Encyclopedia of Inland Waters || Africa

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    the Nile, by the Omo River and by the Awash River,and the North African ranges, Atlas and Aures drained

    Zambezi and Congo rivers, the Central Africa high-

    is linked to the Congo basin by the Lukuga Riverand Lake Malawi overflows to the Zambezi by theby Moroccan rivers (Sebou, Oum Er Bia, Moulouya),Algerian and Tunisian rivers (Medjerda). Local volca-noes such as Kilimandjaro, Ruzizi, Mount Kenya, andMount Cameroon may exceed 4000m; however they

    Shire River. Lake Victoria is a result of regionaltectonic uplift and is relatively shallow regarding itsarea. It is the headwater of the Victoria Nile, whichflows to Lake Albert, itself connected to lakeSouth Atlantic and North Atlantic Oceans, and forfew African regions presently not connected withoceans (endorheic rivers).

    Relief

    Africa has the least rugged relief of all continentstogether with Australia. Relief categories are definedon the basis of mean altitude and relief rugosity at the0.5 space resolution. They are aggregated hereinthree clusters (Table 1): low relief (2000m).There are very few regions in Africa with developed

    high relief: the Ethiopian Plateau, which is drained bythe Blue Nile and the Atbara Rivers, both tributaries of

    lands, headwater of the Oubangui River, the majortributary of Congo and of the Chari River. In theSahara desert, the Ahaggar, Tibesti, and Darfourmountains, which reach an altitude of 3000m, areonly fed by very rare rain events.The Rift Valley, which divides the East African

    Plateau from the Red Sea to Lake Malawi, is aunique and relatively young feature of the continent.It shapes hydrological networks and has generatedtwo sets of lakes; some of them are among theworlds largest and deepest: in the Western Riftlakes Albert, Edward, Kivu, Tanganyika, andMalawi (former Nyassa), in the Eastern Rift lakesAbbe, Turkana. Under the present tectonic andclimate conditions the Kivu/Tanganyika lake systemcoasts of the Mediterranean Sea and of the Indian,General Features of the African Continent

    The relief, climate, and lithological features of thecontinent are summarized (Table 1) for 21 aggregatedcoastal catchments that link river networks to the

    Other relief features include the Fouta Djalon,shared by Senegal and Guinea, headwater of Senegaland Niger rivers, the Drakensberg in South Africaand Lesotho mountains (3482m), headwater of theOrange River, the Katanga highlands, headwater ofRIVERS AND STREAMS (FODISTRIBUTION)

    Contents

    Africa

    Asia Eastern Asia

    Asia Monsoon Asia

    Asia Northern Asia and Central Asia Endorheic River

    Australia (and Papua, New Guinea)

    Climate and Rivers

    Ecology and Role of Headwater Streams

    European Rivers

    Flood Plains

    Geomorphology of Streams and Rivers

    Riparian Zones

    South America

    Streams and Rivers of North America: Overview, Easte

    Streams and Rivers of North America: Western, Northe

    AfricaM Meybeck, Universite Pierre et Marie Curie, Paris, Fr

    2009 Elsevier Inc. All rights reserved.do not correspond to important river basins.RMATION, DIVERSITY,

    and Central Basins

    and Mexican Basins

    eEdwards.

    295

  • Table 1 General characteristics of African coastal catchments (Meybeck et al. (2006))

    Sea basin name Code

    (1)

    Principal rivers Sea

    basin

    area

    Runoff Population

    density/

    sea basin

    Sediment

    yield

    Relief Climate Geology

    Mkm2 mm

    year1people

    per

    km2

    t km2

    year1%

    Low

    %

    Mid

    %

    High

    %

    Temper-

    ate

    % Dry

    < 3mm

    (2)

    % Dry

    3mm(2)

    % Tropical

    < 680mm

    (3)

    % Tropical

    680mm(3)

