* Alternative plan may be cheaper
* BHP Billiton seen as potential client
CAPE TOWN, June 29 (Reuters) - Current plans to develop the stalled $8-$10 billion Inga 3 hydropower project on the Congo river may be too risky because of costs and time, a senior African Development Bank (AfDB) official said on Wednesday.
The bank is financing a study for the Democratic Republic of Congo (DRC) government to optimize development of the Congo river's immense hydropower potential, with a pre-feasibility study expected in September.
Current plans for the development of the Inga 3 project entail drilling up to 70 kilometres of tunnels into rock formations whose geology is not well known, and only drawing a maximum of 3,500 megawatts of power.
Hela Cheikhrouhou, director energy and environment at AfDB, told Reuters on the sidelines of a G20 infrastructure meeting that preliminary findings suggested this was a very risky option because it could cost more and take more time than anticipated.
Cheikhrouhou said the findings showed it would be better to remove the tunnelling option in favour of open channels which could be helped with a dam.
"With that solution, the DRC government ... could build a 3,500 up to 7,000 megawatt project which will be per cost of electricity generated cheaper, faster to implement and less risky," Cheikhrouhou said.
"We think this is actually a game-changer," she said.
The Inga 3 hydropower scheme on the Congo is one of the largest proposed projects in Africa aimed at overcoming power shortages that have curtailed economic growth.
Cheikhrouhou said rough estimates suggested it would cost in the region of $7 billion for a 3,500 MW project, doubling to $14 billion for 7,000 MW, with first power only likely in 2020 in what would be a public-private partnership.
She said global mining group BHP Billiton , South Africa and Nigeria would probably be the main clients.
(Reporting by Wendell Roelf, editing by Ed Stoddard and Keiron Henderson)
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