Temperature - European Investment Bank

WEST AFRICAN POWER POOL (WAPP) PÖYRY ENERGY LTD.
Mount Coffee HPP ESIA and RAP 2012-09-18
ESIA Report Page 28
I. THE PHYSICAL ENVIRONMENT
6 GEOLOGY AND SOILS
6.1 Theoretical Considerations
6.2 Geology
The geological conditions of the project site are decisive for the design and layout of a
dam and hydropower project, and for this reason, geology has to be investigated a part
of the technical studies for the project. However, the geology as such will not be
influenced by the project. This Chapter only provides a short description of the
situation.
For the purpose of the ESIA for Mt. Coffee HPP, geology is of minor concern. No
specific investigation or in-depth analyses are foreseen in this respect. The risk of a dam
break, and the measures to be taken for such a case, will have to be considered.
However, the reservoir is very small and will certainly not lead to a reservoir-induced
increase in seismicity.
Furthermore it can be stated that the Mount Coffee Hydropower Plant has been in
operation 20 years ago. No noticeable old landslides have been seen in the project area.
For this reason, because of the small drawdown, given the local topography (gentle hills
without steep slopes and because of the fact that all land not immediately used for
agriculture is covered by dense secondary forest it is expected that the risk that Mt
Coffee reservoir will trigger landslides is negligible.
Geological investigations in Liberia have shown that nearly all of the terrain is
underlain by Precambrian crystalline metamorphic rocks which form part of the West
Africa shield known as the Guinea Shield. The rocks forming this crystalline shield are
a series of granite, gneiss, and schist beds which have resulted from metamorphism by
tectonic forces acting on a regional scale. The structural features of the rocks in this
region are uniform over relatively large areas. Gneissic structures and schistosity dip at
high angles in most places and are often vertical.
Geologically, the Mount Coffee HPP project location is described on the USGS
geological map of the region (see detail of this map in Figure 6-1) as a Pre-Cambrian
leucocratic (meaning light coloured), medium to coarse grained, commonly banded
biotite bearing granite to quartz diorite gneiss. The gneiss forms a wide northwest to
southeast belt in which the Mt Coffee site is situated.