of plant and is a net consumer of electricity. Similar to a run-of-river plant, it does not utilize a storage
dam. Instead, the water is pumped through a pipe from
a lower reservoir during off-peak hours when the price
of energy is low. During peak hours, the water is released through the pipe to generate electricity at a
higher price. A storage plant connected to a large
storage dam is the most common type of hydropower
facility and has the greatest capacity for power generation (Novak and others 1996).
Native and stocked fish. Most healthy river systems
constitute important sources of fish for society (Welcomme 1989). Fish is harvested for various reasons,
e.g., consumption, recreational purposes, ecological
studies, and as environmental indicators. Native fish
species are adapted to the natural flow regime and are
often migratory, which means that they utilize the entire river continuum, including the headwaters, floodplains, and estuary to complete their life cycles (Welcomme 1989). Examples of migratory fish species are
carp, salmon, and eel (Rosenberg and others 1997).
The abundance and diversity of the native fish stock
can be deliberately enhanced or complemented by
stocking of desired exotic fish, either in the river channel or in dam reservoirs.
Defining River Services
River services are here defined as processes that are
of societal value and that are naturally generated and
maintained by the river system. Most river services operate over the river’s entire length and generally depend on the natural dynamics of the river system. Although naturally generated, technical devices, dam
operations, and other practices can be used to artificially enhance their generation. For example, transportation and dilution of pollutants can be enhanced by
the release of artificial high flows from dam reservoirs.
Transportation and dilution of pollutants. A river has a
natural capacity to transport and dilute polluted discharges and runoff and to transport the pollutants
downstream, sometimes all the way to the delta and
coastal zone (e.g., Stanley and Warne 1998). This river
service is widely relied upon by governments, cities,
companies, industries, and private persons for disposing of untreated or residual wastes. The transportation
rate of pollutants depends on the flow rate and on the
presence of suspended particles to which the pollutants
can adsorb. High flows, especially flood pulses, and
high concentrations of suspended silt particles accelerate their transportation rate.
Partial water purification. The river system has a natural capacity to purify the river water from pollutants.
Pollutants can be categorized into acids and acidifying
agents, nutrients, degradable organic compounds, inert organic compounds, metals, and metalloids (Falkenmark and Allard 1991). When pollutants are released
into to the water, they can either become diluted, suspended in the water, adsorbed onto particles and various material, assimilated into living organisms (Strange
and others 1999), embedded into the sediments, or
decomposed by biochemical reactions. Their actual
fate depends on their chemical properties and on the
physical, chemical, and biological conditions in the
river. Sedimentation and assimilation into organisms
temporarily remove pollutants from the water, whereas
by biochemical decomposition they are transformed
and possibly detoxified. Thus, various natural processes
can temporarily or partially purify the river water.
Riverbank stabilization. The river system is also capable of maintaining riverbank stability (Patten 1998).
Riverbank stability is supported by the continuous deposition of silt along the riverbanks. It also is favored by
riparian vegetation adapted to the recurrence of seasonal and annual floods and elevated groundwater tables (Naiman and Décamps 1997). With strong and
flexible stems and root systems, the riparian vegetation
can stabilize riverbanks and effectively protect them
from erosion by water currents. The plants can also
contribute to holding the shoreline material in place by
slowing the flow of the river.
With little or no riparian vegetation, riverbanks can
be highly unstable and subject to large soil losses and
River Systems as Providers of Goods and Services
significant channel widening. According to a study by
Beeson and Doyle (1995), extensive bank erosion can
be 30 times more prevalent on nonvegetated banks
exposed to currents than on vegetated banks.
Soil wetting and fertilization of floodplains and deltas.
