Niles Basin: Identification Ofbasin System

Niles Basin: Identification ofBasin System

Quick Overview ofthe water course:

The Nile —6,058-6,695 km (4,200 mi ) long, is the longest river in world. It starts in the subtropical South as the White Nile at Lake Victoria. It passesthrough Ugandagoing through a series of lakes around the equator. It flows into the Sudan subsequently reaching the largest fresh water marsh in the world, the Sudd. Next it joins with the Blue Nile, which originates in Ethiopia, at Khartoum. The last tributary, the Atbara, merges into the combined White and Blue Nile in Sudan, and the river continues to flow through Egypt. The final stop of the river is the delta, where the Nile splits into two branches, the Rosetta distributary to the West and the Damietta distribuatary to theEast. Each dump into the Med Sea. The four principal riparians are Egypt, Sudan, Ethiopia (Blue Nile), and Uganda (White Nile). The total catchment area of the Nile is 3.1 km2, or about 1/10the African continent.

Facts about Specific Regions: Equatorial Lakes ~ Lake Victoria, in the tropics, lies between Tanzania, Uganda, and Kenya. The second largest freshwater lake in the world, the principal source ofthe White Nile. Residing at 1133 m above sea level, only 14% ofits waters are from streams. Thus it serves as a reservoir collecting rain. Ave rainfall = 12-1500 mm/yr, only slightly more than the evaporationrate of 1120 mm/yr. the precip/yr decreasesin volume and increases in variability as you head downstream. Thus the White Nile provides a steady flow of water, though much less quantity than the Blue Nile during the summer. The outflow is 21,000 MCM/yr into Uganda. The White Nile continues through Owen Falls, Lake Kioga, and Lake Mobuta at a gradient of 1:1,216. This varied region ofthe landscape, lakes, waterfalls, is due to tectonic movement ofthe Rift Valley.

Sudan ~ crossing into the Sudan, the White N leis renamed Bahr el-Jebel. here tributaries add 17% to the discharge from the lake region. "'.00 km downstream it reaches a plateau with a gradient of just 1:13,900 until reaching f Sudd marsh where there is no measurable gradient whatsoever. At the Sudd, i. s Bahr el-Ghazal meges from the west, and the Sobat merges from the East. These rivers help to offset the massive quantity of water, 20 BCM/yr, lost due to evaporation and transpiration.The discharge emerging from the Sudd, 25 BCM, is relatively stable throught the year becuase the swamps buffer any variation in flow.

Blue Nile - The second major tributary, the Blue, joins the White at Khartoum. The Blue drains the mountainous region ofEthiopia, starting from an elevation of2,000 m and flowing out ofLake Tana. The Blue Nile unlike the White flutuates greatly according to the monsoon rain season. It receives 1500 mm/yr from June to September, which constitutes the high flood season. During this time the average flow is 10 BCM/month. The Rahad and the Dindar are 2 major tributaries ofthe Blue. During the summer the Blue contributes up to 90% ofthe total flow of the Nile, in winter it contributes as little as .5 BCM/month, whereas the white delivers 2 BCM/month.

Atbara —The final tributary enters 320 km north of Khartoum. It also originates in the Ethiopian highlands and like the Blue fluctuates with the monsoon rains. Its greatest volume is 2 BCM/month, and it practically disappears in the dry season.

Egypt ~ At Lake Nasser the Nile crosses the Egyptian border. Egypt contributes nothing to the flow ofthe Nile. The delta, 200 km wide at the coast, is famous for its fertility because the land is comprised of river sediment carried all the way from the Ethiopian mountains. With the exceptionof the major sources of the Nile ~ the Ethiopianhighlands, and the tropical lakeregion, which each receive about 1,500 mm/yr-- the majority of the landthat the Nile traverses receives no rainfall.The annual discharge measured at Aswan is 84 BCM, but is currently dropping. Fluctuations caused by floods and droughts are substantial. Averageas high as 150BCM in 1878, and as low as 42 BCMin 1913. Morerecently 50 BCM in 1971, and 100 BCM in 1975.More than 80% of this total discharge occurs from Augustto October. 86% of the Nilewatersoriginates in Ethiopia, and flows throughtthe Blue Nile and the Atbara, and 14% comes from the Equatorial Lakes.

