Problems Resulting from Tiga and Challawa
As a result of operation of the Tiga and Challawa Gorge dams, there has not only been a reduction in the magnitude of the floods, but also a decline in their duration, a reduction in the area inundated, a decline in the groundwater tables, a massive invasion of the exotic Typhus reed into the waterways, and a general shortage of water in the lower part of the basin. This translates into a reduction in the areas that can be used for agriculture, a loss of fishery production, and massive siltation of the waterways. Of further concern, many of these issues will only be exacerbated by the current and predicted climatic changes. Notably, reoptimization of the operations of the two large storage reservoirs in this basin could ameliorate every one of the problems stated above.
Improving Food Production Systems
More than 10 million humans' subsistence and livelihoods, including floodplain agriculture, pastoralism, fisheries and game hunting, are dependent on the environmental services provided within the Hadejia-Nguru basin. A combination of flow depletion and alteration due to irrigation and municipal water storage dams has adversely affected the food production systems and downstream ecosystems in the Hadejia-Nguru basin. A major goal of this project is the release of a flow pattern from the irrigation dams that more closely mimics the natural variability in flows that occurred before these dams were built. Restoring a more natural flow pattern means releasing more water during the wet season, to recreate an annual artificial flood event, and releasing less water into the downstream river system during the driest part of the year. This restores river-floodplain-wetland connectivity, which in turn improves the health of the aquatic ecosystems, increasing the diversity of habitats and wildlife species, on which food production is dependent.
Adapting to Climate Change
Climate change and future development will require greater water storage capacity in the Hadejia-Nguru river system in order to carry water over from times of relative abundance to times of relative scarcity and to capture and attenuate large runoff events to prevent flood damage. This reoptimization project will proactively point Nigeria toward environmentally compatible river basin management and development. The proposed project will create alternative ways to store water –in aquifers and floodplains--to buffer the effects of drought and capture the larger flood events. The project will investigate and demonstrate the integration of the surface water storage with groundwater banks in the irrigation area to increase storage capacity and flexibility. It will also show how the land uses in this floodplain can be managed to accommodate controlled flood events, supplementing the flood retention capacity of the reservoirs. That in turn allows the reservoir storage levels to be maintained at a higher level than would otherwise be safe and prudent. Higher storage levels mean both a larger and more reliable water supply in the face of global warming. It also dramatically reduces downstream flood risks.
The project is currently in the appraisal stage for funding from the African Water Facility.
Find out more about our fully developed project on the Lower Volta River, Ghana, as well as other NHI reoptimization projects in Africa.
