Temperature - European Investment Bank

WEST AFRICAN POWER POOL (WAPP) PÖYRY ENERGY LTD.
Mount Coffee HPP ESIA and RAP 2012-09-18
ESIA Report Page 15
3.3 Short Project History
The Mount Coffee Hydropower project, a Run-of-River scheme, was constructed
between 1963 and 1966 and went in operation in 1967. The initial generating capacity
was 30 MW produced by two turbines, which was increased by two additional turbines
to 64 MW in 1973.
Mount Coffee HPP was the most important power plant in Liberia until the civil war
started in 1990. On June 28, 1990, the National Patriotic Front of Liberia (NPFL) took
control of Mount Coffee HPP. The plant operator was ordered to stop supplying
electricity, therefore only Unit 1 was kept in operation to supply the station and the staff
quarters. After the plant operator left on June 30 th , 1990, Unit 1 was taken out of
operation. With no units on-line the spillway gates could not be raised and the Forebay
Dam 1 broke on August 12, 1990. Since then powerhouse, substation and spillway
structures have suffered considerable looting and damage.
During the study the consultant made the effort to contact persons, who have lived in
the project area before the Mt. Coffee HPP was build the first time and who have been
resettled due to the construction of the HPP. There was only one family (household
head: Tommy Urey, 82 years old) who was resettled from there and moved back to the
project area in 1991. Likewise, information was sought on the effects of the dam break
in the downstream area, since this would provide valuable information on risks
associated with such an event. No records of any kind have been found.
3.4 Required Rehabilitation Measures for Mount Coffee HPP
Main Dam and Spillway are located north of the powerhouse, the main dam and
spillway is a reinforced concrete structure with ogee-shaped spillway (crest elevation is
60 ft) and was designed to support a 2,000 acre impoundment. Ten tainter gates
supported by concrete piers maintain normal pool elevation of 95.4 ft. Tainter gate
rehabilitation will require refurbishment of stoplogs, replacement of seals, rollers,
bushings, and chains, new paint system, new gate hoist system, new gantry crane and
rail system. A reinforced concrete bridge spans the spillway to provide access across the
St. Paul River and to the tainter gate hoist machinery. The bridge handrail, guardrail and
splash wall will require replacement. The spillway is flanked by earthen embankments.
The equipment house will require complete reconstruction of the electrical facilities in
addition to structural rehabilitation. The roadway access across the embankments is in
disrepair and rehabilitation would require the replacement of compacted subgrade with
laterite overlay.
The reservoir on the upstream side of the dam will have at full supply level a surface
area of 8.1 km 2 (2001 acres) at a height of 29.08 m asl (95.4 ft). Maximum flood level
will be at 29.56 m asl and the minimum operation level will be at 27.43 m asl. The
drawdown area will have a surface area of 0.91 km 2 (225 acres). It is estimated that 200
acres of the reservoir, originally cleared, have vegetation encroachment and that reclearing
will be required. The reservoir will have a total volume of 62.6 million m 3 and
a live storage of 54.3 million m 3 .
Forebay Dams 1, 2 and 3 are located near the powerhouse to retain water in lower
areas, three zoned earthen embankments were constructed for a total length of
approximately 2,600 ft with heights ranging from 10 to 70 ft. The 3,200 ft access
roadway is located between the main dam/spillway and Forebay Dam 1. A 600 ft