Since ancient times, seasonal floods have been utilized
to irrigate and fertilize agricultural land on river floodplains and deltas. In the developed world, almost all
larger river floodplains and deltas have been isolated
from seasonal flood pulses by levees and barrages
(Sparks and others 1998). In the developing world, a
number of large river floodplains and inland and
coastal deltas still remain (Adams 1993). Apart from
providing important fishing grounds, cattle grazing
land, sources of fuel wood, and groundwater recharge
areas, floodplains and deltas also constitute extensive
farming areas. Today, flood-dependent farming is practiced on most major West African wetlands, such as the
River Senegal floodplain, the Hadejia-Jama’ are River
floodplain in northern Nigeria, the Niger inland delta,
and the Logone-Chari system in Cameroon (Adams
1993).
Floodplain and delta farming relies on the recurrence of floods in the rainy season (Adams 1993).
When the river overflows, the riparian soil becomes
inundated and replenished with water, silt, and nutrients. The duration of the flood season varies, but can
last for a couple of months. While the floodwater is still
high, so-called flood cropping is practiced and watertolerant crops are planted. On the Niger Inland Delta,
rice is planted in the rainy season in July and August,
before the floodwater rises, and is harvested when the
floods recede, between December and February. When
the floodwater has drained off the land, the residual
moisture is utilized for farming of less water-tolerant
crops, such as sorghum, cassava, and groundnuts. This
practice is called flood recession farming (Adams
1993). Although floodplain and delta farming generally constitute sustainable ways of managing river systems, these practices are also associated with great uncertainties related to the timing and magnitude of
floods (Barbier and Thompson 1998).
Flood flow storage on floodplains. The river system also
has a natural ability to control flooding. The presence
of a well-vegetated alluvial floodplain reduces the risk
for downstream flooding (Covich 1993), by slowing the
movement of floodwater and providing a shallow but
extensive natural spongelike reservoir that absorbs a
substantial part of the floodwater (Sparks and others
1998). When the river channel overflows, the floodwater is stored in the soil, taken up by the vegetation, lost
as evapotranspiration, assembled in floodplain lakes, or
percolates into the groundwater aquifers below the
601
floodplain. In order to provide an effective flood control system, the floodplain vegetation must be subject to
the seasonal flow variations to which it is adapted.
Changes to the water level and to the timing, duration,
and frequency of seasonal floods can disturb the regeneration of vegetation and reduce the vegetative cover
and thereby the natural capacity for flood storage
(Sparks and others 1998).
Delta erosion control. Due to its high natural soil fertility, the coastal delta area often functions as an important agricultural zone. The presence of a delta area,
however, depends on the continuous transportation
and deposition of sediments from upper reaches to
withstand erosion by coastal currents (Stanley and
Warne 1998).
On its downstream journey, the river water carries
excess sediments from its headwaters and eroding upper reaches and deposits the sediment downstream, on
the riverbed, banks, floodplains, delta, and at the coast
(Hay 1998). The sediment transport capacity is affected
by the sediment load, the flow volume, and the gradient
(Hay 1998). High flows, particularly flood flows, are
responsible for most of the sediment transportation
downstream, and largely determine the degree to
which sediments are deposited on deltas or discharged
at the coast.
In temperate regions, flood flows cause a dramatic
increase in sediment deposition both at the delta or
estuary and coast. In subtropical and tropical regions, a
large share of the annual sediment deposition at the
delta and estuary comes from just a few intensive rainfalls and flood events (Milliman and Syvitski 1992,
Vaithiyanathan and others 1992). Because the flood
flow is so strong, a relatively high percentage of the
transported silt is discharged at the coast, leaving a
smaller share to be deposited on the estuary (Eyre and
others 1998).
Table 1 summarizes the river goods and services
here addressed.
Assessing Functions and Effects as Altered
Potentials for Goods and Services
Dam Project Involves Manipulation of River Flow
Regime
A large dam project, intended for irrigation and
hydroelectric power purposes, necessitates four main
types of manipulation of the river flow regime: blockage, storage, regulation, and withdrawal of the river
flow. These flow manipulations are necessary to achieve
the intended project functions, i.e., to enhance the
capacity to derive river goods on-site (such as fresh
602
Table 1.
