An ecologically sensitive situation is unfolding in Tanzania. Suzanne Pritchard explains why hydroelectric operations at Kihansi power station may be compromised by a rare toad
Nectophrynoides asperginis is the scientific name for the Kihansi spray toad. Endemic to the Kihansi Gorge in Tanzania the amphibian is considered to be unique — unlike other toads, it actually gives birth to young ones instead of laying eggs. Details on such a rare toad would not usually make headline news in the hydro industry, but the survival of this creature is bringing a recently commissioned hydro power plant in Tanzania under the environmental spotlight.
International project donors and environmentalists have joined together in discussions centring on an ecological controversy, that pits the survival of a rare toad against the generation of 180MW of electricity from the Kihansi hydro power plant. Environmental groups, who are concerned that the rare animal may be in danger due to reduced water flows as a result of abstractions for hydroelectricity, are pressurising project financing agencies into finding a quick solution to the problem.
The World Bank, the Swedish International Development Agency and the Norwegian Agency for International Develop-ment are amongst those that have provided financial support for the power project. Together with the government of Tanzania and the Tanzanian Electricity Supply Company (TANESCO), which owns and operates the plant, they determined that a minimum flow of 1.8m3/sec should be maintained in the gorge while short term emergency measures are worked out to ensure the toad does not become extinct. However, the rare biodiversity in the gorge depends and thrives on spray caused by the Kihansi Falls. The reduced flow of 1.8m3/sec does not generate sufficient spray.
To help rectify this, TANESCO has devised mitigation measures. Artificial spray systems have been established to irrigate portions of the so-called wetlands where concentrations of the toad population are located. Water for this has been sourced from streams and rivulates within the area.
There is still no scientific agreement as to the minimum amount of water needed to ensure the toad’s survival. Environ-mental groups argue that water flows need to be increased to 7m3/sec. But FX Saidi, director of projects at TANESCO, says this measurement is a statistically determined figure from the long term monitoring of minimum flows on the Kihansi river.
‘In any case,’ Saidi says, ‘the hydrological conditions at Kihansi right now do not permit generation of the plant at full capacity — the inflows in the reservoir are very low. But it is the resolve of TANESCO to maintain, at least in the interim, the minimum flow of 1.8m3/sec.’ Discovery TANESCO became aware of the toad in December 1996 but by then construction of the plant had already started and it was too late to stop. The plant design was not altered to reduce planned ultimate capacity and the dam is capable of releasing flows from 0-20m3/sec by means of gates and valves.
Kihansi started generating power at the end of 1999 and, up until about April 2000, was operating without any restrictions on generation (since this was the rainy season). Bypass flow into the gorge was far higher than the stipulated 7m3/sec and so at this time there was no threat to the toad.
Maximum plant output in the dry period has been about 120MW of peaking capacity. ‘The generation of power from Kihansi will continue, albeit at lower than the maximum design capacity,’ says Saidi. ‘It is not easy at this point in time to say what the solution is that balances power demands with the survival of the toad.’ The problem, and the possibility of power shortages, has only just been made public in Tanzania. ‘Before it was felt the timing was not opportune,’ Saidi admitted. ‘Kihansi had only recently started operating and the public would have failed to understand that power production was being curtailed in order to save the life of a toad.’ One of the environmental authorities in Tanzania, the National Environmental Management Council (NEMC), admits that Tanzania needs the power from Kihansi but is still insisting that the toad be saved. Environmentalists say the only alternatives to save the toad are either to provide the rare animal with adequate waterfall spray or relocate it. They claim anything less than that threatens to wipe it out.
This was obviously on the minds of both international project donors and environmentalists who met in Dar-es-Salaam on 25 October 2000. ‘The meeting was called to agree on the most immediate action plan to prevent extinction of the toad,’ says Saidi. Discussions centred on captive breeding of the amphibian in a specialist zoo and the outcome was that this would be the best way forward. Relevant authorities are now working on the modalities.
The Kihansi power project is located in the Rufiji basin, 550km southwest of the capital city Dar-es-Salaam. For more details on the Kihansi project see IWP&DC March 2000, pp18-22.