African Water Development Report 2006 - United Nations Economic ...

Fig 6.15: Comparison of Rainfall, Discharge and Sediment Yield in the Atbara RiverBasin.Protecting Ecosystems in AfricaFig 6.15: Comparison of Rainfall, Discharge and Sediment Yield in theAtbara River Basin. Source: AWDR National Report, 2005Source: AWDR National Report, 2005main canals, 23 per cent in the major canals,33 per cent in the minor canals and 39 per centpassed to the farm fields (tables 6.12 and 6.13).Another serious problem is the growth of aquaticweeds along the irrigation network where it is aggravatingthe sedimentation rate. The sedimentdeposits in turn provide a good environment forweeds to grow. About 60 per cent of the O&Mcosts of the irrigation schemes management inthe Sudan go to sediment and aquatic weedsclearance. This double problem creates many irrigationdifficulties leading to reductions in cropyield and increasing the O&M cost. However,many measures have been applied to mitigate theproblem, with some success (AWDR NationalReport – Sudan, 2005).On the other hand, the hyacinth weeds in theWhite Nile started in 1957 in the Sudd area inthe South, disrupting river traffic, inlet channelsand river life. It is now spreading all overthe equatorial lakes requiring regional and internationalefforts to combat it. However, bothsedimentation and aquatic weeds require jointefforts by the Nile Basin countries. For example,although the sediment problem creates manydifficulties and problems in the Sudan, it also hasa negative impact on the Ethiopian highlandswhere it originates, eroding the land and thereforereducing much needed soil nutrients and,consequently, agricultural productivity.DesertificationAbout one third of the world’s land surface is aridor semi-arid and vulnerable to desertification.Desertification is a process that turns productiveland into non-productive desert as a resultof poor land-management, mainly in semi-aridareas bordering on deserts, with an average annualrainfall of less than 600 mm. It is predictedthat global warming will increase the size of thearea with desert climate by 17 per cent in thenext century. Desertification is rendering approximately12 million hectares useless for cultivationworldwide every year. Desertificationin Africa has caused the degradation of morethan 105 million hectares since the 1970s. One155