NFEPA Atlas 5.3_20111025_FINAL.indd - Biodiversity GIS - SANBI

4.1.2 Flow variability categoriesThe 1:500 000 river network GIS layer was classified into two categories, permanent and notpermanent, using flow descriptions in the Department of Water Affairs 1:500 000 rivers andthe 1:50 000 rivers of the Department Land Affairs: Chief Directorate Surveys and Mapping(2005-2007). ’Permanent‘ includes both perennial and seasonal rivers and ’Not permanent‘includes ephemeral rivers that can go for years without flowing (Figure 4.3). Rivers withdifferent flow variability are expected to have different ecological characteristics. Ideally,flow variability for the 1:500 000 rivers should be described in more than two categories.While this is accomplished by the hydrological index developed by Hannart and Hughes(2003), it is only available for mainstem quaternary rivers. The 1:500 000 rivers require amuch finer resolution than the resolution of the existing hydrological indices. Developinghydrological indices for the 1:500 000 rivers should be a future focus for improving thedescription of river ecosystem types.PermanentNot permanentPermanent riverWilma StrydomKevin Murray500 kmFigure 4.3: Flow descriptions for the 1:500 000 river network GIS layer. ’Permanent’ refersto rivers that flow for at least some time every year; ‘Not permanent’ refers toephemeral rivers that do not flow every year. This GIS layer was one of the threeused to derive river ecosystem types.Not permanent riverInput data layers- 49 -