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

ment has disrupted the benefits of downstreamflows for traditional agriculture, caused waterpollution and increased disease incidence.Dams, and other reservoirs affect water resourcesat various aggregation levels. The primary effectsrelate to blocking of rivers and altering their flowdynamics, the secondary ones are due to changesin river, watershed and ecosystem characteristicsand productivity and the tertiary effects concernimpacts on the biological life of ecosystems. Themodification of the hydrological features of manyrivers through damming has negatively affectedfloodplain livelihoods through loss of vegetation,habitat, species populations, biodiversity, fisheries,wetlands and related riverine and marineecosystems. Also, greenhouse gases are emittedas a result and cause some health problems. Inaddition, locating a number of large dams on thesame river exerts cumulative impacts on flooding,water quality and other aspects of river systemecosystems (Vordzorgbe, S. D, 2003).Specific examples of risks from dams aboundin Africa. Fish production has significantly reducedin several river basins in Africa due todams, such as on the Niger below the Kainjidam, on the Zambezi in Mozambique and in theNile delta. Damming also affects marine fisheriesas in shrimp fishing in the Zambezi delta, andin the Mediterranean due to the Aswan Highdam. Stabilizing river flows by eliminating highdischarges from dams has resulted in increasedinfestation by aquatic weeds, including water hyacinth,ferns and reeds, and increase of black flyinfestation, as in the case of the Orange river inSouth Africa. The impoundment of River Nile,by constructing various dams on it, has led to thedegradation of the downstream delta, throughreduction of sediment movement, thereby leadingto erosion of the delta coastline by up to 5-8 metres a year, and the Akosombo dam on theVolta river in Ghana is causing coastal erosion ofTogo and Benin by up to 10-15 metres a year.Options for addressing dam safety risks in Africaare limited. A first approach is to accept therisk and manage it, through measures such asimproved telemetry, improved dam design, operationalprocedures and maintenance, warningsystems, and, evacuation planning. Another optionis to avoid the risk by removing problematic,old or unsuitable dams. This, however, is not ausual practice in Africa. Similarly, a third optionof risk transfer through dam insurance isnot common in Africa. Overall, mechanisms forreducing risk from dams are not well developedin Africa. Therefore, it is important to developanalytical models to simulate downstream effectsof sudden failure of dams under differenthydrological and hydraulic scenarios. The key isto realize that there will always be residual risksassociated with dams, no matter how well theyare designed and operated. Hence, the key to effectivedam risk reduction is to constantly assessthose risks and plan to mitigate them. Above all,it is prudent to observe the precautionary principlein dam development since information isuncertain, unreliable or inadequate to effectivelyaddress all issues of risk from dams.Monitoring of Hydroclimatic and Socio-economicProcessesCurrently, both scientific and observationalinformation point to an imminent global climatechange with possible differential periodsof inception at regional and global scales. Eventhough scientific evidence is not yet conclusiveas to when such a change would occur, it is advisableto institute demanding measures againstthe possible negative effects on the hydrologicalcycle and consequently on the global or regionalwater resources in time and space. While climaticvariability may modify the frequency-magnituderelations of the hydrological elements within arelatively short period, a climate change wouldbring new and different qualitative relationshipsexpressed in anomalous climatic events at largertemporal and spatial scales - that is to say, whenold trends fail and new ones emerge (Andah,2002a).MANAGING RISKS245