Geographical introduction to the Upper Mefou Sub-catchment
The rivers of Cameroon are grouped in two major settings and five basins. The basins of the Sanaga and the Nyong (and the small coastal rivers) are national Cameroonian rivers that do not cross a border. The three other main basins are trans‐boundary. These are the Congo Basin in the Southeast, the Niger Basin in the West and the Lake Chad Basin in the North.
The Mefou is a right tributary of the Nyong River, so is part of the Basin des Fleuves Côtiers. The outlet of the Upper Mefou Sub‐Catchment, which is its lowest point, is located in Nkolbisson, an area in the northwest of the Cameroonian capital of Yaoundé at UTM 32, 772132, 428414 (701 m a.s.l.). The catchment area is of 97̷km².
The geological setting of the Upper Mefou Catchment is similar to that of Yaoundé and the surrounding areas on the Southern Cameroon Plateau. The Yaoundé belt is a Meso‐ to Neo‐proterozoic unit, aging from 700 to 1000 million years (aka Panafricain), on the southern edge of the Central African Fault Belt. The belt consists of granulites and migmatitic gneisses.
The relief of the Upper Mefou Sub‐catchment can be divided into three major morphological units:
- The valley bottoms, which are covered by the rivers, floodplains, wetlands and the surrounding slopes. They are mainly located at altitude less than 725 m a.s.l. and are occupied by the Mefou Reservoir, and the densely settled areas of Nkolbission and the villages of Minkoamios, Ebot‐Mefou, and Nkolafeme.
- The zone of the middle altitude (peneplains: 725 to 850 m a.s.l.) are rolling hills. Most of the small villages are located here.
- The peaks from more than 850m to the highest point of the Catchment at 1221 m a.s.l. are inselbergs, made up of resistant rock residuals. Except from some rocky outcrops, they are predominantly covered by dense rainforest and are not under human use. The sources of the Mefou River are located here.
The main rivers of the Catchment are the Mefou itself and its main tributaries, which are the Zamengoé, the Nkoi, the Afeumev and the Benyam. The source of the Mefou River is located in the Mt Mbam Minkom area. Having a total length of 121 km, the Mefou joins the Nyong at Odou. A major tributary of the Mefou is the Mfoundi, which is the main drainage of Yaoundé. An important feature of the Upper Mefou (aka Mopfou) is a dam, constructed in 1969 and currently under reconstruction.
The Mefou reservoir (fr. Barrage du Mefou) has a surface of 105 ha, a maximum length of 13 km and a volume 7 million m³. It is located at an altitude approximately 721 m. a.s.l. Between 1976 and 2005 the reservoir was abandoned but the dam wall has been under reconstruction since August 2011. It has an average height of 17.5 m and an average length of 225 m. The water stored in the reservoir will contribute to the freshwater supply of Yaoundé.
The soils of the Mefou Catchment are the typical soils of the southern parts of Cameroon. According to the World Reference Database, the soils might be classified as Ferralosols.
In the local classification system, there a three subtypes of ferralitic soils:
- Red and yellow ferralitic soils cover most of the catchment, especially the mid‐altitudes and the summits. They are deeply weathered (sometimes more than 15 m), have a high clay content and are acidic (pH > 5.5). The main clay minerals are kaolinite, haematite, goethite, quartz and gibbsite. At the foot of the hills the soils are more yellow, also rich in clay minerals (especially quartz) and iron, but less stable than the red soils.
Deep red soils are also known as lateritic soils, because of the presence of an accumulation horizon, containing oxides and hydroxides of iron and aluminium. Agriculture on red or yellow soils is possible after clearing the forest, but due to the low fertility of the soils – most of the nutrients are stored in the biomass – the cultivation system has to take into account the poor soil quality. Besides farming, red soils are used to produce bricks to build traditional houses. They are also a relatively good material for creating unpaved roads.
- Shallower soils are located in areas characterised by high relief and steep slopes. The soils have low humus content and unweathered rocks are close to the surface. These soils are strongly influenced by tree coverage, in that the roots of the trees tend to hold the substratum in place. Due to their topographic position and the shallow depth of these soils they are normally not used for agriculture.
- Hydromorphic ferralitic soils are located In the river valleys. They are of a blackish colour, have higher humus content than the soils higher in the catchment, are therefore more fertile. Yields of plants grown on these hydromorphic soils are much higher than those grown on red or yellow soils. The concentration of sesquioxides (of aluminium and iron) gives the soils a good aggregate stability, which means their susceptibility to being destroyed by raindrops, or to being transported by overland flow, is low. In addition, the high clay content lessens the risk of soil erosion.
