Temperature - European Investment Bank

WEST AFRICAN POWER POOL (WAPP) PÖYRY ENERGY LTD.
Mount Coffee HPP ESIA and RAP 2012-09-18
ESIA Report Page 210
m asl
30.00
25.00
20.00
15.00
10.00
5.00
0.00
Figure 26-4: Maximum flood elevation without and with dam failure
Source for Figures 26-2 to 26-4: Stanley Consultants
The Figures show the following:
Maximum flood elevation without/with dam failure
0 5'000 10'000 15'000 20'000 25'000 30'000
Distance downstream of dam (m)
PMF no break
PMF break
Sunny day no break
Sunny day break
� Dam failure increases flood elevation rapidly, and this then is reduced quickly
further downstream.
� The higher the flow (or the flood), the smaller is the increase in flow level due to
dam failure; this is explained mainly by the higher flow velocity and the larger
surface at higher levels.
� In the case of a flood event (Figure 26-2), the maximum increase in flood level
due to dam failure would be reached immediately below the dam, and it would
be less than 1 m (and only 37 cm in the case of PMF). At about 4 km d/s of the
dam, this increase would have been reduced to less than 0.5 m, decreasing
further towards downstream.
� In the "sunny day" scenario, increase, i.e. difference between the without and
with breach case would be much higher, reaching a maximum of nearly 3.5 m
just below the dam; it would still be about 3 m at a distance of 5 km below the
dam, i.e. in the area of the confluence of the river with the tailrace channel
(Figure 26-3).
� This, however, would occur at an elevation which is far lower than the one
reached during PMF, as is shown in Figure 26-4. This Figure, which compares
the PMF with the "sunny day" case also shows that during a flood event water
levels would be very high (and probably causing damage), while the difference