Temperature - European Investment Bank

WEST AFRICAN POWER POOL (WAPP) PÖYRY ENERGY LTD.
Mount Coffee HPP ESIA and RAP 2012-09-18
ESIA Report Page 80
11.4 Impacts
Impacts identification of Mount Coffee HPP can be approached towards 4 orientations:
impact on physical environment, impact on aquatic biodiversity, impacts on fishing
activities, and impacts on fishers’ communities.
� Dam rehabilitation will generate stagnant water with lower water discharge, and
with changes in water quality both upstream and downstream. Mount Coffee
reservoir, given its small size and the amount of water flowing through, will be
more like a large, slow-flowing river, nevertheless, with more lake-like
conditions than the current running waters of St-Paul River. Vegetation within
the impoundment area upstream of the dam, including crop farms, planted trees
and natural vegetation will be submerged; new trophic webs and feeding niches
will develop and provide better development conditions for plankton and aquatic
organisms feeding on plankton.
� Fish biodiversity will accordingly be modified, as fishing practices, with
transformation of running water system into a more stagnant one, and the
existence of an artificial barrier blocking fish movements. Dealing with fish
species, most cyprinids for instance are used to migrate upstream for
reproductive needs; with the rehabilitation of the dam, they would be
handicapped in this natural behaviour, and mitigating measures need to be taken.
� Fishing gears would certainly change upstream, with promotion of more canoes
and gill nets in the reservoirs section. Cage culture could opportunately be
envisaged in the lake, as pen culture in shallower areas.
� The project will offer employment (even if on a temporary basis) to native and
incoming labourers and technicians, and will improve lodging businesses,
restauration and trading. Following the closure of the dam to be built, the
number of fishers will increase, as will side activities (fish transformation and
commercialisation). New infrastructure thus will be required, including
housings, schools, health centres, markets, security services.
11.4.1 Impacts on Natural Habitats and Biodiversity
The reservoir will extend over 8.1 km 2 upstream of the dam and will permanently
submerge all farms, shrubs and trees currently below contour line 29.08 m above sea
level. Impounding would result in decomposition of organic materials and fertilisation
of waters for the first years following the termination of the rehabilitation work.
Phytoplankton and zooplankton will thus develop massively with light, thus benefitting
to fish production. Afterwards, as it has been observed in many man-made lakes with
small surfaces, the water will become poorer in its natural feeds, to reach a productivity
level lower than before the construction of the dam. Sediments will accumulate in the
reservoir, covering rocky niches formerly occupied by fish species of Cyprinidae and
Mormyridae families. Again, plankton feeders, namely tilapias alongside with their
natural predators (Hemichromis, Clarias) will proliferate in the new environment
(Lowe-McConnell, 1975; Lévêque et al., 1988; Pouomogne, 1988).
A further impact on the fish population will be the migration barrier. To allow migrating
fish species to cross the almost 20 m height dam, auto-crossing infrastructures such as
fish ladders may not be convenient for the current moment. It may be too costly and
probably not useful since no previous viable trial has been done elsewhere for tropical