A. Brismar
Goods and services that may be derived or maintained by a river systema
River goods
Fresh water diverted without flow obstruction or by means of
dams or weirs1
Hydroelectric power generated by run-of-river, pumped
storage, or storage plants2
Fish reproduced naturally in the river (native river fish) or
sustained by stocking in the reservoir (exotic pelagic fish)3
River services
Transportation and dilution of pollutants in the river
water4
Partial water purification by adsorption, sedimentation,
assimilation, chemical transformation, or decomposition5
Riverbank stabilization by silt deposition and riparian
vegetation6
Soil wetting and fertilization of floodplains and inland and
coastal deltas7
Flood flow storage by soil infiltration, evapotranspiration,
and groundwater recharge within floodplains8
Delta erosion control by transportation and deposition of
sediments9
a
Sources: 1Keller and others (2000), 2Novak and others (1996), 3Welcomme (1989), 4Stanley and Warne (1998), 5Strange and others (1999),
Naiman and Décamps (1997) and Patten (1998), 7Adams (1993), 8Covich (1993) and Sparks and others (1998), 9Hay (1998) and Stanley and
Warne (1998).
6
water, hydroelectric power, and hatched pelagic fish).
The character of the flow manipulations depends on
the site, design, and operational schedule of the dam
project, as well as on the natural flow regime.
Modifications to the natural flow regime or hydrology also induce geomorphic and biological effects that
together change the potentials to derive river goods
and maintain river services downstream. Each flow manipulation has its particular effect on the river system
and on the potential to generate river goods and services in the basin.
For multipurpose dam projects, the operational
schedule is a compromise between the different project
objectives. Dam operations designed for irrigation purposes generally imply that water is stored in the highflow season for use in the hot and dry season. Dam
operations adjusted for hydroelectricity generation
generally imply that water is stored at night and over
weekends when the demand for electricity is lower;
relatively more water is released during the day when
the electricity demand is higher (Cushman 1985).
On-Site Improvements in Generation of River Goods
Storage and withdrawal of fresh water. In river basins
characterized by high seasonal and interannual variations in river flow and recurrent periods of critically low
flows, a large dam may significantly enhance the on-site
capacity to utilize the river as a fresh water source. The
reservoir capacity of a large dam may be sufficient to
supply water for large-scale irrigation, even after several
consecutive years of low flow (Keller and others 2000).
In contrast, the reservoir capacity of small dams is
suited to meet the water demands for periods of only a
few months and for smaller sized farmlands (Keller and
others 2000). By replenishing the reservoir in periods
of high flows, reservoir water can be withdrawn during
months, seasons, and years of below average flows.
Thus, natural seasonal and annual fluctuations in the
availability of river water are overcome and a relatively
time-stable availability of fresh water is attained.
In the semiarid and arid subtropics, storage of river
flow is generally associated with high evaporation losses
and high rates of reservoir siltation. Moreover, agricultural chemicals such as pesticides, insecticides, and fertilizers easily leak into the reservoir body and pollute
the reservoir water. Pollution-induced physiochemical
changes to the reservoir water may create unpleasant
odors and tastes and make the reservoir water unfit for
drinking and recreational purposes (Cogels and others
1997).
Generation of hydroelectric power. By means of a storage
power plant, a large dam project enables the generation of hydroelectricity at a relatively constant rate over
the year (assuming sufficiently high inflow rates). With
a large dam, river water can also be stored for periods
of several years in order to meet future electricity demands. In cases where the dam project is used for water
diversion purposes, the generation of hydropower is
also adjusted to the demands for fresh water.
Although a large reservoir takes a longer time to
deplete, it also takes longer time to refill. A longer
period of below-average inflow rates may necessitate
breaks in the power production, in order to raise the
reservoir water level above the minimum operational
level. Thus, even a very large dam may fail to produce
electricity at a constant rate, especially if the demands
of fresh water for other purposes are great.
