Environmental and Social Impact Assessment - Gibe III

Gibe III – Environmental and Social Impact Assessment 300 ENV R CS 002 C - A9003099
Finally it can be considered that Hydroelectric power plant process allows to avoid the emissions of SO2,
NOX, dusts, and wastes usually related to thermal plant.
7.2.1.3 Local Climate Issues
Large bodies of water influence the climate of their surroundings, especially the temperature and the
humidity. The most notable effects are cooling in summer, warming in winter and reduction of the daily
temperature variations. In the case of Gibe III reservoir some effects on temperature and humidity can be
expected. Nevertheless lakes exhibit a beneficial effect on the local micro-climate.
Evaporation from the surface of the reservoir will replace the present evapotranspiration from the soil of the
area to be covered by the reservoir.
In certain months evapotranspiration from the soil would exceed the evaporation from the reservoir as a
result of heavy rainfall periods when the soil becomes saturated.
In addition, vegetation and topographical depressions in the soil create a much greater contact surface with
the air, allowing a greater opportunity for water release than that provided by the surface of the reservoir.
The presence of the reservoir will expand the floodplain microclimate within the buffer zone. Microclimate
changes beyond the buffer zone are not expected to be significant or noticeable except for a certain increase
in fog.
The estimation of the additional evaporation rate, induced by the presence of the reservoir, has been
calculated on the basis of meteorological data in 5 m 3 /s. This value represents 1.1 per cent of the long-period
mean annual flow rate and for this reason it is possible to consider the evaporation losses negligible.
The construction of a reservoir with a surface area of approximately 190 km 2 can cause microclimatic
changes over an average area of some km (1-5 km) from the edge of the reservoir.
In some cases minor climatic changes can occur up to a distances 70-80 km away.
At the edge of the reservoir daily temperature ranges could fall by 2 to 4°C, relative humidity could increase
by 10 to 15 per cent; wind speed could increase; and, there could be reduced soil evapotranspiration. With
protection of the buffer zone and a small amount of management, the area of riparian forest would be greater
after the reservoir fills than under the present conditions.
Due to the fact that the climate variations on the reservoir could not be easily valuable in a short time, no
compensation measures shall be considered.
7.2.2 Geothermal activity
There are no confirmed occurrences of geothermal activity in dam area.
The project does not foresee deep excavations; there are no reasons to think about isolated hot spots in
excess of gradient temperature because the fault areas are exposed and now covered by a quite thick amount
of natural soil.
7.2.3 Seismology
The project area is more than 100 km far from the major Ethiopia seismic centres, located in the rift valley.
Due to the far from the generation area of earthquakes that could happen, tectonical events would have small
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