Hydrological modeling of the Congo River basin: Asoil-water balance approach

CHAPTER TWO

2.0 OVERVIEW OF THE STUDY AREA

2.1 The Study Area

The study area comprises The Congo River Basin, bounded between Latitude 10⁰ and 15⁰S and between longitude 10⁰ and 35⁰ degree East (Figure 1). This area covers several countries in Africa: Democratic Republic of the Congo (DRC), the People's Republic of the Congo, the Central African Republic, and partially through Zambia, Angola, Cameroon, and Tanzania. The Congo River (also known as the Zaire) is over 4,375 km long. It is the fifth-longest river in the world, and the second longest in Africa - second only to the Nile River in North-eastern Africa. The Congo ranges in width from 0.8 to 16 km depending on the location and time of year (The Living Africa, 1998).

N

Cameroon

Congo Rep.

500 0 500 1000 Kilometers

Gabon

Angola

Central Africa

D.R.Congo

Sudan

Rwanda

Uganda

Zambia

Ta

nzania

Figure 1 General Location Map: Position of the study area in Africa

The Congo River forms in the southern-most part of the DRC where the Lualaba and Luvua Rivers meet, then flows to Stanley Falls, near Kisangani, a point just north of the Equator before taking on a counter clockwise course. The Congo loops first to the northeast, then to the west, and then to the south before reaching an outlet into the Atlantic Ocean, feeding a river

basin that covers over 4.1 million km². At the outlet into the Atlantic Ocean, the Congo discharge up to 34,000 m³/s of water per second (The Living Africa, 1998).

Within the Congo's banks can be found over 4,000 islands, more than 50 of which are at least 10 miles (16 km) in length. It is because of these islands that some stretches of the Congo are not navigable. It has been estimated that almost 400 km of the Congo are not navigable due to these islands plus a number of cataracts, in particular at Livingstone Falls.

2.2 Physiography

The Congo basin is the most clearly bounded by various geographic depressions situated between the Sahara to the north, the Atlantic Ocean to the south and west, and the region of the East African lakes to the east (Britanica, 2007). Tributaries flow down slopes that vary from 274.3 m to 457.2 m into a central depression that forms the basin. It measures more than 193 1.2 km north to south (from the Congo-Lake Chad watershed to the Angolan plateaus). West to east - from the Atlantic to the Nile-Congo watershed - it also measures 193 1.2 Km (Butler, 2006).

The Congo basin has a large depression in the central portion. Referred to as a "cuvette", it is a large, shallow, saucer-shaped area. This depression contains Quaternary alluvial deposits which rest on thick sand and sandstone sediment of continental origin. Along the eastern edge of the cuvette outcrops of sandstone are formed. The cuvette has a filling that dates to Precambrian times (570 million years ago). Studies have shown that the sediment has built up over time from the erosion of the formations that surround the cuvette. The Congo River system is composed of three distinct sections - the upper Congo, the middle Congo and the lower Congo.

Kisangani is situated downstream from the Boyoma Falls and is at the beginning of where the Congo River becomes navigable. For 1000 miles (1610 km) the river flows towards Kinshasa. At first the river is narrow but soon widens as it enters the alluvial plain. From the point where the river widens, strings of islands occur which divide the river into different forms. The width of the Congo River can vary from 3.5 miles to 7 miles, reaching up to 8 miles at the mouth of the Mongala River. Along the banks of the river are natural levees which have been formed by deposits of silt. When the river floods these levees are washed away and the river banks increased in width.

The middle Congo is characterized by the narrowing of the river. The banks are a half-mile to a mile apart, the river is much deeper and its current is high. This section of the Congo is referred to as the Chenal (Channel) or Couloir (Corridor). It is along this stretch of the river that its principal tributaries flow into the Congo. They include the Ubangi River, Sangha River and the Kwa River.

This results in a tremendous increase in the flow of water from 7079 m³/s at Kisangani to its maximum when it reaches Kinshasa

NE

Figure 2 The Congo River Basin Elevation System. The highest station elevation is located in the Tanzanian region while the lowest, at the Atlantic Ocean (Note: this elevation grid is derived from the elevation of the selected 145 meteorological stations falling inside the study area)

From the middle Congo (Chenal) the river divides into two. One branch forms Malebo Pool, which is 24 mile by 27.3 miles large. This is the end of the middle Congo. Just downstream are the first of 30 waterfalls as the river continues to flow towards Matadi. At Matadi, the Congo's estuary begins in a narrow channel only half a mile to a mile wide. Eventually it widens below Boma but islands are once again a factor, dividing the river into several forms. The Congo now flows freely into the Atlantic Ocean.