The Tana River Delta

Fig. 1: Map of the Tana Delta

The functioning of the coastal wetlands associated to the lower valley of the Tana has been strongly impacted by the alterations in its catchment. The study of how this came about and what it implies is highly relevant for the implementation of our research. 

The Tana is the largest river in Kenya. It originates in the Aberdare Mountains and the Mount Kenya and subsequently flows through about a thousand kilometres of drylands in eastern Kenya where its average flow is around 150m³/s. Its river basin covers approximately 127,000 km². In its lower part, the river has built up a delta of about 1300 km². Five hydropower dams were constructed in its upper reaches: Kindaruma (1968), Kamburu (1975), Gitaru (1978), Masinga (1981) and Kiambere (1988). These 5 dams produce 3/4 of the power needs of Kenya and also supply the capital Nairobi with domestic water. 

The Tana River Delta is currently confronted to a substantial reduction of river discharge and a decrease in the amplitude of the flood peaks, which is bimodal because of the two rainy seasons. The decrease in the amplitude of the flood peak is particularly significant since the completion of the Masinga Dam in 1981 (Maingi & Marsh, 2002). A new dam, downstream of the 5 existing dams, has been proposed at Mutonga-Grand Falls. This dam would further more attenuate the bimodal flood peak with highly negative impacts on fish production (Mavuti 1994 in Emerton 2003) and on the riverine forest (Maingi & Marsh, 2002). The livelihoods of the 200,000 inhabitants of the Lower Valley, dependent on recession agriculture, fisheries and livestock keeping, would be seriously affected (Emerton 2003). The attenuation of the flood peaks will also have impacts on the livelihoods of the nomadic livestock keepers and their estimated 2.5 million heads of cattle that currently use the pastures in the middle and lower reaches of the valley (CADP 1991 in Emerton 2003). 

Still, none of these impacts were quantified in detail, nor spatialised. The ecological studies in the Lower Valley were primarily targeted at the floodplain forests upstream of the delta because of the presence of the red-listed endemic primates Tana River Red Colobus (Procolobus rufomitratus) and Tana Mangabey (Cercopithecus galeritus). But studies in the Tana Delta itself are insufficient and its biodiversity value is largely unknown.

The Tana Delta was declared a wetland of international importance under the Ramsar Convention in September 2012, a process that involved several years of consultation and a great amount of scientific input from KENWEB. This is the first official recognition of its natural & cultural heritage. The delta now requires a management plan which in itself is a process that must ensure application of the principles of co-management ensuring complete participation of the local communities. There is a great need also to consider the various projects including vast areas proposed for irrigated sugar cane projects and Jatropha plantations both for biofuel production, These projects will strongly impact the wetland functioning reducing with major threat to its biodiversity value, a disruption of the ecosystem services provided and a strong impact on the local economies.