The Present Day Drainage Patterns of the Congo River System and their Neogene Evolution - Geology and Resource Potential of the Congo Basin - page 305

15

The Present Day Drainage Patterns of the Congo
River System and their Neogene Evolution

Tyrel J. Fl ¨ gel, Frank D. Eckardt, and Fenton P.D. Cotterill

“ A river or a drainage basin might best be considered to have a heritage rather than an origin. It is like an

organic form, the product of a continuous evolutionary line through time ” p. 421 Leopold et al. ( 1964 )

15.1 Introduction

better understanding of their evolution will provide insights
into the evolution of the broader landscape of the CB.
The river systems of the CB are described in terms of
their present day drainage pattern and fluvial evolution in
order to better understand the geomorphic evolution of the
basin during the Neogene. Here, the term CB refers to the
hydrographic network of the CRS and its associated
landscapes. This network incorporates the geologically
delimited central Congo Basin and extends eastward to
include the Lake Tanganyika and Malagarasi systems
(Figs. 15.1 , 15.2 and 15.3 ). Ultimately, the water from the
CRS flows into the Atlantic Ocean via the CR mouth near
Monanda (Fig. 15.1c ). The discharge of the CR is connected
to an active deep sea fan by the 1,135 km long, meandering
and deeply incised submarine Congo Canyon (Fig. 15.2 ;
Babonneau et al. 2002 ). The outflow and sedimentary load
of the CR comprises of integrated chemical and lithological
inputs from runoff across a diverse range of climatic and
tectonic terranes of its catchments (Dupr ´ et al. 1996 ; Lavier
et al. 2001 ). The CR exports a total of 87

The immense ca . 3.67 million km 2 Congo Basin (CB) is an
intracontinental basin occupying central Africa. This
roughly circular basin stretches across 22 of longitude
(from ~12 E to ~34 E) and 21 of latitude (from ~9 N
to~13 S) (Figs. 15.1 and 15.2 ). The basin

s unique location
straddling the Equator and its size and shape allows the
Congo River (CR) to maintain a near constant flow year
round: its immense size and exposure to continuous precipi-
tation results in an annual discharge of 1,250

'

10 9 m 3
(Meade 1996 ). This discharge makes the CR Africa ' s largest
river and the world

s second largest river in terms of volume,
only being surpassed by the Amazon with a discharge
6,300

'

10 9 m 3 (Meade 1996 ). The CR is the culmination
of a complex and extensive drainage network that exhibits
localised drainage patterns and controls. As there appears to
be no clear correlation between the present day solid loads of
the large river systems and the climatic conditions, Pinet and
Souriau ( 1988 ) consider that relief is the major controlling
factor of the development of the drainage systems of the CB.
The drainage network of the Congo River System (CRS)
suggests a multi-stage and sometimes interlinked develop-
ment of the basins river systems (Figs. 15.3 and 15.4 ). As
rivers are one of the major drivers of topographic change, a

10 6 t of matter
per a year (Laraque et al. 2009 ), with a mechanical and
chemical erosion rate of 8 t/km 2 yr 1 and 5 t/km 2 yr 1
respectively, as measured at Pool Malebo (Stanley Pool)
(Fig. 15.5 ; Gaillardet et al. 1995 ).
The high rainfall associated with the Africa Equatorial
region also sustains the world

s second large continuous
forest covering a ca . 2.8 million km 2 area that stretches
from ~5 Sto~4 N (Fig. 15.1b ). This Equatorial forest
supports exceptionally rich biodiversity with the highest
species richness in Africa (WWF 2006 ) and is bisected by
the CR. Both the basin s extent and its vast, dense forests

have impeded detailed geomorphic investigations. This is
especially true of the central basin ( Cuvette Central )
landscapes, and much of the existing data and chronology
has been derived from studies closer

'

s
peripheries. The study of the rivers that flow through the

to the basin '