Deltas are highly dynamic sediment constructions, depending on the balance between river and ocean dynamics. Unique and productive ecosystems have developed in these deltas, primarily flooded grasslands, riverine forest and salt-adapted vegetation such as mangroves at the marine fringes. These ecosystems support diversified livelihoods adapted to the flooding patterns. Traditionally these include flood-recession and tidal agriculture, fishing, livestock keeping and utilization of forest products. Deltas are important, well beyond their physical perimeter, as carbon sinks, as coastal defence and as nursery areas for fish and crustaceans. In the past fifty years, deltas have been targeted by contradictory policies: large-scale land conversion for large-scale irrigation or aquaculture in one hand and in the other hand, conservation measures and creation of protected areas (Ramsar sites, Biosphere reserves, National Parks).
Deltas of the Western Indian Ocean region: the 4 deltas highlighted are specifically studied
The Tana is Kenya‟s longest and most important river in terms of discharge. Downstream from Garsen town, the river divides into multiple branches and secondary channels, thus forming the Tana Delta.
The Tana Delta is one of the less well known areas of the Kenyan coast and often presented as being devoid of people, an empty wasteland that should be converted to something „more useful‟ sooner rather than later.
Nothing could be further from the truth. In actual fact the Tana Delta is a highly productive coastal wetland, extremely rich in biodiversity and in cultural heritage. Its landscapes, a complex mosaic of forests, woodlands and floodplain grasslands, have been shaped by centuries of intensive use by a range of stakeholders and have thus become a “cultural landscape”.
All the local activities (recession agriculture, livestock keeping, fisheries and forestry) are linked to the flooding rhythm of the river. The floods are vital as they provide a range of services such as soil fertilization, groundwater recharge, irrigation, forestry and grazing. The floodplains and mangrove are important as fish nurseries, for coastal protection and for ecotourism. Their total economic value far exceeds what could be gained by converting the delta into a single “modern” land-use such as biofuel production.
Betsiboka delta in Madagascar
On the North-West side of Madagascar, the Betsiboka Delta is built by the water of the Betsiboka River, second biggest river of Madagascar in terms of flow. It is well-known for its red-colored waters, highly loaded with sediment from the deforested catchment. The hydrological regime of the river is very contrasted with low water levels and frequent violent brief floods. The large central floodplain and islands of the delta, flooded during the rainy season (December to April) are characterized by a mangrove vegetation.