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dam-l Reviving Living Rivers/LS
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REVIVING LIVING RIVERS
A Presentation at the European NGO Hearing on WCD Related Issues
Bratislava, Slovakia; January 17th 2000
Philip B. Williams Ph. D., Eur. Ing.
President, International Rivers Network
The end of the 2oth Century has witnessed a belated realization that
human influences are having profound adverse impacts on the global
environment. The worldwide deterioration of fresh water resources,
the destruction of river, wetland, and estuarine ecosystems that
supports a rich diversity of abundant species, the degradation and
impoverishment of the lives of millions of river dependent people, is
one more dimension to this global environmental crisis. Almost
everywhere on the planet, rivers have been affected by pollution,
channelization, destruction of their watersheds, - and by the
construction and continued operation of large dams.
In parts of the world there is a growing interest in restoring
rivers, to benefit both the environment and the people who live in
their valleys. Some governments now accept the need to invest
resources to clean up pollution; they are starting to recognize the
benefits of reconnecting rivers to their floodplains; programs have
been established to reforest eroding watersheds; but in contrast the
central role of dams in perpetuating and accelerating environmental
degradation has not yet been acknowledged. Such an understanding is
essential if we are to stop repeating the mistakes of the past and
start healing the problems of the present. Providing a well
substantiated, scientifically credible explanation of this
understanding is a key responsibility of the WCD.
This presentation is intended to assist WCD staff by describing a
conceptual model of the river system that practitioners in river
restoration now use in addressing the impact of human interventions,
such as dams, on river ecosystems. This concept can be used the WCD
as a basis for impact analysis, mitigation planning, restoration
design post-project audits, and multi-objective river management
solutions.
The scientific concept of a 'living river'
Every river basin has a unique geologic and climatologic history that
has created a particular landform at a given time. This landform,
from mountain peak to estuarine mudflat, has been created by
geomorphic processes - the action of flowing water eroding and
depositing sediments. Certain dynamic features of the landscape,
such as the alluvial floodplains, or the meandering river channels
can persist over tens of thousands of years in an evolving
equilibrium, responding to periodic floods, tectonic movements, and
sea level rise. Thus the form of each river basin is a product of
its own evolution and this unique form determines the physical
character of the particular river that drains it.
Over time fish, plants and other species biota evolve to take
advantage of the river's physical processes and the forms they
create. For example, fish migrate at certain times of year when
flows and water temperature are advantageous, riparian trees have
adapted to winter flooding, estuarine shellfish rely on nutrients
released from decayed leaves from floodplain forests. This
evolutionary history means that the integrity of the whole ecosystem
is dependent on the integrity of the physical processes that sustain
it. This dynamic sustainable interaction between river flow, river
form, plants, fish and wildlife is what is instinctively meant when
we use the term 'Living River' to describe the river ecosystem.
Like any other biota, humans have taken advantage of and interacted
with the river ecosystem for tens of thousands of years. The
abundance of fish and wildlife, the fertility of floodplain soils
enabled river communities to prosper even as they transformed the
landscape into fields and villages. Only in the industrial age, with
the onset of massive pollution, and construction of massive river
engineering projects has this mutual prosperity of river ecosystem
and human settlement been compromised. The main reason for recent
degradation of river ecosystems is that now human intervention has
drastically changed river processes as well as the landscape.
An alternative concept -the ecosystem as a broken machine
With our current knowledge of the science of ecology it is reasonable
to say that most of the biologic interactions within a river system
have not even be conceptualized. let alone understood. This makes it
difficult to articulate in a scientifically defensible way what we
mean by a healthy functioning ecosystem if we only define it in terms
of biologic interactions. This uncertainty and complexity has also
led to a mistaken and conveniently utilitarian concept in ecosystem
management. This is the idea that a disturbed ecosystem is analogous
to the scattered pieces of a broken machine and we are smart enough
to put the pieces back together in whatever way we like. This
approach is not guided by a definable concept of a healthy river and
leads us to recreate highly managed, expensively maintained,
'gardened' habitats of limited value.
Defining a healthy living river.
When we investigate the science of fluvial geomorphology, the science
that describes and explains these physical processes, we see that any
river is both a river of water and a river of sediment, with most of
the sediment moved during the smaller more frequent floods We find
that river systems are resilient and persistent because the erosion
and deposition of sands and muds, together with regrowth of riparian
vegetation, can quickly recreate disturbed landscapes sometimes
within a few decades A straightened river will always tend to
recreate its meander; a mined gravel bar rebuilds in the same place.
In other words the 'living river' is inherently self healing always
evolving back to recreating its healthy form, provided the movement
of sediment is not impaired.
A.conceptual model of the living river focuses our attention on
understanding, maintaining and restoring definable key physical
processes that sustain the landscape; processes like regular
inundation of floodplains, movement of gravels along the river bed,
or summer flow levels. These physical processes , while still
uncertain in some areas, are amenable to quantification, prediction,
and analysis They allow us to articulate what a particular healthy
living river looks like, by reference to similar processes in other
rivers, and by what we know of the history of the river itself.
How dams have affected river physical processes
In the last 60 years human technology has become capable of
constructing dams large enough to eliminate and transform key
physical processes in the world's largest rivers. Major dam projects
have been planned and executed with little understanding of the
consequences of these alterations on the health of the river. Using
a medical analogy, the initial construction of the dam is an acute
shock to the system, but it is the continued operation of the
reservoir that creates chronic illness in a healthy river by changing
its hydrology and geomorphology. There are many ways dams affect
physical processes essential for sustaining a healthy living river
ecosystem., but in problems of river management and restoration these
three are the most important pathologies:
1. Diversions. The impacts of reductions in flow due to water
supply diversion are easily understandable. The greatest impacts
occur in the low flow season of drought years, but in some semi arid
regions the downstream river channel has been almost permanently
completely dried up. For many years returning flows to restore river
habitat has been a main focal point of environmental restoration
efforts, and more recently this has extended to efforts to restore
freshwater flows to sustain major estuaries like San Francisco Bay .