Over time, the power generation capacity generally
declines due to reservoir siltation, which reduces the
reservoir volume available for water storage. Reservoir
River Systems as Providers of Goods and Services
siltation is particularly high in erosion-prone watersheds, such as the Chinese Yellow River basin, which
continuously receives large amounts of sediment from
the Loess Plateau (Douglas 1989).
Stocked exotic and native fish in the reservoir. A large
dam reservoir also provides the opportunity for stocking of fish species that can thrive in lake environments.
Fish stocking is often promoted by commercial interests
but can also be intended for local subsistence fishing.
Because the physiochemical properties of the reservoir
lake closely resemble those of a natural lake, pelagic
fish populations can be established rather easily. With
high reproduction rates, fish yields can be substantial.
If the stocked fish is properly selected and managed,
yields can remain high for several years or decades.
According to Covich (1993), however, the stocked fish
populations rarely remain stable in the long run.
In many cases, exotic pelagic fish species have been
found to compete with and predate on native fish
species, sometimes to the extent that the latter are
eliminated within a few years (Strange and others
1999). The capacity of native river fish species to survive
in the reservoir varies. Migratory white fish are the
earliest to disappear from the reservoir body, while
black and gray fish species tend to colonize littoral
areas and the main reservoir body, respectively (Welcomme 1989).
Downstream Threats to Provision of River Goods
and Services
Fresh water. Effects on the downstream availability of
fresh water depend on the manner in which the river
flow is stored, regulated, and diverted. Storage of river
flow in the reservoir accelerates the evaporation of river
water by increasing the evaporating surface area. This
lowers the annual average flow available downstream, as
does withdrawal of water from the reservoir.
Flow regulation has both positive and negative effects on the availability of fresh water in downstream
reaches. In general, flow regulation increases minimum
monthly flows and average monthly flows during the
low-flow season (Casado and others 1989). In seasons of
natural high flows and flood flows, peak and average
monthly flows are reduced (Liu and Yu 1992). This
results in reduced availability of water in downstream
reaches during these periods. However, flow stabilization by upstream dams is desired in areas where the
existing storage capacity is not sufficiently high to protect against flooding.
The downstream water availability is also influenced
by dam operations for hydroelectric power generation.
Such operations generally result in rapid daily fluctuations with higher daily flows than night flows and re-
603
duced weekend flows (Casado and others 1989, Cushman 1985). Daily fluctuations can be neutralized by
construction of a reregulating dam closely downstream.
Hydroelectricity. Dam-related flow manipulations for
irrigation and hydroelectricity generation affect the potential for hydroelectricity generation in downstream
reaches. Generally, reservoir replenishment in the
high-flow season results in reduced average monthly
flows and peak flows, which together reduce the potential for hydroelectricity generation downstream. In the
low-flow season, however, increased minimum monthly
flows would generally improve downstream hydropower potentials as more water can be stored and
released from downstream reservoirs to generate power.
Yet, the actual effects downstream depend on the manner
by which the river flow is stored, regulated, and diverted
upstream, as well as by the natural flow regime.
Native fish. Dam-related manipulations of the natural flow regime can threaten the diversity and abundance of native fish populations (e.g., Brooker 1981,
Rosenberg and others 1997, Swales 1989). The natural
timing of high and low flows provides important cues
for migratory fish to initiate new life-cycle stages, such
as spawning, egg hatching, rearing, or migration (Poff
and others 1997). When the flow regime is regulated,
these natural cues are eliminated and the natural reproduction system of native fishes is impaired (Poff and
others 1997). Reduction of high flows and flood flows
also threatens the quality of the floodplains of large
alluvial rivers, which constitute important grounds for
feeding, spawning, and rearing (Sparks and others
1998).
Stored water undergoes important changes in temperature, turbidity, and concentrations of dissolved oxygen, silt, and nutrients (Petts 1984). As water is released from the reservoir, these physiochemical
changes are transmitted downstream, thus altering the
living environment of downstream fish populations
(Casado and others 1989, Liu and Yu 1992). Effects on
fish populations have been identified in the form of
altered spawning behavior and reduced growth rate of
individual fish (Zhong and Power 1996).