    % Shield

    plutonic

    %

    Volcanic

    %

    Carbon

    %

    Others

    Algerian Basin 1.0 Moulouya, Cheliff,

    Medjerda

    0.25 86 104 53 1.2 98.8 0.0 78.0 21.0 1.0 0.0 0.0 0.0 1.0 47.5 51.5

    South Ionian

    Sea

    2.0 Irharhar, Araye (4) 2.26 0 8 1 53.3 46.7 0.0 1.7 97.7 0.6 0.0 0.0 2.8 4.2 37.6 55.5

    East

    Mediterranean

    3.0 Nile, Qattara 4.52 18 28 26 46.9 51.3 1.8 6.9 59.9 8.2 24.8 0.2 28.8 5.4 10.1 55.7

    West Red Sea 4.0 No important rivers 0.33 14 37 12 3.5 95.6 0.9 0.0 83.7 12.8 3.5 0.0 61.8 20.2 0.0 18.0

    South Aden Gulf 5.0 No important rivers 0.10 0 25 4 4.3 95.7 0.0 0.0 100.0 0.0 0.0 0.0 26.5 5.9 50.0 17.6

    Somali Coast 6.0 Jubba, Tana (Kenya) 1.36 14 18 96 49.9 47.6 2.5 7.7 73.8 7.3 8.0 0.0 8.5 11.5 49.4 30.6

    Zanzibar Coast 7.0 Rufiji, Rovuma, Galana,

    Pangani, Lurio, Wami

    0.85 187 40 132 22.9 75.3 1.8 13.0 11.8 10.2 64.6 0.4 57.4 9.0 5.0 28.6

    North

    Madagascar

    8.0 0.17 676 31 69 26.7 73.3 0.0 44.6 0.0 0.0 39.3 16.1 45.4 7.2 21.9 25.5

    Coast Ikopa, Sofia

    Mascarenes- 9.0 0.21 913 31 78 13.4 86.6 0.0 41.7 0.0 0.0 11.5 42.0 71.9 19.7 1.4 7.0

    Madagascar

    Basin

    Mananara

    South West

    Madagascar

    Coast

    10.0 Mangoky, Tsiribihina,

    Onilahy

    0.24 291 20 257 28.4 71.6 0.0 45.3 35.0 2.4 17.3 0.0 40.6 2.5 21.7 35.2

    Mozambique

    Coast

    11.0 Zambezi, Save,

    Pungoe, Licungo,

    Buzi

    1.73 251 20 33 13.7 86.3 0.0 59.7 5.6 7.8 26.1 0.7 42.0 1.2 8.3 48.4

    Agulhas Basin 12.0 Limpopo, Gourits,

    Incomati, Gamtoos,

    Great Fish, Great Kei

    0.88 43 39 182 20.8 78.9 0.3 36.1 54.9 3.8 5.1 0.0 26.8 9.9 8.2 55.1

    296

    Rivers

    andStre

    ams

    _Afric

    a

  • Cape Basin 13.0 Orange, Olifants 1.29 9 14 28 0.4 97.7 1.9 14.8 83.3 1.9 0.0 0.0 24.1 6.9 12.7 56.3

