Concerning hydrography, Cameroon can be divided into four areas, corresponding from North to South to the basins of Tchad, of Niger, to the Atlantic basins (Sanaga, Nyong, Ntem…) and to the Congo basin. The compilation and the processing of rainfall and runoff data available on the Cameroonian drainage network (76 stations in use in 1981), from the beginning of the network until the end of the 70’s or the early 80’s depending on the basin, were performed by Olivry (1986)

The mean hydropluviometric parameters concerning the five studied catchments during the 1998/99 – 2001/02 period are shown in Table III. The mean discharge of the low water level month (February or March) is 7 to 9% of the discharge corresponding to the high flow month (November).

Pluviomètre à ouverture automatique

Figure 5. Automatic rain collector

  Nsimi Messam Pont So'o Mbalmayo Olama
area (km²) 0,60 206 3,070 13,555 18,510
rainfall (mm/an) 1,779±254 1,779 1,749±225 1,579±159 1,636±181
rainfall (m³/s) (7,6±2,6)*10-3 3,60±1,48 43,9±15,7 133,8±31,5 201,3±47,0
runoff (mm/an) 397±133 551±226 451±161 311±73 343±80
Ke (%) 22,3 31,0 25,8 19,7 21,0

Table III. Hydropluviometric mean data at the 5 stations of the upper Nyong River (cycles 1998/99 to 2001/2002)

Rainfalls have been estimated from measurements at the stations of Yaoundé, Abong-Mbang, Sangmélima and Nsimi; flow ratio Ke = 100*(drainage height)/(rainfall), water cycles go from the beginning of March to the end of February.