Bart Schultz
On the African continent, I have identified 28 countries with polders, with a quantifiable area of 1.52 million hectares. The total area of polders should be considerably larger, but is very difficult to determine.
The vast majority of polders consist of reclaimed low-lying land. Only in Guinea-Bissau and Madagascar there are lands gained on the sea. These are rice polders along river mouths. In Egypt and Tunisia, there are a few drained lakes. In Egypt, these are reclaimed lands of, or in, the following lakes: Abou Qir, Idku, Manzala, Mansour, Mariut, and Zawia, with, as far as I know, a total area of at least 51,000 hectares. In Tunisia, this only concerns the 1,300 hectares Berges du Lac polder in Lake Tunis.
The land use in the vast majority of the polders is agriculture, a significant portion of which are rice polders. I could only identify two urban polders: the Wellington Polder in Sierra Leone and the aforementioned Berges du Lac Polder in Tunisia. Bentiu Polder in South Sudan, where a refugee camp is located, has a special position.
As I described in my previous contribution to Flevolands Geheugen about the polders in the Nile Delta, the oldest reclamation project was located upstream of the delta along the Nile. During the reign of King Menes these were flood protection structures built around 3400 BC at Memphis. After that, I could not find any clear references until the construction of the polder in Lake Abu Qir in Egypt in 1887. At the end of the nineteenth century, there is another reference from 1898. This concerns a reclamation project in the El Max region, also in Egypt.
In itself, it is, of course, surprising that polders exist in one of the driest regions of the world. This is partly due to the presence of very old, highly developed civilizations in Egypt, and partly because the silt deposited along the Nile and in the Nile Delta was extremely fertile. And that the vast majority of the country consists of more or less uninhabitable desert areas.
Since the first dam was built on the Nile at Aswan in 1889, all the silt present in the river water has been deposited in reservoirs, thus ending the deposition of silt downstream along the Nile and in the delta. A similar development has also occurred in many other major rivers, resulting in many deltas experiencing coastal erosion.
Another interesting area regarding polders in Africa is the area along the rivers that flow into Lake Chad and along the lake itself. The drainage basins of these rivers are located in Cameroon, Nigeria, Niger, Chad, and the Central African Republic. With the exception of the Central African Republic, I have found polders in all these countries, the development of which must have influenced the discharge into the lake.
In addition, the development of irrigated areas in the river basins has increased the evapotranspiration in these areas, and discharge into the lake has decreased more or less accordingly. As a result, the water level in the lake gradually dropped over the years until, around 1985, measures were taken to maintain the water level as much as possible. There are several polders along the lake. Some of these eventually rose so high above the lake level that excess water could freely discharge, and thus they are no longer considered as real polders anymore.