The fish stock is also affected by changes in the
distribution of aquatic plants and invertebrate communities that depend on the natural flow regime (Petts
1990). Moreover, blockage of the river flow isolates
upstream spawning areas, impedes ascending fish migration, and kills descending fish individuals that are
too big to pass through the turbines. The effects on a
particular fish species also depend on its adaptive capacity. Thus, some species are exterminated, while others recover slowly, and still others are able to grow and
spawn (Liu and Yu 1992).
604
A. Brismar
Transportation and dilution of pollutants. Dam-related
flow manipulations generally reduce a river’s capacity
to transport and dilute polluted water (Petts 1990, Barodawala and others 1992). The greatest impact on the
river’s transportation capacity is caused by flow regulation. While discharges above the normal dry-season
flow increase the transportation capacity of the river, in
the rainy season, neutralization of natural high flows
greatly reduce the transportation rate. High flows are
particularly important for the discharge of coarser particles from the delta into the coastal water (Vaithiyanathan and others 1992). Coarser particles are heavier
and thus more difficult to flush out than lighter finer
particles. Many heavy metals, for example, iron, lead,
copper, zinc, nickel, chromium, and arsenic, are dominantly present on finer silt and sand particles with sizes
less than 20 ␮m (Vaithiyanathan and others 1992) and
are thus more easily flushed out. Similarly, water withdrawal and subsequent reductions in average monthly
flows shorten the transportation distance of sedimentattached pollutants, especially those attached to coarser
particles.
Flow blockage and storage also modify the downstream transportation of pollutants. Pollutants are often attached to sediment particles of various sizes. In
the reservoir, coarser particles and attached pollutants
settle on the reservoir floor, while pollutants attached
to finer particles tend to stay in solution. Pollutants
attached to finer particles thus have a greater chance of
being released from the reservoir.
Partial water purification. A large dam project may
also alter the capacity of the river system to partially or
temporarily purify the water. When river flow is stored
behind the dam and little or no vertical mixing occurs,
the waterbody in the reservoir undergoes stratification
(Petts 1984). This means that two distinct water layers
develop, with different temperatures and dissolved oxygen concentrations. In the bottom layer, organic matter from the in-flowing water is decomposed under the
consumption of dissolved oxygen. If no mixing with the
upper, more oxygen-rich layer occurs, the bottom water
layer eventually becomes anoxic. In the warm season,
the bottom layer also has lower temperatures than the
upper layer. As a result, water drawn from the bottom
layer of stratified reservoirs generally has lower concentrations of dissolved oxygen and lower warm-season
temperatures than the incoming water to the reservoir
(Zhong and Power 1996). Reduced water temperatures
and concentrations of dissolved oxygen both lower the
rate of aerobic decomposition of organic pollutants
(Petts 1984).
Flow stabilization may also lower the concentration
of dissolved oxygen in downstream waters, by reducing
mixing with the air. Moreover, a reduction of the flood
flows lowers the decomposition and assimilation of pollutants on downstream floodplains, by reducing the
inundated area.
Riverbank stabilization. Manipulation of the natural
flow regime also disrupts the natural capacity of the
river to maintain riverbank stability (Petts 1984, Cushman 1985). A reduction in the amount of sediment that
can be transported downstream (due to reservoir sedimentation) and a reduction in the transport capacity of
the river (due mainly to flow regulation) lower the
deposition of sediment along the riverbanks and increase their susceptibility to erosion. In addition, rapid
daily variations in the water level have an eroding impact on the riverbanks. Higher-than-normal water levels
can cause flooding of the upper banks and subsequent
degradation of the riparian vegetation. This also increases the susceptibility of the banks to erosion. Destabilized riverbanks, in turn, may undermine bridges,
culverts, and road embankments (Petts 1984). In some
places, the new neutralized flow regime may encourage
the establishment of new species on the riverbank that
can take over the role as stabilizing agents (Petts 1984).