The Upper Mefou sub‐catchment is located in the equatorial Guinean‐type climate, which is characterized by high temperatures (21–23 °C) around the year and a high humidity with pronounced dry seasons. Maximum temperatures are seldom more than 35°C. It is a bimodal climate with two rainy seasons and two dry seasons:
- long dry season from mid‐November to mid‐February
- short rainy season from mid‐February to June
- short dry season in July and August
- long rainy season from September to the first half of November.
The average annual rainfall is approximately 1600 mm, with extremes between 1000 and 2100 mm.
Concerning its natural vegetation, the upper Mefou sub‐catchment is located in a transition zone between the dense humid forest of the bimodal precipitation regime and the zone of lesser forests. So there tend to be single huge trees with a more dense coverage of smaller trees and shrubs. The mountainous areas in the north‐west and east of the catchment have relatively dense vegetation coverage, except of some rocky outcrops, while the south‐east is peri‐urban and only the wetlands are covered by natural vegetation.
In accordance to the two rainfall seasons, there are two growing seasons, one from mid‐February to June and one from September to mid‐November, where the first is most important for agriculture. Planting starts at the beginning of the rainy season. Sometimes maize is sown earlier and cassava is planted when other crops are already growing. Preparation of the fields starts one month before the planting, and includes cutting trees and bush when the field is used the first time, or clearing the fallow. After the field is burned, tillage is done by simple hand‐held hoes. There are two types of tillage: with and without ridges. Maintenances of the fields – weed removing – takes place once or twice a growing season. Some crops are harvested after the rainy season, while cassava will be harvested after a second rainy season.
The farming system might be classified as shifting cultivation. So, a short period of growing (one or two years) will be followed by a long period of fallowing (up to 15 years). In areas with a higher population density, the period of the fallow is shorter.
One main feature of the farming system is intercropping, also known as mosaic or mixed cultivation. Up to four crops may be planted in one field. The major crop associations are: maize or cassava combined with groundnuts, beans or sweet potatoes. Makabo or yams are also associated, but may also occur as more or less single plants. Plantain is a major food tree found on fields. Sometimes single palms are used for the production of palm wine (vin blanc).
Besides this ways of subsistence farming, the surplus in the production is often sold on the market of Mokolo in Yaoundé. The main cash crops are cacao and palm oil. The plantains meanwhile cover only a small area of the catchment and are owned by local farmers.
According to the National Census of 2005, the total population of the area is approx. 22 000 people, of which 50.3 % are women. The majority of the people live in the densely settled urban part of Yaoundé in the southeast of the upper Mefou sub‐catchment and along the paved roads from Carrefour Nkolbisson in a northerly and westerly direction. The overall population density in the catchment is 227 people per km². The rural areas have an average population density of 76 people per km². An average household consists of 5.6 people. The upper Mefou sub‐catchment is located in the French‐speaking part of Cameroon, traditionally settled by Eton‐speaking people. In the urban areas, there is a mixture of people with various mother tongues.
The main economic activity of the population in the rural parts of the catchment is subsistence farming but other income‐generating activities are also carried out. In the primary sector these includes the production of cash crops, especially cacao, plantations of which are common all over the catchment. Palm‐oil production for food preparation takes place on a relatively small scale. Animal husbandry (chicken, but also some goats and sheep) is mainly a subsistence activity, but a few wealthier farmers produce cattle for the local market in Yaoundé.
The main sources of non‐agrarian income are fishing, aquaculture and selling of timber and related products, e.g. for electricity poles. There are a few small enterprises and shops, so working as a taxi driver (“benskin”) is the major source of income in the tertiary sector.
The entire upper Mefou Sub‐catchment is located in the Central Region of Cameroon (region du centre). The southeast is located in the Mfoundi division (département), which includes the sub‐divisions (arrondissement) of Yaoundé VII and Yaoundé II. The other part of the catchment is in the Lekie division, which is divided in the sub‐divisions Lobo and Okola. The majority of the villages in the catchment are in this division.
Besides this system of administrative organisation, there is also a traditional system of hereditary chiefdoms. Each village in the catchment has its own chief (chef de 3em degree) which is supervised by a chef de groupement and a chef supérieure. The role of a chief is to solve problems of the people living in his area and between the people in his area. This especially comprises questions of land ownership and water resources management.
(This introduction was written during an IWM-workshop in Yaoundé (15th November 2013 to 23rd November 2013) by academics, practitioners and locals)