Itezhi-Tezhi Dam

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The Itezhi-Tezhi Dam on the Kafue River in west-central Zambia was built between 1974 and 1977 at the Itezhi-Tezhi Gap, in a range of hills through which the river had eroded a narrow valley, leading to the broad expanse of the wetlands known as the Kafue Flats.

[edit] Dimensions and purpose

The dam has a height of 62 m, a crest length of 1800 m and forms a reservoir of 390 km² which flooded part of Kafue National Park including the only road within the park from the south to the centre and north. Formerly this provided a very good game drive close to the west bank of the river, now a longer road outside the park on the east side and further from the river, has to suffice.

The purpose of the dam is to store water for the hydroelectric power station of the Kafue Gorge Dam more than 260 km downstream. The Kafue River, like most in south-central Africa, has a very high seasonal variation, flooding in the rainy season and slowing to perhaps a twentieth of the peak flow rate at the end of the dry season. Power generation however requires a steady flow, which can only be achieved by having a reservoir large enough to store the rainy season flood for use in the dry season. At the Kafue Gorge the topography does not allow a large enough reservoir to form. The designers of the dam therefore had the idea of siting the main reservoir at Itezhi-Tezhi, and releasing the water in a steady flow down the river along the Kafue Flats to the Kafue Gorge Dam. ^[1]

[edit] Environmental impact of the dam on the Kafue River Flats

“Not all floods are unwanted”— NASA.^[2] The eastern (lower) half of the Kafue Flats in the middle of the dry season, one year apart. Water shows as dark areas, the Kafue’s main channel shows as the sqiggle running left to right. In early 2004 the floodgates of the Itezhi-Tezhi Dam (about 80 km off to the left of the photo) were opened to allow the natural flooding which used to happen before the dam was built. Compared to the previous year, much more of the flats remain inundated in the dry season and there is lot more vegetation (green colour). (Key: 1 Lusaka, 2 Kafue town, 3 Kafue Gorge Dam, 4, Mazabuka and Nakambala Sugar Estates, 5 Blue Lagoon National Park, 6 Lochinvar National Park, 7 Chunga Lagoon, 8 Kasenga.) Photo credit NASA/GSFC/LaRC/JPL, MISR Team.

The designers of this scheme seemed to view the peak of the flood in March-April, and the great drying out in October-November, as some kind of disaster in need of a solution. The problem with this view is that the Kafue Flats ecosystem has evolved in response to these conditions, to regular extremes of flooding and drying out, and was well able to cope with them. The flood charges the soil with water. Fish, and animals adapted to swim or wade, help spread nutrients, and when the waters recede, grasses grow rapidly and sustain herbivores such as buffalo, lechwe, and cattle. The natural seasonal cycle has been fairly dependable and plants, fish, animals have adapted to the March-April inundation in their nutrition and breeding. So have the people who depend on them, and they move their settlements annually to cope with the regular cycle of flooding.^[3]

The dam removes the peak of the flooding and the trough of low water in the dry season. It reduces the natural seasonal variation of the river flow.^[4] The designers intended the dam would 'open the floodgates' for the whole of March and allow a flow of 300 m²/s to flood the flats to maintain natural cycles. However this has not happened in practice, mainly because the reservoir has not had sufficient water in it at the right time to sustain such a flow. The demand for electric power takes priority, and compounded by erratic rainfall since 1990, the dam has allowed flooding at the wrong time, or it has not been of sufficient duration or has not allowed some areas of the flats to dry out.

The Itezhi-Tezhi Dam has had these negative effects on the ecology of the Kafue Flats:^[3]

• fish production has significantly declined;
• wildlife such as Lechwe and Sitatunga which rely on particular timing and extent of the floods in their breeding grounds have had their breeding behaviour disrupted, leading to population decline;
• in the dry season the amount of grass for grazing has been reduced for both wildlife and cattle, and woody species are invading grasslands on the floodplain;
• uncertainty of timing of flooding disturbs traditional human settlements.

The 2003/4 rainy season was particularly wet in Zambia and the dam did allow the flats to flood. The effect is shown in the NASA photos. According to a NASA website, in June 2004 an agreement was made with the hydroelectricity company to restore water releases from the dams according to a more natural flooding regime, prsumably by keeping to the original intention of a 300 m²/s flood for the whole of March.^[2]

[edit] References

1. ^ Zesco: “History of Itezhi-Tezhi” website accessed 1 March 2007.
2. ^ ^{a b} NASA Visible Earth website: “Floodwaters Renew Zambia’s Kafue Wetland” Accessed 5 March 2007.
3. ^ ^{a b} American Association for the Advancement of Science website: H N. Weza Chabwela & Wanga Mumba, “Integrating Water Conservation and Population Strategies on the Kafue Flats”, Report of a Workshop on Water and Population Dynamics, Montreal, Canada, October 1996.
4. ^ FAO Fisheries Dept: “Status of fish stocks and fisheries of thirteen medium-sized African reservoirs” Website accessed 1 March 2007.

Coordinates: 15°45′55″S, 26°01′05″E