Data availability and requirements for flood hazard mapping in South Africa

Thesis (MSc)--Stellenbosch University, 2011.

ENGLISH ABSTRACT: Floods have been identified as one of the major natural hazards occurring in South Africa. A disaster risk assessment forms the first phase in planning for effective disaster risk management through identifying and assessing all hazards that occur within a geographical area, as required by the Disaster Management Act (Act No. 57 of 2002). The National Water Act (Act No. 36 of 1998) requires that flood lines be determined for areas where high risk dams exist and where new town developments occur. However, very few flood hazard maps exist in South Africa for rural areas. The data required for flood modelling analysis is very limited, particularly in rural areas. This study investigated whether flood hazard maps can be created using the existing data sources. A literature review of flood modelling methodologies, data requirements and flood hazard mapping was carried out and an assessment of all available flood-related data sources in South Africa was made. The most appropriate data sources were identified and used to assess an evaluation site. Through combining GIS and hydraulic modelling, results were obtained that indicate the likely extent, frequency and depth of predicted flood events. The results indicate that hydraulic modelling can be performed using the existing data sources but that not enough data is available for calibrating and validating the model. The limitations of the available data are discussed and recommendations for the collection of better data are provided.

AFRIKAANSE OPSOMMING: Vloede is van die vernaamste natuurlike gevare wat in Suid-Afrika voorkom. 'n Ramprisiko-analise is die eerste stap in die proses van suksesvolle ramprisiko-beplanning deur middel van die identifisering en analise van alle gevare wat voorkom in 'n geografiese gebied, soos vereis deur die Rampbestuurwet (Wet 57 van 2002). Die Nasionale Waterwet (Wet 36 van 1998) bepaal dat vloedlyne slegs vir gebiede waar hoë-risiko damme voorkom en vir nuwe uitbreidingsplanne in dorpe vasgestel moet word. Egter is die data wat vir vloedmodelleringsanalises benodig word baie skaars in Suid-Afrikaanse landelike gebiede. Hierdie studie het ondersoek of vloedgevaar-kartering met die beskikbare data moontlik is. 'n Literatuurstudie oor vloedmodelleringsmetodologieë, data-vereistes en vloedgevaarkartering is voltooi en alle beskikbare vloed-verwante data in Suid-Afrika is geëvalueer. Geskikte data-bronne is gekies en gebruik om 'n toetsgebied te assesseer. Deur GIS en hidrouliese modellering te kombineer, is die omvang, waarskynlikheid en diepte van die voorspelde vloedgebeurtenisse gemodelleer. Die studie het bevind dat, alhoewel vloedgevaarkartering met die beskikbare data moontlik is, daar nie genoeg data beskikbaar is om die model te kalibreer en te valideer nie. Tekortkominge van die bestaande data word bespreek en aanbevelings oor die verbetering van die bestaande data vir toepassings in vloedgevaarkartering word gemaak.