Soil wetting and fertilization of floodplains and deltas.
Dam-related flow manipulations can drastically reduce
the fertility of floodplains and deltas. Flow regulation
alters the timing and reduces the area, depth, and
period of floodplain inundation (Adams and Hughes
1986). The repression of high flows in the rainy season,
which normally would carry large amounts of water, silt,
and nutrients downstream, weakens the transport capacity of the river and reduces the amount of silt and
nutrients that are deposited on the floodplains. Reservoir siltation also contributes to lower the amount of silt
and nutrients that are transported downstream (Stanley
and Warne 1998). Yet, the actual concentration of nutrients in the release water depends in part on the
position of the outlet gates; water releases through
bottom outlets are higher in total dissolved solids (Petts
1984).
Although erosion and resuspension of sediments
from the riverbed could partially offset the effects of
reservoir siltation and repressed high flows, the result
of a large dam project is still generally a net reduction
in the amount of silt and water that inundates the
floodplain (Petts 1984).
Flood flow storage. Reductions in average water flows
and repression of flood flows may threaten the capacity
of floodplains to function as natural flood control systems. If the flood flow and average water level are
sufficiently reduced, the floodplain may desiccate.
When the old vegetation dies, new adaptive plant species may emerge and become established on the flood-
River Systems as Providers of Goods and Services
plain. Yet, the new vegetation is less tolerant to flooding
and less capable of absorbing excess water of future
floods. In recent years, losses of floodplains have been
shown to aggravate the consequences of floods (Rapport and others 1998).
In flood prone areas, the recurrence of great floods
has promoted the construction of large dam projects to
reduce the extent of downstream flooding. While large
dam projects would introduce man-made flood protection measures, they would simultaneously jeopardize
the natural capacity of the river system to mitigate
flooding.
Delta erosion control. As a result of widespread dam
construction during the twentieth century, the net
amount of suspended load reaching the oceans has
been dramatically reduced in many places (Hay 1998).
By trapping sediment in the reservoir and reducing the
transport capacity of the river, large dam projects have
significantly accelerated delta erosion at the coast.
A large reservoir can trap a significant share of the
suspended sediment load and most of the bed load,
particularly the coarser particles (Vaithiyanathan and
others 1992). The reservoir hereby substantially reduces the amount of sediment that is transported to the
coastal delta (Stanley and Warne 1998). The trapping
efficiency depends on the position of the outlet gates
and on the presence of flushing operations (Hassanzadeh 1995). In Egypt, the High Dam at Aswan traps
more than 125 million tons per year, which is more
than 98% of the incoming sediment load (Stanley
1996). The Low Dam, High Dam, and downstream
barrages have together trapped substantial sediment
loads, reduced sediment deposition at the delta and
coastline, and caused a significant retreat of the shoreline (Stanley 1996).
Flow regulation may also increase the risk for coastal
delta erosion. A reduction in high flows, in particular,
may significantly shorten the distance by which sediments are transported downstream, resulting in early
deposition within the basin (Stanley and Warne 1998).
This is particularly the case in river basins where most
of the annual catchment runoff is delivered during
short flood periods of less than a month (Eyre and
others 1998). The transport capacity is also weakened
by reduced daily average flows (Benn and Erskine
1994) and by reduced annual average flows (Stanley
1996). When more sediment is eroded than is deposited at the delta shoreline, net erosion and shoreline
retreat set in.
Table 2 below summarizes the identified river goods
and services and their key characteristics before and
after dam project implementation.
605
Discussion and Conclusion
In the last decade, calls for environmentally sustainable development have put pressure on the dam-building industry to integrate ecological concerns in dam
project planning and decision-making. Yet, environmental impact statements (EISs) of potential adverse
ecological effects of large dam projects are often presented in technical terms that have limited practical use
to planners and decision-makers. Most ecological effects are diffuse, intangible, and difficult to evaluate
economically, and thus are not easily compared with
the desired functions and expected societal benefits of
the project. As a result, ecological interests rarely have
any significant influence over the choice of dam site,
design, and operational rules, and the dam project is
planned primarily or exclusively with regard to political, economic, and technological concerns.
