Rivers in crisis
By: Nasir Ali Panhwar
The
world’s rivers are in crisis, and the drivers of river
degradation are numerous.
While pollution in its
many forms impairs the quality of our river waters, dams
also impact both water quality and the very functionality of
rivers, and of planetary lifecycle processes.
Roughly two-thirds of the
world’s rivers have suffered harm from the 50,000 large dams
that have been built over the past century.
Many of the world’s great
rivers, such as the Indus, the Colorado and the Yellow
Rivers, no longer reach the ocean, turning once productive
deltas into deserts.
Healthy, flowing rivers are
the lifelines of our planet. They provide people with water,
food, medicines, building materials, land-replenishing
silts, navigation, recreation, and cultural and spiritual
strength.
Rivers and their catchments,
and the rich variety of life they sustain reduce the impacts
of floods and droughts, support forests, recharge
groundwater supplies, sustain fisheries and maintain the
ecological integrity of local ecosystems.
For instance, the river’s
estuary, where fresh water mixes with the ocean saltwater,
is one of the most biologically productive parts of the
river and of the planet.
Rivers and riverine
ecosystems are also one of the most threatened in the world.
Historically, key stressors have included the
over-extraction of water, pollution, diversions and
channelisation.
In the past 50 years, the
amount of run-off flowing into rivers has changed
substantially in many basins due to the combined effects of
withdrawals, dams and climate change.
Traditionally, rivers have
been the main source of food, water and primary livelihoods
like fishing, flood plain farming, etc.
Later, rivers came to be used
for navigation purposes, power generation, canal irrigation,
industries, tourism etc., increasing the diversity and
complexity of river use over the years.
Rivers have also been the
cultural and religious meeting places for many communities.
Out of all the different
human interventions, dams have been the direct and often
irreversible modifiers of river flows.
The World Commission on Dams
has estimated that around 47,000 dams of more than 15-metre
height had been built all over the world by the year 2000.
About half of the world’s large dams were built primarily
for irrigation.
However, of all the human
interventions on river systems, dams have been the most
significant, often irreversible and direct modifiers of
river flows, at the cost of the ecological health and
ecosystem services of such river systems.
Globally, over half of the
292 large river systems are affected by dams. Presently, the
number of dams blocking our rivers has crossed 50,000.
Among all the environmental
changes wrought by dam construction and operation, the
alteration of natural flow regimes has the most pervasive
and damaging effects on river ecosystems.
Dams can heavily modify the
amount of water flowing through the river. Once dammed, the
river is at the mercy of the dam operator and the river
loses its natural flow pattern.
The operation of a hydropower
dam can operate at either its peak or at its base load and
can fluctuate between the two states on a daily basis.
The operation pattern of the
power station henceforth decides the timing, frequency and
duration of high and low flows, and alters the natural rates
at which rivers rise and fall during run-off events.
Dams and diversion of water
are capable of affecting several kilometres of downstream
ecosystems, depending on the size and design of the
structure, and the dynamism of the river, thus fragmenting
rivers into static reservoirs and channels.
A flowing river is indeed one of the most important and
beautiful natural entities on earth. A river is the only
ecosystem that connects other ecosystems, carries water, and
transports dissolved minerals, sediments and nutrients to
maximum places before emptying into its natural outlet.
How much water flows through
a river channel and the sediment and nutrient load carried
by a river is decided by the nature of the catchment and the
rainfall or snowfall pattern.
Flowing rivers connect
different ecosystems like glaciers, forests, riparian zones,
flood plains, mangroves, etc. on their way.
They also create flood
plains, sand deposits, deltas, etc. Rivers, while draining
the land, carry out groundwater recharge by percolating into
deeper aquifers.
Take the case of the Indus
River basin. Originating from the Himalayas, the Indus flows
2,900 kilometres through four countries (China, India,
Afghanistan and Pakistan) before it drains into the Arabian
Sea.
The Indus delta covers an
area of some 5,000 square kilometres, of which 2,000 square
kilometres is protected area. The fan-shaped delta is the
fifth largest in the world and supports a large population,
whose livelihood is directly or indirectly dependent on the
Indus River.
The delta is rich in
mangroves, which provides habitat for fish and shrimp and
together with the tidal mudflats, supports a rich variety of
flora and fauna, and are particularly important as resting
and feeding grounds for migratory birds.
From a biodiversity
perspective also, the delta is important, with 10 species of
mammals, 143 species of birds, 22 species of reptiles, over
200 species of fishes, many invertebrate species, including
15 species of shrimp found here.
The Indus River is also home
to one of the few species of freshwater dolphin, Platanista
minor, and to the fishing cat.
At least 84 per cent of
people living in the delta comprise fishing communities,
which catch an estimated 247,000 million tonnes of fish per
annum.
Due to heavy abstraction and diversions, the amount of water
in the Indus River has decreased dramatically. Little
freshwater now reaches the lower Indus.
As a result of the reduced
flow into the fertile Indus delta, the extent of mangrove
forest and biodiversity has declined, shrimp and fisheries
reproduction has been reduced due to change in seasonal
water availability and modified water quality, and
agricultural chemicals have accumulated in the soil.
Increased salinisation of the
lower Indus has resulted in a decline of fish species, which
are sensitive to changes in temperature and salinity.
Also, saline water has
intruded 64 kilometres inland, because of which acres and
acres of farmland have been lost.
The loss of delta has led to
a decline in the potential of fisheries by 70 per cent.
Climate change, if factored into the problems, will worsen
the state of the river unless steps are taken to mitigate
its impact.
March, 2015
Source: The
Express Tribune