NFEPA Atlas 5.3_20111025_FINAL.indd - Biodiversity GIS - SANBI

3.5 High water yield areasFigure 3.5 shows those sub-quaternary catchments where mean annual run-off (mm per year)is at least three times more than the average for the related primary catchment. Mean annualrun-off is the amount of water on the surface of the land that can be utilised in a year, whichis calculated as an average (or mean) over several years.High water yield areas are important because they contribute significantly to the overallwater supply of the country. They can be regarded as our water factories, supportinggrowth and development needs that are often a far distance away. Deterioration ofwater quantity and quality in these high water yield areas can have a disproportionatelylarge adverse effect on the functioning of downstream ecosystems and the overallsustainability of growth and development in the regions they support. High water yieldareas should therefore be maintained in a good condition (A or B ecological category).This requires minimising land use activities that reduce stream flow in these areas(e.g. plantation forestry), as well as any activity that would affect water quality (e.g.timber mills, mining, over-grazing). Wetlands also play an important role in these areas,regulating stream flow and preventing erosion. Additionally, clearing of invasive alienplants in these areas would deliver large water yield benefits relative to clearing in otherparts of the catchment.High water yield areas are our waterfactories, supporting growth anddevelopment needs that are often a longdistance away. Land uses that reducestream flow or affect water quality (e.g.mining, plantations, overgrazing) should beavoided in these areas, wetlands should bekept in good condition or rehabilitated, andinvasive alien plants should be cleared.Figure 3.5: Mountain Catchment Areas, delineated by hand in 1959 (Department of Agricultural TechnicalServices. 1961)< 100%100-300%300-500%> 500%High water} yield areasRevitalising the MountainCatchment Areas Act anddeclaring additional MountainCatchment Areas could makea significant contribution toprotecting South Africa’s waterresources.The Mountain Catchment Areas Act (Act 63 of 1970) recognises the need to managehigh water yield areas wisely for the benefit of both people and ecosystems. It enablesmechanisms for prevention of soil erosion, protection of the natural vegetation, clearing ofinvasive alien plants, and implementation of fire protection plans. As early as 1959, MountainCatchment Areas of South Africa had been delineated by hand (Figure 3.5). These correspondwell with the high water yield areas identified by NFEPA (Figure 3.6).Unfortunately only a few Mountain Catchment Areas have been declared in terms of theMountain Catchment Areas Act. These declared Mountain Catchment Areas make a relativelylarge contribution to freshwater ecosystem conservation and management relative toother protected area systems (Nel et al. 2009b). Ideally, all high water yield areas should bedeclared in terms of the Mountain Catchment Areas Act, as the Act provides mechanismsand incentives for appropriate land management in these areas. Revitalising the MountainCatchment Areas Act and declaring further Mountain Catchment Areas in high water yieldareas, with a view to protecting the country’s water resources, is a strong recommendation ofthe NFEPA project.Figure 3.6: Hat least three times more than the average for the related primary catchment500 kmNational map products - 44 -