This has led to the formulation of minimum or 'in-stream' flow
requirements for fish. Some dams have now changed their operation to
release a fraction of their inflow to provide such flow releases,
with their proponents claiming that this action alone will mitigate
downstream ecologic impacts. These claims are at best
unproven.Restoring minimum flows does nothing to sustain and
replenish critical habitats created by floods and flow variabiity.
2. Elimination of the flood flow pulse. Typically large reservoirs
are operated to store seasonal high flows to release them for power
generation or irrigation later in the year. This has the affect of
greatly reducing flow variability downstream by capturing smaller
frequent floods. Larger infrequent hazardous floods are much less
affected as they tend to fill the reservoir and then spill
uncontrolled at the flood peak These changes in flow variation and
flood frequency have major adverse impacts on key processes. For
example they typically eliminate regular floodplain river ecologic
interactions without eliminating flood hazards; they eliminate
natural periodic disturbance essential for rejuvenating wetland
habitats; they prevent pulses of freshwater that sustain estuarine
ecologic processes, and they reduce the capability of the river to
move sediment downstream and allow choking of the channel with
riparian and emergent vegetation. Recently attempts have been made
to release small flood pulses from some reservoirs to mitigate these
adverse affects. Such measures alone are unlikely to be more than
marginally useful. If they do not also restore the flow of sediment
to the river.
3. Trapping sediment. Large reservoirs have the capability of
capturing almost all of the sediment carried by a river. Until the
reservoir completely silts up releases downstream are 'clear water'
flows that erode the bed and banks of the river channel until the
natural sediment transport capacity of the river has been regained.
which may be tens of kilometers downstream. The impacts on river
system habitats are profound. Lowering the channel bed isolates the
floodplain from ecologic interaction with the river channel as
effectively as if it were leveed. and channel lowering lowers the
watertable drying up floodplain wetlands and woodlands. Silts and
muds no longer replenish floodplain soils, the complexity of habitats
in the river channel is simplified into a single uniform thread..
Further downstream muds no longer replenish estuaries and deltas,
sands are no longer delivered to beaches, degrading estuarine and
coastal habitats.
Restoring physical processes: promoting self healing
The history of dam construction has been a history of environmental
devastation. However in the last two decades some attempts are being
made to mitigate adverse impacts on fisheries, endangered species and
wetlands; and recently in the U.S. there has been a growing
acceptance of the need to redesign the operating regimes of existing
large dams for this purpose A continued failing of these attempts to
mitigate adverse environmental impacts of dams are that they address
symptoms not causes. In the U.S. we know that technical fixes like
fish hatcheries are not working very well, but we also see attempts
to restore landscapes without restoring physical processes. Examples
are attempts to restore floodplain forests that are no longer
inundated by floods, or efforts to create artificial fish spawning
channels without scouring flows
It has taken us a long time to recognize that the essential processes
that need to be restored are those that sustain the life of river;
the vigour of its flow, its flood flow 'pulse', and its lifeblood;
sediment These are the processes most affected by large dams.
Our conceptual model of a living river leads us to a meaningful
approach to restoration. We can progressively remove or limit human
interventions such as dams so that the river can restore itself.
Practically. this means reestablishing the seasonal and annual
variation in flow, in particular the smaller floods that do most of
the work in scouring and depositing sediments, inundating and
replenishing floodplain woodlands and farmland, and re-watering
aquifers and wetlands. It also means reestablishing a way for the
river sediments to move downstream.
The task of the WCD
We expect the WCD to document the catastrophic decline in river
ecosystems over the last century and clearly explain the central role
of big dams as a major cause. In order to do this it will have to
explain how river ecosystems work and how key processes have been
adversely affected. We expect to see a recognition that the planning
of existing projects was based on an outdated development ideology
where ecologic impacts, and their consequent societal and economic
impacts, were discounted or ignored.
As well as insuring the same mistakes are not made in planning of new
projects, we expect the WCD to address an equally important question
of the 21st century: How do we retrofit this obsolete water
management infrastructure to reflect modern societal goals? These
goals now include protecting the rights and values of river dependent
people, protecting the river ecosystem, and insuring economic
accountability for river management decisions. In order to answer
this question we need to change our view of the dam as an everlasting
concrete structure, to the dam as a continued human decision to
perpetuate a certain type of intervention on a healthy living river.
This should lead the WCD to recommend a periodic audit process for
reevaluating the rationale for continued operation of all existing
dams. This audit similar to a re-licensing process, would include an
environmental and social assessment of projected future operation and
determine whether the dam will meet contemporary societal goals.
From such an audit, decisions can be made to continue a dam in
operation, modify its operation or decommission it.
In proposing such a process the WCD would lay the groundwork for a
new direction in river management. Instead of being trapped into
more and more extensive and expensive attempts to mitigate the ever
expanding negative impacts of obsolete poorly planned dams, we would
have the freedom and opportunity to realize the cumulative social and
ecologic benefits of restoring and managing our river valleys. It is
possible to envisage a future, say 50 years from now, where rivers
and water resources are managed in harmony to sustain a viable
ecosystem and a modern economy. To get there, we have to first break
free from the legacy of greed and bad planning that has imposed big
dams on most of our rivers. This is what we are looking for the WCD
to help us do
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Lori Pottinger, Director, Southern Africa Program,
and Editor, World Rivers Review
International Rivers Network
1847 Berkeley Way, Berkeley, California 94703, USA
Tel. (510) 848 1155 Fax (510) 848 1008
http://www.irn.org
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