    Angola Basin 14.0 Congo Zaire, Cuanza,

    Cunene, Kouilou

    4.38 344 18 13 27.4 72.4 0.1 13.3 1.4 1.0 82.7 1.5 38.9 0.5 11.6 48.9

    Sao Tome-

    Principe Basin

    15.0 Ogooue, Sanaga,

    Cross, Ntem, Nyong

    0.53 793 25 34 36.6 63.4 0.0 0.6 0.0 0.0 51.2 48.2 76.8 5.3 6.6 11.3

    Niger Delta

    Cone

    16.0 Niger, Oueme 2.46 172 47 17 78.7 21.3 0.0 0.2 45.4 10.5 38.8 5.0 39.4 1.0 8.8 50.8

    Guinea Basin 17.0 Volta, Bandama,

    Comoe, Sassandra,

    Pra

    0.78 177 51 19 94.1 5.9 0.0 1.2 1.6 4.7 91.4 1.2 73.7 0.0 0.0 26.3

    Sierra Leone

    Basin

    18.0 Cavally 0.26 1431 35 189 68.4 31.6 0.0 0.0 0.0 0.0 6.0 94.0 81.6 0.0 0.0 18.4

    Cape Verde

    Basin

    19.0 Senegal, Gambia 1.11 111 15 27 95.3 4.7 0.0 0.0 58.9 16.9 20.9 3.3 3.8 4.8 3.8 87.6

    South Canary

    Basin

    20.0 Tamanrasett 2.17 0 3 0 76.3 23.6 0.1 0.0 99.9 0.1 0.0 0.0 23.8 2.6 13.2 60.4

    North Canary/

    Madeira Basin

    21.0 Sebou, Oum Er Rbia,

    Tensift, Sous

    0.36 26 52 55 29.4 68.2 2.4 24.3 72.1 3.6 0.0 0.0 8.1 11.4 30.9 49.6

    Tenere A None 0.15 0 0 0 0.0 100.0 0.0 0.0 100.0 0.0 0.0 0.0 40.9 1.9 0.0 57.1

    North Chad,

    Batha, Shari/

    Logone

    A Chari, Logone 1.55 52 21 12 65.0 35.0 0.0 0.0 42.3 22.9 34.6 0.2 25.5 1.2 1.6 71.7

    Bodele * 0.76 18 0 0 55.5 44.5 0.0 0.0 96.1 3.9 0.0 0.0 9.0 1.5 9.6 79.8

    Danakil B 0.02 0 35 1 12.5 87.5 0.0 0.0 100.0 0.0 0.0 0.0 0.0 100.0 0.0 0.0

    Awash/Ethiopia B Awash 0.14 200 80 81 2.2 67.4 30.5 28.3 26.0 28.3 13.0 0.0 0.0 76.6 6.4 17.0

    Turkana B Omo 0.23 200 48 133 4.1 82.5 13.5 31.0 29.8 8.1 28.4 1.3 18.7 58.6 0.0 22.7

    Ngomba

    (Chilwa)

    * 0.07 155 24 8 0.0 100.0 0.0 36.3 0.0 4.6 59.1 0.0 82.6 0.0 0.0 17.4

    Okawango-

    Kalahari

    C Okawango 0.76 72 2 11 0.0 100.0 0.0 17.4 76.0 6.6 0.0 0.0 7.4 3.4 3.4 85.7

    Etocha C 0.11 6 2 4 0.0 100.0 0.0 14.4 85.6 0.0 0.0 0.0 5.6 0.0 13.8 80.6

    (1) See Figure 1 for location of coastal basins. (2) Annual runoff. (3) Annual precipitation. (4) Presently not flowing.

    *Smaller endorheic basins.** Presently dry; carbon carbonated rocks.

    Rivers

    andStre

    ams

    _Afric

    a297

  • tially found in the NE part of the Sahara, i.e., theyare not presently drained by rivers, and in the

    from 800 to 1600mm year1 with local maximums

    smaller endorheic basins as the Awash River-Lake

    298 Rivers and Streams _ Africaexceeding 4000mm year1 as on Mount Cameroon(9600mm year1).

    River Network Organisation and RiverRegimes

    Exorheism, Endorheism, and Arheism are

    Continuously Changing

    Geographers make a clear distinction between riversconnected to oceans (exorheism) and those connectedAfrican Horn (Table 1, coastal catchments # 05and 06).

    Climate

    African climate and hydrology have been synthesizedby Korzun. Four major types of seasonal precipitation(P) regimes, the major drivers of Africa river flowregimes, have been identified:

    . subtropical regime North of the Sahara (P between250 and 800mm year1) and south of OrangeRiver (P 600mm year1) characterized by a wintermaximum precipitation and a summer minimum,

    . the Saharan regime (Sahara, Namibian desert) verydry with indefinite seasonal and inter annualP variations and precipitation less than 100mmyear1,

    . the tropical regime (Sahelian belt from Guinea toEthiopia and south of 5 S (excepted the southerntop of the continent and Namibia) with a summermaximum and a winter minimum,

    . the equatorial regime, roughly between 5 S and8N, across the continent.