In planning large dam projects, EIA consultants
have an important role to play in predicting, assessing,
and communicating potential adverse on-site and
downstream effects to planners and decision-makers,
and the present usefulness of the EIS in planning and
decision-making needs to be improved. Based on an
interdisciplinary language that integrates ecological
and economic perspectives, the EIS could communicate the societal implications of predicted ecological
effects and thus function as a basis for comparing desired functions and undesired effects of the proposed
dam project. Ultimately, the EIS could be used to support compromise building between conflicting interests.
This study has attempted to develop a basic framework for assessing the societal implications of key river
ecological effects that large dam projects may induce,
in order to facilitate comparison of desired and undesired effects of dam project proposals. The framework
is based on a view of the river system as a provider of
river goods and services. It can be used as a tool for
assessing the desired functions and undesired ecological effects of a proposed dam project in terms of altered
potentials to derive river goods and services on-site and
downstream. This approach differs from conventional
EIA procedures, in which the environmental impacts
are assessed in terms of changes to the flora, fauna,
hydrology, geology, climate, archaeology, settlements,
human health, etc (OECD 1992).
This paper defines river goods as products that are
generated or made accessible partly by human means.
They are of societal use when extracted or diverted
from the river system. River services are defined as
processes that are naturally generated in the river system but that can be enhanced by human means. Three
606
Table 2.
project
A. Brismar
Potentials to derive river goods and maintain services before and after implementation of a large dam
After implementation
Character
River goods
Fresh water
Hydroelectric power
Fish
River services
Transportation and dilution of
pollutants
Partial water purification
Riverbank stabilization
Soil wetting and fertilization
Flood flow storage
Delta erosion control
Before implementation
Can be provided by pumping or
diversion through canals, furrows,
etc, often with support of smaller
dams
Can be generated by run-of-river or
pumped-storage plants or by
storage plants connected to
smaller dams
Can naturally produce native river
fish that are adapted to predam
habitat conditions in the river
Provided particularly by high flows
which can transport pollutants all
the way to the delta and coast
Provided by adsorption,
sedimentation, assimilation,
chemical transformation, or
decomposition in the river channel
and on the floodplains
Provided by silt deposition and by the
roots and stems of riparian
vegetation
Provided by high flows that inundate
floodplains and deltas and
replenish the soil with nutrients,
organic matter, and water
Provided by soil infiltration,
evapotranspiration, and
groundwater recharge within
floodplains
Provided by continuous deposition of
silt at the coastal delta, which
counteracts delta erosion by
currents
key river goods and six key river services that could be
provided by a river system are identified here: The river
goods are fresh water, hydroelectricity, and fish; the
river services are transportation and dilution of pollutants, partial water purification, riverbank stabilization,
soil wetting and fertilization, flood flow storage, and
delta erosion control. Since the identification of any
river good or service depends on what features of the
river system are perceived as valuable to human societies, the list of river goods and services presented does
not claim to be complete. For any specific dam project,
attempts should be made to identify the river goods and
services that are of societal value in the concerned river
basin.
