[en] Landscape Ecological Survey of the Bipindi-Akom II ... - ITTO

Long-term averages of monthly rainfall totals of the Kribi, Lolodorf and Ebolowa stations are
presented in Fig. 2.2. Due to the geographic position of the TCP research area, the rainfall
pattern in the area is likely to resemble those at Lolodorf and Ebolowa, rather than that at Kribi.
Wind speeds are generally low and the direction is predominantly W-SW throughout the year
(Dolman and Waterloo, 1995).
The duration of bright sunshine has not been measured at any of the weather stations in South
Cameroon. However, the mean daily value of 3.4 h day-! observed at the weather station in
Douala is a fair approximation (Dolman and Waterloo, 1995).
2.3 HYDROLOGY
The hydrography of Southwest Cameroon is characterized by a high drainage density as a result
of a humid climate and the low permeability of the crystalline rock formations (Franqueville,
1973). The main rivers draining the TCP research area are the Lokoundje, Tchangue, Kienke,
Moungue, Biwome, Sonkwe and Messambe. Their flow direction is generally NNE-SSW,
following the regional pattern of faulting. Smaller streams have a flow direction essentially
perpendicular to the main rivers, resulting in a drainage pattern that has both dendritic and
trellised characteristics.
Swampy areas are commonly found in the valleys of the smaller rivers. The soils in these areas
, remain waterlogged even during dry periods due to a continuous supply of groundwater from
the hill slopes and due to relatively thin valley soils underlain by massive rock of low
permeability.
;:Prior ;: Prior to 1995, hydrological studies have not been carried out at any location within the TCP
research area. Hydrometric stations of the 'Centre de Recherches Hydrologiques' of the
'Institute de Recherche Geologique et Miniere' (CRH-IRGM) were located in Lolodorf in the
Lokoundje river (draining the area north of the TCP research area) and in the Kienke river
(partly draining the TCP research area) and the Lobe river (draining the area south of the TCP
research area) at Kribi. However, all stations in South Cameroon have been abandoned since
1987 (pers. comm. J.c. J.C. Ntonga, 1996).
The discharge patterns of the rivers correspond to the seasonal rainfall pattern with maxima in
October and May and minima in August and February (Olivry, 1986). Fig. 2.2 shows the monthly
discharges of the Lokoundje, Kienke and Lobe rivers for the 1953 -1977 period.
The average annual discharge of the Lokoundje river (at Lolodorf) amounted to 773 mm,
whereas those of the Kienke and Lobe rivers amounted to 1082 mm and 1397 mm, respectively.
Rainfall on the Lokoundje basin and the Kienke and Lobe basins could be estimated at 1880 mm
and 2425 mm, respectively, resulting in runoff coefficients varying between 41 % for the Lokoundje
basin and 45% and 58% for the Kienke and Lobe basins (Olivry, 1986).
Annual evaporation rates obtained with the water balance method varied between 1107 mm for
the Lokoundje basin and 1345 mm and 1025 mm for the Kienke and Lobe basins (Olivry, 1986).
The electric conductivity of stream water in the TCP research area is extremely low and varies
between 13 IlS cm-! and 28 IlS cm-! in the dry season (Dolman and Waterloo, 1995). On the
basis of data collected in one rainy season two EC zones can be discerned, the eastern part of
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