118 Riversof Eden The Mighty Nile 119

the^Blue Nile, which is a perennial stream, tL: ASara_shrinks d the jhe White Nile. The_ united Nile's annual deliyery-to- Aswan_generally ••V^ dry season to little more than a series ofsta£ iols7 irraHg^^m]?rrbillion to9^bmionû.b"Lcjmettrs. However,dependlngon., , V the vagaries ofthe monsoonal weather over Ethiopia, the variation can be .„y After its junction with Atbara, the Nile wends its way northward for more l ©uch*greater. Since modern measurements were begun, the yearly dis- "ânJ^SOjD^lorneter^ further addition o£ | charge at Aswan has varied from ahigh of about 137 BCM in 1879 and 0 water Through mostofthat length, thejiver traverses thebreached desert, I 126BCM in 1885 to a lowof 45.5 BCM in 1913 and only 37.5 BCMin t „v& with only the narrow strips ofits banks tinged with greeja. En route, the I.198Z. (following the severe and prolonged^drought that prevailed in east- ,. river slkes through several cataracts, therebyNbecomingXinnavigable, as it I crn Africa and the Sahel during the earfy and mid" 1980s)rPrioTTc) the \^ swings through awide S-shaped curve before resuming" its northerly direc |W«»n,^n nf>hr High Dam aodiÊj^S^m^r^tCatM TOtCr StJOT' yp-^ tion. At Wadi Haifa, a vallev lone inljabited-buVhowhow submersedsubmerged under ur *« "age, years of suchJow_ flow_wo.uldJiave_speUed immedjate_disaster in" v\|jfW *" Lake Nasser, the river crosses the rder between^ Sudan ancr^ *Êgypt.8- EgYPi- \ \ j* The annual flow ofthe Nile atAswaiUaycjraged over the period 1900- Inside Egypt, the Nile flows sinuously iitâ. rela»yely_narrow, flat-bot- i ill959) is abouTS4îmc^xuEc^mettrÂpproxirnaTely^86TKTC tomed bed, generally incised iptb the underlying^bectroc^Xwhich consists I ' flow originates in Ethiopia: the Blue Nile contributes 59 percent, the ofsand«tDri€sandTlimestonejormations—except at Aswan "inhere granitic lAtbara 13 percent, and the Sobat (a tributary ofthe White Nile) 14 per rocks outcrop). Themaximum flwdâgejwrmally arrives attmsôint in, cent. The remainder (14 percent on average) originates in the East African mjd September, when the flow rate .mayexceed 700 million cubic metersj i»equatorial plateau. per day.Ofthat flow, the Blue Nile ^coumsfcF^pefcelu^tfie Atbara I' From Aswan north the river is entirely navigable, and it descends '22_perccntândjthcIWhlte-'Nilc..lO-percent, on average. The minimumi if gently at agradient ofabout 1:14,000. Its floodplain is seldom more than flow rate normally_occursjn.earlyMay,~and mayawindle tono more thinJ |a few hundred meters wide, in avalley that seldom exceeds 20 kilometers 45 million cubic meters per day, contributed mainly by the steady flow of [ m widthand is often much narrower. Asthe Nile tends to hug the eastern sedge ofthe valley, the greater part ofcultivable land is found on the west- em bank. < North ofCairo, the clifflike walls ofthe rocky plateau that hem inthe upper Nile's floodplain disappear, and the river fans out in several distrib utaries within theiriangular lowlandlhatjcjonstitutes the Delta. In thefirst Nile below Atbara 11

I !i Nile at Khartoum m

,I *** MfldKamnisn 3000 " 2OO0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec DISTANCE FROM THE MEDITERRANEAN 0>ml Figure 6.4 Relative contributions of the White Nile and Blue Nile and of the m Vlmtrt fi.fi Slnort ofthe Nile's maior tributaries from their sources tothe Med-