Newsletter and Technical Publications
<Lakes and Reservoirs - Similarities, Differences and Importance>
Reservoir Development in the Future
  Reservoirs
represent an important component of the social and economic structure of both
developed and developing countries. Reservoir construction is largely completed
in North America and Europe, but continues in the developing world, and most new
reservoirs in the future will be located in Asia, Africa and Latin America. In
some cases it has been found that the environmental disbenefits of dams outweighs
their economic benefit. Thus, in the United States, the federal government has
refused to renew the operating licenses of some reservoirs in several locations
throughout the USA.
  Particular
interest is now being directed to ongoing or planned construction of large dams.
In some cases, these have incited serious public and international concern, as
in the case of the Sardar Sarovar Dam in India (Photos 20 and 21). On the one
hand, proponents of large dams say that they bolster local economies, improve
energy supply and flood control, and help manage the world’s water resources more
effectively. The opponents of large dams say that dams cause significant damage
to the environment and the local culture, and produce little overall economic
gain.
 These conflicting points
of view require major attention be given to balancing the beneficial and adverse
environmental and socio-economic impacts to be expected with the construction
of large dams (Table 2). This attention must begin early in the planning stage
to insure that it is properly considered by all relevant parties and interests
prior to initiation of construction activities. The Sanmenxia Dam on the Yellow
River, China (Photo 24), provides an example of problems that were not sufficiently
considered prior to dam construction. Finished in 1960, the goals of the
reservoir construction were to prevent floods, provide water for irrigation, and
produce hydroelectric power. However, significant silt loads in the Yellow River
were not adequately considered in the planning sstage. The reservoir water basin
was largely filled with silt only four years after construction, and the reservoir
was subsequently taken out of operation.
 
Another example is the construction of the Aswan High Dam (Photo 25) which impounded
the Nile River. The dam has now been in operation for about 30 years, and based
on a comprehensive assessment report of 1989, both positive and negative impacts
have resulted from this reservoir project. The economic positive impacts include
(i) an improvement of summer crop rotations and guaranteed availability of irrigation
water for agricultural production, (ii) expanded rice cultivation (iii), conversion
of about one million acres from seasonal to perennial irrigation, (iv) an expansion
of about 1.2 million acres of new land due to increased water availability, (v)
protection from high floods and droughts, (vi) generation of significant quantities
of hydroelectric power, (vii) improved navigation possibilities, and (viii) increased
tourism. The negative environmental and social impacts include (i) declining water-levels
at Nile River barrages downstream of the dam, (ii) rising water-levels upstream
of the Delta Barrage, (iii) increased riverbank erosion and river meandering,
(iv) production of river channel scour holes downstream of existing river barrages,
(v) decreased water quality due to increased industrial and agricultural discharges,
(vi) increased reservoir siltation, (vii) increased reservoir eutrophication,
(viii) increased water evaporation, (ix) increased coastal erosion at the mouth
of the Nile River, (x) decreased human health due to increased incidence of schistosomiasis
and spread of water-related vectors, and (xi) inundation of historical monuments.
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