    In addition to the seasonal distribution of rainfall, thetotal amount of precipitation should be considered. Itranges in the Northern tropics from 200mm in theSahelian region (e.g., 208mm at Toumbouctou,Mali)to 1250mm year1 at Addis Adeba, Ethiopia, andreaches 3600mm year1 in Sierra Leone; for theSouthern tropics it ranges from 200mm year1 inLesotho to 3400mm year1 in places of Madagascar.In the equatorial belt, annual precipitations rangeLithology

    The continent is largely dominated by shields, plu-tonic, and metamorphic rocks (Table 1) Recentvolcanic rocks are abundant in the Rift Valley regionand in Cameroon, where numerous small crater lakesas the ill-famous Lake Nyos are found. Limestoneregions, which result in hard water rivers, are essen-Abbe system in Ethiopia, and the Omo River-LakeTurkana system (Ethiopia/Kenya).These endorheic systems are not stable and are very

    sensitive to climate variation and/or to tectonic: vol-canic movements: (i) the Logone River (Chad Basin)may overflow during very high water periods to theUpper Benue Basin, a main tributary of the NigerRiver, (ii) there is also evidence of former high waterstages of Lake Chad which could exceed 100 000 km2

    in area, (iii) the Okawango swamp may overflowduring the wettest years to the Zambezi River basinthrough the Selinda spillway, (iv) Lake Victoria hasonce been cut-off from the White Nile system due totectonic tilting, (v) Lake Turkana system has once beenoverflowing to the White Nile during Holocene wetterperiods, (vi) the Lukuga River is very sensitive to theclimate variations; during dryer periods Lake Tanga-nyika has partially evaporated over hundreds ofmeters,and (vii) during thewetter Sahara event some 6000yearBP, river networks fed by the Ahaggar, Tibesti andDarfour rains were extended and the lowest tributariesof the Nile basin, now completely arheic, were acti-vated. Similar changes are likely to have occurred inSouthern Africa in the Etosha Pan and in the OrangeRiver basin during wetter periods.The exact timing and mapping of these hydrologi-

    cal changes, which can be very important for thepresent aquatic biodiversity, remains to be establishedfor this continent.

    River Regimes in Africa

    River regimes of small andmediumbasins are essentiallycontrolled by the seasonal rainfall regimes since thepotential evapotranspiration (Eo) does not presentimportant seasonal variations and is very high through-out thewhole continent; from1200 to 2300mmyear1.Also, the snowmelt regime is restricted to the head-waters of some North African rivers. Many large riverbasins exceeding 500 000km2 are flowing across differ-ent climate belts and have complex regimes whichshould be covered separately (e.g., Nile and Niger).to internal regions (endoreism). They also use theterm arheism to describe the permanent absence offlow as in deserts (refer to see also section), whichcan be conventionally limited at 3mm year1 runoffcorresponding to about one flood event every decade.In Africa, endorheic basins are important and numerous(Figure 1) including Lake Chad basin, South of theSahara, the biggest endorheic basin (1million km2) inthe middle of the Sub Sahelian region, and the Oka-wango Basin in Southern Africa. Both are locatedbetween the desertic area and the tropical regions.The Rift Valley is also characterized by numerous

  • Rivers and Streams _ Africa 299Natural regimes are illustrated in Table 2 forrivers with minimal impoundment impact based onthe first Unesco discharges register (1969) and on aselection of the 1996 register. They are defined on thelong-term mean yearly and monthly specific dis-charges (q and qmin in l s

    1 km2) and are presentedaccording to their mean latitudes from Morocco toMadagascar (Table 2).The Sebou River (Morocco) drains the Atlas

