Temperature - European Investment Bank

WEST AFRICAN POWER POOL (WAPP) PÖYRY ENERGY LTD.
Mount Coffee HPP ESIA and RAP 2012-09-18
ESIA Report Page 116
the reservoir again within the same 24 h period. This could mean that no water
would be discharged from the turbines for a minimum of 4 and a maximum of 9
h per hour of operation. Such a situation could arise frequently during the dry
season, mainly January to March.
� Under conditions of extremely low flows, all inflow would have to be released, a
situation which will occur on about 4 days per year. Here again, there would be
no change in comparison to the natural situation.
The quintessence of this is that the reservoir is too small as to have a noticeable effect
on downstream river discharge (downstream of the confluence of the original riverbed
and the tailrace channel), which would largely remain the same as it is under natural
conditions. On the other hand then, it is obviously also too small to allow additional
water to be released under conditions of extreme low flow. If this were possible, this
would have a positive impact on the water intake in White Plains, and would actually
contribute to prevent salt water intrusion. In order to reach this situation, however, Via
reservoir would need to be in place, as was shown in Chapter 27 (CIA for Cascade).
Given this situation, and the lack of impact of Mt. Coffee HPP on the water intake at
White Plains, the following recommendations are made:
� A monitoring program of water quality, and especially of conductivity as a
direct measure of salt content of water, should be implemented. The monitoring
carried out presently and described shortly above must be maintained. However,
it is recommended that conductivity is also measured in the raw water, in
addition to the measurements made in treated water. Water intake should be
stopped at moments of too high salt content (presumably at high tides during
conditions of extremely low flows).
� It might be advisable to operate Mt. Coffee HPP in a way that closing down the
turbines completely during high tide conditions would be avoided.
� It is recommended to evaluate the possibility for rehabilitating the pipe line from
the reservoir in order to have a water intake for White Plains treatment plant
which is outside of the reach of salt water intrusion. As reported above, LWSC
is undertaking efforts in this direction.
� If this is being implemented, water quality monitoring should be extended to
water taken in from the reservoir; this could be done either at the intake (i.e. in
Mt. Coffee) or at the water treatment plant. In any case, there should not be two
monitoring programs carrying out the same analyses; synergies should be used.