Implementation of a large dam project involves four
main types of flow manipulations or interventions. Together, these flow manipulations are to some extent
necessary to provide or increase the on-site capacity to
generate hydroelectricity, to secure a time-stable supply
of fresh water, and to provide opportunities for hatching of pelagic fish. At the same time, these flow manipulations induce river ecological effects that threaten
the provision of and potential for river goods and services downstream (Figure 1). Because the river system is
On-site
Downstream
Increased and more time-stable
water availability in dry season and
in years with below-average annual
flow
Increased capacity to attain a higher
and more time-stable
hydroelectric power generation
Increased and more time-stable water
availability in the dry season but
reduced annual averages and
rainy season flows
Reduced generation potentials in the
rainy season, but increased in the
dry season
Enables stocking of pelagic fishes in
the reservoir, but the native fish
stock may be reduced
Risk for reduced abundance and
diversity of native fish species,
especially migratory species
—
—
—
—
—
—
Reduced transportation and dilution
of pollutants in the rainy season,
but increased in the dry season
Risk for reduced rate of
decomposition and biological
assimilation, due to reduced water
temperatures and oxygen
concentrations
Risk for reduced stability along
erosion-prone and nonvegetated
riverbanks
Reduced soil wetting and fertilization
on deltas and floodplains in
general, particularly in the flood
season, but possibly increased in
the dry season
Risk for reduced capacity to store or
divert flood water, if floodplains
become desiccated
Risk for increased delta erosion at
the coast, due to lowered
sediment deposition over the year
characterized by complex physical, chemical, and biological interactions in time and space, it is not possible
to maximize the on-site production of river goods while
simultaneously maintaining the downstream provision
of river services unaffected.
In other words, unavoidable conflicts of interest prevails: whereas the achievement of intended project
functions requires stabilization of the natural flow regime, maintenance of existing river services is favored
by flow operations that mimic the natural flow regime.
Moreover, river services are provided naturally and free
of charge and often operate over the entire river basin.
As a result, their economic values are difficult to appreciate and they often become neglected in dam project
planning and decision-making.
In order to minimize the risk for reductions in the
potential to derive valuable river goods and services
from the world’s river systems, dam projects should be
planned with careful consideration to the likely on-site
and downstream effects on perceived river goods and
services in the basin. The site, design, and operational
schedule should be chosen with knowledge of how the
four main types of flow manipulations, i.e., blockage,
storage, regulation, and withdrawal of river flow, may
River Systems as Providers of Goods and Services
607
Figure 1. The diagram illustrates how a large dam project, by four main types of flow manipulations, may alter the on-site
capacity and downstream potentials to derive river goods (in light gray) and river services (in dark gray) in the river basin. The
diagram provides a basic framework for comparing desired and undesired effects of large dam projects designed for irrigation
and hydroelectric power generation.
affect the on-site capacity and downstream potentials
for river goods and services. This requires knowledge of
how the generation of river goods and services is naturally influenced by changes in the hydrology, geomorphology, and biology of the concerned river system.
Dam project planning of course also necessitates information on the natural flow regime, i.e., the timing,
magnitude, and duration of natural high and low flows,
as well as monthly and annual average flows (Poff and
others 1997).
Ultimately, making necessary dam project adjustments demands political will to sacrifice the extent to
which intended project functions are attained, i.e., the
capacity and rate by which hydroelectric power can be
generated and river water can be stored and withdrawn.
Compromises between the on-site provision of river
goods and the downstream provision of river goods and
services are thus needed. Mitigation and compensation
measures should be identified to promote a minimum
of adverse effects and a maximum of positive effects on
the provision of river goods and services in the basin at
large.
To continue work along this line, future studies
should be initiated to apply the developed framework
to specific dam project situations. This would involve
attempts to identify methods for quantitatively evaluating the societal benefits or opportunity costs of protecting certain river goods or services by making necessary
adjustments to the site, design, and/or operational
schedule of a proposed dam project. Some related work
along this line has already been made. According to
Bathia (2000), in the Subernarekha River basin in eastern India, attempts have been made to estimate the
reduction in aggregate economic benefits when part of
608
A. Brismar
the reservoir water is reserved for protecting certain
ecosystem services in downstream reaches.
Acknowledgments
The author is grateful to all those who have been of
help in the working process. Particular thanks go to
Malin Falkenmark, Jan Lundqvist, and Hans Bergh for
valuable discussions. This article has also benefited
from comments of referees on an earlier draft. The
study has been made with the financial support of the
Bank of Sweden Tercentenary Foundation.
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