    Mountains and is one of the rare African rivers thatis also influenced by snowmelt. The Dra River, also inMorocco, originating from the SE side of the Atlas isfacing the Sahara desert and is a very dry basin with acomplete dry-out during 5months, typical of suchtype of rivers termed ephemeral rivers or waddis.Waddis are also found South of the Sahara as in theEastern part of the Niger River basin but most ofthem do not reach the Niger main course anymore

    Figure 1 African rivers coastal catchments (Numbers 121) and ma(e.g., Azaouak River). A similar hydrological featureis observed in the Darfour region located between theLake Chad and Nile River basins where rivers do notgenerally reach the Nile main course. In the SouthernHemisphere, the Fish River, a large basin in Namibia,is not always flowing to the Orange River.The tropical regime of the Northern Hemisphere is

    here illustrated by the Senegal, the Upper Niger atKoulikouro (Mali), the Volta, the Comoe (IvoryCoast), the Benue (N. Cameroon) (Table 2), charac-terized by one maximum discharge occurring duringthe rainy season between August and September. TheAtbara River basin, the ultimate tributary to the Nilefrom the Ethiopian Plateau has a similar summer highwater period but completely dries out from February toApril. The other hydrological extreme of the tropicalregime is illustrated by the Moa River (Sierra Leone),a small basin where q exceeds 60 l s1 km2 annually, a

    in endorheic regions (AC).

  • Table 2 Flow regimes of African rivers before damming (Unesco, 1969 and 1996) presented from North to South, endorheic rivers and Nile stations in the end

    River Station Country Janl. s1 km2

    Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year A103 km2

    Period

    Nile (Main) Kajnarty Sudan 0.51 0.39 0.33 0.30 0.27 0.30 0.76 2.90 3.37 2.19 1.10 0.67 1.09 2500 1931/33

    Sebou Azil el

    Soltane

    Morocco 11.6 11.1 10.3 7.7 4.0 2.9 1.6 1.3 0.94 1.25 3.15 7.2 5.25 17.25 1959/64

    Dra Zagora Morocco 0.18 0.21 0.015 0.25 0.06 0.015 0.01 0.01 0.00 0.00 0.00 0.15 0.075 20.13 1963/64Senegal Bakel Senegal 0.59 0.35 0.21 0.10 0.45 0.56 2.63 10.8 15.9 7.8 2.55 1.05 3.5 218 1901/66

    Niger Koulikoro Mali 3.35 1.6 0.85 0.56 0.82 3.0 10.4 26.9 44.8 39 17.8 7.3 13.0 120 1907/66

    Moa Moa Bridge Sierra Leone 13.4 7.7 4.2 21.7 21.2 33.9 35.2 55.2 65.1 59.8 52.9 25.1 31.2 17.15 1976/77Volta Senchi Ghana 0.25 0.14 0.11 0.12 0.28 0.96 2.35 4.75 12.5 13.0 3.3 0.61 3.2 394 1936/63

    Comoe Aniasse Ivory Coast 0.43 0.21 0.28 0.36 0.50 0.93 2.4 5.85 12.8 12.0 4.55 1.57 3.5 1953/62

    Benoue Garoua Cameroon 0.40 0.19 0.08 0.03 0.28 1.23 5.1 16.9 29.8 13.4 2.7 0.97 5.95 64 1930/60

    Cross Manfe Cameroon 10.0 9.1 12.6 19.8 40.6 77.6 136.6 220 216.5 139.4 51.9 20.4 80.9 6.81 1967/79Sanaga Edea Cameroon 6.9 4.5 4.1 5.4 8.0 11.1 16.3 20.1 32.3 44.9 27.9 11.9 16.3 131.5 1950/63

    Tana Garissa Kenya 2.5 1.6 1.65 5.2 8.8 4.35 2.4 1.95 1.67 2.14 5.7 4.8 3.6 42.2 1933/65

    Oubangui Bangui Rep. C. Afr 4.5 2.6 2.0 2.4 3.65 5.75 8....